Anaerobic digestion of alcohol sulfate (anionic surfactant) rich wastewater – batch experiments. Part II: influence of the hydrophobic chain length

High-strength wastewater of some industries contains high concentrations of surfactants and readily biodegradable compounds like starch and other carbohydrates. Wastewater of this type is found in the textile wet-processing industry (e.g., cotton desizing). The anaerobic degradation process in such wastewater is inhibited due to the high surfactant content. Alcohol sulfate (AS) of increasing hydrophobic chain length (C8 to C18, surfactant) and soluble starch (size) were used as model compounds in a series of batch experiments with high loadings of the biomass (65 g AS/kg cell dry weight; 910 g starch/kg cell dry weight). The strongest inhibition of the hydrolysis, acidogenesis and acetogenesis was found in reactors containing medium chain ASs like dodecyl sulfate. Starch hydrolyzation rates decreased by nearly 90% in the presence of dodecyl sulfate. Decyl sulfate caused the strongest inhibition of the methanogenesis and a decrease of the methane evolution by 75% within 87 days experimental time. It was found that short as well as long chain ASs caused only minor inhibition phenomena. The presented data can be used as a basis for the selection of suitable surfactants that do not (or not seriously) inhibit the anaerobic digestion of industrial effluents.