Simultaneous removal of phosphorus and dissolved organic matter from a sludge: In situ reduction process effluent by coagulants

Abstract

Owing to the long solids retention time and effective sludge decay, the increase in the amount of phosphorus and dissolved organic matter (DOM) in effluents is a major obstacle to the sludge in situ reduction process. In this study, the coagulants hydrated aluminum sulfate (Al2(SO4)3), ferric trichloride (FeCl3), and polyaluminum chloride (PAC) were applied for the simultaneous removal of phosphorus and DOM from the secondary effluent of a sludge process reduction-activated sludge wastewater treatment system. The results indicated that in most cases, Al2(SO4)3 exhibited the best coagulation performance, followed by FeCl3 and PAC. Three-dimensional excitation-emission matrix fluorescence spectroscopy and gel permeation chromatography (GPC) were used for the detailed characterization of the DOM after the coagulation treatment. Herein, two humic-like components and a protein-related component were identified in the wastewater samples by parallel factor (PARAFAC) analysis. The protein-related component was removed more effectively by FeCl3 and PAC, whereas Al2(SO4)3 was more effective for the removal of humic-like components. The GPC analysis showed that FeCl3 exhibited the best removal performance for large molecules with a MW > 1000 kDa, whereas Al2(SO4)3 showed a relatively good removal performance for small molecules with a MW < 2 kDa. The correlation analysis showed that for the Al2(SO4)3 samples, there were significant correlations (p < 0.01) between the total organic carbon, UV absorbance at 254 nm, total phosphorus, and maximum fluorescence intensity of the three PARAFAC components; on the other hand, for the FeCl3 and PAC samples, DOM removal was mostly correlated with the humic-like components, and the correlation coefficients among the seven variables were lower than those for the Al2(SO4)3 samples.