,
?Part I Wastewater Engineering
?1 Wastewater Engineering,An Overview
Fig,1-1 Schematic diagram of a wastewater management infrastructure
1-1 Terminology
Table 1-1 Terminology commonly used in the field of wastewater engineering
1-2 Impact of Regulations on Wastewater Engineering
1-3 Health and Environmental Concerns in Wastewater
Management
Fig,1-2 Covered treatment plant facilities for the control of odor emissions
1-4 Wastewater Characteristics
Tab 1-2 Levels of wastewater treatment
Tab 1-3 Unit Operations and Processes used to Remove Constituents Found in
Wastewater
1-5 Wastewater Treatment
Fig 1-3 Facilities used for chemical treatment of odors from treatment facilities
Fig,1-4 UV lamps used for the disinfection of wastewater
1-6 Wastewater Reclamation and Reuse
1-7 Biosolids and Residuals Management
Fig,1-5 Egg-shaped digesters used for the anaerobic treatment of biosolids
2 Constituents in Wastewater
An understanding of the nature of wastewater is essential in the
design and operation of wastewater collection,treatment,and
reuse facilities,and in the engineering management of
environmental quality,
(1) the constituents found in wastewater,
(2) sampling and analytical procedures,
(3) physical characteristics,
(4) inorganic nonmetallic constituents,
(5) metallic constituents,
(6) aggregate organic constituents,
(7) individual organic constituents and compounds,and
(8) biological characteristics,
2-1 Wastewater Constituents
Constituents Found in Wastewater
Table 2-1 Common analyses used to assess
the constituents found in wastewater
Many of the physical properties and chemical and
biological characteristics are interrelated,For example,
temperature,a physical property,affects both the
amounts of gases dissolved in the wastewater and the
biological activity in the wastewater…
Constituents of Concern in Wastewater Treatment
Tab 2-2 Principal constituents of concern in wastewater
treatment
Suspended solids can lead to sludge deposition and
anaerobic conditions;
Biodegradable organics composed of proteins;
carbohydrates and fats,and are measured most commonly
in terms of BOD and COD;
Pathogens can transmite Communicable diseases;
Priority pollutants include carcinogenicity,metogenicity,
teratogenicity or high acute toxicity;
Nutrients lead to the growth of undesirable aquatic life;
Refractory organics include surfactants,phenols,and
agricultural pesticides,
2-2 Sampling and Analytical Procedures
Sampling
(1) routine operating data for accessing overall plant
performance
(2) data that can be used to document the performance of a
given treatment operation or process
(3) data that can be used to implement proposed new
programs
(4) data needed for reporting regulatory compliance,
The data collected must be,
(1),Representative,
(2).Reproducible.The data must be reproducible
by others following the same sampling and
analytical protocols,
(3),Defensible,The data must have a known
degree of accuracy and precision,
(4),Useful,The data can be used to meet the
objectives of the monitoring plan,
There are no universal procedures for sampling,
Sampling programs must be tailored individually to fit
each situation,
Quality assurance project plan (QAPP) (known
previously quality assurance/quality control,QA/QC),
(1).Sampling plan,
(2).Sample types and size,
(3).Sample labeling and chain of custody,
(4).Sampling methods,
(5).Sampling storage and preservation,
(6).Sample constituents,
(7).Analytical methods,
If the physical,chemical,and/or biological integrity of
the samples is not maintained during interim periods
between sample collection and sample analysis,a
carefully performed sampling program will become
worthless,
Prompt analysis is undoubtedly the most positive
assurance against error due to sample deterioration,
Probable errors due to deterioration of the sample
should be noted in reporting analytical data,
Methods of Analysis
The analyses used to characterize wastewater vary from
precise quantitative chemical determinations to the more
qualitative biological and physical determinations,
The quantitative methods of analysis are either gravimetric,
volumetric,or physicochemical,
Turbidimetry,colorimetry,potentiometry,polarography,
adsorption spectrometry,fluorometry,and nuclear
radiation are representative of the physicochemical
analyses,
Units of Measurement for Physical and
Chemical Parameters
kg/m3,%(by volume or by mass),pg/L,ng/L,μg/L,mg/L,
g/L,ppb,ppm,mol/L,eq/L,meq/L,
The concentration of trace constituents is usually
expressed as micrograms per liter (μg/L) or nanograms per
liter (ng/L),
For dilute systems,one liter of sample weighs
approximately one kilogram,the units of mg/L or g/m3 are
interchangeable with ppm,
"parts per billion" (ppb) and "parts per trillion"(ppt) are
used interchangeably with μg/L and ng/L
2-3 Physical Characteristics
The most important physical characteristic of
wastewater is its total solids content,which is
composed of floating matter,settleable matter,
colloidal matter,and matter in solution,Other
important physical characteristics include particle
size distribution,turbidity,color,transntittance,
temperature,conductivity,and density,specific
gravity and specific weight,Odor,sometimes
considered a physical factor,is discussed in the
following section,
Solids
In the characterization of wastewater,coarse materials are usually
removed before the sample is analyzed for solids,
Tab 2-3 Definitions of solids found in wastewater
Fig,2-1 Interrelationships of solids found in water and wastewater,
In much of the water quality literature,the solids passing through
the filter are called dissolved solids,
A filtration step is used to separate the total suspended solids (TSS)
from the total dissolved solids (TDS),Filters with nominal pore sizes
varying from 0.45 μm to about 2.0 μm have been used for the TSS test,
Fig,2-2 Size ranges of organic contaminants in wastewater and size
separation and measurement techniques used for their quantification
Particle Size Distribution
Information on particle size is of importance in assessing
the effectiveness of treatment processes (e.g.,secondary
sedimentation,effluent filtration and effluent disinfection),
The biological conversion rate of these particles is
dependent on size,
The methods used most commonly to study and quantify
the particles in wastewater are serial filtration,electronic
particle counting,and microscopic observation,
Serial Filtration
2.0 μm as specified in Standard Methods for the TSS test,
More than 20 mg/L of additional TSS would have been
measured,
Electronic Particle Size Counting
Diluted sample through a calibrated orifice, The
conductivity is correlated to the size of an equivalent
sphere,
Fig,2-5 Volume fraction of particle sizes found in the
effluent from two activated-sludge plants with clarifiers
having different side water depths
However,the particle size data for the large particles are
quite different,owing primarily to the design and operation
of the secondary clarification,
Microscopic Observation
Various types of stains can be used on a routine basis,to
qualitatively assess microscope slide,
Video camera attached to a microscope and transmitted to a
computer are dependent on the computer software,the
mean,minimum,and maximum diameter,length to width
ratio,the circumference,the surface area,the volume,and
the centroid, Particle imaging greatly reduces the time
required but the cost of the software and equipment is
often prohibitive for many small laboratories,
Turbidity
Turbidity,a measure of the light-transmitting properties of
water,is another test used to indicate the quality of waste
discharges and natural waters with respect to colloidal and
residual suspended matter,
The results of turbidity measurements are reported as
nephelometric turbidity units (NTU),
It should be noted that the presence of air bubbles in the
fluid will cause erroneous turbidity readings,In general,
there is no relationship between turbidity and the
concentration of total suspended solids in untreated
wastewater,
There is,however,a reasonable relationship between
turbidity and total suspended solids for the settled and
filtered secondary effluent from the activated sludge
process,
The conservation factors for settled secondary effluent and
for secondary effluent filtered with a granular-medium
depth filter will typically vary from 2.3 to 2.4 and 1.3 to
1.6,respectively,
However,turbidity readings at a given facility can be used
for process control,Some on line turbidity meters used to
monitor the performance of microfiltration units are
affected by the air used to clean the membranes,
Color
Condition refers to the age of the wastewater,which is
determined qualitatively by its color and odor,Fresh
wastewater is usually a brownish-gray color,sequentially
from gray to dark gray,and ultimately to black that is
often described as septic,
In most cases,the gray,dark gray,and black color of the
wastewater is due to the formation of metallic sulfides,
which form as the sulfide produced under anaerobic
conditions reacts with the metals in the wastewater,
Absorption/Transmittance
The absorbance measured using a spectrophotometer and a
fixed path length (usually 1.0 cm) is a measure of the
amount of light,of a specified wave-length,
The factors that affect the percent transmission include
selected inorganic compounds (e.g.,copper; iron,etc.),
organic compounds (e.g.,organic dyes,humic substances,
and conjugated ring compounds such as benzene and
toluene),and TSS,
Iron is considered to be the most important with respect to
UV absorbance because dissolved iron can absorb UV
light directly and because iron will adsorb onto suspended
solids,bacterial clumps and other organic compounds,
The sorbed iron can prevent the UV light from penetrating
the particle and inactivating organisms that may be
embedded within the particle,Dosage control is extremely
important when UV disinfection is to be used,
Organic constituents,are compounds with six conjugated
carbons or a five- or six-member conjugated ring,The
reduction in transmittance observed during storm events is
often ascribed to the presence of humic substances from
stormwater flows,
Fig,2-6 Transmittance measured at various wavelengths
for activated-sludge effluents and lagoon effluents
Unfiltered and filtered transmittance are mearsured in
wastewater in connection with the evaluation and design of
UV disinfection systems,
Temperature
The temperature of wastewater is commonly higher than
that of the local water supply,because of the addition of
warm water from households and industrial activities,As
the specific heat of water is much greater than that of air,
the observed wastewater temperatures are lower only
during the hottest summer months,
Effects of Temperature
The temperature of water is a very important parameter
because of its effect on chemical reactions and reaction
rates,aquatic life,and the suitability of the water for
beneficial uses,
Industrial establishments that use surface water for cooling
water purposes are particularly concerned with the
temperature of the intake water,
In addition,oxygen is less soluble in warm water than in
cold water,The the rate of biochemical reactions that
accompanies an increase in temperature,combined with
the decrease in the quantity of oxygen present in surface
waters,can often cause serious depletions in dissolved
oxygen concentrations in the summer months,
A sudden change in temperature can result in a high rate of
mortality of aquatic life,Moreover,abnormally high
temperatures can foster the growth of undesirable water
plants and wastewater fungus,
Optimum Temperatures for Biological Activity
Optimum temperatures are in the range from 25 to 35℃,
Aerobic digestion and nitrification stops at50℃, At 15℃,
methane-producing bacteria become quite inactive,and at
about 5℃,the autotrophic-nitrifying bacteria practically
cease functioning,At 2℃,even the chemoheterotrophic
bacteria dormant,
Conductivity
The conductivity increases as the concentration of ions
increases,In effect,the measured EC value is used as a
surrogate measure of TDS concentration,
2-4 Inorganic Nonmetallic Constituents
Inorganic chemical constituents of concern include
nutrients,nonmetallic constituents,metals,and gases,
Inorganic nonmetallic and metallic constituents derive from
the background levels in the water supply and from the
additions resulting from domestic use,from the addition of
highly mineralized water from private wells and
groundwater,and from industrial use,
Inorganic nonmetallic consfituents considered in this
section include pH,nitrogen,phosphorus,alkalinity,
chlorides,sulfur,other inorganic constituents,gases,and
odors,
Chlorides
Chlorides in natural water result from the leaching of
chloride-containing rocks and soils with which the water
comes in contact,and in coastal areas from saltwater
intrusion,
Human excreta contain about 6 g of chlorides per person
per day,If hardness of water is high,home regeneration
type water softeners will also add large quantities of
chlorides,
Because conventional methods of waste treatment do not
remove chloride to any significant extent,higher than usual
chloride concentrations can be taken as an indication that a
body of water is being used for waste disposal,
Alkalinity
Alkalinity in wastewater results from the presence of the
hydroxides [OH-],carbonates [CO32-],and bicarbonates
[HCO3- ] of elements such as calcium,magnesium,sodium,
potassium,and ammonia,Of these,calcium and magnesium
bicarbonates are most common,
The alkalinity in wastewater helps to resist changes in pH
caused by the addition of acids,Alkalinity is determined by
titrating against a standard acid,
In practice,alkalinity is expressed in terms of calcium
carbonate,3 meq/L of alkalinity would be expressed as 150
mg/L as CaCO3,
Nitrogen
Nitrogen is an essential building block in the synthesis of
protein, Insufficient nitrogen can necessitate the addition
of nitrogen to make the waste treatable,
Sources of Nitrogen
(1) plant and animal origin,
(2) sodium nitrate,
(3)atomspheric nitrogen,
Forms of Nitrogen
The chemistry of nitrogen is complex because of the
several oxidation states,
The most common and important forms of nitrogen are
ammonia,ammonium,nitrogen gas,nitrite ion,and
nitrate ion, The oxidation state of nitrogen in most organic
compounds is -III,
Tab 2-5 Definition of the various terms used to define
various nitrogen species
Urea readily converted to ammonium carbonate,is seldom
found in untreated municipal wastewaters,Organic
nitrogen is determined analytically using the Kjeldald
method,
Total Kjeldabl nitrogen is the total of the organic and
ammonia nitrogen,
Ammonia nitrogen exists in aqueous solution as either the
ammonium ion (NH4+) or ammonia gas (NH3),depending
on the pH of the solution,
Nitrite nitrogen,determined colorimetrically,is relatively
unstable oxidized to the nitrate form,Nitrite can be very
important in wastewater or water pollution studies because
it is extremely toxic to most fish and other aquatic species,
Nitrites present in wastewater effluents are oxidized by
chlorine and thus increase the chlorine dosage
requirements and the cost of disinfection,
The U.S,EPA primary drinking water standards limit
nitrogen to 45 mg/L as NO3-,because of its serious and
occasionally fatal effects on infants,Nitrates may vary in
concentration from 0 to 20 mg/L as N in wastewater
effluents,
Nitrogen Pathways in Nature
Fig,2-7 Generalized nitrogen cycle in the aquatic and
soil environment
Decomposition by bacteria readily changes the organic
form to ammonia,The age of wastewater is indicated by
the relative amount of ammonia that is present,
The predominance of nitrate nitrogen in wastewater
indicates that the waste has been stabilized with respect to
oxygen demand,Nitrates,however,can be used by plants
and animals to form protein,
Phosphorus
Municipal wastewaters may contain from 4 to 16 mg/L of
phosphorus as P,
The usual forms of phosphorus that are found in aqueous
solutions include the orthophosphate,polyphosphate,and
organic phosphate,
Polyphosphates undergo hydrolysis in aqueous solutions
and revert to the orthophosphate forms; however,this
hydrolysis is usually quite slow,The organically bound
phosphorus can be an important constituent of industrial
wastes and wastewater sludge,
The polyphosphates and organic phosphates must be
converted to orthophosphates using an acid digestion step,
Sulfur
The sulfate ion occurs naturally in most water supplies and
is present in wastewater as well,Sulfur is required in the
synthesis of proteins and is released in their degradation,
Hydrogen sulfide gas,which will diffuse into the
headspace above the wastewater sewers that are not
flowing full,tends to collect at the crown of the pipe,The
accumulated H2S can then be oxidized biologically to
sulfuric acid,which is corrosive to concrete sewer pipes,
This corrosive effect,known as "crown rot," can seriously
threatened the structural integrity of the sewer pipe,
Sulfates may upset the biological process if the sulfide
concentration exceeds 200 mg/L,If burned in gas engines,
the products of combustion can damage the engine,
Gases
Gases commonly found in untreated wastewater include
nitrogen (N2),oxygen (O2),carbon dioxide (CO2),
hydrogen sulfide (H2S),ammonia (NH3),and
methane(CH4),The latter three are derived from the
decomposition of the organic matter present in wastewater
and are of concern with respect to worker health and safety,
Environmental engineer must be familiar include chlorine
(Cl2) and ozone (O3),and the oxides of sulfur and
nitrogen,
It will be useful to review the ideal gas law and to consider
the solubility of gases in water and Henry's law as applied
to the gases of interest,
Solubility of Gases in Water
The actual quantity of a gas that can be present in solution
is governed by,
(1) the solubility of the gas as defined by Henry's law,
(2) the partial pressure of the gas in the atmosphere,
(3) the temperature,and
(4) the concentration of the impurities in the water (e.g.,
salinity,suspended solids,etc.),
The Ideal Gas Law
Boyle's law (volume of a gas is inversely proportional to
pressure at constant temperature)
Charles' law (volume of a gas is directly proportional to
temperature at constant pressure)
Dissolved Oxygen
Oxygen is only slightly soluble in water,Dissolved oxygen
levels tend to be more critical in the summer months,The
presence of dissolved oxygen in wastewater is desirable
because it prevents the formation of noxious odors,
Hydrogen Sulfide
Hydrogen sulfide is formed from the reduction of mineral
sulfites and sulfates, This gas is a colorless,inflammable
compound having the characteristic odor of rotten eggs,
The loss of smell can lead to a false sense of security that
is very dangerous,The blackening of wastewater and
sludge usually results from the formation of hydrogen
sulfide,Various other metallic sulfides are also formed,
Methane
Methane is a colorless,odorless,combustible hydrocarbon
of high fuel value,
Because methane is highly combustible and the expolosion
hazard is high,access ports (manholes) and sewer
junctions or junction chambers where there is an
opportunity for gas to collect should be ventilated with a
portable blower during and before the time required for
operating personnel to work in them for inspection
renewals,or repairs,
Odors
Odors in domestic wastewater usually are caused by gases
produced by the decomposition of organic matter or by
substances added to the wastewater,
Industrial wastewater may contain either odorous
compounds or compounds that produce odors during the
process of wastewater treatment,
Odors have been rated as the foremost concern of the public
relative to the implementation of wastewater treatment
facilities,
Within the past few years,the control of odors has become a
major consideration in the design and operation of
wastewater collection,treatment,and disposal facilities,
especially with respect to the public acceptance of these
facilities,
In many areas,projects have been rejected because of the
concern over the potential for odors,
Effects of Odors
Effects of odors is related primarily to the psychological
stress rather than to the harm they do to the body,
Offensive odors can cause poor appetite for food,lowered
water consumption,impaired respiration,nausea and
vomiting,and mental perturbation,and can lead to the
deterioration of personal and community pride,interfere
with human relations,discourage capital investment,lower
socioeconomic status,and deter growth,
These problems can result in a decline in market and rental
property values,tax revenues,payrolls,and sales,
Detection of Odors
One of the difficulties in developing a universal theory has
been the inadequate explanation of why compounds with
similar structures may have different odors and why
compounds with very different structures may have similar
odors,
Tab 2-7 Major categories of odorous compounds
associated with untreated wastewater
Odor Characterization and Measurement
It has been suggested that four independent factors are
required for the complete characterization of all odor,
intensity,character,hedonics,and detectability,
Odor can be measured by sensory methods,and specific
odorant concentrations can be measured by instrumental
methods,
MDTOC ----minimum detectable threshold odor
concentration
The ED50 value represents the number of times all odorous
air sample must be diluted before the average person(50
percentile) can barely detect an odor in the diluted sample,
TON---- threshold odor number
2-5 Metallic Constituents
Many of these metals are also classified as priority
pollutants,
The presence of any of these metals in excessive quantities
will interfere with many beneficial uses of the water
because of their toxicity; therefore,it is frequently
desirable to measure and control the concentrations of
these substances,
Importance of Metals
All living organisms require varying amounts (macro and
micro) of metallic elements,such as iron,chromium,
copper,zinc,and cobalt,for proper growth,but the same
metals can be toxic when present in elevated
concentrations,
Where composted sludge is applied in agricultural
applications,arsenic,cadmium,copper,lead,mercury,
molybdenum,nickel,selenium,and zinc must be
determined,
Sources of Metals
These are found particularly in metal-plating wastes and
should be removed by pretreatment at the site of the
industry rather than be mixed with the municipal
wastewater,Fluoride,a toxic anion,is found commonly in
wastewater from electronics manufacturing facilities,
Tab 2-9 Typical waste compounds produced by
commercial,industrial,and agricultural activities that
have been classified as priority pollutants
Sampling and Methods of Analysis
Metals are determined typically by flame atomic absorption,
electrothermal atomic absorption,inductively coupled
plasma,or IPC/mass spectrometry,
2-6 Aggregate Organic Constituents
The organic matter in wastewater typically consists of
proteins (40 to 60 percent),carbohydrates (25 to 50 per
cent),and oils and fats (8 to 12 percent),Because urea
decomposes rapidly it is seldom found in other than very
fresh wastewater,
In general,the analyses may be classified into those used to
measure aggregate organic matter comprising a number of
organic constituents with similar characteristics that cannot
be distinguished separately,
Measurement of Organic Content
Gross concentrations of organic matter are greater than
about 1.0 mg/L and trace concentrations are in the range
of l0 –12 to 100 mg/L,
Laboratory methods include,
(1) biochemical oxygen demand(BOD),
(2) chemical oxygen demand (COD),
(3) total organic carbon (TOC),
Complementing these laboratory tests is the theoretical
oxygen demand (ThOD),which is determined from the
chemical formula of the organic matter,
Trace organics in the range of 10–12 to 10-13 mg/L are
determined using instrumental methods including gas
chromotography and mass spectroscopy,
Biochemical Oxygen Demand (BOD)
Despite the widespread use of the BOD test,it has a
number of limitations,BOD test results are now used
(1) to determine the approximate quantity of oxygen that
will be required to biologically stabilize the organic matter
present,
(2) to determine the size of waste treatment facilities,
(3) to measure the efficiency of some treatment processes,
(4) to determine compliance with wastewater discharge
permits,
Basis for BOD Test
The term COHNS(which represents the elements carbon,
oxygen,hydrogen,nitrogen,and sulfur) represent the
organic waste and the term C5H7NO2 (first proposed by
Hoover and Porges) to represent cell tissue,
If only the oxidation of the organic carbon,The oxygen
demand is known as the ultimate carbonaceous or first-
stage BOD,and is usually denoted as UBOD,
BOD Test Procedure
To ensure that meaningful results are obtained,the samples
must be suitably diluted with a specially prepared dilution
water so that adequate nutrients and oxygen will be
available during the incubation period,Normally,several
dilutions are prepared to cover the complete range of
possible values,
Tab 10 Measurable of BOD using various dilutions of
samples
The BOD of the sample is the difference in the dissolved
oxygen concentration values,expressed in milligrams per
liter,divided by the decimal fraction of sample used,
When testing waters with low concentrations of
microorganisms,a seeded BOD test is conducted,
Fig,2-8 Procedure for settling up BOD test bottles,
(a)with unseeded dilution water and (b) with seeded
dilution water
The organisms contained in the effluent from primary
sedimentation facilities are used commonly as the seed for
the BOD test,Seed organisms can also be obtained
commercially,When the sample contains a large
population of microorganisms (e.g.,untreated wastewater),
seeding is not necessary,
Longer time periods (typically 7 days),which correspond
to work schedules,are often used,especially in small
plants where the laboratory staff is not available on the
weekends,
The 20℃ temperature used is an average value for slow-
moving streams in temperate climates and is easily
duplicated in an incubator,
After incubation,the dissolved oxygen of the sample is
measured and the BOD is calculated using the following
Eq.,
BOD,mg/L = (D1-D2)/P
When diluted water is seeded,
BOD,mg/L = [(D1-D2)-(B1-B2)]f/P
Within a 20-day period,the oxidation of the carbonaceous
organic matter is about 95 to 99 percent complete,and in
the 5-day period used for the BOD test,oxidation is from
60 to 70 percent complete,
Effect of particle size on BOD Reaction Rates
The observed BOD reaction rate coefficients are affected
significantly by the size of the particles in wastewater,
Limitations in the BOD test
The limitations of the BOD test are as followings
(1)a high concentration of active,acclimated seed bacteria
is required;
(2)pretreatment is needed when dealing with toxic wastes,
and the effects of nitrifying organisms must be reduced;
(3)only the biodegradable organics are measured;
(4)the relatively long period of time required to obtain test
results,
Of the above,perhaps the most serious limitation is that the
5-day period may or may not correspond to the point
where the soluble organic matter that is present has been
used,
Total and soluble chemical oxygen demand(COD
and SCOD)
The COD test is used to measure the oxygen equivalent of
the organic material in wastewater that can be oxidized
chemically using dichromate in an acid solution,
CnHaObNc + dCr2O72- + (8d+c)H+ → NCO 2 + [(a+8d-3c)/2]
H2O + cNH4+ + 2dCr3+
Some of the reasons for the observed difference are as
follows:(1)many organic substances which are difficult to
oxidize biologically,such as lignin,can be oxidized
chemically,(2)inorganic substances that are oxidized by the
dichromate increase the apparent organic content of the
sample,(3)certain organic substances may be toxic to the
microorganisms used in the BOD test
One of the main advantages of the COD test is that it can
be completed in about 2.5 h,To reduce the time further,a
rapid COD test that takes only about 15 min has been
developed,
The principal fractions are particulate and soluble COD,
Fractions that have been used include,
(1)readily biodegradable soluble COD,
(2)slowly biodegradable colloidal and particulate COD,
(3)nonbiodegradable soluble COD,and
(4)nonbiodegradable colloidal and particulate COD,The
readily biodegradable soluble COD is often fractionated
further into complex COD that can be fermented to volatile
fatty acids(VFAs) and short chain VFAs,Unfortunately,as
noted previous
Oil and Grease
The term oil and grease,as commonly used,includes the
fats,oils,waxes,and other related constituents found in
wastewater,
The oil and grease content of a wastewater is determined
by extraction of the waste sample with
trichlorotrifluoroethane
Other extractable substances include mineral oils,such as
kerosene and lubricating and road oils,Oil and grease are
quite similar chemically; they are compounds (esters) of
alcohol or glycerol(glycerin) with fatty acids,The
glycerides of fatty acids that are liquid at ordinary
temperatures are called oils,and those that are solids are
called grease (or fats),
If grease is not removed before discharge of treated
wastewater,it can interfere with the biological life in the
surface waters and create films,
The low solubility of fats and oils reduces their rate of
microbial degradation,Mineral acids attack them,however,
resulting in formation of glycerin and fatty acid,In the
presence of alkalis,such as sodium hydroxide,glycerin is
liberated,and alkali salts of the fatty acids are formed,
These alkali salts are known as soaps,
They are soluble in water,but in the presence of hardness
constituents,the sodium salts are changed to calcium and
magnesium salts of the fatty acids,or so-called mineral
soaps,These are insoluble and are precipitated,
Kerosene,lubricating,and road oils are derived from
petroleum and coal tars and contain essentially carbon and
hydrogen,These oils sometimes reach the sewers in
considerable volume from shops,garages,and streets,
To an even greater extent than fats,oils,and soaps,the
mineral oils tend to coat surfaces,The particles interfere
with biological action and cause maintenance problems,
Surfactants
Surfactants,or surface-active agents cause foaming in
wastewater treatment plants and in the surface waters into
which the waste effluent is discharged,Surfactants are
most commonly composed of a strongly hydrophobic
group combined with a strongly hydrophilic group,
In the United States,ionic surfactants amount to about
two-thirds of the total surfactants,
Surfactants tend to collect at the air-water interface with
the hydrophilic in the water and the hydrophobic group in
the air
During aeration of wastewater,these compounds collect on
the surface of the air bubbles and thus create a very stable
foam,
ABS was especially troublesome because it resisted
breakdown by biological means.As a result of legislation
in 1965,ABS has been replaced in detergents by lineax-
alkyl-sulfonate (LAS),which is biodegradable, So-called
"hard" synthetic detergents axe still used extensively in
many foreign countries,
Two tests are now used to determine the presence of
surfactants in water and wastewater,The MBAS
(methylene blue active substances) test is used for anionic
surfactans,Nonionic surfactants are measured using the
CTAS (cobalt thiocyanate active substances) test,
2-7 Individual Organic Compounds
Individual organic compounds are determined to assess the
presence of priority pollutants identified by the U.S,
Environmental Protection Agency (U.S,EPA) and a
number of new emerging compounds of concern,
Priority pollutants (both inorganic and organic) have been
and are continuing to be selected on the basis of their
known or suspected carcinogenicity,mutagenicity,
teratogenicity,or high acute toxicity,
Priority Pollutants
The Environmental Protection Agency has identified
approximately 129 priority pollutants in 65 classes to be
regulated by categorical discharge standards,
Two types of standard are used to control pollutant
discharges to publicly owned treatment works (POTWs),
One is prohibited discharge standards,the other is
Categorical standards
Disinfection Byproducts
It has been found that when chlorine is added to water
containing organic matter a variety of organic compounds
containing chlorine are formed,Collectively,these
compounds,along with others,are known as disinfection
byproducts (DBPs),Although general present in low
concentrations,they are of concern because many of them
are known as suspected potential human carcinogens,
Typical classes of compounds include trihalomethanes
(THMs),haloacetic acids (HAAs),trichlorophenol,and
aldehydes,
More recently,N-nitrosodimethylamine (NDMA) has been
found in the effluent from wastewater-treatment plants,
Nitrosamines are among the most powerful carcinogens
known,The U.S,EPA action limit for NDMA is 2 parts
per trillion,NDMA appears to be formed during the
chlorination process,in treated effluent,the nitrite ion can
react with hydrochloric acid,
Dimethylamine is also part of polymers used for water
treatment and for ion-exchange resins,
Considerable attention has been focused over the past five
years on the use of ultraviolet disinfection as a possible
replacement for chlorine,
2-8 Biological Characteristics
The biological characteristics of wastewater are of
fundamental importance in the control of diseases caused
by pathogenic organisms of human origin,and because of
the extensive and fundamental role played by bacteria and
other microorganisms in the decomposition and
stabilization of organic matter,both in nature and in
wastewater treatment plants,
Microorganisms Found in Surface Waters and
Wastewater
Organisms found in surface water and wastewater include
bacteria,fungi,algae,protozoa,plants and animals,and
viruses,
Living single-cell microorganisms that can only be seen
with a microscope are responsible for the activity in
biological wastewater treatment,
The prokaryotes have the simplest cell structure and
include bacteria,blue green algae (cyanobacter),and
archaea,
Many archaea are bacteria that can grow under extreme
conditions of temperature and salinity,and also include
methanogethc methane-producing bacteria,important in
anaerobic treatment processes,
The absence of a nuclear membrane to contain the cell
DNA is also a distinguishing feature of the prokaryota
organisms,
Viruses are obligate intracellular parasites that require the
machinery of a host cell to support their growth,Although
viruses contain the genetic information (either DNA or
RNA) needed to replicate themselves,they are unable to
reproduce outside of a host cell,Viruses are classified
separately according to the host infected,Bacteriophage,as
the name implies,are viruses that infect bacteria,
3 Analysis and Selection of Wastewater Flowrates and
Constituent Loadings
Reliable data for existing and projected flowrates affect the
hydraulic characteristics,sizing,and operational
considerations of the treatment system components,
Constituent mass 1oading,the product of constituent
concentration and flowrate,is necessary to determine
capacity and operational characteristics of the treatment
facilities and ancillary equipment to ensure that treatment
objectives are met,
3-1 Components of Wastewater Flows
1,Domestic (also called sanitary) wastewater,
2,Industrial wastewater,
3,Infiltration/inflow (I/I)
4,Stormwater,Infiltration is extraneous water that enters
the collection system through leaking joints,cracks and
breaks,or porous walls,
Wastewater flows in sanitary collection systems consist of
three major components,
(1) domestic wastewater,
(2) industrial wastewater,and
(3) infiltration/inflow,
3-2 Wastewater Sources and Flowrates
Domestic Wastewater Sources and Flowrates
The principal sources of domestic wastewater in a
community are the residential areas and commercial
districts,Other important sources include institutional and
recreational facilities,
For areas now served with collection systems,wastewater
flowrates are commonly determined from existing records
or by direct field measurements,
For new developments,wastewater flowrates are derived
from an analysis of population data and estimates of per
capita wastewater flowrates from similar communities,
on the average about 60 to 90 percent of the per capita
water consumption becomes wastewater,
The higher percentages(90%) apply to the northern states
during cold weather; the lower percentages(60%) are
applicable to the semiarid region of the southwestern
United States where landscape irrigation is used
extensively,
Residential Areas
Wastewater flowrates can vary depending on
various situations such as economic,social,and
other characteristics of the community,
Tab 3-1 Typical wastewater flowrates from
urban residential sources in the U.S,
Reduced household water use changes not only
the quantity of wastewater generated but also the
characteristics of wastewater as well,
Commercial Districts
Depending on the function and activity,unit flowrates for
commercial facilities can vary widely,Because of the wide
variations that have been observed,every effort should be
made to obtain records from actual or similar facilities,
Unit----passenger,bedroom,vehicle serviced,employee,
seat,guest,
Flowrates were generally expressed in terms of quantity of
flow per unit area,
Institutional Facilities
Tab 3-2 Typical wastewater flowrates from institutional
sources in the U.S,
Recreational Facilities
Wastewater flowrates from many recreational facilities are
highly subject to seasonal variations,
Tab 3-3 Typical wastewater flowrates from recreational
facilities in the U.S,
Strategies for Reducing Interior Water Use and
Wastewater Flowrates
Tab 3-4 Typical rates of water use for various devices
and appliances in the U.S,
Tab 3-5 Flow-reduction devices and appliances in the
U.S,
Water Use in Developing Countries
Water use and,consequently,wastewater-generation rates
in developing countries,however,are significantly lower,
In some cases,the water supply is only available for
limited periods of the day,
Sources and Rates of Industrial (Nondomestic)
Wastewater Flows
Extremely high peak flowrates may be reduced by the use
of onsite detention tanks and equalization basins,
Typical design values are 7.5 to 14 m3/ha·d for light
industrial developments and 14 to 28 m3/ha·d for medium
industrial developments,For industries without internal
water recycling or reuse programs,it can be assumed that
about 85 to 95 percent of the water used in the various
operations and processes will become wastewater,
Average domestic (sanitary) wastewater contributed from
industrial facilities may vary from 30 to 95 L/capita·d,
Infiltration/Inflow
Fig,3-1 Graphic identification of infiltration/inflow
Infiltration,Water entering a collection system
from a variety of entry points including service
connections and from the ground through such
means as defective pipes,pipe joints,connections,
or access port (manhole) walls,
Steady inflow,Water discharged from cellar and
foundation drains,cooling-water discharges,and
drains from springs and swampy areas,This type
of inflow is steady and is identified and measured
along with infiltration,
Direct inflow,Those types of inflow that
have a direct stormwater runoff' connection
to the sanitary collection system and cause
an almost immediate increase in wastewater
flowrates,Possible sources are roof leaders,
yard and areaway drains,access port covers,
cross connections from storm drains and
catch basins,and combined systems,
Infiltration into Collection Systems
The proportion of the rainfall that percolates into the
ground depends on the character of the surface and soil
formation and on the rate and distribution of the
precipitation,Any reduction in permeability,such as that
due to buildings,pavements,or frost,decreases the
opportunity for precipitation to become groundwater and
increases the surface runoff correspondingly,
The presence of high groundwater results in leakage into
the collection systems and in an increase in the quantity of
wastewater and the expense of disposing of it,
Infiltration/inflow is a variable part of the wastewater,
depending on the quality of the material and workmanship
in constructing the collection systems and building
connections,the character of the maintenance,and the
elevation of the groundwater compared with that of the
collection system,
The rate and quantity of infiltration depend on the length of
the collection system,the area served,the soil and
topographic conditions,and,to a certain extent,the
population density (which affects the number and total
length of house connections),
The use of high quality pipe with dense
walls,pre-cast access port sections,and
joints sealed with rubber or synthetic
gaskets is standard practice in modern
collection-system design to reduce
infiltration,
Exfiltration from Collection Systems
Collection systems that have high infiltration rates
and are in need of rehabilitation also may exhibit
high exfiltration,
If the piping and joints are in poor condition,
significant quantities of wastewater may seep into
the ground,travel through the gravel bedding of
the piping system,or even surface in extreme
cases,
Combined System Flowrates
During a rainfall event,the amount of storm
flow is normally much larger than the dry-
weather wastewater flow,and the observed
flows during wet weather can mask
completely the dry weather flow patterns,
When the collection system capacity is
exceeded,a portion of the flow may be
discharged directly into a receiving body
through overflows(maybe intentionally
most of times),or routed to a special
combined sewer overflow (CSO) treatment
facility,
In some cases where the combined system
is undersized,flooding or surcharging may
occur at various upstream locations within
the system,
In contrast,the hydrograph at the treatment
plant shows less distinct flow peaks and a
lag time of several hours for flows to return
to normal dry-weather levels following
rainfall cessation,
The peak flowrates and accompanying
mass loadings,however,must be accounted
for in the hydraulic design of the treatment
plant and in the selection of appropriate unit
operations and processes,
3-3 Analysis of Wastewater Flowrate Data
In cases where only flowrate data in the collection system
is available,it must be recognized that the flowrates may
differ somewhat from the flowrate entering the treatment
plant because of the flow-dampening effect of the sewer
system,
Peak hourly flowrates may also be attenuated by the
available storage capacity in the sewer system,
Definition of Terms
Tab 3-6 Terminology used to quantify observed
variations in flowrate and constituent concentrations
Wastewater flowrates vary during the time of day,day of
the week,season of the year,or depending upon the nature
of the dischargers to the collection system,
Short-Term Variations
Fig,3-3 Typical hourly variations in domestic wastewater
flowrates
Minimum flows occur during the early morning hours
when water consumption is lowest and when the base flow
consists of infiltration and small quantities of sanitary
wastewater,
A second peak flow generally occurs in the early evening
between 7 and 9 P.M,The time of occurrence and the
amplitude of the peak flowrates vary with the size of the
community and the length of the collection system,
As the community size increases,the variations between
the high and low flows decrease due to (1) the increased
storage in the collection system of large communities that
tends to equalize flowrates and (2) changes in the
economic and social makeup of the community,When
extraneous flows are minimal,wastewater discharge
curves resemble water consumption curves,but with a lag
of several hours,
Seasonal Variations
Seasonal variations in domestic wastewater flows are
commonly observed at resort areas,in small communities
with college campuses,and in communities that have
seasonal commercial and industrial activities,
Industrial Variations
Industrial wastewater discharges are difficult to predict,
Many manufacturing facilities generate relatively constant
flowrates during production,but the flowrates change
markedly during cleanup and shutdown,
Industrial discharges are most troublesome in smaller
wastewater-treatment plants where there is limited capacity
to absorb shock loadings,
Wastewater Flowrate Factors
Peaking factors can be developed based on
maximum hour,maximum day,maximum
month,or other time periods,and are applied
most frequently to determine the peak
hourly flowrate,
The most common method of determining
the peaking factor is from the analysis of
flowrate data,
3-5 Analysis of Constituent Mass Loading Data
From the standpoint of treatment processes,one of the
most serious deficiencies results when the design of a
treatment plant is based on average flowrates and average
BOD and TSS loadings,with little or no recognition of
peak conditions,
In many communities,peak influent flowrates and BOD
and TSS loadings can reach two or more times average
values,it must also be emphasized that,in nearly all cases,
peak flowrates and BOD and TSS mass-loading rates do
not occur at the same time,
Wastewater Constituent Concentrations
Composite samples made up of portions of samples collected
at regular intervals during a day are used,
Quantity of Waste Discharged by Individuals in the
United States,
Tab,3-7 Quantity of waste discharged by individual on a
dry weight basis
If one or more members of a family are ill and shedding
pathogens,the number of measured organisms can increase by
several orders of magnitude,
Composition of Wastewater in Collection Systems
Tab,3-8 Typical composition of untreated domestic
wastewater
Because there is no "typical" wastewater,it must be
emphasized that the typical data presented in Table 3-8
should only be used as a guide,
Mineral Increase Resulting from Water Use
Tab,3-9 Typical mineral increase from domestic water
use
Increases in the mineral content of wastewater may be due
in part to addition of highly mineralized water from private
wells and groundwater and from industrial use,Domestic
and industrial water softeners also contribute significantly
to the increase in mineral content,
Variations in Constituent Concentrations
Short-Term Variation in Constituent Values
Fig,3-4 Typical hourly variations in flow and strength of
domestic wastewater
The BOD variation generally follows the flow,The peak
BOD (organic matter) concentration often occurs in the
evening,
Seasonal Variation in Constituent Values,
Variations in Industrial Wastewater
In some cases,flow values and water quality measurements
may vary by several orders of magnitude over a period of a
year,
For example,the BOD and TSS concentrations contributed
from vegetable-processing facilities during the noon wash-
up period may far exceed those contributed during working
hours,Problems with high short-term loadings most
commonly occur in small treatment plants that have
limited reserve capacity to handle "shock loadings." The
seasonal impact of industrial wastes such as canneries can
cause both the flow and BOD loadings to increase from
two to five times average conditions,
If industrial wastes are to be discharged to the collection
system for treatment in a municipal wastewater facility,it
will be necessary to characterize the wastes adequately to
identify the ranges in constituent concentrations and mass
loadings,Such characterization is also needed to determine
if pretreatment is required before the waste is permitted to
be discharged into the collection system,
With sufficient characterization of the wastewater from
industrial discharges,suitable pretreatment facilities can be
provided and plant upsets can be avoided,
Variations in Constituent Values in Combined
Collection Systems,
Tab,3-10 Typical factors influencing the characteristics
of combined wastewater
Fig,3-5 Typical variations of flowrate,BOD,TSS,and
fecal coliform in a combined collection system during a
storm event
As shown,the BOD and fecal coliform bacteria
concentrations are low during the storm when runoff flows
are high,After the storm,when runoff subsides and the
flow consists primarily of wastewater,concentrations rise
significantly,
Unlike BOD and fecal coliform bacteria,TSS
concentrations rise slightly during the storm,and remain
unchanged after the storm,
The slight rise in the TSS concentration during the peak
flow may be due to a phenomenon common to many
combined sewer systems known as the "first flush”,
Much of the accumulated surface contaminants are washed
into the combined system,In combined collection systems,
the increased flows may be capable of resuspending
material deposited previously during low-flow periods,
Factors known to contribute to the magnitude and
frequency of the first-flush effect include combined sewer
slopes; street and catch basin cleaning frequency and
design; rainfall intensity and duration; and surface buildup
of debris and contaminants,
Wastewater from combined collection systems usually
contains more inorganic matter than wastewater from
sanitary collection systems because of the larger quantities
of storm drainage that enter the combined sewer system,
Effect of Mass Loading Variability on Treatment
Plant Performance
Fig,3-6 Illustration of diurnal Wastewater flow,BOD and
Mass loading variability
The variations are more pronounced in small collection
systems where the collection system storage capacity does
not provide a significant dampening effect,The impact of
these load variations is seen most dramatically in the
effects on biological treatment operating conditions,
Fig,3-7 Example variations of TSS and BOD
concentrations and mass loadings over a monthly period
3-6 Selection of Design Flowrates and Mass Loadings
The rated capacity of wastewater-treatment plants is
normally based on the average annual daily flowrate at the
design year plus an allowance for future growth,
Conditions that must be considered include peak and
minimum hydraulic flowrates and the maximum,minimum
and sustained process constituent mass loading rates,
Additionally,periods of initial operation and low flows
and loads must be taken into consideration in design,
Tab,3-11 Typical flowrates and mass loading factors
used for the design and operation of wastewater-
treatment facilities
The overall objective of wastewater treatment is to provide
a wastewater-treatment system that is capable of coping
with a wide range of probable wastewater conditions while
complying with the overall performance requirements,
Design Flowrates
Flowrates need to be developed both for the initial period
of operation and for the future (design) period,
Consideration of the flowrates during the early years of
operation is often overlooked,and oversizing of equipment
and inefficient operation can result,
Rationale for the Selection of Flowrates
The process units and hydraulic conduits must be sized to
accommodate the anticipated peak flowrates, Provisions
have to be made to ensure bypassing of wastewater does
not occur either in the collection system or at the treatment
plant,
Forecasting Flowrates
A yardstick by which total dry-weather base flow can be
measured is 460 L/capita·d,established by the U.S,EPA as
a historical average where infiltration is not excessive,
Minimum Flowrate
In cases where very low nighttime flow is expected,
provisions for recycling treated effluent may have to be
included to sustain the process,
In the absence of measured flowrate data,minimum daily
flowrates may be assumed to range from 30 to 70 percent
of average flowrates for medium- to large size
communities,respectively,
Peak Flowrate Factors
Tab,3-11 Typical flowrates and mass loading factors
used for the design and operation of wastewater-
treatment facilities
Peak hourly flowrates are used to size the hydraulic
conveyance system and other facilities such as
sedimentation tanks and chlorine contact tanks where little
volume is available for flow dampening,
Other peaking factors such as maximum week or maximum
month may be used for treatment facilities such as pond
systems that have long detention times or for sizing solids
and biosolids processing facilities that also have long
detention times or ample storage,
?Part I Wastewater Engineering
?1 Wastewater Engineering,An Overview
Fig,1-1 Schematic diagram of a wastewater management infrastructure
1-1 Terminology
Table 1-1 Terminology commonly used in the field of wastewater engineering
1-2 Impact of Regulations on Wastewater Engineering
1-3 Health and Environmental Concerns in Wastewater
Management
Fig,1-2 Covered treatment plant facilities for the control of odor emissions
1-4 Wastewater Characteristics
Tab 1-2 Levels of wastewater treatment
Tab 1-3 Unit Operations and Processes used to Remove Constituents Found in
Wastewater
1-5 Wastewater Treatment
Fig 1-3 Facilities used for chemical treatment of odors from treatment facilities
Fig,1-4 UV lamps used for the disinfection of wastewater
1-6 Wastewater Reclamation and Reuse
1-7 Biosolids and Residuals Management
Fig,1-5 Egg-shaped digesters used for the anaerobic treatment of biosolids
2 Constituents in Wastewater
An understanding of the nature of wastewater is essential in the
design and operation of wastewater collection,treatment,and
reuse facilities,and in the engineering management of
environmental quality,
(1) the constituents found in wastewater,
(2) sampling and analytical procedures,
(3) physical characteristics,
(4) inorganic nonmetallic constituents,
(5) metallic constituents,
(6) aggregate organic constituents,
(7) individual organic constituents and compounds,and
(8) biological characteristics,
2-1 Wastewater Constituents
Constituents Found in Wastewater
Table 2-1 Common analyses used to assess
the constituents found in wastewater
Many of the physical properties and chemical and
biological characteristics are interrelated,For example,
temperature,a physical property,affects both the
amounts of gases dissolved in the wastewater and the
biological activity in the wastewater…
Constituents of Concern in Wastewater Treatment
Tab 2-2 Principal constituents of concern in wastewater
treatment
Suspended solids can lead to sludge deposition and
anaerobic conditions;
Biodegradable organics composed of proteins;
carbohydrates and fats,and are measured most commonly
in terms of BOD and COD;
Pathogens can transmite Communicable diseases;
Priority pollutants include carcinogenicity,metogenicity,
teratogenicity or high acute toxicity;
Nutrients lead to the growth of undesirable aquatic life;
Refractory organics include surfactants,phenols,and
agricultural pesticides,
2-2 Sampling and Analytical Procedures
Sampling
(1) routine operating data for accessing overall plant
performance
(2) data that can be used to document the performance of a
given treatment operation or process
(3) data that can be used to implement proposed new
programs
(4) data needed for reporting regulatory compliance,
The data collected must be,
(1),Representative,
(2).Reproducible.The data must be reproducible
by others following the same sampling and
analytical protocols,
(3),Defensible,The data must have a known
degree of accuracy and precision,
(4),Useful,The data can be used to meet the
objectives of the monitoring plan,
There are no universal procedures for sampling,
Sampling programs must be tailored individually to fit
each situation,
Quality assurance project plan (QAPP) (known
previously quality assurance/quality control,QA/QC),
(1).Sampling plan,
(2).Sample types and size,
(3).Sample labeling and chain of custody,
(4).Sampling methods,
(5).Sampling storage and preservation,
(6).Sample constituents,
(7).Analytical methods,
If the physical,chemical,and/or biological integrity of
the samples is not maintained during interim periods
between sample collection and sample analysis,a
carefully performed sampling program will become
worthless,
Prompt analysis is undoubtedly the most positive
assurance against error due to sample deterioration,
Probable errors due to deterioration of the sample
should be noted in reporting analytical data,
Methods of Analysis
The analyses used to characterize wastewater vary from
precise quantitative chemical determinations to the more
qualitative biological and physical determinations,
The quantitative methods of analysis are either gravimetric,
volumetric,or physicochemical,
Turbidimetry,colorimetry,potentiometry,polarography,
adsorption spectrometry,fluorometry,and nuclear
radiation are representative of the physicochemical
analyses,
Units of Measurement for Physical and
Chemical Parameters
kg/m3,%(by volume or by mass),pg/L,ng/L,μg/L,mg/L,
g/L,ppb,ppm,mol/L,eq/L,meq/L,
The concentration of trace constituents is usually
expressed as micrograms per liter (μg/L) or nanograms per
liter (ng/L),
For dilute systems,one liter of sample weighs
approximately one kilogram,the units of mg/L or g/m3 are
interchangeable with ppm,
"parts per billion" (ppb) and "parts per trillion"(ppt) are
used interchangeably with μg/L and ng/L
2-3 Physical Characteristics
The most important physical characteristic of
wastewater is its total solids content,which is
composed of floating matter,settleable matter,
colloidal matter,and matter in solution,Other
important physical characteristics include particle
size distribution,turbidity,color,transntittance,
temperature,conductivity,and density,specific
gravity and specific weight,Odor,sometimes
considered a physical factor,is discussed in the
following section,
Solids
In the characterization of wastewater,coarse materials are usually
removed before the sample is analyzed for solids,
Tab 2-3 Definitions of solids found in wastewater
Fig,2-1 Interrelationships of solids found in water and wastewater,
In much of the water quality literature,the solids passing through
the filter are called dissolved solids,
A filtration step is used to separate the total suspended solids (TSS)
from the total dissolved solids (TDS),Filters with nominal pore sizes
varying from 0.45 μm to about 2.0 μm have been used for the TSS test,
Fig,2-2 Size ranges of organic contaminants in wastewater and size
separation and measurement techniques used for their quantification
Particle Size Distribution
Information on particle size is of importance in assessing
the effectiveness of treatment processes (e.g.,secondary
sedimentation,effluent filtration and effluent disinfection),
The biological conversion rate of these particles is
dependent on size,
The methods used most commonly to study and quantify
the particles in wastewater are serial filtration,electronic
particle counting,and microscopic observation,
Serial Filtration
2.0 μm as specified in Standard Methods for the TSS test,
More than 20 mg/L of additional TSS would have been
measured,
Electronic Particle Size Counting
Diluted sample through a calibrated orifice, The
conductivity is correlated to the size of an equivalent
sphere,
Fig,2-5 Volume fraction of particle sizes found in the
effluent from two activated-sludge plants with clarifiers
having different side water depths
However,the particle size data for the large particles are
quite different,owing primarily to the design and operation
of the secondary clarification,
Microscopic Observation
Various types of stains can be used on a routine basis,to
qualitatively assess microscope slide,
Video camera attached to a microscope and transmitted to a
computer are dependent on the computer software,the
mean,minimum,and maximum diameter,length to width
ratio,the circumference,the surface area,the volume,and
the centroid, Particle imaging greatly reduces the time
required but the cost of the software and equipment is
often prohibitive for many small laboratories,
Turbidity
Turbidity,a measure of the light-transmitting properties of
water,is another test used to indicate the quality of waste
discharges and natural waters with respect to colloidal and
residual suspended matter,
The results of turbidity measurements are reported as
nephelometric turbidity units (NTU),
It should be noted that the presence of air bubbles in the
fluid will cause erroneous turbidity readings,In general,
there is no relationship between turbidity and the
concentration of total suspended solids in untreated
wastewater,
There is,however,a reasonable relationship between
turbidity and total suspended solids for the settled and
filtered secondary effluent from the activated sludge
process,
The conservation factors for settled secondary effluent and
for secondary effluent filtered with a granular-medium
depth filter will typically vary from 2.3 to 2.4 and 1.3 to
1.6,respectively,
However,turbidity readings at a given facility can be used
for process control,Some on line turbidity meters used to
monitor the performance of microfiltration units are
affected by the air used to clean the membranes,
Color
Condition refers to the age of the wastewater,which is
determined qualitatively by its color and odor,Fresh
wastewater is usually a brownish-gray color,sequentially
from gray to dark gray,and ultimately to black that is
often described as septic,
In most cases,the gray,dark gray,and black color of the
wastewater is due to the formation of metallic sulfides,
which form as the sulfide produced under anaerobic
conditions reacts with the metals in the wastewater,
Absorption/Transmittance
The absorbance measured using a spectrophotometer and a
fixed path length (usually 1.0 cm) is a measure of the
amount of light,of a specified wave-length,
The factors that affect the percent transmission include
selected inorganic compounds (e.g.,copper; iron,etc.),
organic compounds (e.g.,organic dyes,humic substances,
and conjugated ring compounds such as benzene and
toluene),and TSS,
Iron is considered to be the most important with respect to
UV absorbance because dissolved iron can absorb UV
light directly and because iron will adsorb onto suspended
solids,bacterial clumps and other organic compounds,
The sorbed iron can prevent the UV light from penetrating
the particle and inactivating organisms that may be
embedded within the particle,Dosage control is extremely
important when UV disinfection is to be used,
Organic constituents,are compounds with six conjugated
carbons or a five- or six-member conjugated ring,The
reduction in transmittance observed during storm events is
often ascribed to the presence of humic substances from
stormwater flows,
Fig,2-6 Transmittance measured at various wavelengths
for activated-sludge effluents and lagoon effluents
Unfiltered and filtered transmittance are mearsured in
wastewater in connection with the evaluation and design of
UV disinfection systems,
Temperature
The temperature of wastewater is commonly higher than
that of the local water supply,because of the addition of
warm water from households and industrial activities,As
the specific heat of water is much greater than that of air,
the observed wastewater temperatures are lower only
during the hottest summer months,
Effects of Temperature
The temperature of water is a very important parameter
because of its effect on chemical reactions and reaction
rates,aquatic life,and the suitability of the water for
beneficial uses,
Industrial establishments that use surface water for cooling
water purposes are particularly concerned with the
temperature of the intake water,
In addition,oxygen is less soluble in warm water than in
cold water,The the rate of biochemical reactions that
accompanies an increase in temperature,combined with
the decrease in the quantity of oxygen present in surface
waters,can often cause serious depletions in dissolved
oxygen concentrations in the summer months,
A sudden change in temperature can result in a high rate of
mortality of aquatic life,Moreover,abnormally high
temperatures can foster the growth of undesirable water
plants and wastewater fungus,
Optimum Temperatures for Biological Activity
Optimum temperatures are in the range from 25 to 35℃,
Aerobic digestion and nitrification stops at50℃, At 15℃,
methane-producing bacteria become quite inactive,and at
about 5℃,the autotrophic-nitrifying bacteria practically
cease functioning,At 2℃,even the chemoheterotrophic
bacteria dormant,
Conductivity
The conductivity increases as the concentration of ions
increases,In effect,the measured EC value is used as a
surrogate measure of TDS concentration,
2-4 Inorganic Nonmetallic Constituents
Inorganic chemical constituents of concern include
nutrients,nonmetallic constituents,metals,and gases,
Inorganic nonmetallic and metallic constituents derive from
the background levels in the water supply and from the
additions resulting from domestic use,from the addition of
highly mineralized water from private wells and
groundwater,and from industrial use,
Inorganic nonmetallic consfituents considered in this
section include pH,nitrogen,phosphorus,alkalinity,
chlorides,sulfur,other inorganic constituents,gases,and
odors,
Chlorides
Chlorides in natural water result from the leaching of
chloride-containing rocks and soils with which the water
comes in contact,and in coastal areas from saltwater
intrusion,
Human excreta contain about 6 g of chlorides per person
per day,If hardness of water is high,home regeneration
type water softeners will also add large quantities of
chlorides,
Because conventional methods of waste treatment do not
remove chloride to any significant extent,higher than usual
chloride concentrations can be taken as an indication that a
body of water is being used for waste disposal,
Alkalinity
Alkalinity in wastewater results from the presence of the
hydroxides [OH-],carbonates [CO32-],and bicarbonates
[HCO3- ] of elements such as calcium,magnesium,sodium,
potassium,and ammonia,Of these,calcium and magnesium
bicarbonates are most common,
The alkalinity in wastewater helps to resist changes in pH
caused by the addition of acids,Alkalinity is determined by
titrating against a standard acid,
In practice,alkalinity is expressed in terms of calcium
carbonate,3 meq/L of alkalinity would be expressed as 150
mg/L as CaCO3,
Nitrogen
Nitrogen is an essential building block in the synthesis of
protein, Insufficient nitrogen can necessitate the addition
of nitrogen to make the waste treatable,
Sources of Nitrogen
(1) plant and animal origin,
(2) sodium nitrate,
(3)atomspheric nitrogen,
Forms of Nitrogen
The chemistry of nitrogen is complex because of the
several oxidation states,
The most common and important forms of nitrogen are
ammonia,ammonium,nitrogen gas,nitrite ion,and
nitrate ion, The oxidation state of nitrogen in most organic
compounds is -III,
Tab 2-5 Definition of the various terms used to define
various nitrogen species
Urea readily converted to ammonium carbonate,is seldom
found in untreated municipal wastewaters,Organic
nitrogen is determined analytically using the Kjeldald
method,
Total Kjeldabl nitrogen is the total of the organic and
ammonia nitrogen,
Ammonia nitrogen exists in aqueous solution as either the
ammonium ion (NH4+) or ammonia gas (NH3),depending
on the pH of the solution,
Nitrite nitrogen,determined colorimetrically,is relatively
unstable oxidized to the nitrate form,Nitrite can be very
important in wastewater or water pollution studies because
it is extremely toxic to most fish and other aquatic species,
Nitrites present in wastewater effluents are oxidized by
chlorine and thus increase the chlorine dosage
requirements and the cost of disinfection,
The U.S,EPA primary drinking water standards limit
nitrogen to 45 mg/L as NO3-,because of its serious and
occasionally fatal effects on infants,Nitrates may vary in
concentration from 0 to 20 mg/L as N in wastewater
effluents,
Nitrogen Pathways in Nature
Fig,2-7 Generalized nitrogen cycle in the aquatic and
soil environment
Decomposition by bacteria readily changes the organic
form to ammonia,The age of wastewater is indicated by
the relative amount of ammonia that is present,
The predominance of nitrate nitrogen in wastewater
indicates that the waste has been stabilized with respect to
oxygen demand,Nitrates,however,can be used by plants
and animals to form protein,
Phosphorus
Municipal wastewaters may contain from 4 to 16 mg/L of
phosphorus as P,
The usual forms of phosphorus that are found in aqueous
solutions include the orthophosphate,polyphosphate,and
organic phosphate,
Polyphosphates undergo hydrolysis in aqueous solutions
and revert to the orthophosphate forms; however,this
hydrolysis is usually quite slow,The organically bound
phosphorus can be an important constituent of industrial
wastes and wastewater sludge,
The polyphosphates and organic phosphates must be
converted to orthophosphates using an acid digestion step,
Sulfur
The sulfate ion occurs naturally in most water supplies and
is present in wastewater as well,Sulfur is required in the
synthesis of proteins and is released in their degradation,
Hydrogen sulfide gas,which will diffuse into the
headspace above the wastewater sewers that are not
flowing full,tends to collect at the crown of the pipe,The
accumulated H2S can then be oxidized biologically to
sulfuric acid,which is corrosive to concrete sewer pipes,
This corrosive effect,known as "crown rot," can seriously
threatened the structural integrity of the sewer pipe,
Sulfates may upset the biological process if the sulfide
concentration exceeds 200 mg/L,If burned in gas engines,
the products of combustion can damage the engine,
Gases
Gases commonly found in untreated wastewater include
nitrogen (N2),oxygen (O2),carbon dioxide (CO2),
hydrogen sulfide (H2S),ammonia (NH3),and
methane(CH4),The latter three are derived from the
decomposition of the organic matter present in wastewater
and are of concern with respect to worker health and safety,
Environmental engineer must be familiar include chlorine
(Cl2) and ozone (O3),and the oxides of sulfur and
nitrogen,
It will be useful to review the ideal gas law and to consider
the solubility of gases in water and Henry's law as applied
to the gases of interest,
Solubility of Gases in Water
The actual quantity of a gas that can be present in solution
is governed by,
(1) the solubility of the gas as defined by Henry's law,
(2) the partial pressure of the gas in the atmosphere,
(3) the temperature,and
(4) the concentration of the impurities in the water (e.g.,
salinity,suspended solids,etc.),
The Ideal Gas Law
Boyle's law (volume of a gas is inversely proportional to
pressure at constant temperature)
Charles' law (volume of a gas is directly proportional to
temperature at constant pressure)
Dissolved Oxygen
Oxygen is only slightly soluble in water,Dissolved oxygen
levels tend to be more critical in the summer months,The
presence of dissolved oxygen in wastewater is desirable
because it prevents the formation of noxious odors,
Hydrogen Sulfide
Hydrogen sulfide is formed from the reduction of mineral
sulfites and sulfates, This gas is a colorless,inflammable
compound having the characteristic odor of rotten eggs,
The loss of smell can lead to a false sense of security that
is very dangerous,The blackening of wastewater and
sludge usually results from the formation of hydrogen
sulfide,Various other metallic sulfides are also formed,
Methane
Methane is a colorless,odorless,combustible hydrocarbon
of high fuel value,
Because methane is highly combustible and the expolosion
hazard is high,access ports (manholes) and sewer
junctions or junction chambers where there is an
opportunity for gas to collect should be ventilated with a
portable blower during and before the time required for
operating personnel to work in them for inspection
renewals,or repairs,
Odors
Odors in domestic wastewater usually are caused by gases
produced by the decomposition of organic matter or by
substances added to the wastewater,
Industrial wastewater may contain either odorous
compounds or compounds that produce odors during the
process of wastewater treatment,
Odors have been rated as the foremost concern of the public
relative to the implementation of wastewater treatment
facilities,
Within the past few years,the control of odors has become a
major consideration in the design and operation of
wastewater collection,treatment,and disposal facilities,
especially with respect to the public acceptance of these
facilities,
In many areas,projects have been rejected because of the
concern over the potential for odors,
Effects of Odors
Effects of odors is related primarily to the psychological
stress rather than to the harm they do to the body,
Offensive odors can cause poor appetite for food,lowered
water consumption,impaired respiration,nausea and
vomiting,and mental perturbation,and can lead to the
deterioration of personal and community pride,interfere
with human relations,discourage capital investment,lower
socioeconomic status,and deter growth,
These problems can result in a decline in market and rental
property values,tax revenues,payrolls,and sales,
Detection of Odors
One of the difficulties in developing a universal theory has
been the inadequate explanation of why compounds with
similar structures may have different odors and why
compounds with very different structures may have similar
odors,
Tab 2-7 Major categories of odorous compounds
associated with untreated wastewater
Odor Characterization and Measurement
It has been suggested that four independent factors are
required for the complete characterization of all odor,
intensity,character,hedonics,and detectability,
Odor can be measured by sensory methods,and specific
odorant concentrations can be measured by instrumental
methods,
MDTOC ----minimum detectable threshold odor
concentration
The ED50 value represents the number of times all odorous
air sample must be diluted before the average person(50
percentile) can barely detect an odor in the diluted sample,
TON---- threshold odor number
2-5 Metallic Constituents
Many of these metals are also classified as priority
pollutants,
The presence of any of these metals in excessive quantities
will interfere with many beneficial uses of the water
because of their toxicity; therefore,it is frequently
desirable to measure and control the concentrations of
these substances,
Importance of Metals
All living organisms require varying amounts (macro and
micro) of metallic elements,such as iron,chromium,
copper,zinc,and cobalt,for proper growth,but the same
metals can be toxic when present in elevated
concentrations,
Where composted sludge is applied in agricultural
applications,arsenic,cadmium,copper,lead,mercury,
molybdenum,nickel,selenium,and zinc must be
determined,
Sources of Metals
These are found particularly in metal-plating wastes and
should be removed by pretreatment at the site of the
industry rather than be mixed with the municipal
wastewater,Fluoride,a toxic anion,is found commonly in
wastewater from electronics manufacturing facilities,
Tab 2-9 Typical waste compounds produced by
commercial,industrial,and agricultural activities that
have been classified as priority pollutants
Sampling and Methods of Analysis
Metals are determined typically by flame atomic absorption,
electrothermal atomic absorption,inductively coupled
plasma,or IPC/mass spectrometry,
2-6 Aggregate Organic Constituents
The organic matter in wastewater typically consists of
proteins (40 to 60 percent),carbohydrates (25 to 50 per
cent),and oils and fats (8 to 12 percent),Because urea
decomposes rapidly it is seldom found in other than very
fresh wastewater,
In general,the analyses may be classified into those used to
measure aggregate organic matter comprising a number of
organic constituents with similar characteristics that cannot
be distinguished separately,
Measurement of Organic Content
Gross concentrations of organic matter are greater than
about 1.0 mg/L and trace concentrations are in the range
of l0 –12 to 100 mg/L,
Laboratory methods include,
(1) biochemical oxygen demand(BOD),
(2) chemical oxygen demand (COD),
(3) total organic carbon (TOC),
Complementing these laboratory tests is the theoretical
oxygen demand (ThOD),which is determined from the
chemical formula of the organic matter,
Trace organics in the range of 10–12 to 10-13 mg/L are
determined using instrumental methods including gas
chromotography and mass spectroscopy,
Biochemical Oxygen Demand (BOD)
Despite the widespread use of the BOD test,it has a
number of limitations,BOD test results are now used
(1) to determine the approximate quantity of oxygen that
will be required to biologically stabilize the organic matter
present,
(2) to determine the size of waste treatment facilities,
(3) to measure the efficiency of some treatment processes,
(4) to determine compliance with wastewater discharge
permits,
Basis for BOD Test
The term COHNS(which represents the elements carbon,
oxygen,hydrogen,nitrogen,and sulfur) represent the
organic waste and the term C5H7NO2 (first proposed by
Hoover and Porges) to represent cell tissue,
If only the oxidation of the organic carbon,The oxygen
demand is known as the ultimate carbonaceous or first-
stage BOD,and is usually denoted as UBOD,
BOD Test Procedure
To ensure that meaningful results are obtained,the samples
must be suitably diluted with a specially prepared dilution
water so that adequate nutrients and oxygen will be
available during the incubation period,Normally,several
dilutions are prepared to cover the complete range of
possible values,
Tab 10 Measurable of BOD using various dilutions of
samples
The BOD of the sample is the difference in the dissolved
oxygen concentration values,expressed in milligrams per
liter,divided by the decimal fraction of sample used,
When testing waters with low concentrations of
microorganisms,a seeded BOD test is conducted,
Fig,2-8 Procedure for settling up BOD test bottles,
(a)with unseeded dilution water and (b) with seeded
dilution water
The organisms contained in the effluent from primary
sedimentation facilities are used commonly as the seed for
the BOD test,Seed organisms can also be obtained
commercially,When the sample contains a large
population of microorganisms (e.g.,untreated wastewater),
seeding is not necessary,
Longer time periods (typically 7 days),which correspond
to work schedules,are often used,especially in small
plants where the laboratory staff is not available on the
weekends,
The 20℃ temperature used is an average value for slow-
moving streams in temperate climates and is easily
duplicated in an incubator,
After incubation,the dissolved oxygen of the sample is
measured and the BOD is calculated using the following
Eq.,
BOD,mg/L = (D1-D2)/P
When diluted water is seeded,
BOD,mg/L = [(D1-D2)-(B1-B2)]f/P
Within a 20-day period,the oxidation of the carbonaceous
organic matter is about 95 to 99 percent complete,and in
the 5-day period used for the BOD test,oxidation is from
60 to 70 percent complete,
Effect of particle size on BOD Reaction Rates
The observed BOD reaction rate coefficients are affected
significantly by the size of the particles in wastewater,
Limitations in the BOD test
The limitations of the BOD test are as followings
(1)a high concentration of active,acclimated seed bacteria
is required;
(2)pretreatment is needed when dealing with toxic wastes,
and the effects of nitrifying organisms must be reduced;
(3)only the biodegradable organics are measured;
(4)the relatively long period of time required to obtain test
results,
Of the above,perhaps the most serious limitation is that the
5-day period may or may not correspond to the point
where the soluble organic matter that is present has been
used,
Total and soluble chemical oxygen demand(COD
and SCOD)
The COD test is used to measure the oxygen equivalent of
the organic material in wastewater that can be oxidized
chemically using dichromate in an acid solution,
CnHaObNc + dCr2O72- + (8d+c)H+ → NCO 2 + [(a+8d-3c)/2]
H2O + cNH4+ + 2dCr3+
Some of the reasons for the observed difference are as
follows:(1)many organic substances which are difficult to
oxidize biologically,such as lignin,can be oxidized
chemically,(2)inorganic substances that are oxidized by the
dichromate increase the apparent organic content of the
sample,(3)certain organic substances may be toxic to the
microorganisms used in the BOD test
One of the main advantages of the COD test is that it can
be completed in about 2.5 h,To reduce the time further,a
rapid COD test that takes only about 15 min has been
developed,
The principal fractions are particulate and soluble COD,
Fractions that have been used include,
(1)readily biodegradable soluble COD,
(2)slowly biodegradable colloidal and particulate COD,
(3)nonbiodegradable soluble COD,and
(4)nonbiodegradable colloidal and particulate COD,The
readily biodegradable soluble COD is often fractionated
further into complex COD that can be fermented to volatile
fatty acids(VFAs) and short chain VFAs,Unfortunately,as
noted previous
Oil and Grease
The term oil and grease,as commonly used,includes the
fats,oils,waxes,and other related constituents found in
wastewater,
The oil and grease content of a wastewater is determined
by extraction of the waste sample with
trichlorotrifluoroethane
Other extractable substances include mineral oils,such as
kerosene and lubricating and road oils,Oil and grease are
quite similar chemically; they are compounds (esters) of
alcohol or glycerol(glycerin) with fatty acids,The
glycerides of fatty acids that are liquid at ordinary
temperatures are called oils,and those that are solids are
called grease (or fats),
If grease is not removed before discharge of treated
wastewater,it can interfere with the biological life in the
surface waters and create films,
The low solubility of fats and oils reduces their rate of
microbial degradation,Mineral acids attack them,however,
resulting in formation of glycerin and fatty acid,In the
presence of alkalis,such as sodium hydroxide,glycerin is
liberated,and alkali salts of the fatty acids are formed,
These alkali salts are known as soaps,
They are soluble in water,but in the presence of hardness
constituents,the sodium salts are changed to calcium and
magnesium salts of the fatty acids,or so-called mineral
soaps,These are insoluble and are precipitated,
Kerosene,lubricating,and road oils are derived from
petroleum and coal tars and contain essentially carbon and
hydrogen,These oils sometimes reach the sewers in
considerable volume from shops,garages,and streets,
To an even greater extent than fats,oils,and soaps,the
mineral oils tend to coat surfaces,The particles interfere
with biological action and cause maintenance problems,
Surfactants
Surfactants,or surface-active agents cause foaming in
wastewater treatment plants and in the surface waters into
which the waste effluent is discharged,Surfactants are
most commonly composed of a strongly hydrophobic
group combined with a strongly hydrophilic group,
In the United States,ionic surfactants amount to about
two-thirds of the total surfactants,
Surfactants tend to collect at the air-water interface with
the hydrophilic in the water and the hydrophobic group in
the air
During aeration of wastewater,these compounds collect on
the surface of the air bubbles and thus create a very stable
foam,
ABS was especially troublesome because it resisted
breakdown by biological means.As a result of legislation
in 1965,ABS has been replaced in detergents by lineax-
alkyl-sulfonate (LAS),which is biodegradable, So-called
"hard" synthetic detergents axe still used extensively in
many foreign countries,
Two tests are now used to determine the presence of
surfactants in water and wastewater,The MBAS
(methylene blue active substances) test is used for anionic
surfactans,Nonionic surfactants are measured using the
CTAS (cobalt thiocyanate active substances) test,
2-7 Individual Organic Compounds
Individual organic compounds are determined to assess the
presence of priority pollutants identified by the U.S,
Environmental Protection Agency (U.S,EPA) and a
number of new emerging compounds of concern,
Priority pollutants (both inorganic and organic) have been
and are continuing to be selected on the basis of their
known or suspected carcinogenicity,mutagenicity,
teratogenicity,or high acute toxicity,
Priority Pollutants
The Environmental Protection Agency has identified
approximately 129 priority pollutants in 65 classes to be
regulated by categorical discharge standards,
Two types of standard are used to control pollutant
discharges to publicly owned treatment works (POTWs),
One is prohibited discharge standards,the other is
Categorical standards
Disinfection Byproducts
It has been found that when chlorine is added to water
containing organic matter a variety of organic compounds
containing chlorine are formed,Collectively,these
compounds,along with others,are known as disinfection
byproducts (DBPs),Although general present in low
concentrations,they are of concern because many of them
are known as suspected potential human carcinogens,
Typical classes of compounds include trihalomethanes
(THMs),haloacetic acids (HAAs),trichlorophenol,and
aldehydes,
More recently,N-nitrosodimethylamine (NDMA) has been
found in the effluent from wastewater-treatment plants,
Nitrosamines are among the most powerful carcinogens
known,The U.S,EPA action limit for NDMA is 2 parts
per trillion,NDMA appears to be formed during the
chlorination process,in treated effluent,the nitrite ion can
react with hydrochloric acid,
Dimethylamine is also part of polymers used for water
treatment and for ion-exchange resins,
Considerable attention has been focused over the past five
years on the use of ultraviolet disinfection as a possible
replacement for chlorine,
2-8 Biological Characteristics
The biological characteristics of wastewater are of
fundamental importance in the control of diseases caused
by pathogenic organisms of human origin,and because of
the extensive and fundamental role played by bacteria and
other microorganisms in the decomposition and
stabilization of organic matter,both in nature and in
wastewater treatment plants,
Microorganisms Found in Surface Waters and
Wastewater
Organisms found in surface water and wastewater include
bacteria,fungi,algae,protozoa,plants and animals,and
viruses,
Living single-cell microorganisms that can only be seen
with a microscope are responsible for the activity in
biological wastewater treatment,
The prokaryotes have the simplest cell structure and
include bacteria,blue green algae (cyanobacter),and
archaea,
Many archaea are bacteria that can grow under extreme
conditions of temperature and salinity,and also include
methanogethc methane-producing bacteria,important in
anaerobic treatment processes,
The absence of a nuclear membrane to contain the cell
DNA is also a distinguishing feature of the prokaryota
organisms,
Viruses are obligate intracellular parasites that require the
machinery of a host cell to support their growth,Although
viruses contain the genetic information (either DNA or
RNA) needed to replicate themselves,they are unable to
reproduce outside of a host cell,Viruses are classified
separately according to the host infected,Bacteriophage,as
the name implies,are viruses that infect bacteria,
3 Analysis and Selection of Wastewater Flowrates and
Constituent Loadings
Reliable data for existing and projected flowrates affect the
hydraulic characteristics,sizing,and operational
considerations of the treatment system components,
Constituent mass 1oading,the product of constituent
concentration and flowrate,is necessary to determine
capacity and operational characteristics of the treatment
facilities and ancillary equipment to ensure that treatment
objectives are met,
3-1 Components of Wastewater Flows
1,Domestic (also called sanitary) wastewater,
2,Industrial wastewater,
3,Infiltration/inflow (I/I)
4,Stormwater,Infiltration is extraneous water that enters
the collection system through leaking joints,cracks and
breaks,or porous walls,
Wastewater flows in sanitary collection systems consist of
three major components,
(1) domestic wastewater,
(2) industrial wastewater,and
(3) infiltration/inflow,
3-2 Wastewater Sources and Flowrates
Domestic Wastewater Sources and Flowrates
The principal sources of domestic wastewater in a
community are the residential areas and commercial
districts,Other important sources include institutional and
recreational facilities,
For areas now served with collection systems,wastewater
flowrates are commonly determined from existing records
or by direct field measurements,
For new developments,wastewater flowrates are derived
from an analysis of population data and estimates of per
capita wastewater flowrates from similar communities,
on the average about 60 to 90 percent of the per capita
water consumption becomes wastewater,
The higher percentages(90%) apply to the northern states
during cold weather; the lower percentages(60%) are
applicable to the semiarid region of the southwestern
United States where landscape irrigation is used
extensively,
Residential Areas
Wastewater flowrates can vary depending on
various situations such as economic,social,and
other characteristics of the community,
Tab 3-1 Typical wastewater flowrates from
urban residential sources in the U.S,
Reduced household water use changes not only
the quantity of wastewater generated but also the
characteristics of wastewater as well,
Commercial Districts
Depending on the function and activity,unit flowrates for
commercial facilities can vary widely,Because of the wide
variations that have been observed,every effort should be
made to obtain records from actual or similar facilities,
Unit----passenger,bedroom,vehicle serviced,employee,
seat,guest,
Flowrates were generally expressed in terms of quantity of
flow per unit area,
Institutional Facilities
Tab 3-2 Typical wastewater flowrates from institutional
sources in the U.S,
Recreational Facilities
Wastewater flowrates from many recreational facilities are
highly subject to seasonal variations,
Tab 3-3 Typical wastewater flowrates from recreational
facilities in the U.S,
Strategies for Reducing Interior Water Use and
Wastewater Flowrates
Tab 3-4 Typical rates of water use for various devices
and appliances in the U.S,
Tab 3-5 Flow-reduction devices and appliances in the
U.S,
Water Use in Developing Countries
Water use and,consequently,wastewater-generation rates
in developing countries,however,are significantly lower,
In some cases,the water supply is only available for
limited periods of the day,
Sources and Rates of Industrial (Nondomestic)
Wastewater Flows
Extremely high peak flowrates may be reduced by the use
of onsite detention tanks and equalization basins,
Typical design values are 7.5 to 14 m3/ha·d for light
industrial developments and 14 to 28 m3/ha·d for medium
industrial developments,For industries without internal
water recycling or reuse programs,it can be assumed that
about 85 to 95 percent of the water used in the various
operations and processes will become wastewater,
Average domestic (sanitary) wastewater contributed from
industrial facilities may vary from 30 to 95 L/capita·d,
Infiltration/Inflow
Fig,3-1 Graphic identification of infiltration/inflow
Infiltration,Water entering a collection system
from a variety of entry points including service
connections and from the ground through such
means as defective pipes,pipe joints,connections,
or access port (manhole) walls,
Steady inflow,Water discharged from cellar and
foundation drains,cooling-water discharges,and
drains from springs and swampy areas,This type
of inflow is steady and is identified and measured
along with infiltration,
Direct inflow,Those types of inflow that
have a direct stormwater runoff' connection
to the sanitary collection system and cause
an almost immediate increase in wastewater
flowrates,Possible sources are roof leaders,
yard and areaway drains,access port covers,
cross connections from storm drains and
catch basins,and combined systems,
Infiltration into Collection Systems
The proportion of the rainfall that percolates into the
ground depends on the character of the surface and soil
formation and on the rate and distribution of the
precipitation,Any reduction in permeability,such as that
due to buildings,pavements,or frost,decreases the
opportunity for precipitation to become groundwater and
increases the surface runoff correspondingly,
The presence of high groundwater results in leakage into
the collection systems and in an increase in the quantity of
wastewater and the expense of disposing of it,
Infiltration/inflow is a variable part of the wastewater,
depending on the quality of the material and workmanship
in constructing the collection systems and building
connections,the character of the maintenance,and the
elevation of the groundwater compared with that of the
collection system,
The rate and quantity of infiltration depend on the length of
the collection system,the area served,the soil and
topographic conditions,and,to a certain extent,the
population density (which affects the number and total
length of house connections),
The use of high quality pipe with dense
walls,pre-cast access port sections,and
joints sealed with rubber or synthetic
gaskets is standard practice in modern
collection-system design to reduce
infiltration,
Exfiltration from Collection Systems
Collection systems that have high infiltration rates
and are in need of rehabilitation also may exhibit
high exfiltration,
If the piping and joints are in poor condition,
significant quantities of wastewater may seep into
the ground,travel through the gravel bedding of
the piping system,or even surface in extreme
cases,
Combined System Flowrates
During a rainfall event,the amount of storm
flow is normally much larger than the dry-
weather wastewater flow,and the observed
flows during wet weather can mask
completely the dry weather flow patterns,
When the collection system capacity is
exceeded,a portion of the flow may be
discharged directly into a receiving body
through overflows(maybe intentionally
most of times),or routed to a special
combined sewer overflow (CSO) treatment
facility,
In some cases where the combined system
is undersized,flooding or surcharging may
occur at various upstream locations within
the system,
In contrast,the hydrograph at the treatment
plant shows less distinct flow peaks and a
lag time of several hours for flows to return
to normal dry-weather levels following
rainfall cessation,
The peak flowrates and accompanying
mass loadings,however,must be accounted
for in the hydraulic design of the treatment
plant and in the selection of appropriate unit
operations and processes,
3-3 Analysis of Wastewater Flowrate Data
In cases where only flowrate data in the collection system
is available,it must be recognized that the flowrates may
differ somewhat from the flowrate entering the treatment
plant because of the flow-dampening effect of the sewer
system,
Peak hourly flowrates may also be attenuated by the
available storage capacity in the sewer system,
Definition of Terms
Tab 3-6 Terminology used to quantify observed
variations in flowrate and constituent concentrations
Wastewater flowrates vary during the time of day,day of
the week,season of the year,or depending upon the nature
of the dischargers to the collection system,
Short-Term Variations
Fig,3-3 Typical hourly variations in domestic wastewater
flowrates
Minimum flows occur during the early morning hours
when water consumption is lowest and when the base flow
consists of infiltration and small quantities of sanitary
wastewater,
A second peak flow generally occurs in the early evening
between 7 and 9 P.M,The time of occurrence and the
amplitude of the peak flowrates vary with the size of the
community and the length of the collection system,
As the community size increases,the variations between
the high and low flows decrease due to (1) the increased
storage in the collection system of large communities that
tends to equalize flowrates and (2) changes in the
economic and social makeup of the community,When
extraneous flows are minimal,wastewater discharge
curves resemble water consumption curves,but with a lag
of several hours,
Seasonal Variations
Seasonal variations in domestic wastewater flows are
commonly observed at resort areas,in small communities
with college campuses,and in communities that have
seasonal commercial and industrial activities,
Industrial Variations
Industrial wastewater discharges are difficult to predict,
Many manufacturing facilities generate relatively constant
flowrates during production,but the flowrates change
markedly during cleanup and shutdown,
Industrial discharges are most troublesome in smaller
wastewater-treatment plants where there is limited capacity
to absorb shock loadings,
Wastewater Flowrate Factors
Peaking factors can be developed based on
maximum hour,maximum day,maximum
month,or other time periods,and are applied
most frequently to determine the peak
hourly flowrate,
The most common method of determining
the peaking factor is from the analysis of
flowrate data,
3-5 Analysis of Constituent Mass Loading Data
From the standpoint of treatment processes,one of the
most serious deficiencies results when the design of a
treatment plant is based on average flowrates and average
BOD and TSS loadings,with little or no recognition of
peak conditions,
In many communities,peak influent flowrates and BOD
and TSS loadings can reach two or more times average
values,it must also be emphasized that,in nearly all cases,
peak flowrates and BOD and TSS mass-loading rates do
not occur at the same time,
Wastewater Constituent Concentrations
Composite samples made up of portions of samples collected
at regular intervals during a day are used,
Quantity of Waste Discharged by Individuals in the
United States,
Tab,3-7 Quantity of waste discharged by individual on a
dry weight basis
If one or more members of a family are ill and shedding
pathogens,the number of measured organisms can increase by
several orders of magnitude,
Composition of Wastewater in Collection Systems
Tab,3-8 Typical composition of untreated domestic
wastewater
Because there is no "typical" wastewater,it must be
emphasized that the typical data presented in Table 3-8
should only be used as a guide,
Mineral Increase Resulting from Water Use
Tab,3-9 Typical mineral increase from domestic water
use
Increases in the mineral content of wastewater may be due
in part to addition of highly mineralized water from private
wells and groundwater and from industrial use,Domestic
and industrial water softeners also contribute significantly
to the increase in mineral content,
Variations in Constituent Concentrations
Short-Term Variation in Constituent Values
Fig,3-4 Typical hourly variations in flow and strength of
domestic wastewater
The BOD variation generally follows the flow,The peak
BOD (organic matter) concentration often occurs in the
evening,
Seasonal Variation in Constituent Values,
Variations in Industrial Wastewater
In some cases,flow values and water quality measurements
may vary by several orders of magnitude over a period of a
year,
For example,the BOD and TSS concentrations contributed
from vegetable-processing facilities during the noon wash-
up period may far exceed those contributed during working
hours,Problems with high short-term loadings most
commonly occur in small treatment plants that have
limited reserve capacity to handle "shock loadings." The
seasonal impact of industrial wastes such as canneries can
cause both the flow and BOD loadings to increase from
two to five times average conditions,
If industrial wastes are to be discharged to the collection
system for treatment in a municipal wastewater facility,it
will be necessary to characterize the wastes adequately to
identify the ranges in constituent concentrations and mass
loadings,Such characterization is also needed to determine
if pretreatment is required before the waste is permitted to
be discharged into the collection system,
With sufficient characterization of the wastewater from
industrial discharges,suitable pretreatment facilities can be
provided and plant upsets can be avoided,
Variations in Constituent Values in Combined
Collection Systems,
Tab,3-10 Typical factors influencing the characteristics
of combined wastewater
Fig,3-5 Typical variations of flowrate,BOD,TSS,and
fecal coliform in a combined collection system during a
storm event
As shown,the BOD and fecal coliform bacteria
concentrations are low during the storm when runoff flows
are high,After the storm,when runoff subsides and the
flow consists primarily of wastewater,concentrations rise
significantly,
Unlike BOD and fecal coliform bacteria,TSS
concentrations rise slightly during the storm,and remain
unchanged after the storm,
The slight rise in the TSS concentration during the peak
flow may be due to a phenomenon common to many
combined sewer systems known as the "first flush”,
Much of the accumulated surface contaminants are washed
into the combined system,In combined collection systems,
the increased flows may be capable of resuspending
material deposited previously during low-flow periods,
Factors known to contribute to the magnitude and
frequency of the first-flush effect include combined sewer
slopes; street and catch basin cleaning frequency and
design; rainfall intensity and duration; and surface buildup
of debris and contaminants,
Wastewater from combined collection systems usually
contains more inorganic matter than wastewater from
sanitary collection systems because of the larger quantities
of storm drainage that enter the combined sewer system,
Effect of Mass Loading Variability on Treatment
Plant Performance
Fig,3-6 Illustration of diurnal Wastewater flow,BOD and
Mass loading variability
The variations are more pronounced in small collection
systems where the collection system storage capacity does
not provide a significant dampening effect,The impact of
these load variations is seen most dramatically in the
effects on biological treatment operating conditions,
Fig,3-7 Example variations of TSS and BOD
concentrations and mass loadings over a monthly period
3-6 Selection of Design Flowrates and Mass Loadings
The rated capacity of wastewater-treatment plants is
normally based on the average annual daily flowrate at the
design year plus an allowance for future growth,
Conditions that must be considered include peak and
minimum hydraulic flowrates and the maximum,minimum
and sustained process constituent mass loading rates,
Additionally,periods of initial operation and low flows
and loads must be taken into consideration in design,
Tab,3-11 Typical flowrates and mass loading factors
used for the design and operation of wastewater-
treatment facilities
The overall objective of wastewater treatment is to provide
a wastewater-treatment system that is capable of coping
with a wide range of probable wastewater conditions while
complying with the overall performance requirements,
Design Flowrates
Flowrates need to be developed both for the initial period
of operation and for the future (design) period,
Consideration of the flowrates during the early years of
operation is often overlooked,and oversizing of equipment
and inefficient operation can result,
Rationale for the Selection of Flowrates
The process units and hydraulic conduits must be sized to
accommodate the anticipated peak flowrates, Provisions
have to be made to ensure bypassing of wastewater does
not occur either in the collection system or at the treatment
plant,
Forecasting Flowrates
A yardstick by which total dry-weather base flow can be
measured is 460 L/capita·d,established by the U.S,EPA as
a historical average where infiltration is not excessive,
Minimum Flowrate
In cases where very low nighttime flow is expected,
provisions for recycling treated effluent may have to be
included to sustain the process,
In the absence of measured flowrate data,minimum daily
flowrates may be assumed to range from 30 to 70 percent
of average flowrates for medium- to large size
communities,respectively,
Peak Flowrate Factors
Tab,3-11 Typical flowrates and mass loading factors
used for the design and operation of wastewater-
treatment facilities
Peak hourly flowrates are used to size the hydraulic
conveyance system and other facilities such as
sedimentation tanks and chlorine contact tanks where little
volume is available for flow dampening,
Other peaking factors such as maximum week or maximum
month may be used for treatment facilities such as pond
systems that have long detention times or for sizing solids
and biosolids processing facilities that also have long
detention times or ample storage,
