Anaerobic Degradability: Effect of Particulate COD

Batch bioassay tests were conducted to evaluate the effect of particulate chemical oxygen demand (COD) (CODP) on anaerobic digestion of wastewater at different ratio of food to microorganism (F/M). Synthetically prepared soluble and complex wastewaters were used. Experiments were conducted in seven sets of serum bottles maintained at F/M ranging from 0.18 to 2.0. Each set contained six bottles having a total COD (CODT) of 500 mg and CODP from 0 to 100%. Methane generation conforms to the first order rate kinetics. At all F/M, k (day–1) decreased linearly with increase in fraction of CODP (CODPF=CODP/CODT). Biomethane potential (BMP), and substrate and sludge activities also exhibited declining trend with increasing CODPF. The optimum value of F/M ranged from 0.57 to 0.68. The two variables, CODPF and F/M, were compounded to yield the ratio of CODP to microorganisms [M, measured as volatile suspended solids (VSS)]. On increasing the CODP/VSS from 0 to 0.9, the rate constant for methane generation is reduced by 81%. BMP30, percent sludge activity, and substrate utilization rate are lowered by 52–55%. These correlations could serve as useful guidelines to quantitatively assess the impact of particulate COD on biodegradability parameters.