Use of a 6-steps microcosm for studying a wastewater discharge in a freshwater ecosystem: A multidisciplinary study

Abstract

An experimental microcosm has bccn designed for simulating and studying impacts of a wastewatcr treatment plant (WTP) discharge on a freshwater/sediment ecosystem. The study was focused on the changes in biodiversity of benthic populations, especially bacteria and oligoehaetes. Effluents were discharged in the Sa6ne river, near Lyon (France) from a small treatment plant which treatcd domestic raw water by an activated sludge process. Freshwater and sediments were sampled in the Sa6ne river upstream of the discharge point and placed in microcosms. Following the WTP discharge, physicochemical parameters of the overlying water column and sediments exhibited only a slight change, as compared to a reference.Characterization of the sediment bacterial populations was conducted with the Biolog and APt systems. Strain identification and interpretation of data was difflcuh using thesetwo systems. Bacterial taxa in the sediments increased slightly below the WTP discharge. Gram negative strains dominated in the effluents, but G + and G bacteria were balanced in the sediments. Pseudomonas sp, and Bacillus sp,, were the dominant strains. Invertebrate populations indicated an effect of the WTP discharge, with increasing of pollution resistant strains (Tubificidae) and disappearance of pollution intolerant strains such as LimmMrilus udekemianus and Quistadrilus nmltirTaken as a whole, biological parameters indicated an environmental changes despite only slight changes in the physicochemistry of water. This cxperimcntal microcosm has proven to be a useful tool for studying impact of wastewater discharge on oenthic populations