Simultaneous removal of macromolecular microbial metabolites and nitrogen in a receiving river of wastewater treatment plants lacking ecological base flow via the combination of anaerobic and aerobic biofilters

Abstract

Efficient removal of macromolecular microbial metabolites and nitrogen in receiving rivers lacking ecological base flow is needed to meet the stringent surface water quality standards in northwestern China. This study investigated the characteristics of water quality of a receiving river, further, the conversion of microbial metabolites and its influences on denitrification in pilot anaerobic biofilter (ABF) and biological aerated filter (BAF) were revealed. On this basis, the feasibility of using the combination of ABF and BAF to purify the receiving river was verified. Results showed that organics dominated by macromolecular microbial metabolites and nitrogen severely polluted the receiving river. Microbial metabolism along the river aromatized the organics and enlarged their molecular weight but failed to effectively remove them. In ABF, the bioavailability of organics was at least triply improved by cleaving macromolecular aromatic rings into small molecular aliphatic compounds. Under this circumstance, denitrifiers utilized aromatic carbon sources preferentially and generated aliphatic products. Low hydraulic loading (HL) enhanced not only the hydrolysis of macromolecular ingredients but the dearomatization. Similarly, although high HLs allowed retaining more aromatic compounds, they worsened the conversion of macromolecules. When the HL was 0.2 m/h, the balance was achieved and more than 80% of the nitrates were removed in ABF. Nearly 90% of both ammonia nitrogen and small molecular organics were removed in BAF under the optimal operating conditions, but the refractory macromolecules impeded the removal of organics and nitrogen. AFB and BAF showed a complementation. The effluent from BAF that followed ABF could meet the latest surface water quality standards. This combination is feasible to efficiently and stably purify the polluted receiving rivers of wastewater treatment plants.