Sequencing adsorption and degradation cycles towards the methanization of long chain fatty acids : comparison between granular and suspended sludge

Abstract

The aim of the present work was to study the maximum potential methane production in batch assays of sludge samples taken along the operation of two EGSB reactors (RI inoculated with granular sludge and RII inoculated with suspended sludge) fed with increasing oleic acid concentrations between 2 and 8 gCOD/l (HRT=1 day). After removing the residual substrate, the sludge was incubated in batch vials without any added carbon source. A maximum methane production rate of 152±21 mlCH4(STP)/gVS.d was obtained for the RII-suspended sludge taken on day 70, when oleate at a concentration of 2 g COD/l was fed with a cosubstrate (50% COD). The maximum plateau achieved in the methane production curve was 1145±307 mlCH4(STP)/gVS, obtained for the RII-suspended sludge taken on day 162, when oleate was fed as the sole carbon source at 6 g COD/l. Methanization rate of the adsorbed substrate was enhanced under stirring conditions and was inhibited by adding oleic acid. Extraction and GC analysis confirmed that the main adsorbed substrate was palmitate, and not oleate, as previously suspected. These results evidence the advantage of sequencing adsorption and degradation cycles for the treatment of effluents with high lipid content.