Environmental Concerns
Elliott Goldberg and Maung K. Min
1.0 ENVIRONMENTAL REGULATIONS AND TECHNOLOGY
1.1 Regulatory Concerns
Environmental laws and regulations including permits are reviewed in
this chapter. Included are the Federal Clean Air Act Amendment (CAAA),
the Federal Clean Water Act (CWA) regulations, the Resource Conservation
and Recovery Act (RCRA) or, as it is also known, the Solid Waste Disposal
Act. Also discussed along with the regulations under OSHAare the National
Institute for Occupational Safety and Health (NIOSH) and the Hazardous
Waste Operations and Emergency Response (HAZWOPER).
The environmental regulations covered here are not intended to be all-
inclusive but to provide a basic understanding ofthe important environmental
laws and regulations.
1.2 Technology
The environmental technology section includes reviews of waste water
treatment and air and waste minimization/pollution prevention. Waste water
treatment procedures discussed include biological treatment, activated car-
bon adsorption, air and steam stripping, chemical precipitation, ion ex-
change, and membrane separation.
635
636 Fermentation and Biochemical Engineering Handbook
Air pollution control technology includes thermal incineration, cata-
lytic incineration, carbon adsorption, absorption, condensation, baghouse
filtration, wet scrubbing, and electrostatic precipitation.
The range of technology will provide the engineer with a sufficient
background to understand the important air control measures.
2.0 LAWS, REGULATIONS AND PERMITS
2.1 Air
The Federal Clean Air Act Amendments (CAA) were initially enacted
in 1963 and modified in 1970 and 1977. The Clean Air Act Amendments of
1990 involved major changes to environmental regulations. These included
a national permitting system to regulate air pollution emissions. Its purpose
was to protect the public health and environment by indicating how and when
the various industries involved must control a list of air toxics. The
regulatory authority was given to the states and local governments. Congress,
through the CAA, authorized the EPA to develop the necessary regulations
to carry out the provisions of the act.
The EPA established the National Ambient Air Quality Standards
(NAAQS), which included allowable ceilings for specific pollutants. How-
ever, the states have the option to make any or all parts of the Clean Air Act
requirements more stringent than the minimums set by EPA. The EPA is
required to regularly evaluate the compliance status of all geographic areas
with respect to pollutants, that is, whether the NAAQS is being met for each
criteria pollutant. An area where NAAQS is not met is designated as a non-
attainment area (N.A.) for that pollutant.
Areas where the Federal Ambient Air Quality Standards are being met
are designated attainment and are subject to Prevention of Significant
Deterioration (PSD) requirements and are required to identify those areas
that are attaining or not attaining the standards.
Compliance and noncompliance can be costly. It has been estimated
that the installed cost of equipment and systems to control emissions could
range from $20 to $50 billion or higher. The technologies expected to be used
include wet scrubbing, thermal incineration, catalytic incineration, carbon
absorption, and solvent recovery. New sources and modifications ofexisting
sources of air pollution in an attainment area are regulated under the
Environmental Concerns 637
Prevention of Significant Deterioration Program (PSD). PSD review is
required if the new source or modifications result in a net emission increase
above specified levels.
The specific pollutants referred to include carbon monoxide, nitrogen
dioxide, lead, ozone, inhalable particulates, and sulfur dioxide.
Primary and secondary standards also were set by EPA, with second-
ary standards reflecting levels necessary to protect welfare in addition to
health.
An area may be in an attainment status for one pollutant and in a non-
attainment status for another pollutant. In most areas, PSD authority has
been assigned to either the state or local jurisdiction. The use of the Best
Available Control Technology (BACT) is required for each pollutant and is
based on the emission level and capital and operating costs. Regulations in
non-attainment areas are required to meet the EPA’s New Source Review
(NSR) regulations.
The Clean Air Act of 1990 included a list of 189 toxic chemicals to be
controlled and such emissions are to be reduced 90% by theyear 2000. It also
included the phasing out of chlorinated fluorocarbons (CFC’s) and carbon
tetrachloroflurocarbons (HCFC’s) by 2030.
All new and modified emission sources must meet the New Source
Performance Standards (NSPS). These standards are generally less strin-
gent than either the Best Available Control Technology (BACT) or the
Lowest Available Emission Rate (LAER).
The National Emission Standards for Hazardous Air Pollutants
(NESHAPS) specie emission standards for various hazardous air pollut-
ants and cover asbestos, arsenic, benzene, beryllium, mercury, vinyl chlo-
ride, PVC, etc.
The CAAA was promulgated to strengthen the federal air protection
program and concerns about air toxics by including an expanded National
Emission Standards for Hazardous Air Pollutants (NESHAP) program.
Concerns over the effects of hazardous air pollutants (HAP) or air toxics
resulted in the Title Voperating permit program. The relationship ofthe Title
V program to other CA4 titles is shown in Fig. 1.
638 Fermentation and Biochemical Engineering Handbook
Air Toxics Acid Rain
i-xq Permit Program
Program
- I
Figure 1. The relationship of the Title V program to other CAA titles.
2.2 Water
In 1972 Congress enacted the Federal Water Pollution Control Act
known as the Clean Water Act (CWA). In 1977 further amendments were
enacted which strengthened the provisions of the Clean Water Act. Further
refinements were enacted by Congress with the Water Quality Act Amend-
ments of 1987. The purpose of the CWA was to restore and maintain the
chemical, physical, and biological integrity ofour country's waters. It set up
specific effluent guidelines for SIC industry categories and BOD and
suspended solids continued to serve as the primary parameters. The National
Pollutant Discharge Elimination System (NPDES) was set up and authorized
EPA to establish and enforce effluent limitations on waste water discharges.
Designated priority pollutants were introduced with a permit program
and aquatic toxicity also became a permit requirement. Volatile Organic
Compounds (VOC) emissions from waste water treatment plants were
severely restricted and control of nutrients such as nitrogen and phosphorous
were required.
The Clean Water Act established standards that area-wide waste water
treatment plants be developed and implemented to assume adequate control
Environmental Concerns 639
of the quality of the effluent for industrial discharges of toxic pollutants into
Publicly Owned Treatment Works (POTW). It also stated that federal
financial assistance would be provided to construct publicly owned waste
water treatment works.
It also established that the federal agencies, the state water pollution
control agencies, interstate agencies, and the municipalities and industries
involved, prepare or develop comprehensive programs for preventing, reduc-
ing or eliminating the pollution of navigable waters and ground waters and
improving the sanitary condition of surface and underground waters. Due
regard shall be given improvements which are necessary to conserve such
waters for the protection and propagation of fish and aquatic life.
The Clean Water Act lays the basis for technology based effluent
standards of conventional pollutants such as Biochemical Oxygen Demand
(BOD), Total Suspended Solids (TSS), fecal coliform, oil and grease, pH,
toxic pollutants, and non-conventional pollutants such as active pesticides,
ingredients used in the pesticide manufacturing industry, etc.
A complete list of toxic pollutants can be found in the Code of Federal
Regulations, 40 CFR, Part 40 1.15.
The CWA established requirements for setting standards for dis-
charges from new sources for specific industries. It also lists requirements
for preventing and responding to accidental discharges of oil or hazardous
substances into navigable waters with notification requirements for releases,
removal requirements, liability standards and civil penalties. Furthermore,
the CWA established permitting programs to control discharges and severe
civil and criminal enforcement provisions for failure to comply with the law.
Compliance with the CWA must be incorporated into the design and
operation of every chemical process plant.
To summarize, the focus of the CWA is the control of pollutants in
effluent discharged from a facility through any conveyance to virtually any
stream or significant body of water. These discharges are primarily
controlled through the National Pollution Discharge Elimination System
(NPDES).
If the discharge is to a Publicly Owned Treatment Works, the plant
needs to meet pretreatment standards to limit pollutants that cannot be readily
removed by the POTW.
Discharges from the POTW are required to be in accordance with the
effluent limitations contained in the NPDES permit for the POW. If the
facility discharges directly into receiving waters, the facility must file for and
obtain its own NPDES permit.
640 Fermentation and Biochemical Engineering Handbook
2.3 Solid Waste
Resource Conservation and Recovery Act (RCRA) (Solid Waste
Disposal Act) was originally enacted by Congress in 1976 and amended
several times subsequently. The 1984 amendments set deadlines for enforc-
ing the regulations. They also placed restrictions on disposal of wastes on
land and forced tighter regulation of hazardous wastes.
In effect, Congress gave EPA the authority to control hazardous wastes
from their generation to their ultimate disposal.
Congress also sought to encourage the recycling of recoverable
material. The RCRA included the statements that:
Millions oftons of recoverablematerial which could be used
are needlessly buried each year.
Methods are available to separate usable materials from
solid waste.
The recovery and conservation of such materials can reduce
the dependence ofthe United States on foreign resources and
reduce the deficit in its balance of payments.
Principally, however, Congress aimed at the environment and
Disposal of solid waste and hazardous waste in or on the
land without carehl planning and management can present
a danger to human health and the environment.
As aresult ofthe Clean Air Act, the Water Pollution Control
Act, and other federal and state laws respecting public
health and the environment, greater amounts of solid waste,
in the form of sludge and other pollution treatment residues,
have been created. Similarly, inadequate and environmen-
tally unsound practices for the disposal or use of solid waste
have created increased amounts of air and water pollution
and other problems for the environment and health.
Open dumping is particularly harmful to health since it can
contaminate drinking water from underground and surface
supplies and pollutes the air and land.
health:
Environmental Concerns 641
Alternatives to existing methods of land disposal must be
developed, since many of the cities in the United States will
be running out of suitable solid waste disposal sites within
five years, unless immediate action is taken. Objectives of
the Act are to promote the protection of health and the
environment and to conserve valuable material and energy
resources by providing technical and financial support to
state and local governments and interstate agencies for the
development of solid waste management plans, including
resource recovery and resource conservation systems.
Furthermore the act proposed to prohibit future open dumping on the
land and required the conversion of existing open dumps to facilities which
do not pose a danger to the environment or health. The Act requires that
hazardous waste be properly managed, thereby reducing the need for
corrective action at a future date. An important consideration of RCRA was
that it required the promulgation of guidelines for solid waste collection,
transport, separation, recovery, and disposal practices and systems.
The Act set up specific procedures for establishing standards. Enforce-
ment of job safety and health standards were also written into the Act.
2.4 Occupational Safety and Health Act (OSHA)
In 1970, Congress enacted the Occupational Safety and Health Act,
which requires employers to provide safe and healthful working conditions
for their employees. It authorized the Secretary of Labor to set mandatory
occupational safety and health standards to protect employees.
As a result, the Occupational Safety and Health Review Commission
was created to review the enforcement actions taken by OSHA. The National
Institute for Occupational Safety and Health (NIOSH) was set up to research
work place safety and health and to recommend standards to OSHA for
controlling exposure to harmful and toxic substances.
The OSHA act of 1970 is comprehensive in scope and covers enforce-
ment of standards, penalties, research activities, state programs, financial
assistance, employees duties and rights, and OSHA’s effect on other laws.
The Hazardous Waste Operations and Emergency Response Standard
(HAZWOPER; 29 CFR 1910.120) was issued by OSHA in March 1990.
These regulations serve as a guide to a safety and health plan for hazardous
waste operations.
642 Fermentation and Biochemical Engineering Handbook
The HAZWOPER regulations includes the following:
RCRA Corrective Actions
Clean up operations for uncontrolled hazardous waste sites,
including voluntary operations, and routine operations
Emergency responses where there is a release of hazardous
substances or a potential release of hazardous substances
exists
The formulation of safety and health plans for hazardous waste
A preliminary site characterization analysis and hazard as-
signment before entering a site known to be contaminated
A site specific safety and health program to control safety
and health hazards
A training program for all employees and contractors em-
ployed on the site who may be involved in hazardous waste
activities
operations, which include the following:
A medical surveillance program
Proper work practices, including appropriate personnel
A site control system to prevent contamination of personnel
A monitoring program to establish the appropriate levels of
Decontamination procedures before entering a site
Observation of applicable regulations issued by the Depart-
ment of Transportation, Environmental Protection Agency,
and the Occupational Safety and Health Act, in handling,
labelling, moving and disposing of containers containing
contaminated material
An emergency response plan for emergencies which may
occur on site
The preliminary site plan characteristic analysis and hazard assess-
ment should be performed by an experienced and trained technician before
entering the site. A more detailed site evaluation and analysis must be done
to establish the necessary engineering controls and personnel protective
equipment. All potential hazards must be identified and evaluated and an air
protective equipment.
and equipment
personnel protective equipment
Environmental Concerns 643
monitoring program must be set up to ascertain that it is safe for work to begin
and proceed. In summary, the hazards must be identified, a health risk
assessment performed, a medical surveillance program instituted, potential
sources of fire and explosion identified, and other possible risks and hazards
evaluated. Site specific safety and health rules must be set up, distributed and
posted. Such a plan should include the applicable items from the following
list. Workers at the site must be informed of the potential hazards and must
be cognizant of the site specific safety and health plan.
Safe@ and Health Plan:
Safety and Health Procedures
Personnel Responsibilities
Decontamination Procedures
Required Monitoring
Training Requirements
Hazards Identification
Personnel Protective Equipment
Emergency Procedures
Hazardous and Toxic Materials On Site
Medical Surveillance
Hospital Location
Emergency Response Personnel
2.5 Environmental Auditing
Environmental auditing can cover a wide range of objectives. The
approach can focus on how well a manufacturing facility is complying with
the various environmental regulations, such as the Clean Air Act Amend-
ments (CAAA), the Clean Water Act (CWA), the Resource Conservation and
Recovery Act (RCRA), Title I11 of the Supehnd Amendments and Reautho-
rization Act (SARA), the Comprehensive Environmental Response, Com-
pensation and Liability Act (CERCLA), the Toxic Substances Control Act
(TSCA), various aspects ofthe Occupational Safety andHealth Act (OSHA),
and can also cover property acquisition. It can also cover the various State
regulations, for instance, in New Jersey an environmental audit can cover the
Toxic Catastrophe Prevention Act (TCPA), the Spill Act, and the State
644 Fermentation and Biochemical Engineering Handbook
Permit Compliance. If desired, it can also cover waste minimization and
pollution prevention.
The environmental audit offers a comprehensive assessment of a
facility’s compliance with applicable federal, state and local regulations. It
also can identify problems before the local or state regulator can be made
aware of them and allows time to correct the inadequacies.
Other advantages of the environmental audit is to allow time to
properly assess the problem, plan its solution and allow for funding the capital
cost required. There are potential problems in having an environmental audit
performed. The results of recent court decisions indicate that the environmen-
tal audit results may not be able to be kept in confidence and furthermore, they
may be used as evidence of noncompliance in civil or criminal court actions.
It is conceivable that an audit can increase the potential liabilities. Conse-
quently, management should be prepared to commit to satisfy any negative
findings before the audit is undertaken.
The Department of Justice has developed guidelines for compliance
and reporting that will be taken into consideration before assessing penalties
for environmental regulations. Consequently, the scope and purpose of the
audit should be filly understood and agreed to by both management and the
consultant prior to undertaking the audit, and questions such as who does the
consultant report, who will be given copies of the environmental audit, who
will be in charge of document control, who should meet with the consultant,
etc., should be decided.
Audit-Environmental auditing consultants have developed forms
for collectingldeveloping information on various aspects of the site. The
more important of these will include the following:
Site information data
Types of adjacent land use
Primary site use
Site configuration
Buildings on site, number and size
For manufacturing on site:
- Products
- Intermediates
- Waste materials disposal
Solid
Liquid
Gaseous
Environmental Concerns 645
Chemical storage on site
Solid
Liquid
Gas
Are underground storage tanks used
Number
How long in service
Volume
Material stored
Material of construction
Leak tested
Above ground storage tanks
Number
How long in service
Volume
Material stored
Material of construction
Leak tested
Waste piles
Size/volume
How long used
Material
How contained
Hazardous/toxic wastes generated on site
How are wastes handled
on site/off site treatment
Disposal-How
Site ownership history
Regulatory/environmental history
Spills history
Accident history
Environmental problems
646 Fermentation and Biochemical Engineering Handbook
List of permits
Air emissions
Waste water
Solid wastesihazardous wastes
2.6 National Environmental Policy Act
The purpose of the Act as stated in a Congressional Declaration of
National Environmental Policy is:
To declare a National Policy which will encourage produc-
tive and enjoyable harmony between man and his environ-
ment; to promote efforts which will prevent or eliminate
damage to the environment and biosphere and stimulate the
health and welfare of man; to enrich the understanding of the
ecological systems and natural resources to the Nation; and
to establish a Council on Environmental Quality.
Congress further agreed that to carry out the policy set forth in this Act;
it is the continuing responsibility of the federal government to use all
practicable means to improve and coordinate federal plans, function pro-
grams, and resources that the nation may:
Fulfill the responsibilities ofeach generation as trustee ofthe
To assure for all Americans safe, healthful, productive area,
Attain the widest range of beneficial uses ofthe environment
. undesirable and unintended consequences.
Preserve important historic cultural and natural aspects of
our national heritage and maintain, whenever possible, an
environment which supports diversity and variety of indi-
vidual choice
which will permit high standards of living and a wide sharing
of life’s amenities
Enhance the quality of renewable resources and approach
the maximum attainable recycling of depletable resources
environment for succeeding generations
aesthetically and culturally pleasing surroundings
without degradation, risk to health or safety, or other
Achieve a balance between population, and resource use
Environmental Concerns 647
2.7 Storm Water Regulations
An overview of storm water regulations is included in this section. As
a result of the 1987 amendments to the Federal Clean Water Act, the United
States Environmental Protection Agency (EPA) adopted rules in 1990 which
require permit applications for a number of storm water discharges. The
intent of storm water regulations is to reduce and prevent pollution due to
storm water. A primary approach is source reduction and pollution minimi-
zation. A number of different regulatory programs cover storm water, which
may be treated as either a point or a non-point source discharge. The new
federal storm water permitting regulations require permit applications to be
submitted for all large and medium municipal separate storm sewer systems.
Storm water discharges from residential or commercial sites, except
for construction activities, are not subject to current federal storm water
permit application regulations; however, such storm water discharges may be
subject to existing state regulations and may be subject to future federal
regulations.
The discharge of contaminated storm water to surface water or ground
water, including discharges through separate storm sewers, requires an
NJPDES permit in the State of New Jersey and other states. Traditionally,
discharges of storm water in ground water have not been controlled by the
NPDES program.
3.0 TECHNOLOGY (WASTE WATER)
3.1 NPDES
Under the NPDES program, all industrial and municipal facilities that
discharge waste water directly into Unites States waters must obtain a permit.
Specifically, the water act requires NPDES permits for discharges from point
sources such as municipal waste water treatment plants, industries, animal
feed lots, aquatic animal production facilities, and mining operations.
NPDES permits specifjl effluent limitations for each individual industrial and
municipal discharge, a compliance schedule, monitoring and reporting
requirements, and other terms and conditions necessary to protect water
quality. NPDES permits are valid for five years, although EPA may issue
them for shorter terms. NPDES permits may be revoked, transferred, or
modified.
648 Fermentation and Biochemical Engineering Handbook
NPDES permits are available from the EPA or from a state authorized
to issueNPDES permits. Upon authorization of a state NPDES program, the
state is primarily responsible for issuing permits and administrating the
NPDES permit program. State NPDES programs must be consistent with
minimum federal requirements.
Under the Federal Clean Water Act’s National Pollutant Discharge
Elimination System (NPDES) permitting program, two approaches exist for
controlling pollutant discharges from individual and municipal waste water
treatment facilities: the technology-based approach and the water-quality
based approach
Technology-based controls consist of uniform EPA established stan-
dards of treatment that apply to direct industrial dischargers and publicly
owned waste water treatment works. These uniform standards, known as
effluent limitations, generally are in the heart of NPDES permits and place
numeric limits on the amount of effluent pollutant concentrations permitted
at the point of discharge (end-of-pipe).
Industrial effluent limitations are derived from technologies that are
available for treating the effluent and removing pollutants, and also are based
on considerations of cost and economic achievability. The water quality
based approach is used to develop stricter effluent limitations where technol-
ogy based controls will not be stringent enough to ensure that waters can
support their intended uses.
3.2 Emuent Limitations
EPA and the states issue waste water discharge permits to individual
factories, power plants, refineries, and other private companies, based on
national effluent limitation guidelines. These are based on chemical, physical
and biological characteristics of effluent that industry may dump into water
ways. An effluent limitation guideline sets the degree of reduction of a
pollutant that can be achieved through the application of various levels of
technology. An effluent limitation is a restriction on the amount of a pollutant
that can be released from a point source into a water body. The discharge of
waste water containing metals has effluent limitations, standards, or prohi-
bitions, expressed in terms of the total metal, that is, the sum of the dissolved
and suspended fractions of the metal.
Environmental Concerns 649
3.3 Continuous Discharger
All permit effluent limitations, standards, and prohibitions, including
those necessary to achieve water quality standards, will be stated as maxi-
mum daily and average monthly discharge limitations for all dischargers.
3.4 Non-Continuous Discharger
A permittee’s noncontinuous discharge is limited and described as
Frequency
Total mass
Maximum rate of discharge of pollutants during the dis-
Prohibition or limitation of specified pollutants by mass,
follows:
charge
concentration, or other appropriate measure
3.5 Mass Limitations
All pollutants limited in a discharger’s permit will have limitations,
standards, or prohibitions expressed in terms of mass except:
pH, temperature, radiation, or other pollutants which
cannot be expressed by mass
when standards and limitations are expressed in terms of
other units of measurement
ifthe permit limitations were issued on a case-by-case basis,
limitations expressed in terms ofmass are infeasible because
the mass of the pollutant discharged cannot be related to a
measure of operation
permit conditions to ensure that dilution will not be used as
a substitute for treatment
A permittee must comply with pollutants limited in terms of mass.
Additionally, pollutants may be limited in terms of other units of measure-
ment, in which case a permittee must comply with both limitations.
650 Fermentation and Biochemical Engineering Handbook
3.6 Waste Water Characterization
An understanding of the nature of the physical, chemical, and biologi-
cal characteristics of waste water is essential in the design and operation of
collection, treatment, and disposal facilities, and in the engineering manage-
ment of environmental quality.
The analyses performed on waste waters may be classified as physical,
chemical, and biological. These analyses vary from precise quantitative
chemical determinations to the more qualitative biological and physical
determinations.
Physical Characteristics. The most important physical characteristic
ofwaste water is its total solids content, which is composed offloating matter,
matter in suspension, colloidal matter, and matter in solution. Other physical
characteristics include temperature, color, and odor.
These consist of organic matter, the
measurement of organic content, the inorganic matter, and the gases found in
waste water. The measurement of organic content is very important because
of its importance in both the design and operation of waste water treatment
plants and the management of water quality.
BioIogicaI Characteristics. Biological aspects with which the sani-
tary engineer must be familiar include knowledge of the principal groups of
microorganisms found in surface and waste waters, as well as those respon-
sible for biological treatment, knowledge of the organisms used as indicators
of pollution and their significance, and knowledge of the methods used to
evaluate the toxicity of treated waste waters.
Chemical Characteristics.
3.7 Common Pollutants
Generally, under NPDES program, the following pollutants are re-
Oxygen Demand
quired to be monitored and reported.
- Biochemical Oxygen Demand
- Total Oxygen Demand
- Total Organic Carbon
- Total Suspended Solids
- Total dissolved Solids
Solids
Environmental Concerns 651
Nutrients
- Inorganic Phosphorus Compounds
- Inorganic Nitrogen Compounds
Detergents and Grease
- MBAS (Methylene Blue Active Substances)
- OilandGrease
- Calcium
- Chloride
- Fluoride
- Magnesium
- Sodium
- Potassium
- Sulfur
- Sulfate
- Total Alkalinity
- Total Hardness
- Aluminum
- Cobalt
- Iron
- Vanadium
- Cyanide
- Total Residual Chlorine
Minerals
Metals
Inorganics
4.0 WASTE WATER TREATMENT STRATEGY
Different types of waste water streams are generated from various
processes in pharmaceutical and biotechnology industries. Treatment of
these streams is not only ethically required for not polluting the waters of the
nation, but USEPA and the states have mandated strict discharge standards
that their plants must meet with their NPDES (or equivalent) permitting
requirements. Waste water treatment can no longer be considered as a
secondary issue in the plant’s scheme of things, but must be considered an
integral issue. The cost of operation and the capital cost are considerable and,
therefore, should attract management’s attention.
652 Fermentation and Biochemical Engineering Handbook
Waste water treatment process is generally divided into two types:
Biological Treatment
Physical Treatment
Biological treatment utilizes microbial organisms to reduce pollutant
loadings of process waste streams to EPA (andor state) acceptable limits.
Physical treatment involves reduction of pollutant of process waste stream
utilizing physical procedures, such as stripping, ion exchange, membrane
separation, etc.
4.1 Activated Carbon
Activated carbon is a recommended and established process used in
separating organic and certain inorganic species from aqueous waste streams.
Normally, concentration of the waste species should be 1% or less so that
carbon regeneration is less frequent. Since this process is generally cost-
effective, it has been applied in numerous industrial municipal and pharma-
ceutical waste water treatment facilities.
Adsorption is based on physicaVchemica1 interaction between the
organic pollutant and the carbon surface. In this process, a filter bed of
activated carbon is placed in a vessel and used to adsorb certain components.
A large adsorptive surface area is generally used for the process. Different
raw materials, including coal, wood, coconut shells, peat, and coke, are used
to produce activated carbon. These products may impact carbon effective-
ness for a given application. Carbons for waste water adsorption generally
havea large adsorptive surface area, about 2.5 to 7.5 million ft./lb. Pore sizes
range within 50 8, and 1000 A. Activated carbon is available in granular and
powdered form. Granular carbons are used in the treatment of continuous and
semi-continuous waste water streams. It can be packed in canisters or beds
which then constitute a process unit. Powdered carbon is used for batch
adsorption applications and in conjunction with biological treatment.
Favorable results are achieved when the pollutant is slightly soluble in
water, has a high molecular weight, high polarity, and low ionization
capability, and when the concentration of any suspended solids is less than
50 ppm.
Once the carbon has become saturated, regeneration of the carbon is
required. Regeneration methods include the following:
Environmental Concerns 653
Thermal reactivation in a multiple hearth furnace or rotary
Steam stripping
Ozone medicated on-site oxidation
The method used will vary according to characteristics of the plant site
and properties of agiven system. Energy cost from carbon adsorption ranges
from 5 to 25% ofthe total operating cost. If carbon is thermally regenerated,
equipment cost increases since a furnace, after burner, and a scrubber are
needed. If carbon is not regenerated, a means of carbon disposal is needed.
kiln at temperatures of 1200’F to 1700’F
4.2 Air Stripping
For pharmaceutical waste water streams containing volatile organic
compounds (VOC’s), air stripping can be used to reduce containment
discharge. Air stripping can be used for treating waste water containing less
than 100 ppm VOC and insoluble organics, such as methylene chloride and
toluene. Treatment efficiency using air stripping is dependent on Henry’s
law, which is as follows:
where,
PA = Vapor pressure of compound A (atm)
HA = Henry’s law constant of compound A (atm)
X, = Liquid phase mole fraction of compound A
Henry’s constant is a function of temperature and a weak function of
composition and pressure, however, the air stripping process is normally run
at ambient conditions and published data within 20’ and 3OoC is available.
Maximum pollutant removal by air stripping can be predicted by the
following:
% Removal = ‘Ai -‘A0 100 = 1- XlOO
‘Ai l+H,R,,RT
654 Fermentation and Biochemical Engineering Handbook
where:
CAi = initial concentration
C,, = final concentration
HA = Henry’s constant atm m3 / mole
R, = volumetric air / water ratio = V / L
V = airfedinch
L = water fed inch
R = gas constant = 8.206 x lom5 atm m3/mol K
T = temperatureK
The packed tower is compact and efficient for air stripping. The waste
water, in a lime slurry (for phosphate removal and pH control), is first sent
to a mixing tank and then to a shell settling tank to settle out calcium
phosphate and calcium carbonate. The clarified waste water enters near the
top ofthe packed tower, while air is introduced countercurrently at the bottom
ofthe tower. Waste water product is then sent to a recarbonation basin so that
calcium carbonate may be precipitated, removed, and reused.
Air strippers are typically 15 to 60 feet in height, and have diameters
ranging from 1 to 10 feet. Water flow rates are typically in the range of 40
to 250 lb/ch air and aidwater volumetric ratios are typically in the range of
10 to 300. Generally, contaminated air from the stripper may be routed to an
incubator or vapor phase carbon adsorption.
4.3 Steam Stripping
Steam stripping is used to remove dilute concentrations of ammonia,
hydrogen sulfide, and other volatile components from pharmaceutical waste
stream. Steam stripping can typically achieve contaminant removal of 99%
or better and is effective for the removal of organics having boiling points of
less than 150°C. The steam stripping process is carried out in a distillation
column, which may be either a packed or tray tower. Steam enters at the
bottom ofthe column while waste water is countercurrently supplied from the
top of the distillation column. The product stream, rich in volatile compo-
nents, may further be treated to recover these components.
Steam strippers are generally designed by the use of computer simula-
tion programs, although preliminary estimates can be prepared by modifica-
Environmental Concerns 655
tions of McCabe-Thiele or Fenske-Underwood-Gilliland methods. The
development of reliable equilibrium data is critical to the completion of a
successful design. In general, such data should be obtained through pilot
scale testing on the actual waste water stream to be treated.
4.4 Heavy Metals Removal
While heavy metals (i,e., chromium, copper, nickel) are not typical
pollutants in apharmaceutical waste water stream, removal becomes an issue
in some segments of the industry, namely chemical intermediates. These
streams are generally treated at the process source in order to minimize the
waste water volume. Also, heavy metal streams must be treated prior to any
biological treatment that the waste water also requires. Since heavy metals
are toxic to microorganisms (even at very low concentrations), their presence
reduces biological treatment efficiency.
4.5 Chemical Precipitation
Waste stream metal loading can be reduced by hydroxide precipitation.
Hydroxide precipitation uses lime or liquid sodium hydroxide as reactants to
form insoluble metal hydroxide. Solids are settled, filtered, and removed as
sludge. Liquid sodium hydroxide or quick lime are commonly used as
precipitation reagents. Generally, lime is cheaper than other reagents,
however, it has a higher operating cost because it is difficult to handle.
Chrome bearing waste water requires pretreatment, since hexavalent
chromium will not react with hydroxide. Hexavalent chrome must be reduced
to the trivalent form by reaction with ferrous sulfate, sodium meta-bisulfite
or sulfur dioxide. The reduction must be carried out at a pH below 3.0.
Achieving complete reduction is important, since any remaining hexavalent
chromium will remain in solution in the effluent. The pH is then raised to pH
4.5 to 8.0 and hydroxide precipitation is carried out.
Sludge generated from this process requires carefil handling as this
waste is considered hazardous. Water content of the sludge can be reduced,
generally using plate and frame presses or clarifiers. Plate and frame presses,
generally require more operation and attention, however, they can achieve
higher solids concentration in the cake, typically 50% to 60%.
656 Fermentation and Biochemical Engineering Handbook
4.6 Electrolysis
Electrolysis is the reaction of either oxidation or reduction taking place
at the surface of conductive electrodes immersed in an electrolyte, under the
influence of an applied potential. This process is used for reclaiming heavy
metals from concentrated aqueous solutions. Application to waste water
treatment may be limited because of cost factors. A frequent application is
the recovery for recycle or reuse of metals, like copper, from waste streams.
Pilot applications include oxidation of cyanide waste and separation of oil-
water mixtures. Gaseous emissions may occur and, ifthey are hazardous and
cannot be vented to the atmosphere, firther treatment, such as scrubbing, is
required. Waste water from the process may also require further treatment.
The most common waste water treatment application of electrolysis is
the partial removal of heavy metals from spent pickling solutions. When the
typical concentration of the spent pickling solution is a 2 to 7% copper, the
system design is similar to that of a conventional electroplating bath. When
recovering from more dilute streams, mixing and stirring are necessary to
increase the rate of diffusion; it may also be necessary to use a large electrode
surface area and a short distance between electrodes.
Another concern with this method is the removal of collected ions from
the electrodes. This removal may or may not be difficult, but must be
addressed. The material collected must be ultimately disposed of if it is not
suitable for reuse.
4.7 Ion Exchange
Ion exchange can be useful for heavy metal removal, particularly for
nickel, zinc, copper, or chrome, where the metals can be recovered from the
regenerating solution and recycled to the process or sold. Ion exchange has
also been applied to treatment of streams containing complexing agents or
their compounds, that would interfere with a precipitation process.
Ion exchange is a two-step process. First, a solid material, the ion
exchanger, collects specific ions after coming into contact with the aqueous
waste stream. The exchanger is then exposed to another aqueous solution of
a different composition, that picks up the ions originally removed by the
exchanger. The process is usually accomplished by sending the two aqueous
streams through one or more fixed beds of exchangers. The ion-rich product
stream may be recovered or disposed and the ion-poor stream is usually dilute
enough for discharge to sewers.
Environmental Concerns 657
The chemistry of the ion exchange process may be represented by the
following equilibrium equations:
Reaction:
RH+Na+ f RNa+H+
RNa, + Ca" +; RCa + 2Na'
Regeneration:
RNa+HCl S RH+NaCl
RCa + 2NaCI S RNa, + CaCl,
where R represents the resin.
These equations represent the reactions involved in the removal of
sodium and calcium ions from water, using a synthetic cationic-exchange
resin. The extent of completion of the removal reactions shown depends on
the equilibrium that is established between the ions in the aqueous phase and
those in the solid phase. For the removal of sodium, this equilibrium is defined
by the following expression:
where
KH + Na = selectivity coefficient
[ 3
X,
XRNa
= concentration in solution phase
= mole fraction of hydrogen on exchange resin
= mole fraction of sodium on exchange resin
The selectivity coefficient depends primarily on the nature and valence
of the ion, the type of resin and its saturation, and the ion concentration in
waste water. Although both natural and synthetic ion exchange resins are
available, synthetic resins are used more widely because of their durability.
To make ion exchange economical for advanced waste water treat-
ment, it would be desirable to use regenerants and restorants that would
remove both the inorganic anions and the organic material from the spent
resin. Chemicals successfbl in the removal of organic material from resins
include sodium hydroxide, hydrochloric acid, and methanol.
658 Fermentation and Biochemical Engineering Handbook
4.8 Membrane Technology
Reverse osmosis uses semipermeable membranes and high pressure to
produce a clean permeate and a retentate solution containing salts and ions,
including heavy metals. The technique is effective ifthe retentate solution can
be reused in the process. The equipment tends to be expensive, and fouling
of the membranes has been a common problem. Considerable research effort
is being carried out on membrane processes, however, and they are likely to
be more commonly applied in the future. Concentrations of dissolved
components are usually about 34,000 ppm or less.
Reverse osmosis employs a semipermeable membrane that allows
passage of the solvent molecules, but not those of the dissolved organic and
inorganic material. A pressure gradient is applied to cause separation of the
solvent and solute. Any components that may damage or restrict the function
of the membrane must be removed before the process is performed. Capital
investment and operating costs depend on the waste stream composition.
4.9 Organic Removal
Sequencing Batch Reactor (SBR). SBRs are used in batch modes.
They consist of one or more reactors used for equalization, aeration and
clarification in sequence.
Operation cycle of atypical SBR system consists of five steps, (A) fill,
(B) react, (C) settle, (0) draw and (a idle.
A. Fill-the waste water is pumped into reactor tank, con-
trolled either by volume or time.
B. React-in this step, the aeration equipment is energized to
supply air to the batch, where oxidation of the organic
occurs.
C. Settle-solids are separated from the liquid in this step
and the clarified liquid is then discharged from the system.
D. Draw-in this step, clarified water is discharged from the
reactor.
E. Idle-this step is used where two or more reactors are
connected in an SBR system. One reactor remains idle
while others (one or more) are filled.
Environmental Concerns 659
SBR systems are generally advantageous to use over conventional flow
One SBR tank can serve as an equalization tank, reactor
tank and clarifier.
SBR can tolerate high peak hourly flows, since it serves as
an equalization tank. Effluent quality is not compromised.
Operating level in SBR tank is adjustable. Hence, during
low flow conditions, a smaller batch can be collected and
treated as desired.
Solids in tank do not get washed out by hydraulic surges as
solids can be held in the tank as long as necessary.
systems. They include:
4.10 Activated Sludge Systems
Different types of activated sludge systems are used in treating
pharmaceutical waste water. Some sludge systems include conventional,
complete mix, contact stabilization, extended aeration, and step aeration.
Conventional-This type includes an aeration basin, a
clarifier, and a sludge recycle system. The recycle sludge
(RAS) and influent enter the aeration basin at the inlet and
leave the basin in the opposite or outlet end. The solids in
the mixed liquor get separated out in the clarifier and are
recycled back to the aeration basin. Aeration in the basin
can be achieved by diffused air or mechanical aerations.
CompleteMix-The influent and the RAS are introduced at
several points in the center of the aeration basin from a
header or central channel. Effluent from the aeration basin
is collected from both sides of the basin by means of two
effluent channels. A clarifier is used to separate the solids
in the basin effluent before the sludge is recycled back to the
head of the system. Excess sludge is sent to the sludge
handling facility of the treatment plant. Aeration can be
accomplished by diffused air or mechanical aeration.
660 Fermentation and Biochemical Engineering Handbook
Contact Stabilization-The influent is first mixed with the
return activated sludge for approximately 30 minutes or
long enough for the organics to be absorbed in a contact
basin. Effluent from the contact basin is fed to a clarifier,
where the activated sludge is settled out and returned to
another aeratiodstabilization basin. Inside the stabilization
basin the activated sludge is aerated for 3-6 hours before it
is mixed with the influent in the contact basin. The absorbed
organics are converted to carbon dioxide, water, and new
cells, by means of biochemical oxidation. Excess sludge,
generated from the process, can be wasted from the bottom
of the clarifier or from the stabilization basin outlet.
Extended Aeration-In this process, aeration time is about
24 hours. The activated sludge system operates in an
endogenous respiration phase in which there is inadequate
organic material in the system to support all the microorgan-
isms present, due to a low BOD loading. Under this type of
operating condition, extended aeration process can produce
low sludge and a highly treated effluent.
Step Aeration-Influent to the aeration basin is split up into
four or more equal streams and are then fed into four parallel
channels separated by baffles. Each channel is equivalent to
a separate step and these steps are connected together in
series, very similar to having four small plug-flow systems
arranged in series. The first step is commonly used to
reaerate the return activated sludge, assuming the sludge is
not oxygen starved when it comes in contact with the
influent. With the return activated sludge aerated, the
organic material in the influent can be readily absorbed and
broken down within a relatively short contact time.
5.0 AIR (EMISSIONS OF CONCERN)
A major concern associated with chemical processing is the emission
of air pollutants. The greatest mass of air contaminants consists primarily of
the following pollutants:
Environmental Concerns 661
Volatile Organic Compounds (VOC)
Inorganics
Particulates
5.1 Volatile Organic Compounds (VOC)
VOC's are emitted from chemical processes either controlled or
uncontrolled. Control techniques are provided in the following sections.
Emission can also result from the incomplete combination of organic
constituents and conversion of certain constituents present in the raw
material, auxiliary fuel, andor combustion air.
5.2 Inorganics
Inorganic pollutants, such as HCL, HF, NO,, SO,, are also formed as
Hydrogen chloride and small amounts of chlorine from the
combustion of chlorinated hydrocarbons
Sulfur oxides, mostly as sulfur dioxide (but also SO,)
formed from sulfur or sulfur compounds present in the
products andor fuel mixture
Nitrogen oxides from the nitrogen in the combustion air and
or from organic nitrogen present in the product.
a result of incomplete combustion. Inorganics include:
5.3 Particulates
Particulates emissions are strongly influenced by the chemical
composition of the raw material and the auxiliary fuel, type of combustion
process, the operating parameters, and the air pollution control system. Most
of the pollutants of concern, other than VOC and inorganics, are collected as
particulates.
6.0 SELECTING A CONTROL TECHNOLOGY
There are a number of control options for air toxics, particulates, SO,
and NO,. It is up to the chemical engineer to choose the most cost-effective
control equipment for the source application.
662 Fermentation and Biochemical Engineering Handbook
Selection of control equipment begins with gathering relevant data on
the emissions and key process parameters. The properties ofthe exhaust-gas
stream and the pollutants need to be characterized. These include:
6.1 Exhaust Stream
Pollutant concentration
Flowrate
Temperature
Pressure
Moisture content
Oxygen content
Heat content
Corrosiveness
Explosivity
6.2 Pollutant
Particle size distribution
Molecular weight
Vapor pressure
Solubility
Adsorptive properties
Lower explosive limits
Reactivity
This infomation can be obtained from vent testing, a mass balance,
engineering calculations, or simple engineering estimates (using AP-42).
Vent testing, though expensive, is the most accurate method. Other important
required information is as follows:
The level of control required by the regulatory agency must
be known. This will allow the minimum control efficiency
to be established.
Environmental Concerns 663
Site-specific issues impacting the selection of the control
equipment, must be quantified. These include availability of
utilities, pace constraints, disposal options, and cost of
residue generated by emissions control.
Cost effectiveness has to be judged. Cost effectiveness is
defined as the annual operating expense required to control
each zone of emissions. The cost effectiveness calculation
provides a gauge for ranking various control combinations
within a facility so that the greatest emission reduction can
be selected for the least cost.
Secondary environmental impacts, as well as energy im-
pact, also must be considered.
Consideration must be given to potential for waste minimi-
zation at the facility. If feasible, this could reduce or even
eliminate the need for emission control equipment.
7.0 VOLATILE ORGANIC COMPOUND (VOC) EMISSIONS
CONTROL
The control of VOC’s is the single largest environmental challenge
facing CPI companies, especially with the enactment of CAAA of 1990.
About 80% of the annual air toxic emissions (per SARA Title 111, Sec. 3 13,
Form R Reporting) are VOC’s.
Most commonly employed control technology for VOC emissions
control are as follows:
Thermal Incineration
Catalytic Incineration
Carbon Adsorption
Condensation
Absorption
The choice is often dependent on VOC concentration of the stream
being controlled, because control efficiency depends on VOC content.
664 Fermentation and Biochemical Engineering Handbook
7.1 Thermal Incineration
In incineration, gaseous organic-vapor emissions are converted to
carbon dioxide and water through combustion. There are two types of
thermal incinerator, based on heat recovery employed, regenerative and
recuperative.
Thermal incinerators depend upon contact between the contaminant
and the high-temperature combustion flame to oxidize the pollutants. The
incinerator, generally consists of refractory-lined chamber, one or more
burners, a temperaturecontrol system, and heat-recovery equipment.
Contaminated gases are collected by a capture system and delivered to
the preheater inlet, where they are heated by indirect contact with the hot
incinerator exhaust. Gases are mixed thoroughly with the burner flame in the
upstream portion of the unit, and then passed through the combustion zone,
where combustion process is completed. An efficient thermal incinerator
design must provide:
Adequate residence time for complete combustion
Sufficiently high temperature for VOC destruction
Adequate velocities to ensure proper mixing
The residence times for incinerators are on the order of 0.5 to 1 seconds,
at a temperature ranging from 1200°F to 1600°F. Destruction efficiencies in
excess of 95% can be commonly achieved.
Advantages:
Simple operating concept
Nearly complete (>95%) destruction of VOC's
No liquid or solid residual waste generation
Low maintenance requirements
Low initial capital costs
Disadvantages:
High fuel cost
The fuel costs can be minimized by utilizing air pre-heaters incorpo-
rated into the incinerator design. With a recuperative heat exchanger,
efficiency of 60% is typical. Thermal incinerators with regenerative heat
exchangers can recover 80-95% of the systems energy demands. Regenera-
tive incinerators can initially cost roughly 80% more than recuperative
Environmental Concerns 665
designs. With annual fuel costs of about 10-30% those of recuperative units,
the savings can be significant if contaminated air has a low VOC concentra-
tion (<25 ppmv) and auxiliary fuel costs are high (>$YmmBTU).
7.2 Catalytic Incineration
The operation of catalytic incineration is similar to thermal incinera-
tion in that heat is used to convert VOC to carbon dioxide and water. The
presence of a catalyst lowers the oxidation activation energy, allowing the
combustion to occur at about 600°F.
Operation. fie preheatedgas stream is passedthrough a catalyst bed,
where the catalyst initiates and promotes the oxidation of the organic without
being permanently altered. The catalyst is normally an active material, such
as platinum, copper chromite, chromium, or nickel, on an inert substrate,
such as honeycomb-shaped ceramic. For the catalyst to be effective, the
active sites upon which the organic gas molecules react must be accessible.
The buildup of polymerized material or reaction with certain metal particu-
lates will prevent contact between active sites and the gas. A catalyst can be
reactivated by removing such a coating.
Catalyst cleaning methods are as follows:
Air blowing
Steam blowing
Operating at elevated temperature (about 100°F above
Advantages:
Nearly complete destruction of VOC (>95%)
No residual waste generation
0 Low maintenance cost
Disadvantages :
High capital costs
Catalyst deactivation over time
Inability to handle halogenated organics
Supplement fuel cost
operating temperature)
666 Fermentation and Biochemical Engineering Handbook
7.3 Carbon Adsorption
Adsorption is a process by which organics are retained on the surface
ofgranulated solids. The solid adsorbent particles are highly porous and have
very large surface-to-volume ratios. Gas molecules penetrate the pores ofthe
adsorbent and contact the large surface area available for adsorption.
Activated carbon is the most common adsorbent for organic removals.
The amount of VOC retained on the carbon may be represented by
adsorption isotherm, which relate the amount of VOC adsorbed to the
equilibrium pressure (or VOC concentration) at a constant temperature. The
adsorptive capacity of the carbon (expressed as VOClb/Clb) depends not
only on properties on the carbon, but also on the properties of the organic.
Generally, the adsorptive capacity increases with:
Increased molecular weight of the VOC
Polarity
Degree of cyclization (ringed compound more easily ad-
Regenerative carbon adsorption systems operate in two modes-
adsorption and desorption. Adsorption is rapid and removes essentially all
the VOCs in the stream. Eventually, the adsorbent becomes saturated with
the VOC and system efficiency drops. At this breakthrough point, the
contaminated stream is directed to another bed containing regenerated
adsorbent and the saturated bed is then regenerated. The adsorption cycle
typically lasts two hours to many days, depending on the inlet VOC
concentration, the variability of organic loading, and the design parameters
of the carbon bed. The regenerative cycle typically lasts from one to two
hours, including the time needed for drying and cooling the bed.
One important consideration of this system is the operating tempera-
ture of the process gas stream. Operating temperature must be less than
100OF. This is because the adsorption capacity decreases with the increase
in temperature. The efficiency of carbon adsorption depends on both the
concentration of VOC in the gas stream and its composition. Generally,
efficiencies of over 95% can be achieved when the organic concentrations are
greater than 1,000 ppmv.
Advantages:
Recovery of relatively pure product for recycle
High removal efficiency (>95%)
Low fuel costs
sorbed than straight chain hydrocarbons)
Environmental Concerns 667
Disadvantages:
Potential generation of hazardous organic wastes
Generation of potentially contaminated waste water
Higher operating and maintenance cost for disposal of these
waters
7.4 Adsorption and Incineration
This process involves a combination of activated carbon adsorption
with incineration. The adsorber concentrates the organic laden air before
treatment by incineration. This approach is particularly useful for organic
streams with a low concentration and higher volumes (e100 ppmv and
flowrates over 20,000 ch), such as paint spray booths. This process has
many advantages. These include:
High destruction efficiency
Little or no generation of liquid or solid waste of incineration
Low fuel consumption
7.5 Condensation
Condensation is a basic separation technique where a contaminatedgas
stream is first brought to saturation and then the contaminants are condensed
to a liquid. The conversion of vapor to liquid phase can be accomplished
either by increasing the pressure at constant temperature, or reducing the
temperature, keeping the pressure constant. Generally, condensation systems
are operated at a constant pressure.
The design and operation of the system is affected by the concentration
and type of VOC’s in the emission stream. Before condensation can occur,
the dew point of the system (where the partial pressure of the organic is the
same as the system pressure) must be reached. As condensation continues,
VOC concentration in the vapor decreases, and the temperature must be
lowered even further.
The removal efficiency of the condenser ranges from 50% to 95% or
more and depends on the partial pressure of the organic in the gas stream,
which is a function of the concentration of the organic and the condenser
temperature. For a given temperature, the greatest potential removal
efficiencies are achieved with the largest initial concentrations. VOC
removal efficiencies via condensation may reach 95% or more for concentra-
tions in excess of 5,000 ppmv.
668 Fermentation and Biochemical Engineering Handbook
Plots of vapor pressure versus temperature (Cox charts) are used to
determine the temperature required to achieve the desired removal efficiency.
Generally, the condenser outlet organic concentration will be greater than
10,000 ppmv for a water-cooled system. For higher removal efficiencies,
other coolants, such as a brine solution (-30°F to 40°F) may be used.
Condensation offers the advantage of:
Product recovery
No disposal problems
Modest space requirements
Disadvantages include:
LimitedapplicabilitytostreamswithhighVOCconcentrations
Limited applicability to streams with single components if
the product is to be recycled and reused.
7.6 Absorption
Absorption is the mass transfer of selected components from a gas
stream into a nonvolatile liquid. Such systems are typically classified by the
absorbent used. The choice of absorbent depends on the solubility of the
gaseous VOC and the cost of the absorbent.
Absorption is a fbnction of both the physical properties of the system
and the operating parameters of the absorber. The best absorption systems
are characterized by low operating temperatures, large contacting surface
areas, high liquid/gas (L/G) ratios, and high VOC concentration in the gas
stream, For inlet concentration of 5,000 ppmv, removal efficiencies of
greater than 98% may be achieved. Absorption may also be efficient for
dilute streams provided the organic is highly soluble in the absorbent,
removals of 90% may be attained for concentrations as low as 300 ppmv.
Packed towers, venturi scrubbers, and spray chambers may be used for
absorption.
The efficiency of an absorber depends on:
Solubility of VOC in solvent
Concentration of VOC in the gas stream
Temperature
L/G ratio
Contact surface area
Environmental Concerns 669
Higher gas solubilities and inlet gas concentrations provide a greater
driving force and hence, a higher efficiency. Also, lower temperature causes
higher solubility, absorption as enhanced at lower temperatures. Generally,
the most economical absorption factor is 1.25 to 2 times the minimum L/G.
Absorption increases with contact surface are, thereby, removal efficiency,
however, this also raises overall pressure drop through the packed bed, hence
increasing energy costs.
8.0 PARTICULATE CONTROL
Most commonly used particulate control technologies are:
Fabric filters (baghouses)
Cyclones/mechanical collectors
Electrostatic precipitators
8.1 Fabric Filters (Baghouses)
The basic components of a baghouse are:
Filter medium in form of fabric bags
Tube sheet to support the bags
Gas-tight enclosures
Mechanism to dislodge accumulated dust from the bags
The particulates laden gas normally enters the lower portion of the
baghouse near the collection hoppers, then passing upward through the
device, either on the outside or the inside of the bags, depending on the
specific design.
Commercially available baghouses employ either felted or woven
fabric. A fabric is selected based on its mechanical, chemical, and thermal
characteristics. Some fabrics (like nomex) are better suited than others (like
polyester) for high temperature operations, some perform well in the presence
of acid gases, while others are especially good at collecting sticky particulates
because of good release characteristics.
The two design and operational parameters that determine fabric filter
performance are air-to-cloth ratio and pressure drop. The air-to-cloth ratio
is the volumetric flowrate of the gas stream divided by the surface area of the
fabric. The higher the ratio, the smaller the baghouse and higher the pressure
670 Fermentation and Biochemical Engineering Handbook
drop. Shaker and reverse-air baghouses with woven fabrics, generally have
alowerair-toclothratic+rangingfiom2.0 to3.5, dependingonthedusttype
being collected. Pulse-jet collectors with felted fabrics have higher air-to-
cloth ratios, ranging from 5 to 12.
The pressure drop across the filter medium is a fknction of the velocity
of the gas stream through the filter and the combined resistance of the fabric
and accumulateddust layer. Pressure drop across the filter medium is usually
limited to 6-8 in. H,O.
Advantages:
Performance
Uniform collection efficiency independent of particle
resistivity
Collection efficiencies exceeding 99 wt%
Disadvantages:
Clogging ofthe filter medium, due to condensation in the gas
stream
Cementation of the filter cake in humid, low-temperature
gases (especially in the presence of lime from a scrubber)
Excursions of high particulate concentrations during bag
breaks
8.2 CyclonedMechanical Collectors
Cyclones are seldom used as the primary means of particulate collec-
tion, but often serve asfirst-stage air cleaning devices that are followed by
other methods of particulate collection. Cyclone collection efficiency is
probably more susceptible to changes in particulate characteristics than are
other types of devices, therefore, care should be taken if used. Cyclone
operation is dependant, generally, on physical parameters such as particle
size, density, and velocity, as opposed to the chemical nature or properties of
the material being collected.
8.3 Electrostatic Precipitators
ESP's are generally used to remove particulates from gas streams that
can be easily ionized. A typical ESP consists of charged wires or grids and
positively grounded collection plates. A high voltage is applied between the
Environmental Concerns 671
negative electrodes and the positive collection plates, producing an electro-
static field between the two elements. In the space between the electrodes, a
corona is established around the negatively charged electrode. As the
particulate-laden gas passes through this space, the corona ionizes molecules
of the electronegativegases present in the stream. These particles get charged
and migrate to the oppositely polarized collection plates.
ESP's can be designed for virtually any control efficiency, with most
units operating in the 9599% range. ESP control factors include the Specific
Collection Area (SCA), which is the area ofthe collecting electrodes or plates
divided by the volumetric flowrate of the gas, The higher the SCA, the greater
the collection efficiency.
Particles with resistivities in the range of 104-1010 ohm-cm are the
most suitable for control by ESP's and most common industrial particulates
will exhibit resistivities in this range. Less resistive particles will give up their
charge too easily when they contact the collection plates and may be re-
entrained in the flue gas. More resistive particles will adhere to the collection
plates and be difficult to dislodge, acting as an insulator and reducing the
ability of the electrode to hrther collect particulate matter. Since resistivity
changes with temperature, efficient particulate collection requires selection
of an optimum ESP operating temperature.
Entrained water droplets in the flue-gas can encapsulate the particles,
thus lowering resistivity. High flowrates decrease the residence time of the
particles in the ESP, reducing the number of charged particles that migrate
to the collection plates.
The particle migration velocity, the rates at which charged particles
travel toward the collection plates, also affects ESP efficiency and the unit's
design specifications. A slow migration velocity indicates less particle
capture per unit of collection plate area. The surface area of the collecting
electrode would, therefore, have to be increased for applications involving
large quantities of small particles.
Advantages:
Reliability and low maintenance requirements
Relatively low power requirements, due to low pressure
High collection efficiencies over a wide ranges of particle
Ability to treat relatively humid gas streams
drops
sizes
672 Fermentation and Biochemical Engineering Handbook
A 50,000 ach ESP operating on a coal fired boiler, with an estimated
mean particle diameter of 7 micrometers, could achieve 99.9% control with
a total ESP pressure drop of 0.38 in H,O.
Disadvantages:
Collection efficiency unreliable if gas property or particle
Inorganic particulates difficult to collect
Requires heating during start-up and shutdown to avoid
size distribution changes.
corrosion because of condensation of acid gases
9.0 INORGANICS
With the passage of the CAAA, emissions control for numerous
inorgaincs have become mandatory. Technologies that can be used effec-
tively to control emissions include:
Wet scrubbing
Adsorption
Incineration
Adsorption and incineration are discussed in Sec. 7.
9.1 Wet Scrubbing
The ionic nature of acids, bases and salts are removed from flue gases
by wet scrubbing because the ionic separation that occurs in water creates
advantageous equilibrium conditions. Removal may often be enhanced by
manipulation of the chemistry of the scrubbing solution.
Both spray towers and packed-bed towers operate based on common
principles of absorption. Pollutants in the form ofgases are transferred from
the gas stream to the scrubbing liquid as long as the gas is not equilibrium in
the liquid stream. An important consideration in design of the spray or
packed-bed towers isflooding. Flooding, where liquid is carried back up the
column by the gas stream, occurs when the gas stream velocity approaches
the flooding velocity. Tower diameter is established based on superficial gas
velocity ranging from 50% to 75% of the flooding velocity.
Spray towers operate by delivering liquid droplets through a spray-
distribution system. Generally, the droplets fall through countercurrent gas
Environmental Concerns 673
stream by gravity. A mist eliminator removes liquid entrained in the gas
stream prior to its discharge to the exhaust stack. Typical pressure drops in
a spray tower are 1-2 in H20, and design L/G ratios are, generally, about 20-
100 gaVl000 ft3. Spray towers have relatively low energy requirements
(about 3 x 104kW/actm airflow), however, water usage is high. Economics
of spray tower operation is influenced by waste water disposal costs. Capital
costs consists mainly of cost of the vessel, chemical treatment system, and
waste water treatment system.
In packed-bed scrubbers, liquid is flown from the top of the tower and
it flows over a random or structured packing. Generally, in the industry,
countercurrent flow with high LIG ratio packed-bed scrubber are prevalent,
when particulate loadings are higher. These provide the highest theoretical
removal efficiencies, because gas with the lowest pollutant concentration
contacts liquid with the lowest pollutant concentration, thus maximizing the
absorption driving force. Pressure drops of 1-8 in H20 are typical, while an
L/G ratio range of 10-20 gaVlOOO ft3 is generally employed.
Packed-bed towers can achieve removal efficiencies of over 99% and
have relatively lower water consumption requirements. They also offer
design and retrofit flexibility. Disadvantages include high system pressure
drops, relatively high clogging and fouling potential, potentially high main-
tenance costs, and waste water disposal requirements. Packed-bed scrubbers
are also more expensive to install and operate than spray towers.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
Kirschner, E., Prevention Takes Priority Over Cure, Chemical Week, p.
2732 (June 2, 1993)
Clean Air Act Amendments of 1990 Overview - Policy Guide 1993,
Bureau of National Affairs, Inc., 1OO:lOl-110.
Ambient Air Quality Standards Overview -Policy Guide 1993, Bureau of
National Affairs, Inc., pp. 101:lOl-1003.
Clean Air Act, 71:llOl-1182, Bureau ofNationa1 Affairs, Inc. (1984)
Zahodiakin, P., Puzzling Out the New Clean Air Act, Chem. Engineer-
ing, p. 2427 @ec 1990)
Hiller, K., Clean Air: A Fresh Challenge, Chemical Week, p. 2223 (Nov.
13, 1991)
Eckenfelder, W. W., Industrial Wastewater Management, Industrial
Wastewater, p. 7072 (April 1993)
674 Fermentation and Biochemical Engineering Handbook
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
Davenport, Gerald B., Understanding the Water Pollution, Laws Govern-
ing CPI Plants, Chemical Engineering Progress, p. 3033 (Sept. 1992)
Environmental Statutes, 1990 Edition, Government Institutes, Inc.
Roughten, James E., A Guide to Safety and Health Plan Development for
Hazardous Waste Operations, EtAZU4T World, pp. 40-43 (Jan. 1993)
Occupational Safety and Health Act - Policy Guide, The Bureau of
National Affairs, Inc., 291:301-306 (1988)
Resource Conservation and Recovery Act, RCRA - Policy Guide, The
Bureau of National Affairs, Inc., 291:401-408 (1991)
Balco, John J., Avoiding Environmental Audit Pitfalls, The National
Environmental Journal, p. 12 14 (MayIJune 1993)
Theodore, L. and Reynolds, J., Introduction to Hazardous Waste Incin-
eration, Wiley-Interscience, New York (1 987)
National Technical Information Services, Physical, Chemical, and Bio-
logical Treatment Techniques for Industrial Wastes, Vol. 1, PB-275-054
(1977)
Metcalf & Eddy, Wastewater Engineering - Treatment, Disposal, and
Reuse, McGraw-Hill Book Company, Third Edition, New York (1 99 1)
Office of Research & Development, USEPA, Treatability Manual: Vol-
ume III - Technologies for ControlLRemoval ofPolIutants, EPA-60018-
Noll, K., et al., Recovery, Recycle, andReuse oflndustrial Wastes, Lewis
Chelsea, Ann-Arbor, MI (1985)
Tavlarides, L. L., ProcessModifcation for Industrial Source Reduction,
Lewis Clark, Ann-Arbor, MI (1985)
USEPA, Control of Volatile Organic Compound Emissions from Air
Oxidation Processes in Synthetic Organic Chemical Manufacturing
Industry, PB85 - 1 6427 5.
80-042C (July 1980)