Trace organic contaminant removal in six full-scale integrated fixed-film activated sludge (IFAS) systems treating municipal wastewater

摘要

Trace organic contaminants (TrOCs) often pass through conventional activated sludge wastewater treatment plants (CAS-WWTPs) and are discharged into surface waters, where they can threaten aquatic ecosystems and human health, largely due to the hormone disrupting effects of certain TrOCs. The integrated fixed-film activated sludge (IFAS) process is a cost-effective means of upgrading CAS-WWTPs by adding free-floating carrier media, which promotes biofilm formation in the well-mixed suspended growth reactors, providing a potential niche for slow-growing microorganisms. Although IFAS upgrades are typically aimed at enhancing nutrient removal, limited bench- and pilot-scale data indicate that TrOC removal may also be improved. However, only limited reports which focus on a small number of compounds in individual full-scale IFAS-WWTPs have been published to date, and no data is available regarding the removal of estrogenic activity in full-scale IFAS-VVWTPs. In this study, six full-scale IFAS-WWTPs were surveyed to quantify TrOC and estrogenic activity removal. Twenty-four hour composite samples of secondary influent and effluent (pre-disinfection) were analyzed for total suspended solids (TSS), chemical oxygen demand (COD), ammonia, total nitrogen (TN), total phosphorus (TP), estrogenic activity, and 98 TrOCs. The biomass distribution between the suspended growth phase (i.e. mixed liquor) and IFAS media was also assessed. All IFAS-WWTPs performed well in terms of TSS, COD, and ammonia removal. TN removal varied in accordance with nitrate removal. Total solids per liter of wetted reactor volume ranged from 2.5 to 7.6 g, with 40-60% attached to media. TrOCs with no detection (17) and those with high median removal (23, = 90% average removal) were observed. Other TrOCs had lower and more variable removal efficiencies. Qualitative comparison with CAS literature shows potentially higher IFAS removal efficiencies for a number of compounds including several which have been previously indicated in bench- or pilot-scale studies (atenolol, diclofenac, gemfibrozil, DEET, 4-nonylphenol, and 4-tertoctylphenol), as well as the chlorinated flame retardants TCIPP and TDCIPP. Effluent estrogenic activity was found to be similar to that reported for full-scale CAS-WWTPs. These results provide the first survey of multiple full-scale IFAS-WWTPs employing mobile plastic carrier media in terms of basic chemical endpoints (removal of ammonia, TN, TP, and COD), the distribution of solids within the systems, and the removal of TrOCs and estrogenic activity. (C) 2018 Elsevier Ltd. All rights reserved.