Anaerobic Degradability: Effect of Particulate COD

Batch bioassay tests were conducted to evaluate the effect of particulate chemical oxygen demand (COD) $\left({\mathrm{COD}}_P\right)$ 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 $\left({\mathrm{COD}}_T\right)$ of 500 mg and ${\mathrm{COD}}_P$ from 0 to 100%. Methane generation conforms to the first order rate kinetics. At all $F∕M$ , $k\left({\text{day}}^{-1}\right)$ decreased linearly with increase in fraction of ${\mathrm{COD}}_P({\mathrm{COD}}_{\mathrm{PF}}={\mathrm{COD}}_P∕{\mathrm{COD}}_T)$ . Biomethane potential (BMP), and substrate and sludge activities also exhibited declining trend with increasing ${\mathrm{COD}}_{\mathrm{PF}}$ . The optimum value of $F∕M$ ranged from 0.57 to 0.68. The two variables, ${\mathrm{COD}}_{\mathrm{PF}}$ and $F∕M$ , were compounded to yield the ratio of ${\mathrm{COD}}_P$ to microorganisms [ $M$ , measured as volatile suspended solids (VSS)]. On increasing the ${\mathrm{COD}}_P∕\mathrm{VSS}$ from 0 to 0.9, the rate constant for methane generation is reduced by 81%. ${\mathrm{BMP}}_{30}$ , 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.