Preparation of Magnetic Excess Sludge and Removal of Phosphate

TAO Huchun†, ZHANG Xiao, LI Jinbo, HUANG Shuaibin, MA Biao

ACTA Scientiarum Naturalium Universitatis Pekinensis - - News -

Shenzhen Key Laboratory for Heavy Metal Pollution Control and Reutilization, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055; † E-mail: taohc@pkusz.edu.cn

Abstract MNPS were prepared using coprecipitation method, with Fecl3, Fecl2 and ammonia. MNPS were compounded with excess sludge (moisture content of 99%) to prepare magnetic excess sludge (MES). Alternating gradient magnetometer was used to measure the magnetic response of MES and scanning electron microscope (SEM) to observe morphology of excess sludge and MES. After magnetic separation, the water content of MES was calculated to investigate the degree of sludge thickening. The adsorption property of total phosphorus onto MES was investigated. According to the results, MES had superparamagnetism, and its saturation magnetization was 42 emu/g. Within 30 s it could be separated from liquid. The optimal conditions for adsorption of total phosphorus on MES were the initial ph value of solution ranging in 4–6, an initial concentration of phosphorus solution of 16 mg/l (calculated as P), adsorption equilibrium was achieved within 600 min. The kinetics data were fitted well with the pseudo-second order model. The adsorption fitted the Langmuir isotherm well with the equilibrium data and the theoretical maximum adsorption capacity was 3.00 mg/g (calculated as P). MES could accelerate the separation of sludge and wastewater, and the volume of excess sludge was reduced largely. The adsorption performance of total phosphorus on MES was better than that on excess sludge. The study provided a new handling method of excess sludge for sewage treatment plant whose secondary treatment process was activated sludge process. Key words magnetic excess sludge; magnetic separation; adsorption; phosphate

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