Origin and nature of refractory organic compounds produced during anaerobic treatment of easily biodegradable substrate

Anaerobic processes used for wastewater treatment produce soluble residual microbial products (SMPR) which are both easily degradable and difficult to biodegrade. Reducing these residual organic matters requires the knowledge of their origin and nature. Anaerobic batch cultivations of readily degrad able substrate (C-14-glucose) were performed and C-14 flows in soluble and insoluble liquid fractions and in gaseous fractions were investigated. Resu lts of experiments indicated that the soluble residual microbial products r epresented 1.0 +/- 0.1 % of the initial carbon concentration for a ratio of the initial substrate concentration to the initial biomass concentration ( S-0/X-0 as COD/VSS) of between 0.1 and 1.6. Biodegradability level of anaer obic SMPR was estimated in aerobic cultivation with activated sludge. Biode gradability tests showed that half of the anaerobic SMPR were biodegradable and that the anaerobic SMP produced during lysis and degradation of microo rganisms was completely oxidized in (CO2)-C-14.