Origin and Nature of Refractory Organic Compounds Produced During Anaerobic Treatment of Easily Biodegradable Substrate

Abstract

Anaerobic processes used for wastewater treatment produce soluble residual microbial products (SMP_R) 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 degradable substrate (¹⁴C-glucose) were performed and ¹⁴C flows in soluble and insoluble liquid fractions and in gaseous fractions were investigated. Results of experiments indicated that the soluble residual microbial products represented 1.0 ± 0.1 % of the initial carbon concentration for a ratio of the initial substrate concentration to the initial biomass concentration (S₀/X₀ as COD/VSS) of between 0.1 and 1.6. Biodegradability level of anaerobic SMP_R was estimated in aerobic cultivation with activated sludge. Biodegradability tests showed that half of the anaerobic SMP_R were biodegradable and that the anaerobic SMP produced during lysis and degradation of microorganisms was completely oxidized in ¹⁴CO₂.

Keywords:

• Anaerobic digestion
• 14C-glucose
• soluble residual microbial products
• biodegradability
• activated sludge