Extraction of poly-phosphate from the activated sludge with thermal treatment for phosphorus recovery

Fast consumption of high quality phosphorus mines and uneven distribution in the world result in the shortage crisis for phosphorus, meanwhile lots of phosphate compounds which are discharged into nature water bodies by human beings have already induced many environmental problems. Because of this situation, phosphorus recovery from sewage sludge working in the aeration tank of wastewater treatment plant (WWTP) has been researched in the present study. Poly-phosphate (poly-P) and total phosphate (T-P) accumulated inside activated sludge could be released by thermal treatment at low temperature, 30% poly-P and 29% T-P could be released from sludge by heating at 70 °C. Different kinds of pretreatments had been tested to improve phosphorus release from activated sludge in thermal treatment; addition of chelating reagent at final concentration of 2 mM before thermal treatment could improve the phosphorus release obviously, 68% poly-P and 53% T-P could be released into liquid phase. Approximately 85% T-P could be precipitated with calcium at pH 11; it was interesting to find precipitation occurred in neutral condition without pH adjustment.