A new enzymatic method assessing the impact of wastewater treatment plant effluents on the assimilative capacity of small rivers

Abstract

Microorganisms play an important role in maintaining a good water quality in rivers by degrading organic material, including toxic substances. In the present study, we analyzed the potential impact of municipal wastewater treatment plant (WWTP) effluents as a major stress factor on the assimilative capacity of small rivers. It was the aim to develop a new bioassay for assessing such impacts in the receiving rivers by measuring the activity of extracellular enzymes (exoenzymes) in bacteria. Therefore, we established a specific in-vitro assay to detect inhibitory effects of solid phase-enriched water samples on β-glucosidase (BGL) activity of the actinobacterium Cellulomonas uda as a proxy for the microbial decomposition of organic substances and thus for the assimilative capacity of surface waters. We found significant reductions of BGL activity in the WWTP effluents and in the receiving waters directly downstream as well as a relative quick recovery over the further course of the water bodies. The new bioassay offers a promising tool for the assessment of the assimilative capacity in surface waters and a potential impact of WWTP effluents on this key ecosystem function.AbbreviationsWWTPwastewater treatment plantBGLβ-glucosidaseEU-WFDEuropean Water Framework DirectiveFAUFormazin Attenuation UnitsPEpopulation equivalentsREFrelative enrichment factor;SPEsolid phase extractionMTBEmethyl-tert-buthyl-etherDMSOdimethyl-sulfoxideNPG4-nitrophenol-β-d-glucopyranosideDOCdissolved organic carbon