Cogeneration of methane and microbial protein from the anaerobic treatment of rendering waste

The purpose of this study was to characterize the by-products formed during the anaerobic treatment of animal rendering waste, and to evaluate the possibilities of energy recovery and feed supplement production. Three lab-scale upflow anaerobic sludge blanket (UASB) reactors were utilized to anaerobically treat two combinations of rendering wastewater. Raw blood/cooker condensate was digester feed for the first phase of experiments. Wash-up water/condensate was tested as feed for the second phase of the study. Both mixtures were characterized as concentrated influents with low chemical oxygen demand (COD) to total nitrogen ratios. The phase 1 experiments utilized COD loading rates ranging from 0.17 to 1.68 g/L-d. The phase 2 trials encompassed COD loading rates varying from 0.34 to 1.01 g/L-d at a feed strength of 5300 mg COD/L. The COD removal efficiencies for the COD loading rates utilized in phase 1 varied from 28 to 74%, while the removal percentages for the four phase 2 trials ranged from 72 to 86%. At identical COD loading rates of 1.01 g/L-d (5300 mg/L), the digesters receiving the mixture of 56% wash-up water/44% condensate removed double the COD compared to the UASB reactors treating 2% raw blood/98% condensate. The difference in COD removal was attributed to a phosphorus deficiency in the phase 1 trials and the physical entrapment of suspended COD within the sludge bed for the phase 2 trials. The biogas produced from all trials contained over 75% methane and traces of hydrogen sulfide. The methane production for phase 1 trials ranged from 0.16 to 0.23 L/gCOD...