Comparison of diclofenac transformation in enriched nitrifying sludge and heterotrophic sludge: Transformation rate, pathway, and role exploration

摘要

The adverse effects of diclofenac (DCF) on ecosystems and human health have induced increasing in-terest in its elimination in environment. DCF can be removed to some extent by nitrifying and heterotrophic microbes during wastewater treatment process. However, the actual roles of nitrifying and heterotrophic microbes in the transformation of DCF remain unclear. In this study, batch experiments were conducted to explore the biological transformation of DCF in enriched nitrifying sludge (NS), heterotrophic sludge (HS) and activated sludge (AS) systems. DCF was removed three times faster in enriched NS than in HS. Three transformation pathways of DCF in enriched NS, HS, and AS were proposed and compared. Hydroxylation was the crucial transformation step in the three transformation pathways. A faster hydroxylation reaction contributed to the faster removal of DCF in enriched NS. More transformation products (TPs) and reaction types (i.e. reductive dechlorination, sulphidation and methylation reactions) were observed in HS. Furthermore, some TPs that were resistant to degrade in enriched NS, such as DCF-benzoic acid, could be further transformed in HS. Accordingly, enriched NS could remove DCF more rapidly while HS could further transform some TPs resistant to degrade in enriched NS. Nitrifying and heterotrophic microbes may cooperatively and rapidly eliminate not only DCF, but also its TPs. (c) 2020 Elsevier Ltd. All rights reserved.