Influence of support media on biomass growth and retention in anaerobic filters

Three laboratory-scale upflow anaerobic filters (AFs) containing different support media were subject to identical volumetric organic loadings and hydraulic retention time in treating synthetic protein–carbohydrate waste. The objective was to examine the influence of support media on biomass growth and retention and their resulting impact on system performance and failure. At the organic loading of 16 g COD/l/d, the reactor packed with the support media of open-pored texture exhibited 78% COD removal efficiency attributable to its higher retention of attached biofilm. On the other hand, the reactor with larger media porosity indicated comparable removal efficiency of 77% attributable to higher growth of suspended biomass, as opposed to a much lower removal efficiency of 57% in the unit associated with media of smooth surface and low porosity. Quantitative estimation of the organics removed by the biomass suspended within the interstitial void spaces showed that about 56–58% of the methane was produced by the suspended biomass in the reactor containing media of larger porosity, while about 56% of the methane was produced by the biofilm in the unit associated with media of open-pored texture operated at 12 and 16 g COD/l/d. The estimation of dead space based on a tracer study indicated that the effective volume of the bed was markedly reduced to 43–57% due to accumulation of biomass at the organic loading of 16 g COD/l/d. The tracer study also revealed that AF failure at high loadings is likely attributed to biomass washout rather than short-circuiting which suggests that impact of clogging to anaerobic filter system failure may not be as significant as originally thought.