Anaerobic digestion of desizing wastewater: influence of pretreatment and anionic surfactant on degradation and intermediate accumulation

Abstract

Sizing agents like starch or partly hydrolyzed starch are applied to yarn for an efficient weaving process. The corresponding desizing wastewater makes up about 50% of the organic load in wastewater from textile wet-processing. During the size preparation and desizing process, the degree of polymerization of the starch is reduced. The degradation of starch products (with a decreasing degree of polymerization) with and without surfactant was studied in a series of batch experiments. Glucose, two different dextrines, soluble and native starch were used as model compounds. Decyl sulfate served as model compound for surfactants used in the desizing process. Without surfactant, the rate of the total organic carbon removal from the solution was nearly independent of the degree of polymerization (as long it was sufficient soluble). The period of intermediate degradation was about 100 h for glucose, but 300 h for potato starch. The accumulation of intermediates was comparable after 1 day with and without surfactant (substrate: glucose) and slightly lower where carbohydrates with higher degrees of polymerization were used. In contrast to experiments without surfactant, these intermediates were accumulated for a long period of time as the surfactant inhibited the degradation of the intermediates. The experiments demonstrate that the design of an anaerobic digestion process for this wastewater must take into account the finishing process as well as the material used.