Ultrasound-promoted extraction of cheap microbial flocculant from waste activated sludge

Ultrasound was uniquely applied to promote the extraction of cheap microbial flocculant (MBF) from waste activated sludge (WAS) of municipal wastewater treatment plants (WWTPs). Various influencing factors, including ultrasonic conditions (frequency, power density and treatment time) and WAS features (pH, concentration and source), were systematically investigated. The propitious ultrasonic conditions for MBF preparation from WAS were 20 kHz, 2.1 to 2.7 kW/L and 1 to 3 min. Natural sludge pH (about 7) was preferable to the MBF preparation. The major components of the extracted MBF contained polysaccharides, proteins and nucleic acids. The yield of the extracted MBF increased with rising sludge concentration. The wide application potential of the developed method was testified by the successful MBF extraction from the WAS samples of four full-scale municipal WWTPs with different typical processes. The ultrasonic method applied to extract MBF from WAS would not only provide a new way for WAS resource reuse, but also markedly cut down the cost of MBF preparation.