Bacterial Diversity Controls Transformation of Wastewater-Derived Organic Contaminants in River-Simulating Flumes.

Malte Posselt,Marcus A Horn,Muhammad Raza,Anna Sobek,Stefan Krause,Karin Meinikmann,Juliane Hollender,Claudia Coll,Jörg Lewandowski,Cyrus Rutere,Jonas Mechelke,Anna Jaeger,Jonathan P Benskin

doi:10.1021/acs.est.9b06928

Abstract

Hyporheic zones are the water-saturated flow-through subsurfaces of rivers which are characterized by the simultaneous occurrence of multiple physical, biological, and chemical processes. Two factors playing a role in the hyporheic attenuation of organic contaminants are sediment bedforms (a major driver of hyporheic exchange) and the composition of the sediment microbial community. How these factors act on the diverse range of organic contaminants encountered downstream from wastewater treatment plants is not well understood. To address this knowledge gap, we investigated dissipation half-lives (DT50s) of 31 substances (mainly pharmaceuticals) under different combinations of bacterial diversity and bedform-induced hyporheic flow using 20 recirculating flumes in a central composite face factorial design. By combining small-volume pore water sampling, targeted analysis, and suspect screening, along with quantitative real-time PCR and time-resolved amplicon Illumina MiSeq sequencing, we determined a comprehensive set of DT50s, associated bacterial communities, and microbial transformation products. The resulting DT50s of parent compounds ranged from 0.5 (fluoxetine) to 306 days (carbamazepine), with 20 substances responding significantly to bacterial diversity and four to both diversity and hyporheic flow. Bacterial taxa that were associated with biodegradation included Acidobacteria (groups 6, 17, and 22), Actinobacteria (Nocardioides and Illumatobacter), Bacteroidetes (Terrimonas and Flavobacterium) and diverse Proteobacteria (Pseudomonadaceae, Sphingomonadaceae, and Xanthomonadaceae). Notable were the formation of valsartan acid from irbesartan and valsartan, the persistence of N-desmethylvenlafaxine across all treatments, and the identification of biuret as a novel transformation product of metformin. Twelve additional target transformation products were identified, which were persistent in either pore or surface water of at least one treatment, indicating their environmental relevance.

Highlights

The design of conventional wastewater treatment plants (WWTPs) is considered inefficient for the removal of organic contaminants present in wastewater
The goal of this study was to evaluate the influence of bacterial taxonomic diversity and hyporheic exchange flows (HEFs) on the dissipation halflives (DT50s) of organic contaminants detected in surface waters and the associated formation of transformation products (TPs)
This may be attributable to the growth of rare slow-growing taxa in the original sediment bacterial community found in the S1 treatment but eliminated in the S3 and S6 treatments through the dilution to extinction approach

Summary

Introduction

The design of conventional wastewater treatment plants (WWTPs) is considered inefficient for the removal of organic contaminants present in wastewater. Hyporheic zones, which form the water-saturated flow-through sediments of rivers, are often considered the last line of defense for preventing wastewater-derived organic contaminants from reaching near-surface aquifers that are used for drinking water production. Hyporheic zones are adjudged an essential role in the self-purification of streams, as the interplay of complex physical, chemical, and biological processes creates ideal conditions for organic matter decomposition, nutrient cycling, and biotransformation of contaminants.[2,3] The sediments provide a large surface area for biofilms with diverse microbial communities, which contribute substantially to global biogeochemical fluxes.[4] Fungi and other microeukaryotes are part of the microbial community in streams, rare relative to bacteria, and potentially contribute to biodegradation processes. It is not surprising that hyporheic zone biofilms are dominated by bacteria.[4−6] The varying redox conditions along many hyporheic flowpaths render the hyporheic zone an efficient

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Results