Waste disposal in the meat industry (a comprehensive review of practice in the United States).

Meat industry waste waters are 5 to 10 times as strong (BOD)as domestic sewage and contain much higher nitrogen, phosphorus and grease concentrations. Conservation measures and pretreatment facilities are aimed principally at blood (or blood water), casing slimes, wet rendering (tank water), paunch manure, yard drainage and hog hair. The answers available are: dry rendering of blood and grease, coagulation of casing slimes, new processes for paunch manure dehydration, and sterilization and disposal of hog hair. Washable trickling filters and conventional activated sludge treatment processes have both had some success, although the latter generally requires pretreatment. Extended aeration systems are in successful use, principally in lagoon-type plants. Disposal of raw meat packing wastes by irrigation has been successful in one installation in Illinois. This is a practical answer and warrants further study particularly to determine suitable crops. Some care is necessary to avoid high sodium concentrations to prevent soil damage. Anaerobic ponds serve successfully as 'roughing' ponds for meat packing wastes principally because these wastes are warm (83 to 87°F), have high BOD and organic solids concentrations, and provide proper nutrient balance. Because aerobic ponds can accept anaerobic effluents at high BOD loadings, combinations of anaerobic ponds with various arrangements of aerobic ponds have become popular. The anaerobic contact process can remove 90 to 96 % of the BOD in a waste of 1400 mg/I, at a digester loading of 0.16 lb/day/cu. ft. with equalized flow. The gas-tight anaerobic digester is a completely mixed system. The mixed liquor is generally degasified by vacuum before gravity separation of sludge. The sludge is returned to the digesters at rates of 3 to 4 times the raw flow. The anaerobic effluent can be polished in aerobic ponds at loadings of 410 lb/day/acre, as well as in activated sludge and trickling filter systems. The US meat industry is tending towards contracting with municipal agencies for waste treatment, often in spite of higher costs and with the danger of later escalation. However, municipal treatment eliminates the fixed costs of industryowned facilities, and permits write-off of the annual costs as operating expenses. The meat packer will generally find that anaerobic pretreatment, either in a concrete digester or in a lagoon, prior to municipal treatment, will reduce his overall costs. Where land is expensive and odour control important, concrete digesters are preferred. The pretreatment facility may be owned by the city or the packer and, if owned by the latter, may be operated by the city. * Formerly of Ralph B. Carter Company, Hackensack, New Jersey, USA.