Removal of emerging contaminants from wastewater during chemically enhanced primary sedimentation and acidogenic sludge fermentation

Abstract

A novel wastewater treatment process, which couples chemically enhanced primary sedimentation (CEPS) of sewage with acidogenic fermentation of sludge in tandem, has recently been developed to improve the removal of pollutants and nutrients, and recover valuable resources such as phosphorus and organics. This study represented the first laboratory-based examination on the level and removal of the emerging contaminants, including retinoids (i.e., retinoic acids (RAs) and their metabolites) and oestrogenic endocrine disrupting chemicals (EDCs; e.g., 4-nonylphenol, bisphenol A, etc.), in sewage, sludge and its supernatant during this novel wastewater treatment process. The results showed that 65% of retinoids and 73% of EDCs were removed from sewage after aluminum (Al) based CEPS, while 80% of retinoids and 72% of EDCs were removed after iron (Fe) based CEPS. After acidogenic fermentation of the CEPS sludge, 50% and 58% of retinoids, and 50% and 47% of EDCs were further removed in the supernatants of Al-sludge and Fe-sludge, respectively. While there were comparable removals for these two classes of emerging contaminants during Al- and Fe-based CEPS and sludge fermentation, Fe-based CEPS of sewage and sludge fermentation should be preferentially considered, given the relatively lower production of Fe-sludge and lower accumulation of retinoids in Fe-sludge. The levels of retinoids and EDCs in the supernatant and sludge changed during acidogenic fermentation of Fe-sludge. The removals of at-4-oxo-RA (i.e., the dominant retinoid) and bisphenol A (i.e., the dominant EDC) in the supernatant followed the pseudo first-order reaction model, with a half-life of 1.62 days (in the first two days) and 1.55 days (in the whole experiment of seven days), respectively. The results demonstrated the effective removal of emerging contaminants from the sewage and the supernatant during the CEPS and acidogenic sludge fermentation.