Membranes technology used in water treatment: Chemical, microbiological and ecotoxicological analysis

Abstract

The increment of world's Human population, with the consequent demand for water supply, plus the need for sustainable development and the conservation of water resources, highlights the urgency of improving water treatment technologies and management actions.The aim of the present study was to characterize and evaluate the efficiency of nanofiltration (NF90, NF270) and reverse osmosis (SW30) membranes, in improving the quality of three types of waters: irrigation, municipal supply and wastewater. The efficiency of using this technology was assessed by: (i) the study of water permeability and rejection of some chemical parameters, such as total nitrogen, total phosphorus, chemical oxygen demand (COD), biochemical oxygen demand (BOD5), feacal coliforms, nitrates, chlorides, iron and manganese; and (ii) the evaluation of their ecotoxicological effects, through the use of representative species of different taxonomic and functional groups (Vibrio fischeri, Thamnocephalus platyurus, Daphnia magna, and Pseudokirchneriella subcapitata). Results indicated that all three membranes have high rejection percentages for the majority of the studied parameters (>90%). All parameters concentrations in the permeate stream were below the limit values from Portuguese legislation and European Directives. With respect to the ecotoxicological effects, in general, the use of membranes removed the toxicity detected in the initial samples (which exhibited significant toxicity). The SW30 membrane showed a greater efficiency for toxicity removal, comparing with the nanofiltration membranes. Further, among the nanofiltration membranes used, the NF90 promoted a greater decrease in the toxicity of the samples. Thus, treatment with the membranes NF90 and SW30 allowed obtaining waters with high quality and low ecotoxicological potential, without risks for human populations and endangering the environmental balance.