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Design & construction of poultry processing plant : part 1
Facilities Required in Specific Areas
General Building
The building
The building and its roof should be an adaptation of local architecture so that it fits in with its surroundings and causes no visual offence. The adaptation should consider the climate and other environmental characteristics of the region while addressing the hygiene concepts of its operation. For example, in earthquake zones, the building should be strengthened to locally recommended levels with reinforced concrete ring beams and no tiling to the walls. Desert areas will need special dustproofing. In areas subject to very wide variations of temperature and humidity, the buildings will have to be suitably adapted, perhaps with heating and ventilation.
Roof
In humid equatorial zones, the building should be adapted to the problems of sharp cloud-bursts, with sloping roofs, wide eaves, deep gutters and downpipes, and substantial storm drains to take away rainwater rapidly. High apex roofs are considered best for hot areas. Flat roofs are unsuitable generally, even though they may be cheaper than the alternatives. Thatched roofs are also not suitable since they house birds and insects and are a fire risk. By the same token, an asbestos roof is considered a health risk and cannot be used either.
Walls
The nature of the materials used in construction of the outside wall should reflect the climate and environment. In the humid tropics, a damp proof course may be necessary. The outside walls may need to be made in a low absorbent material like highly fired brick, marble or other local stone rather than soft blockwork with a cement render which will stain and decay rapidly.
Insects
Insect levels are high in many tropical countries and particularly so around abattoirs where there is often an abundance of static water and nourishment for their survival. Buildings must incorporate suitable screening, remembering that insects, having gained entry should not find difficulty in finding a way out. The screens used must be hygienic, and cleaned frequently if necessary. Inside the building, particularly in production areas, electrical insect attractants with an electrified grid to kill flying insects are particularly useful.
Wood
Some insects live on wood which soon decays and is therefore unsuitable for outside use. Wood and other absorbent materials are not to be used anywhere inside the building for any purposes.
Water and steam
All water entering the abattoir should be of potable quality. Ideally, water should meet the guide-lines set by the World Health Organisation. These are long and involved. For practical purposes, it sets a bacteriological quality (of zero faecal and other coliforms/100ml sample), a chemical quality for nine inorganic and 18 organic substances and a recommendation about aesthetic and organoleptic qualities. The water supply should be chlorinated so that there is a residual concentration of 0.5ppm free chlorine after 20 minutes contact time. It should be supplied at a minimum pressure of 15psi (1 Bar). There should be sufficient water stored for one normal days production, should there be an interruption of normal water supply. Water consumption may be calculated at 25–35 litres/bird slaughtered.
In small plants, it is possible to heat water for scalding and cleaning by electricity, gas or by solar heaters at the place where it is to be used. Savings in water and energy can be effected by provision of low volume, high water pressure systems (LVHP) for product cleaning and plant sterilization. A high pressure system of suspended hose lines at strategic points in the factory will assist high product standards and minimal water consumption provided they do not touch the floor and do not leak. A mobile steam cleaner is very effective in cleaning small plants, particularly where cleaning agents can be added to the water flow. In larger plants this may not be economical and operation of a boiler house to generate steam is desirable. For this, a separate boiler house should be build and provision for fuel, water and steam storage will be necessary. An adequate number of steam hose points and steam lances should be provided at appropriate points in the factory so that flexible hosepipe runs are no more than 15m long.
Drainage
The abattoir should have at least three systems of drainage.
- Storm water drains, used for that purpose only, may be open in places and should flow into the appropriate outlet. They should be designed to withstand the maximum expected precipitation. The meteorological office or local architectural offices will usually be able to provide details. The drains should be designed to be kept clear and they should be cleaned regularly. In areas where rainfall is frequent, heavy and relatively non-seasonal, this usually presents no problems. Where there are distinct wet and dry seasons, storm drains should be specially managed to ensure that they function efficiently before the first rain is expected.
- Drains carrying human waste, again used only for that purpose, should pass by closed 150mm pipe, through a series of gullies and manholes where necessary, into the town sewerage system, where it should be properly treated. If no town sewers exist, the waste is probably best treated by means of a septic tank and soakaway along the lines of domestic waste treatment. In small abattoirs, elaborate treatment systems are probably not necessary.
- Effluent treatment is a specialised topic which will be discussed later in this document. At this point, it is sufficient to say that the drains should flow from clean to dirty areas within the building. Blood and large particles should have been removed before they leave the building. Once the drainage system leaves the building it should be in 150mm or greater pipework and pass through a series of gullies and manholes until further treatment, some distance from the building.
Outside Areas
The area outside the building should be sealed to a distance of at least 3m from the building. Beyond this, a clear, non-dusting finish should be used to 10m. Overhanging trees and vegetation should be cleared to 10m. Potential bird and animal habitats and resting places should be avoided such as trees, wires and the eaves of buildings. Any plantations made to provide a function, service or landscape should be of a type unattractive to local wildlife. For example, bats and monkeys are attracted to fruit and this type of tree should not be chosen. Trees which are particularly unattractive to hawks, crows, vultures and other carrion feeders are recommended.
If the plant is to operate at night, consideration must be given to external lighting. While this is needed for functions performed outside, the lights will attract many night insects. Lighting should therefore be situated on the fence directed towards the building rather than on the building and directed out.
Livestock Reception Area
Like all areas in the poultry processing room, the design of the reception area must reflect its function and management. Livestock is considered dirty. Poultry has a mixture of dirt, faeces, mites and insects embedded in its feathers. The poultry itself may have a microbiological infection. The vehicle and the containers are usually dirty from travel and previous use. The person bringing the stock may be unclean from travel and he/she may have brought his/her family, including the dog from home to the abattoir. It is good practice, therefore, to provide a separate entrance for livestock. Access to the rest of the building by the persons bringing the birds should be prevented. Washing facilities for vehicles and other livestock carriers should be provided. Hot water under pressure and drainage should be supplied. The area should have the geography and space to allow vehicles to manoeuvre and store both full and empty crates or livestock containers. The birds must be stored under cover to await slaughter.
Reception Loading Area
The reception area may also double as the loading area; in small processing plants this is most suitable. Space must be allowed to label and sort stock, man-handle livestock containers and store them when empty. Access to the equipment to hang birds immediately before slaughter should be provided. Livestock handlers should be provided with wash hand basins in the reception area.
The Slaughterhall
The slaughterhall has the potential for being among the dirtiest of rooms in the abattoir. It may contain flapping birds (they do not all settle), steaming scald tanks, flails or whirling rubber fingers removing feathers, dirt, faeces and insects from the newly dead carcases. This situation forms an effective, contaminating acrosol which settles on all the structures, equipment and personnel. When viewed in this light, its design and management principles become apparent. The room must be separated from the rest of the processing rooms as must the staff who work in it.
The room must be big enough to accommodate all the equipment and personnel with adequate circulation space. The layout, using the principles set out above, should allow 12 or more seconds for the birds to settle before low voltage stunning and sticking, two and a half minutes bleeding and up to three minutes scalding at 53°C before defeathering.
Blood released from the birds must be properly handled. It has a high Biological Oxidation Demand and should not pass into the effluent disposal system. If the quantity of blood is small, it can be scooped up and disposed of directly. Other systems involve the use of pumps of vacuum to a tank in the offal room.
The arrangement of the defeathering area must relate to the management system and number and type of equipment in use. If the defeathering machinery is based on a series of pluckers operating on birds suspended from an overhead rail, the length of rail involved will relate to the number of birds to be plucked in a given time, the speed of the rail and the efficiency of the plucker. Such detail is usually worked out by the manufacturer. In systems where scalded carcases are held against a rubber drum with fingers, the position of these will depend on the system to be operated and the number of machines to be used. This relates to the capacity of the machines and the number of birds to be plucked in a unit time. For example, to defeather 200 birds/hour can be achieved by using two pluckers each with an operational capacity of 110/hour or four with a capacity of 60/hour. (These are maximum capacities and allow for some production and unexpected shortfalls). There are advantages to using more machinery of lower capacity in the tropics where throughput may vary considerably from day to day and the number used and staffing levels can match the day's throughput. Also, should one machine be out of service, there are three others (in this case) to help achieve three quarters of the daily throughput as opposed to half with the higher capacity system. Of course four operators will be required to use the lower capacity system and a large building will be required to accommodate the equipment. The risks and economics of the situation must be assessed when the system is chosen.
The floor in this area must be smooth and well drained. Feathers which have been removed from the birds and fall to the floor must be screened from the drains to prevent blockage. This is best achieved by fitting a grill over the channel drain. Wet feathers are particularly difficult to manage but it is essential that they are confined and placed in drained containers on a regular basis in the interests of hygiene and safety.
The defeathering area should leave space for an operative to remove the pin and other remaining feathers by hand and singe the carcase to remove the last feathers and hair.
Defeathering is followed by spray washing in cold water. This area should be properly drained.
If chilled, the carcases are now known as New York Dressed and may be marketed as such. There is much to be said for marketing poultry in this condition at the start of any processing venture. The product is more hygienic than a badly produced eviscerated carcase, will keep for a day or so if kept cool or may appeal as a product only a little removed from that sold by other marketing methods (live or fresh killed but not plucked).
The room will require full ventilation to prevent condensation build-up. A complete change of air each minute is required.
Evisceration and Chilling Room
This must be a separate room. Clean carcases are opened to expose their viscera which contain spoilage and, perhaps, pathogenic bacteria. Great care must be taken not to contaminate the carcase when they are removed. Special facilities are required.
In larger abattoirs, evisceration is performed automatically by machines designed for the purpose. In small processing plants, carcases hanging from overhead rails or hooks are eviscerated by operators using hand tools. About 1 metre/person must be allowed to permit workers to operate on this line. Inspection takes place in this room also and about 3 metres must be allowed for this.
The offal should be dropped into a trough of about 1 metre wide which slopes backwards to the beginning of the line. Offal flow is assisted by the end of line carcase washer.
In the smallest abattoirs, evisceration is performed either on a carousel which operates a little like an overhead rail and offal trough or on tables. This method must be carried out with great care as there is considerable scope for contamination of the carcases and their cross-contamination if the tables are not properly organised.
As evisceration involves removal of material containing considerable numbers of micro-organisms, contamination of the carcases is possible. This may lead to reduction of shelf life. Cutting carcases while they are hot is not considered practical so for both reasons, it is essential to cool them rapidly and hold them under chilled or frozen storage.
A cold spray to remove gross contamination is followed by one of several methods of cooling. The usual method is one of immersion in a tank of water which is cooled (perhaps with ice) and chlorinated. The volumes and temperatures of cooled water used in cold water chilling systems are usually calculated by the manufacturers of the equipment. The USDA regulations demand that there should be a minimum of 2.251 of overflow for each bird. Calculations of the ice, water and chlorine requirements of that system are difficult. Although there are empirical formulae to calculate them, the results usually underestimate the quantities required and the carcases often finish up insufficiently chilled or left for too long in the tank. As a guide, 0.4kg to 1 kg of ice per 1 kg of poultry is used to chill carcases, usually towards the higher end of the range in the tropics. For estimating purposes, 2kg ice/bird slaughtered should be allowed. Use of an insulated slush ice tank will reduce ice consumption.
There are several designs of chiller for hot carcases. These include the continuous drag chiller, slush ice chiller, concurrent tumble system, counterflow tumble system and rocker vat system. Although of differing designs, principles remain broadly similar. The chill system is designed so that ice or ice cold water is fed into the end of the tank or system that the carcases leave. The cooling medium is set to flow towards the carcase entry so that it is in counterflow to the product. There may be a series of tanks through which the birds pass rather than one tank. Often there is some mechanism, eg an auger or the overhead railway system itself which propels the bird from its entry into the coolant to its exit. The ice melts and overflows into the drain at the carcase entry point. The water must be completely changed at least every four hours as it becomes contaminated with blood and carcase material. Chlorine must be added regularly to maintain a total residual level of 50ppm.
As an alternative method of chilling, carcases may be cooled in air at ambient with a forced draught of about 1m/sec followed by spray chilling in water chilled to 2–4°C. Approximately 2.51/bird is required to chill the carcases to 7°C.
The evisceration room should have sufficient space to allow workers and equipment to move around. Personal hygiene facilities are required eg wash hand basins and paper towels or hot air blowers. As the carcases are in a cleaned state, all metal work in the room should be in stainless steel with a specification as set out in the paragraph describing equipment above. The room will be hot and humid, so adequate ventilation is important. A complete change of air each minute is recommended.
In the diagrams in the annexes, the chilled birds emerge in or immediately adjacent to the packing area; this is in the “clean” area.
Packing Room
Poultry which has been chilled by a wet process must be packed rapidly and either dispatched rapidly or frozen. Chilled poultry leaving the ice tank must be hung and allowed to drain for several minutes, preferably into a suspended trough to prevent unnecessary moisture on the floor. The room should be air-conditioned, constructed and finished to full hygienic standards.
Poultry may be graded by class, weight and appearance. They may be packed whole (with or without giblets) or cut into halves, quarters, pieces or deboned partially or completely before packing or processing further. The process employed will depend on the market to be satisfied. Account must be taken of regional preferences eg feet and/or heads may be left on (not recommended) or wings and feet packed separately. Cutting and further processing may be carried out either by simple hand tools or machinery within a full range of sophistication. All machinery must be hygienically constructed and capable of being properly cleaned.
The packing room must have sufficient space to stand packing tables and equipment, immediate storage of packing materials and trolleys for moving material into the chillers or freezing system. Its size will depend on throughput and the nature of the operations to be performed. The room should be light, quiet, well organised so that grading, weighing, cutting, wrapping, marking, packing into secondary containers (eg cardboard cartons) are easily achieved. Passage to the cold storage should be rapid, thereby preventing the carcase from warming unduly. The room should contain hygiene facilities for staff (eg wash hand basins and towels) and adequate drainage for washing down.
Chilling Rooms
Packed poultry may be stored in chill rooms for early dispatch or frozen and stored for dispatch as required.
Poultry which has been eviscerated and chilled in slush ice, followed by chill storage above freezing has the shortest shelf life of all methods of production. Chilled poultry can be stored at 2–4°C for one or two days at maximum before dispatch to retail outlets. Poultry may be kept a day or so longer if stored at -1°C. Poultry kept in frozen storage (-20°C) may be kept for up to 6 months. Sufficient storage space must be provided for the system of operation to be used. It must include adequate circulation space for staff and vehicles.
As turn-round is fairly rapid in chill storage, single height stores are adequate. The ceiling height need be little more than 3.5m. Consideration must be given to the foundations of the building which must bear great weights, stresses and strains. The installation must have adequate insulation to withstand high external temperatures an adequate vapour barrier and protection from physical damage by equipment. A curb between the inside walls and pallets of 150mm should be provided to facilitate air movement and to prevent damage by materials handling equipment and the packaged products. Air curtains should be provided at the doors to help contain the cool air within the chill room.
The product should be stored with adequate dunnage to take advantage of an air flow of about 1m/s. There should be adequate light to read labels and boxes but not so much that it causes significant heat generation. The room should have facilities for easy storage of the product on pallets or shelves. Stock control should be very well organised. There should be floor drainage so that the room may be frequently, regularly and adequately washed down.
The cold stores should be arranged so that the product may pass easily to the dispatch bay or freezer rooms.
Freezing Rooms
Poultry may be frozen by one of several ways. The usual system is to place the wrapped carcases or portions into metal trays and place them in a blast freezer for 2–3 hours at -40°C. The air flow is maintained at about 2–4m/s. The process is followed by storage in a freezer store at -20°C or below for a period up to six months.
There are alternative methods of freezing. Regular packages lend themselves to plate freezing. In this system, “bricks” of meat packages are sandwiched between two plates. There are several plates and each will sandwich several packs of poultry. The plates are brought down into direct contact with the pack and refrigerant is run through so that the packs reach -18°C in about 1 1/2 hours. The packs are then removed, placed in boxes and stored at -20°C.
Other freezing methods include adding refrigerant directly to the pack. The two best known examples are liquid nitrogen and solid carbon dioxide. They are not used frequently in the tropics because of their poor availability, irregularity of supply and high recurrent costs, which may be up to three times as expensive as conventional refrigeration. Nevertheless, it is mentioned as there are circumstances which suit this freezing method and the capital outlay is much less than conventional systems.
The frozen product should be stored at -18°C or below. Although single height stores of up to 3.5m high may be adequate in small scale processing plants, in larger factories the freezer stores may be up to four pallets high. Consideration must be given to the foundations which must bear greater weights, stresses and strains than the chill rooms. The installation must have adequate insulation not only to withstand high external temperatures but prevent freezing the soil underneath. This can cause frost heave and physical damage to the store. The store must have an adequate vapour barrier, protection from physical damage by equipment and a curb of 150mm on the inside walls to facilitate air movement and prevent damage by materials handling equipment and the packaged products. Freezer stores should have an alarm system to attract help should staff be locked into the store accidently. Air curtains should be provided at the doors to help contain the cool air within the room.
Loaded pallets should have adequate dunnage to take advantage of a light air flow. As the room is kept well below freezing temperatures, there will be the inevitable build-up of ice throughout the store, and around and just inside the door, particularly in humid climates. The fabric of the store should be such that this ice can be removed easily and without damage, so that doors can be closed completely to maintain a constant temperature. There should be adequate light to read labels and boxes but not so much that it causes significant heat generation. The room should have facilities for easy storage of the product on pallets or shelves. Stock control should be very well organised. Freeze stores are emptied most infrequently so there is no need to provide a formal drainage system. However, when the stores are emptied, the opportunity should be taken to clean them. A considerable volume of melt will be produced, which may contain drip from product, rubber from wheeled and human traffic, dirt from packaging and pallets etc. The design of the stores should ensure that this melt is hygienically removed.
The freeze stores should be arranged so that the product may pass easily to the dispatch bay.
Dispatch
The dispatch bay should be located near to the storage area and arranged so that loading is conducted speedily. This will prevent unnecessary rise in temperature of the product. Refrigerated dispatch bays are unnecessary in small scale plants. The system of dispatch of product needs careful consideration at the design stage. Should dispatch be planned by means of pick-up, large vehicle, private vehicle or as individual packs from a retail shop, the facilities should be designed accordingly. Considerations should include the slope of the site, height of floor pan of vehicle, use of fork lift vehicle or pallet truck, hand loading, gravity, conveyor etc. Numbers of vehicles collecting poultry at any given time will affect its size eg a bay to accommodate one vehicle twice each day to remove the whole days production for dispatch to a wholesale market will be smaller than a bay used by 20 small pick-up trucks, one from each supermarket in the town, all wanting to collect poultry at 0800 each morning in time to open shop at 0900. Consideration should also be given to parking and manoeuvreing of collection vehicles.
Dry Stores
Bulk supplies of wrapping materials should not be stored in poultry processing rooms. They should have separate facilities in a room off the packing room, and preferably with a door to the outside for deliveries.
The size of dry stores will depend on the type of product prepared, type, size and number of boxes/materials to be stored and their delivery schedules. This is important in the tropics where cartons may be produced in batch operations by a factory dependant on the availability of raw materials or where packaging materials are imported in large quantities on an infrequent or irregular basis. Space must be provided in the store for personnel to identify, sort, collate and collect the materials needed for the occasion.
Provision must be made to manage the dust associated with storage of dry materials. Extractor fans and airlocks are suggested for some areas of the world where dry dust may become airborne easily. In humid climates, the nature of the packaging materials to be used, box designs, adhesives etc must be carefully considered. A soggy box which is poorly glued will not hold the product. Much damage may result from poor storage conditions and, under certain circumstances, the provision of an air conditioned room or one with a modified atmosphere should be considered. The room should be proofed against entry of insects. Packaging materials make excellent breeding grounds and homes for insects if the stores are not well managed. Adequate lighting and stock control are necessary.
Offal Room
The offal room is probably the dirtiest room in the factory and must be designed to address the problems. Inedible offals, in the form of feathers, heads, feet, viscera etc and condemned carcases must be disposed of in facilities especially designed for the purpose. The room should be located next to the defeathering and evisceration areas. Waste products should pass into the offal room from these clean rooms and pass directly out of the building without passing through any other. Offal usually arrives in the room along trenches and chutes with considerable quantities of water. Water and offal are separated before the offal is placed into some form of container before its disposal. The water drains to the floor before it passes to the effluent treatment plant.
The room must be properly isolated from the rest of the building, properly finished, impervious to water to 3m or more from the floor and adequately drained. The floor must be maintained to a high standard and not be slippery. The doors must have bulwarks to prevent waste water from leaving the room. It should be adequately lit and ventilated.
Staff employed in this room should not be permitted to enter any other processing room.
Staff Facilities
Staff facilities comprise changing areas, toilets, showers, washing facilities, lockers and bins for dirty laundry. Separate dining facilities for the consumption of food may be necessary in some locations but probably not in small processing plants.
The design of staff facilities needs much consideration. Separate facilities are required for men and women. Live bird and by-products handlers should also have separate facilities. This is not always possible in small processing plants. In either case, the factory should be designed so that these personnel have direct access between their changing facilities and work areas without passing through the clean areas of production.
The layout of facilities should comply with local legislation. This should include conditions regarding access to operational rooms. Staff arriving for work and leaving at the end of the shift should be able to enter the changing facilities directly and not pass through production areas. Although the rooms should be sited near to the area of greatest number of working personnel (usually the evisceration room), staff not permitted to pass through the nearby room should be able to get to work by a short, logical route. The staff facilities should not open directly onto a production area. There should be some form of air lock.
Changing facilities should comprise a locker for each member of staff and sufficient toilets, showers and wash hand basins for the number of staff employed. The toilets and changing rooms should be separated by a partition from floor to ceiling. The use of paper towels is to be encouraged and proper dispensers should be provided. Benches and storage for footwear must be provided.
The room should be light, well ventilated, insect proofed and fitted with an extractor fan to exhaust air to the outside. Sufficient hot and cold water should be provided for staff to wash their hands and face frequently and shower once each shift. Litter bins should be provided.
Factory workers must neither eat nor smoke in meat production areas. There should be provision made for these activities which do not contravene the spirit of hygienic principles. An area, perhaps designated a recreation area, could be provided outside but under cover, with wash hand basin, tables, chairs, ashtrays, litter bins etc so that eating and smoking is contained.
Hand and Boot Wash
Before entry into the processing rooms, and usually just outside the staff facilities often in a corridor, a boot wash facility should be provided. This need be little more than a tap to which short hose with a car-wash-type brush is attached hanging over a stainless bar, itself over a drained trough. The worker lifts and places his foot on the bar, which is about 300mm from the floor, to clean his boot. It is customary to provide a wash hand basin next to the boot wash with hot and cold water, paper towels and a litter bin.
Laundry
All workers should change their protective clothing at least once each day. In small processing plants, staff are often expected to launder their own clothes. Managers face difficulties if staff have no clean protective clothing. Provision should be made, therefore, for all laundry to be washed by paid staff or under contract to ensure total cleanliness. In the tropics it would not be unusual for a relative of one of the production staff to undertake the task. This should be carried out on site but away from the main building. A small room or lean-to should be provided with a sink, hot and cold water, clothes line etc. Requisites such as soap powder and scrubbing brushes should be provided. It is not unusual to see the family laundry on the line with working clothes and, provided this is not to excess, can be part of a management arrangement to attract suitable staff.
Offices
Offices and their furniture should be provided for the manager, office staff, veterinarians and so on, according to the local custom and legislation. The number, type, style and size of office accommodation will depend on the nature of the business, the numbers of birds slaughtered, the number of clients, both supplying and being supplied and the culture of the region. It is important to provide accommodation which is comfortable for the office staff so that personnel of the right calibre will work in what is a relatively unattractive industry.
Inedible by-Products and Waste Disposal Facilities
Solid by-products
Broiler carcase yield is approximately 65% of liveweight which means that approximately 35% of the liveweight of poultry comprises feathers, blood, viscera, feet, head and trim which is available for solid by-products. The liveweight of the bird will vary with the production systems employed and the market demand. Similarly the weight of solid by-products will vary with the degree of dressing required by the market or, where birds are slaughtered for an owner rather than purchased by the processing plant, the weight of material the owner may wish to take or leave after slaughter. This section will assume that the average liveweight of the bird is 1.5kg and 35% of this weight will require disposal. Additionally, the feathers contain about 75% water. As the dry feather weight is about 4% of liveweight, the quantity of by-products produced by the three model plants is calculated as follows:
| • | 50 birds/day | 30kg/day |
| • | 200 birds/day | 120kg/day |
| • | 350 birds/hour or 2500/day | 1400kg/day |
It should be noted that in the first model, the birds will be New York Dressed, so that only blood and feathers will be available. This will amount to about 10% of body weight or 7.5kg/day.
By-products material should be handled carefully. It should follow marked routes in the plant and be contained. This containment includes troughs, pipes and trunking, bins and bags, skips etc. Waste materials should not be left on the floors, swept into a corner or piled outside. Once it has left the factory, its containment should continue. These materials left lying on the ground, whether the pavement is sealed or not, is unhygienic and attracts vermin, birds and other wildlife.
Inedible material is divided into two classes; that which is condemned as unit for consumption in any form and that which is otherwise healthy. Inedible material should arrive at a disposal point in separate containers. Condemned material should be kept in special containers, appropriately marked. It should be incinerated, if such equipment exists locally, or buried with lime and/or disinfectant to a depth of at least 2m, at some distance from the abattoir but within the compound. Under no circumstances should it be left open and disposed of in such a way that it remains available to humans, dogs, animals or birds.
For the first two models, the total weight of solid by-products is too small to justify, either physically or economically, serious capital investment to process this material further. Its disposal, nevertheless, presents a problem which needs proper management. There are three main methods of disposal:
- Burial or incineration as if it were condemned
- Cooking and feeding as swill to pigs
- Cooking, drying, grinding and using as fertiliser.
Before any of these methods is used however, the cost of the intended process should be examined closely as they are very inefficient in the use of fuel.
Poultry waste should be cooked in a purpose built room separate from the main building where the poultry is kept and slaughtered. It must have its own floors, walls, roof, services and entrance and be constructed so as to keep animals, birds, insects and vermin at bay. The rooms should have a clean rendered finish and be capable of disinfection and cleaning. The building should have separate rooms for the reception of the waste and another for cooking and storage of the swill afterwards.
Raw offals should be handled separately from feathers. Feather meal is more difficult to handle and use. Considering the amounts available, ie 5 & 20 kg/day for the first two models, perhaps direct burial is the most suitable disposal method.
Swill must be prepared daily and immediately after slaughter. Raw offals should be boiled at 100°C for at least one hour before allowing them to cool. Fat should be skimmed from the surface and stored in clean drums until sufficient has accumulated for sale. The equipment for this operation for Models 1 & 2 is very simple. A properly made, thick, open pot, the size of a 44 gallon oil drum will suffice as a cooking vessel. The volume produced daily in Model 2 would half fill the vessel. After cooling, the swill may be fed directly to pigs, or minced and fed as a slurry, after vitamin fortification. It is a variable product but this will be reduced if only poultry offal from the processing plant is used. In some countries, offal may be treated off the compound, although this is not an advisable practice. In these circumstances, other materials may be used in the swill but its composition will be variable.
In dry climates, the minced product may be sun dried on open concrete beds and used as a fertilizer. Care must be taken to ensure that the product is not contaminated by insects, birds and mammals. The dried product should be broken up or ground before bagging, marketing and final use.
Model 3 presents a dilemma as the weight of the waste amounts to a quantity approaching a commercial operation in some countries but not in others. At a production weight of less than 1.5 tonnes/day, economic viability is not assured, indeed daily batch weights of three to five tonnes are not always economically successful.
There is no reason why swill cannot be prepared at the throughput generated from Model 3 but it is very expensive on fuel and, like the product above, has a very short shelf life. The offal produced is equivalent to filling completely seven, 44 gallon oil drums. The equipment needed for this operation could be a series of 14 drums as described for use in the first two models. It may be necessary to invest in a proper cooking vessel from the manufacturers of such equipment. There are three varieties to chose from. The first is a steam jacketed vessel which cooks the material in its own moisture. It is a “dry” cooking method. The second system injects steam into product and is a “wet” cooking method. The third combines the two processes. None of the systems will raise the temperature above about 97°C so the cooking period will have to be extended beyond one hour. The process requires a steam generator. As the equipment has taps and valves to run off generated water and fat a whole range of vessels, pipework and other equipment will be required to service the main cooker. The volumes produced call for an organised distribution and sales system.
The alternative is to cook the offal in an industrial offal rendering plant (melter) to sterility (about 2.5 – 3 hours). The system is vented to remove moisture, the fat drained off and the product centrifuged or pressed by screw to remove the remaining fat. The dry product is then milled and bagged. Energy is used more efficiently than open cooking but the capital cost of the equipment is very high both to purchase, maintain and keep in spare parts. The smallest conventional melter has a charge capacity of 3.5 tonnes but smaller ones can be made to specification, at a cost. A throughput of 10 000 birds/day should generate sufficient waste to charge fully the smallest plant. The equipment requires skilled operation staff.
There are other methods of commercial by-product manufacture (eg continuous and recycling systems, each claiming savings on energy and resource inputs) but all have the same drawbacks in terms of capital outlay, maintenance and staffing requirements. At the throughputs mentioned, some producers find burial the most cost effective solution to offal disposal problems. A novel system proposed in the early 1980's is to mince the offal through a 4mm plate, acidify with 3% formic acid and store at tropical temperatures mixing daily for about seven days. The resultant viscous liquid may be fed to pigs after formulation with other nutrients. The acidified material will store almost indefinitely.
Effluent treatment
Waste water treatment is a study in itself and beyond the scope of this document. It is mentioned here to give some idea of the range of systems used for environmental protection.
The effluent produced by the three processing factories in this document will vary with the nature of the product. The first plant will produce effluent mainly from bird droppings, blood, washdown of the dry-plucked bird, washdown of the plant and staff facilities. The second and third examples of processing plant will produce effluent from the defeathering operations, evisceration, cooling, carcase wash, factory washdown, refrigeration plant, staff facilities etc. Each plant will have its own type of effluent quantity and quality. Table 7 gives an idea of the quantity and quality which might be expected from each of the plants chosen for this document:
The volume of the first two plants is such that the effluent should be screened through a comb to remove gross particles and subjected to settlement/flotation in a baffled tank (see Annex 7). This should remove about 40% of the BOD5 from the liquor by producing floating and sedimentary matter. The resultant liquid can then pass into either sewage discharge (if available) or a septic tank system followed by a ground soakaway, provided that the soil is able to accept such quantities of water.
| No Birds/day | 50 | 200 | 2500 |
|---|---|---|---|
| Flow, m3/day* | 1.5 | 7 | 100 |
| COD, mg/1 | 2500 | 3200 | 3200 |
| BOD5, mg/1 | 2000 | 2500 | 2500 |
| SS, mg/1 | 1000 | 1500 | 1500 |
| TS, mg/1 | 1500 | 2000 | 2000 |
| FOG, mg/1 | 200 | 600 | 600 |
| Temp, °C | 25 | 25 | 25 |
Effluent from the largest plant presents a problem which requires much more processing than the other plants, mainly because such a volume would be difficult to dispose of other than in a sewer, water course or irrigation system. Effluent should be screened using a stationary, rotary cylindrical, brushed or vibrating screen to remove gross solids. The fats should then be removed in a fat trap or settlement/flotation tank as described above. It may be desirable to install a system using dissolved air flotation (DAF) with or without chemical flocculation where there is a shortage of land**. The fats are separated from other suspended matter by floating to the surface of the liquor attached to fine air bubbles. This forms a scum which can be separated later. The use of flocculants, for example, iron salts, alum, sodium carbonate, calcium carbonate, lignin sulphonic acid, sodium lignosulphonate etc is that the process is easier to control than DAF on its own. The effluent is now ready for discharge into a sewer or agricultural land as part of an irrigation scheme.
Further treatment of the effluent is necessary if it must be discharged to a water course or the quality does meet standards set by the appropriate authorities. Effluent will need to be treated by micro-organisms, either by an anaerobic or aerobic system.
Anaerobic systems are conducted in a closed container where there is an enforced absence of oxygen. In this system, the solids break down to form water, carbon dioxide, hydrogen, hydrogen sulphide and ammonia gasses and volatile fatty acids. The volatile fatty acids undergo further reaction to form methane and carbon dioxide gasses. This is the principle behind the biogas plant, which produces inflammable gasses used for cooking and light in warm countries. The anaerobic system is not recommended in poultry plants as the effluent is low in carbohydrates and high in nitrogenous compounds. Reaction containers are therefore malodorous and not very productive.
Aerobic treatment is also conducted in a reactor but air containing oxygen is either forcibly administered by pump or the effluent passes down a trickling filter so that it comes into contact with atmospheric oxygen. The system encourages the growth of micro-organisms and the carbohydrates are oxidised to carbon dioxide and water. The nitrogenous wastes are converted to nitrates and sulphates. The incoming effluent displaces treated material which flows over a weir to settling tanks. Some of the solids are returned to the oxygenation vessel to maintain the microbial culture in peak condition while the sludge is disposed of after further treatment, if necessary. The effluent should then be of a quality to be discharged into a water course. This may be done providing permission is first sought from the appropriate local authorities. They may wish to conduct regular analyses of the treated effluent to maintain quality standards. The sludge may then be disposed of in land fill sites, dried and incinerated or spread on agricultural land. Land disposal carries the risk of infection of grazing stock. Grazing should be avoided for 3 months from spreading.
Where there is space and a warm climate, secondary treatment is sometimes carried out in an aerobic or oxidation pond system. These ponds can be used for both secondary and tertiary effluent treatment for “polishing” to a level where it may reach drinking water standards. Ponds are generally long and narrow. Effluent enters quietly at one end and leaves from the other. The flow is such that there are no dead areas. The ponds are lined with an impervious layer and about 1.5m deep. Algae are encouraged to grow by removal of scum, debris and overgrowth. The algae produce oxygen which oxidises the solid materials rather like the aerobic processes mentioned above. A quality gradient is set up along the length of the pond and fish are introduced at the outflow end. The system is delicate and not open to serious abuse. Inflow quality should be reasonably constant and the loading should be less than 450 kg BOD5/ha/day. The pond size should allow for a residence time of at least seven days. Tertiary ponds for “polishing” should be loaded at no more than 70 kg BOD5/ha/day.
Finally other forms of waste effluent should be treated separately. Storm water should be directed to surface drainage, water courses or whatever is appropriate for the locality. Human effluent wastes should be treated as domestic waste, since the volumes are likely to be small. This may involve disposal to a mains sewer or septic tank before disposal by soakaway.
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