Intermediate accumulation and efficiency of anaerobic digestion treatment of surfactant (alcohol sulfate)-rich wastewater at increasing surfactant/biomass ratios

Textile (eg cotton) finishing industry wastewater is characterised by high concentrations of surfactants (up to 2 g dm−3) and of readily biodegradable biopolymers (COD 5–15 g dm−3). The anionic surfactant decyl sulfate (DS) was chosen as model surfactant and soluble starch (size) as model compound for the readily biodegradable fraction of the wastewater. Twenty‐two batch experiments with increasing DS/biomass ratio (and starch/biomass ratio) were started simultaneously. Biomass concentrations ranged from 50 to 15 000 mg dm−3. Minor inhibition effects were found for the surfactant degradation itself at all DS/biomass ratios (maximum biodegradation rate 7.7 mgDS gbiomass−1 h−1). The starch hydrolysis started without a lag‐phase at DS/biomass ratios of up to 0.15 gDS gbiomass−1. The lag‐phase was prolonged to about 100 h at a very high DS/biomass ratio (3 gDS gbiomass−1). The relative importance of the accumulated intermediates was dependent on the DS/biomass ratio. Above 0.3 gDS gbiomass−1 10% of the substrate organic carbon accumulated as ethanol, but no ethanol accumulation was observed at low DS/biomass ratios. Moderate DS/biomass ratios caused a considerable delay of the methanogenesis; high DS/biomass ratios prevented the methanogenesis almost completely. © 2002 Society of Chemical Industry