Extraction of bioflocculants from activated sludge and their application to wastewater treatment

摘要

Extracellular polymeric substances (EPS) – biopolymers produced by the microorganisms – are effective flocculants of wastewater pollution and lack the shortcomings of traditional coagulants and flocculants, which can pose direct threat to health and human life, as well as to the sustainable existence of aquatic and terrestrial ecosystems. EPS do not form secondary contamination of their degradation intermediates, are biodegradable and eco-friendly. Industrial production of bacterial EPS is associated with high cost of growing specific microbial biomass and the functioning of technologies for the synthesis of microbial products. At the same time, there is an underused resource of excess activated sludge, which can be used as cheap substrate for producing bioflocculants and a possible measure to reduce costs. The conducted researches have shown the prospects of extracting EPS from excess activated sludge for their subsequent use as wastewater treatment bioflocculants. EPS extraction has been conducted using three methods: combination of centrifugation processes, extraction using the aqueous solution of disodium ethylenediaminetetraacetic acid, and precipitation with isopropyl alcohol (the EDTA method); combination of centrifugation, extraction with (NH2)2CO, precipitation and ethanol reprecipitation (the (NH2)2CO method); combination of activated sludge ultrasonic treatment, centrifugation, extraction with glacial acetic acid, and precipitation with acetone (the CH3COOH method). The research has shown that the extraction method affects not only the efficiency of EPS extraction, but also the possibility of EPS application for the purification of certain types of sewage. The (NH2)2CO method has shown the best extraction efficiency, but at the same time EPSs produced have not be able to perform fish processing wastewater treatment. The EDTA and CH3COOH methods are more preferable for producing efficient bioflocculants for fish processing wastewater treatment. The use of EPS obtained by the EDTA method has resulted in the significant reduction of total suspended solids and optical density; EPS produced by the CH3COOH method have reduced the content of dissolved solids and the optical density. According to the conducted research EPS produced from surplus sludge with the EDTA and CH3COOH methods have good flocculation and are harmless for humans and the environment, and thus may be a potential substitute for traditional synthetic flocculants and could be used in the treatment of fish processing plants wastewaters.