ANAEROBIC-DIGESTION OF RENDERING WASTE IN AN UPFLOW ANAEROBIC SLUDGE BLANKET DIGESTER

Rendering wastewater was anaerobically digested in an upflow anaerobic sludge blanket (UASB) digester in 11 trials spanning 11 months. The UASB digester influent was 2% blood/98% condensate for six of the trials (phase one) and 56% wash-up water/44% cooker condensate for the other five trials (phase two). The influent chemical oxygen demand (COD) for both phases was 5300 mg/l The only parameter varied within phases was hydraulic retention time (HRT) which was varied from 5.2 to 15.6 days; however, changing HRT caused loading rate to change because the influent strength was held constant. COD removal efficiencies for phase one ranged from 28 to 72% and for phase two, from 72 to 87%. The biogas production from all trials contained over 75% methane and had traces of hydrogen sulfide. The production of methane was 0.2-0.25 l/gCOD(converted) in phase one and 0.28-0.34 l/gCCD(converted) in phase two.