Abstract
The organic carbon in streambed sediments drives multiple biogeochemical reactions, including the attenuation of organic micropollutants. An attenuation assay using sediment microcosms differing in the initial total organic carbon (TOC) revealed higher microbiome and sorption associated removal efficiencies of trace organic compounds (TrOCs) in the high-TOC compared to the low-TOC sediments. Overall, the combined microbial and sorption associated removal efficiencies of the micropollutants were generally higher than by sorption alone for all compounds tested except propranolol whose removal efficiency was similar via both mechanisms. Quantitative real-time PCR and time-resolved 16S rRNA gene amplicon sequencing revealed that higher bacterial abundance and diversity in the high-TOC sediments correlated with higher microbial removal efficiencies of most TrOCs. The bacterial community in the high-TOC sediment samples remained relatively stable against the stressor effects of TrOC amendment compared to the low-TOC sediment community that was characterized by a decline in the relative abundance of most phyla except Proteobacteria. Bacterial genera that were significantly more abundant in amended relative to unamended sediment samples and thus associated with biodegradation of the TrOCs included Xanthobacter, Hyphomicrobium, Novosphingobium, Reyranella and Terrimonas. The collective results indicated that the TOC content influences the microbial community dynamics and associated biotransformation of TrOCs as well as the sorption potential of the hyporheic zone sediments.
Highlights
Wastewater-derived trace organic compounds (TrOCs) such as pharmaceuticals and personal care products are frequently detected in receiving rivers due to inefficient removal by most conventional treatment processes [1,2]
We investigated the removal efficiency of a set of 13 TrOCs routinely discharged by a wastewater treatment plant (WWTP) using impacted hyporheic zone sediments differing in the initial total organic carbon (TOC) content
Our objectives were to (i) determine TrOC removal efficiencies in hyporheic zone sediments differing in initial TOC concentrations via microbial transformation and sorption mechanisms, (ii) assess the response of the indigenous bacterial communities in the sediments differing in TOC concentrations to TrOC amendment, and (iii) identify potential bacterial TrOC degraders
Summary
Wastewater-derived trace organic compounds (TrOCs) such as pharmaceuticals and personal care products are frequently detected in receiving rivers due to inefficient removal by most conventional treatment processes [1,2]. Despite occurring in trace concentration ranges (ng to μg L−1 ), their persistence and accumulation are of ecotoxicological concern [3] Attenuation of such compounds via microbial transformation and sorption processes has been reported in the hyporheic zone, the saturated sediment directly beneath and lateral to the stream [2,4,5,6]. Both attenuation processes are significantly influenced by the organic matter content in the sediment since organic carbon fuels multiple TrOC-coupled biogeochemical reactions [7] as well as being the main sorbent for organic chemicals [8]. As bacteria dominate microbial communities in streambed sediments [12,13,14,15,16], bacterial populations, turnover and metabolism are virtually higher in the surface sediment layer with corresponding mineralization rates decreasing exponentially with depth [6,17,18,19]
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