2 Facto ry 0 rgan i sat io n PLANT LOCATION The location of the dehydration factory must be considered very carefully, because, whereas at one time proximity to the source of raw materials was of paramount importance, availability of an adequate labour force and the provision for effluent disposal will, perhaps, constitute a more pressing requirement. A rural environment is obviously better than a location in a highly industrialised area, because the operation involves the utilisation of a considerable amount of open space for the reception and storage of raw materials, particularly where vegetable dehydration is being undertaken. This chapter, in dealing with factory planning, proceeds on the premise that vegetables are the principal raw material to be processed. Fruit dehydration is dealt with in Chapter 7. On the assumption that the labour availability factor has been resolved, and co-operation from the Local Authority on effluent disposal has been secured, it is important that the location should be a focal point for the intake of indigenous raw material within a radius of some 80 kilome-. In the case of highly perishable vegetables, such as vined peas and green beans, availability should be within half that radius. These figures are relevant where the scale of operation presupposes an average intake of 70-80 tons of produce per day which is, in effect, a viable level upon which to work. This would be regarded as a medium size plant. Production on a larger scale would call for a wider area of raw material 21 availability but, in the ensuing chapters, it is intended to concentrate on the problems of the medium size operator, coming into the industry for the first time, or developing into dehydration from some other food processing activity. It is, perhaps, more likely, at this stage of the growth of dehydration, that development in Europe will be at this sort of level, rather than at that applying in the US, where plants with an intake capability of upwards of 500 tons a day are not uncommon. RAW MATERIAL Once the vegetable programme has been established, an efficient procurement system is an absolute necessity, as it is vital that the plant be fed with a round-the-clock supply of raw material for many months of the year, with no hiatus or short-fall due to weather conditions, or any other circumstances. Binding contracts must be made with reliable growers to ensure this and also to ensure that suitable varieties of vegetable - ones that lend themselves favourably to the process -are grown. Random purchasing on the open market is a system not to be relied upon by the dehydrator, because wherever the price is right the variety will be wrong, and vice versa. The one exception, when this procedure is varied, is in the case of potatoes, and spot purchases are often made as the season proceeds. Whilst there is an element of risk in this particularly in a Season of low solids and a short crop - potato prices tend to be more stable than those for some other crops, and availability is spread over a much longer period. Some particular potato products, however, do call for special varieties as a first choice. Potato granules and flakes, for example, should be made from high starch content tubers and, if these types am not grown in the traditional growing areas, special plantings under contract may have to be made adjacent to the plant location. On the other hand, some processors find that, to meet a cost problem with some potato products, they have to process culls from ware (table grade) potatoes, and, in this case, contracting is not usually possible. Grading stations can usually supply large quantities of this material, which is satisfactory for the manufacture of some grades of dehydrated pmduct, and long term arrangements can always be made for intake from such sources, provided certain basic quality requirements are covered. Contracts The procurement contract with the grower can take one of two forms, either: (I) A contract wherein the purchaser undertakes to buy from the vendor a specific tonnage of vegetables at a fixed price per ton, delivered to the factory over a specified period, or (2) a contract wherein the purchaser 22 undertakes to buy the produce of a specific acreage laid down by the vendor, at an agreed price per acre. In the first instance, the grower must cover all contingencies arising from total or partial crop failure, and carry a not inconsiderable element of risk of the purchaser buying in against him in the event of a crop failure. The second form of contract implies that the processor takes over some of this risk but, in return, has a reasonable chance of buying his product cheaper, if he has an efficient fieldsman service to supervise the grower and ensure a high level of good husbandry. The contract, in whichever form, will specify varieties and, in some cases, the processor will elect to supply the seed at an agreed cost to the grower. Further stipulations will cover the quality standard, the rate of intake per day and the period over which intake will be accepted. The contract will also state whether the produce is to be delivered in bulk, or in containers and how accepted weights will be established. There is invariably provision for arbitration in the event of a dispute. It is important that the quality clause in the contract should be most specific, so that the grower is made aware of the standard of grading or dressing required. The processor will also underline his right to oversee, through his fieldsmen, the sowing, planting, cultivation and harvesting of the crop. Supervision must also be exercised with types of fertiliser, weedicide and pesticide used in connection with the cultivation, as dangerous residuals can sometimes affect the pduce at maturity. All these factors must be fully considered and covered in the document but, as this procurement procedure has been adopted for many years by canners and freezers, and has equally been accepted by growers, either individually or by their Associations, where group negotiations arise, the dehydrator should not really have any difficulty in getting all the above clauses implemented. LABOUR REQUIREMENTS In selecting a site for the factory, the consideration of suitable labour availability will have been made. On the assumption that the location is rural, certain advantages as to quality of labour are usually apparent, in that both male and female operatives who have agricultural backgrounds and traditions often integrate very satisfactorily into vegetable processing as this is, in effect, an extension of their way of life. The labour content of the putative 70-80 ton per day plant will vary according to the type of drying plant selected and the range of products to be handled but some guide can be given if certain assumptions are made at this point. Let it be supposed that the operation is mounted on a ten months’ 23 programme over the following range of vegetables: peas, green beans, potatoes (granules and cubes), cabbage, leeks, camts, celery, beetroot and turnips. The process staff will require to operate on a three shift system, usually six days per week, with a plant cleaning shift and a maintenance shift in addition at the weekend. Local custom may require that this system be covered by four teams to avoid excessive overtime at weekends but it is by no means uncommon in some factories for staff to accept this overtime, the three eight hour shifts being covered by three teams changing their shifts by rota every week. The many types of dehydration plant will be considered in detail in the following chapters but, for the purpose of assessing the process labour content of a typical medium size plant, it could be assumed that the following dryers would be required to handle the above ten month programme: For Granules: an Air-Lift dryer with a capacity of 1.5 tons of raw potatoes per hour; For peas, green beans, cabbage, celery and leeks one Hot Air Through Conveyor Band Dryer, with a capacity of up to 3 tons of prepared m vegetables per hour- the capacity will vary according to the type of vegetable and size of cut; For mot vegetables and potato cubes: one Hot Air Through Conveyor Band Dryer with the same capacity as mentioned for other vegetables. These dryers would not be operating concurrently throughout the whole of the season but would come into operation in accordance with the availability of the crops. It is vitally important that at certain times some excess drying capacity is available to cope with gluts, or a dryer breakdown, hence the advisability of duplicating the band dryer. Some important crops, which have a short harvest period, such as peas and French beans, can overlap and, in these circumstances, shortage of drying capacity can have dire consequences. The process labour to man this scale of operation, per shift, would be approximately as follows: Shift Superintendent: 1 Foreman: 1 Forewomen: 1 Male Plant Operators: 10 Fitters: 2 (maintenance duties only) Electrician: 1 (maintenance duties only) Boilerman: 1 Quality Control: 2 24 Women: 30-50 (trimming and selection) Permanent night men 15-25 (Trimming and selection) The female labour content will vary according to the types of vegetable being pmcessed. The above numbers in any case assume that, at the selection and packing end of the pmcess, the products e being bulk packed. Where the product is intended for retail distribution in small units, a very much larger female packing staff would be required to operate filling and packing machinery. Such considerations, in this instance, however, have not been taken into account. Male operators will normally substitute for women on the lOpm to 6am shift. It is stressed that the figures given can only be taken as a mugh guide, and they are based on the manning of two particular types of dryer, the methods of operating which are efficient and particularly economical in labour content generally. The conveyor band dryer, either single or multi pass, is probably more versatile than most in the types of vegetable it will handle, and it is particularly suitable for long sustained runs of one product. Its merits, along with those of other dryers, will be described in later chapters but in the context of the present plant under review, it requires a minimum of staff to operate it. As in the canning and freezing industries, the greatest concentration of female labour is in the trimming and selection departments, and unless strict control is exercised in these areas, as to the numbers and efficiency, costs can easily overtake profits. Technology has made great strides, however, in reducing the tedium and unrewarding work of product selection, and there are now very efficient colour sorting devices on the market, which effectively select and reject blemished material in the raw state, or after drying. This reduces the labour requirement for trimming and selection, and the development of these machines to the present peak of efficiency has cut the cost of these operations very considerably. As the particle size of dried vegetables rarely exceeds lOmm by lOmm by lOmm, the electronic colour sorter can scan these particles in their trajectory through an optical box against a predetermined coloured background. Any particle, whose colour, by reason of blemish, differs from that which is acceptable, is pushed into a different trajectory by a jet of compressed air and diverted through a waste spout. These machines have a high efficiency and perform the task of selection at a fraction of the cost of hand labour. Some visual inspection is still advisable after the product has passed 25 through a colour sorter but the labour content at this point is minimal. Intake Staff Very considerable labour economies can be effected in the vegetable intake department by the use of bulk loaders for potatoes and root vegetables, 500kg tanks for peas and large crates or tote boxes for cabbage, leeks, celery, etc. Green beans are perhaps the only vegetable for which bags or nets need to be Also, the use of storage silos for potatoes and roots reduces the intake staff to one, or two at most, per shift, and this staff can be used for fluming the raw material into the plant. This presupposes that an adequate supply of cheap water is available from an adjacent river, waterway or borehole, fmm which the processor has a prescribed right to abstract water. This need not be potable water, as it is only used as a means of moving the vegetables fmm the silos through flumes into a primary washer, and thence into the preparation plant. Such water is normally discharged from the washer into settling tanks, to remove silt and stones washed off the vegetables, before being returned to waste or recycled. In some instances, it may have to go through an effluent treatment plant before it can be discharged but the Local Authority will have to be consulted on this matter. A destoning machine is a necessary adjunct to this part of the system. The shift quality controller has an important part to play at this point, as it is his responsibility to ensure that the quality of the intake measures up Typical box tipper 26 to the contractual requirements of the buying department. Potatoes must be examined for total solids, reducing sugar content, excess soil, blemish and grading. Vined peas are examined for quality and tested for temperature and tenderometer reading. Camts, cabbage, celery, leeks, etc, are checked for the standard of dressing which is called for in the procurement contract. Extraneous matter in vegetables, apart from the waste factor, can also do untold damage to preparation plant later in the process, and intake staff must be very vigilant on this score. The period of intake will normally extend over twelve hours of each day, except during the season when highly perishable vegetables, such as peas and beans, are being handled, then intake and quality control staff will be required round the clock on three shifts. Adequate staffing at this point is, therefore, imperative. Warehousing Staff The staffing of the warehousing and despatch departments will depend, as to numbers, on the nature and size of the packs being produced, and whether a bulk or retail consumer trade is being carried on. If the factory is concerned mainly with bulk packs, two men per shift for stock movement will be adequate, with a daytime superintendent in overall charge. Maintenance Staff Apart from the fitting staff detailed to cover the shift maintenance duties, it is necessary to provide for an adequate day shift maintenance staff in the field of both mechanical and electrical engineering. Dehydration plant, operating round the clock for many months of the year, demands a high standard of maintenance,' and there is invariably a heavy day shift programme of servicing equipment, both mechanical and electrical, temporarily taken out of service for a major overhaul. A minimum of six day shift fitters and three electricians would be required for the size of undertaking under review. These are supplementary to maintenance personnel working on the three shift rota. A carpenter, painter and bricklayer can also be usefully employed all the year round on the day shift maintenance staff because continuous shift operation levies a heavy toll on the buildings, particularly at the wet preparation end of the factory. Laboratory and Horticultural Staff Laboratory staff quired, excluding the shift quality controllers, will be three as a minimum, depending on the range of products being handled. The main duties in the laboratory are the routine analytical tests on the dried 27 product, and these are supervised by a chief technician, assisted by two or more academically unqualified assistants. Some research and development will also be carried out by the senior staff. A horticultural officer and two fieldsmen are also required. WATER For the size of plant under review, the requirements for water washing, process use, boilers, etc, but excluding any fluming operations, will be of the order of 8 million litres per week of eight hour shifts. The quality of the water is important, and it is necessary to know the temporary and permanent hardness characteristics. It may be that the local supply is not entirely suitable for every kind of vegetable to be processed and some treatment may be necessary. For example, peas require soft water for washing and blanching, as a high calcium content in the supply has a toughening effect on the skins. In these circumstances a water softening plant will need to be installed to treat the water which is in contact with the peas in process. Conversely, potatoes, particularly when used for cubing or slicing, require a higher degree of hardness in the processing water, and it is usually necessary to treat this with calcium chloride in the blanching process. Ideal water conditions are, therefore, unlikely to be found in many locations, and perhaps a supply with 8 degrees of hardness might be regarded as a fair average, requiring less treatment overall than most samples. Consideration of the water analysis should, therefore, be treated as of some importance when choosing the factory site. Boiler water should be reasonably soft, to avoid scale formation but, where hard water conditions apply, the supply will have to be treated chemically, or a base exchange softening plant installed. With the latter, some further organic or chemical treatment will be necessary to correct excess alkalinity which is a feature of the base exchange method. It is good boilerhouse practice to =turn all the available condensate from the processing plant, ie, from dryer steam batteries, blancher and lye peeler steam coils and space heating batteries, back to the hot well in the boilerhouse, so that the feed water supply is available at a high temperature. There are several points in the factory where mains water can be conserved by recycling, particularly the washing plant. Care must be exercised here, however, to ensure that recycled water is not contaminated, and some in-plant chlorination willbe necessary to implement this recycling system. 28 Fluming Fluming water, as referred to earlier, must come from a free or, at least, a cheap source. It is not viable to use mains water for this purpose, as the volume required for fluming, say 70-80 tons of root vegetables or potatoes per twentyfour hour day, will be of the order of 1.2 million lihes. It is, thefore, desirable that the factory be situated near a river, or waterway, and that the River Authority can be persuaded to give the necessary licence to abstract water for this particular purpose. An alternative to this sourre of supply is, of course, a borehole, or a series of boreholes capable of that sort of capacity. The sugar beet factories use this system of fluming beet into their plants, some thousands of tons per day being moved from silo to process by high pressure water jets, with a minimum amount of manual effort. It is a system well worth emulating in the dehydration factory, where large quantities of roots and potatoes have to be handled. /.--.-- AI7 r’ I, --___. I.,//;*/, / -v7Ab.- ‘rr I End elevation of root vegetable silo with centrefluming channel Silos The construction of the silos is quite a simple matter and a typical sue for a 100 ton unit would be 30m by 4m. The side walls are lm in height and constructed of 23cm thick masonry. Both ends of the silo are left open to allow incoming bulk loaders or tipper lorries to discharge their loads. The concrete bottom of the silo slopes from either side wall to the fluming channel in the middle. This runs longitudinally down the whole length of the silo with a fall of 50cm in the 30m length. The width of the channel is 30cm, and this is rebated to take 7.5cm thick timber cover boards which are fitted flush with the sloping silo bottom. The shallowest point of the flume channel must be not less than 15cm deep, and it is from here that the water supply is introduced from powerful centrifugal pumps with a capacity of 91,000 to 136,000 litres per hour. The cover boards are removed in that part of the silo which requires to be emptied, and the vegetables feed in a steady stream into the fluming channel, whence they are carried along with the flow of 29 water. Beyond the end of the silo, the fluming channel continues, maintaining the same rate of fall, to the prewasher and destoner. At this point the fluming water is discharged, and the vegetables are elevated into the processing plant. In setting out this system, levels have to be carefully studied, as it may not be possible to arrange for a natural fall for the whole length of the flume, and some elevation may be necessary prior to the washer. This can only be decided by the processor in the light of local circumstances. Adequate protection from bad weather must be provided, and the silos should be under cover in suitable outbuildings wherever possible. Alternatively, 50 ton storage bins may be erected over the silos to discharge directly into the flume channels. A mobile elevator will be needed to fill these from bulk transport. POWER Electricity requirements for the putative plant will be in the range 300- 400KW. Whilst this will normally be taken from the mains, it is a wise precaution to have some internal generating facilities, even if only to keep essential plant running in the event of a mains power failure. Downtime in a continuous process is very expensive indeed and, apart fmm raw material in mid-process being at risk, heavy standing charges have also to be met from reserves. Also, when highly perishable vegetables, such as vined peas, are being handled, every hour lost by breakdown is irrecoverable, as the vining programme on the farms is geared accurately to the plant’s optimum processing throughput, and any hold-up at the factory can result in the loss of many tons of raw material, which could be the processor’s responsibility. This situation is very obvious when it is realised that the whole season‘s pack of fresh peas has to be processed in six weeks, therefore every hour of electrical or mechanical breakdown in the working week can precipitate disastrous losses for both the grower and the dehydrator. The economics of dehydration are elaborated in a later chapter but it cannot be stressed too strongly at this point that any steps, which can be taken by way of ensuring complete reliability and continuity of the power supply, should be taken, in the full knowledge of the consequences of breakdown. It is sound practice to install electric motors rated somewhat in excess of their actual duty, and to ensure that they are adequately protected against water, steam and conditions of high humidity, remembering also that they will probably be running continuously for many hours. It is possible to spray windings, starters and switchgear with a water repellent compound, and this precaution should be taken by the shift maintenance staff as a regular procedure. 30 A spaR motor unit should be kept in the stores for all key plant and, where drives and power requirements can be standardised for several machines, this should be arranged in order to cut down the number of spares carried. Most electrical supply authorities impose a maximum demand tariff on their consumers, and as the dehydrator is involved with a considerable power Ilequirement, and the use of several high powered motors, it is very necessary to install power factor comxtion equipment in the factory to reduce the start-up load on the meters. It is usually found that the cost of such equipment can be recovered within twelve months of normal operation and this will, of course, depend on the Local Authority’s tariff, and to what extent the maximum demand rate is levied on the commercial consumer. For a stand-by supply, a 2OOKVA alternator, driven by a diesel engine or, if a steam supply is available, by a steam turbine, should be adequate to keep the principal preparation plant and the main dryers operational in the event of a mains power failure, and this supply should be arranged so that it can be fed into the mains immediately such a failure occurs. Some factories keep their steam turbine ‘stand-by’ plants continually operating, integrating the supply with that from the mains, and utilising the back p~ssure steam for process heating in the factory This is an efficient and economical method of producing, simultaneously, electricity and low pressure steam at IO-15psi from one power source, ie, the boiler. At the same time the essential plant can be kept operational in the event of an external power cut or supply failure. BOILERS Boiler plant for this scale of operation should be rated at GOO to 7000kg per hour, at 17.5atm, with a stand-by boiler of similar capacity This boiler rating is based on the assumption that the whole of the heat requirement for drying is not expected to be taken from the boilerhouse. This point is considered later in the chapter when fuels for drying operations are specifically reviewed. Some dryers incorporate steam batteries and air fans for convection drying and, if this type is used, then the rating of the boiler plant may have to be increased but with the advent of natural gas, and the various forms of Liquid Petroleum Gas, a very much more efficient heat source for drying is now available to the dehydrator, and steam batteries are figuring less prominently in the many modern drying plants. The boiler rating stated above, therefore, takes into account the steam requirements for peeling, blanching, scalding, jacketed or coil heated vessels, steam batteries for conditioning bins (see Bin Finishing), steam hosing for sterilisation of plant and equipment, and space heating. Dryers relying upon 31 Propane combustion chamber showing burner arrangement and air control damper developed by Aeromatic Ltd. steam heating may require a further 5000kg per hour of steam at 17.5atm. Steam usage is related to evaporation of water from the product, and it requires 1.9kg steam per kg of evaporation. HEAT RAISING PLANT Heating systems used in air drying are either direct or indirect. Direct System Here the fuel is burned in the air stream and has direct impact on the product. This system calls for a high degree of purity and non toxic constituents in the fuel. The development of natural gas propane and butane for commercial applications has provided the dehydrator with an ideal and economical fuel for vegetable drying and, in the author’s opinion, is to be against all other fuels, wheever the dryer lends itself to direct preferred firing. LPG in the form of propane is particularly suitable on account of its very low sulphur content (0.02 percent), its consistency of composition and freedom from unsaturated compounds. It is clean and easily controlled, adjustable to special requirements and, moreover, it is relatively competitive and widely available from the major oil companies as a by-product of The combustion equipment, comprising a series of burners in an insulated chamber, thermostatically controlled and with air and flame failure safety devices built in, is relatively cheap to install and maintain. Natural gas has similar favourable combustion characteristics but may not be so readily available in rural areas, and a special run of mains from the nearest pipeline may involve considerable installation outlay AThrough Conveyor Band Dryer with a raw material throughput of 3 tonnes per hour would require a combustion unit for propane with a maximum rating of 15 million Btu’s per hour. This would call for a seven burner chamber, five burners firing continuously with two on thermostatic control. Satisfactory flame conditions can be maintained with propane at a regulated pressure of 0.95atm and, whilst the fuel consumption will obviously vary in accordance with the evaporative duty demanded, this could be roughly taken at 140kg of LPG per hour, or 36cu m of natural gas. The oil industry, in collaboration with the UK Factory Inspectorate and other experts, has laid down a Code of Practice in relation to the storage and commercial usage of liquid petroleum gas, and the processor intending to use this type of fuel should familiarise himself with the regulations, particularly as to storage tanks and pipelines. Where LPG storage tanks cannot be sited at least 15m away from the factory buildings, and 15m away from the nearest roadway, they wiU almost certainly have to be installed underground, and such installation is relatively expensive compared with ground level tankage. Whilst propane will vaporise naturally from an overground installation, such is not the case from an underground tank. Here the liquid propane has to pass through a steam heated vaporiser to convert it to a gas. Very low temperatures prevail in an underground tank, as vaporisation takes place; these are not relieved by a datively high ambient air temperature as in the case of an overground installation, hence the necessity for assisting vaporisation by supplementary steam heat. Tank pressure will be 4.5 to 6.8atm and this is reduced to 1.36atm by regulators on the pipe main to the combustion plant, where the gas pxessure may be further reduced to suit required combustion conditions and drying requirements. refining. Indirect Systems The indirect system can be applied in several ways, and with some types of dryer there is no alternative method of heat transfer to the product. The Through Conveyor Band Dryer can derive its hot air supply from a heat exchanger used in connection with an oil or coal-fired furnace. The heat exchanger comprises a set of cast iron or steel elements or plates, usually 33 gilled to provide the optimum surface area for heat transfer, and the gases of combustion from the oil or coal fired furnace pass across one side of the plates, transferring heat to the clean air pulled across the xeverse side by the dryer fans. The fans draw the heated air into the dryer proper, either through or across the product which is being continuously conveyed on the dryer belt. Heat exchangers can also be constructed with a series of tubes, instead of gilled plates; this is very similar to the design of an economizer for a boiler plant. The obvious weakness of this system is that there are considerable thermal losses, in spite of the facility, and indeed practice, of recycling the gases of combustion before discharge to atmosphexe. Then there is usually a heavy maintenance factor in cleaning the heat exchanger elements or tubes, to keep the apertures through which the gases flow free from a build up of fly-ash (where solid fuel is used) and carbon and sulphurous deposits from oil. Also, at the cool end of the exchanger, where temperatures are often below the dew point, corrosion can be a pmblem. Another indinxt heat system, which can be used with band, cabinet, tunnel and bin dryers, incorporates the use of steam batteries of gilled tubes through which the drying air passes, either by induction or pressure. Here again there are some thermal losses, and the batteries require constant and careful maintenance to ensure that the air passages are kept free and that they are efficiently trapped on the steam side. Dust is not an uncommon problem in a dehydration factory, and this can be a source of trouble on the air side of this type of steam battery. Combined Systems With air lift and thermal venturi dryers, it is possible to use a combination of the indirect system, with steam batteries, and the direct system of LPG or natural gas - the one system supplementing the other. The use of batteries is often economical when the factory has a surplus of low pressure steam or exhaust steam from a turbine or some other part of the plant. No heat should go to waste, and every conceivable use should be made of it. Gas heat, as a supplementary source, can then be used to obtain the desired processing temperature. The drum dryer is another example of the indirect system. Here, high pressure steam passes through either one or two large rotating steel drums, and the product to be dried is fed by spraying or by feed rollers on to the outer surface of the drums in a thin layer, and heat transfer from the inside to the outside surface of each drum evaporates the water content of the product during the course of about 300" of the drum's revolution. Owing to the 34 thinness of the surface coating, evaporation is extremely rapid, the moisture being flashed off, literally, in seconds. Steam requirements are heavy for this drying method, as a pressureof at least 5.4atm has to be maintained, and the volumetric capacity of the drum is high, some being 4.6m long by 1.8m in diameter. FUELS Suitable fuels, therefore, are coal and oil for the indirect systems, and propane, butane or natural gas for the direct systems. In no circumstances should the gases of combustion of coal or o il be used in the direct airstream when dehydrating food for human consumption. The risks of contamination by sulphur and carbon compounds are very considerable in these circumstances and, whilst this method has been used in the past for dehydrating certain food products, it should certainly be avoided in the context of modern practice. EFFLUENT The subject of waste and industrial effluent disposal is too wide and complicated tobe dealt with in depth in this volume. It has become, in recent times, a problem of national significance and importance, and the dehydrator 1 Screening solids from liquid effluent in Italy 35 must have this subject very high on his list of priorities when contemplating the pros and cons of a factory site, and he must obviously discuss all the implications with the Local Authority or River Board before any location is determined. It has already been established that for a medium size vegetable processing plant, some 1,200,OOO litres of fluming water, where applicable, and an equal volume of processing water are going to be discharged to waste each day. The authorities will need to assess the nature and quality of this discharge before any permission will be given for it to pass into any sewer or waterway. The days when effluent could be flushed down the nearest drain regardless of its ultimate destination, are gone in the Western World and disposal today can be a very laborious and expensive business, and expert advice on the subject must be sought. It is not unknown for an effluent treatment plant to cost one third of the value of the pmcess plant, because in certain conditions very intensive treatment is required by the authorities, particularly where the discharge is made into an inland waterway First, the fluming water is likely to have a high percentage of silt and vegetable matter in it, and, in the processing water effluent, there is likely to be starch, spent lye, solid vegetable matter and various chemical compounds from the blanching water. The scale of treatment required will depend on the level of contamination, and the Biochemical Oxygen Demand of the discharge, and the processor will possibly have to decide between steam and lye, or abrasive peeling of vegetables in the context of the diffenmt effects these methods will have on his effluent pmblems. Lye peeling, involving concentrated solutions of sodium hydroxide, will create a high BOD in the effluent, and the treatment cost on this account may be considerably higher than if steam peeling was used. Steam peelers involve a higher capital plant investment but this may be offset by a lesser involvement in effluent treatment, therefore no hard and fast rules can be laid down for any specific case. Abrasive peeling of potatoes releases large quantities of free starch from potatoes, and this again creates a serious treatment problem. Some large potato processors, who have been committed to abrasive peeling, have had to install expensive starch manufacturing plants to dry the free starch collected in settling tanks used as the first stage of effluent treatment, although the financial recovery from this by-product is so low that it cannot cover the capital investment or the operating costs, but the exercise has to be done as a progressive stage in the overall effluent treatment system. The method of disposal, therefore, must be considered in the light of local circumstances, and the following options may be open to the dehydrator: 36 (1) Simple screening out of solids - this is a prerequisite to all subsequent means of disposal; (2) Filtration through gravel beds: (3) Pumping into settling tanks, followed by treatment with (4) Aeration and lagooning; (5) Spray irrigation; (6) Discharge into a public sewer, after one or other of the above biological agents; treatments - this will invariably involve a charge for the volume accepted by the Local Authority; (7) Discharge into a tidal or other waterway, after whatever treatment is prescribed by the River Board. Solid wastes can sometimes be dried for animal foods but the operating cost of this procedure must be carefully examined to ensure that it is a viable operation. The only satisfactory approach to this major problem is to engage the services of an effluent consultant at the outset of the project, and the expert is likely to fulfil the local requirements very much mo- economically than the dehydrator would do, as the latter invariably enters this field with less than expert knowledge. Contour irrigutiw Central Turkey - - rc ,;- Wasteful control but low capital cost 37 Unlimited potential from Rio Francisco in Pernambuco, Brazil Onion field trials on contour irrigated land in Pernambuco Desert irrigation Khorramshaar, Iran b