An improved primary wastewater treatment system for a slaughterhouse industry: a full-scale experience

The effluent streams from individual slaughtering operations were segregated based on the degree of similarity and were treated separately. The wastewater from lairage and paunch sections was dominant in suspended solids (SS: 6,000-25,000 mg/L) and was separated using a hydrasieve (500 μm) and externally fed rotary drum filter (EFRDF, 200 μm), respectively. The SS removal efficiency of the hydrasieve and EFRDF was 75% and 55%, respectively, and remaining solids were removed through a primary clarifier. The fats, oils and grease (FOG: 12,000-35,000 mg/L) containing streams from the hide fleshing, rendering, intestine, and tripe washing were routed through a skimming tank. The SS and FOG removal efficiencies through the skimming tank were 75% and 90%, respectively. Any FOG remaining after the skimming tank was removed using dissolved air flotation which achieved 95% FOG removal. In addition, the efficiency of chemical oxygen demand removal through the primary treatment system was more than 80%. The effluent obtained after primary treatment was SS and FOG ≤ 200 and 100 mg/L. The segregation of streams and their separate treatment offered benefits such as resource recovery, reduced waste load on downstream secondary treatment and overall ease in slaughterhouse wastewater treatment.