Treatment of wastewater from abattoirs before land application--a review.

Pre-treatments are screening, catch basins, flotation, equalization, and settlers for recovering proteins and fats from abattoir wastewater. With chemical addition, dissolved air flotation (DAF) units can achieve chemical oxygen demand (COD) reductions ranging from 32% to 90% and are capable of removing large amounts of nutrients. Aerobic trickling towers reduced soluble COD by additional 27% but did not reduced total COD. Chemical-DAF reduced 67% of total COD and soluble COD. About 40-60% of the solids or approximately 25-35% of the biological oxygen demand (BOD) load can be separated by pre-treatment screening and sedimentation. Anaerobic systems are lagoon, anaerobic contact (AC), up-flow anaerobic sludge blanket (UASB), anaerobic sequence batch reactor (ASBR), and anaerobic filter (AF) processes. Abattoir wastewater is well suited to anaerobic treatment because it is high in organic compounds. Typical reductions of up to 97% BOD, 95% SS and 96% COD are reported. UASB's average COD removal efficiencies are of 80-85%. UASB seems to be a suitable process for the treatment of abattoir wastewater, due to its ability to maintain a sufficient amount of viable sludge. Wastewater in abattoirs can be reduced by treatment of immersion chiller effluent by membrane filtration which can produce recyclable water. Total organic C can be reduced below 100mg/L, and bacteria can not pass through the membrane pores. The abattoir waste minimization options are also discussed.