E. Sperczyńska
Czestochowa University of Technology, Faculty of Infrastructure and Environment, Department of Chemistry, Water and Wastewater Technology; Częstochowa, PL

USE OF PRECIPITATION PROCESS FOR REJECT WATER TREATMENT


Research work on the possibilities of precipitation processes use for phosphorus removal from reject water was performed. The aim of the study was to evaluate the effectiveness of phosphorus compounds removal from reject water separated after methane digestion. Reject water was taken from municipal wastewater treatment plant of PE over 100 000. They were sampled after mechanical dewatering of digested sewage sludge. Commercial agents containing iron salts - PIX 111, PIX 112, PIX 113, PIX 122 were used. Various doses of coagulants: 1,5; 2,0; 2,5; 3,0, 3,5, 4,0 – time higher than stoichiometric dose were applied. Stoichiometric dose was calculated based on chemical reaction of insoluble iron phosphate formation. Concentrations of Kiejdahl nitrogen (940 mgNKj/dm3), phosphorus (55 mg P-PO43-/dm3) and organic compounds - COD (540 mgO2/dm3) in reject water were very high. The effectiveness of precipitation process increased as the doses of chemical agents increased. The most effective doses were the highest ones used during the experiment. The most effective agent was PIX 122 (82% removal efficiency). As the phosphates concentration decreased COD content declined simultaneously. Maximum COD removal (16%) was obtained in the case of PIX 122. The efficiency of phosphorus removal from digested sludge reject water needn’t to be very high (i.e.P<1mgP/L), because this liquids recycle to the mainstream of MWWTP. The elimination of phosphorus to the level typical in raw wastewater, allows to reduction the concentrations of phosphorus in the main stream of MWWTP.

Acknoledgments: This work was supported by the Czestochowa University of Technology grant BS-PB-402-301/11

Keywords:phosphorus removal, reject water, iron coagulants