No abstract

The objective of this study was to eliminate organic micropollutants in the membrane system concentrates, which is produced by drinking water production plants, in order to protect existing water resources. This work is divided into two parts, pesticide elimination (I) and natural organic matter removal (II) in membrane system concentrates. Seven commonly detected pesticides in French surface waters, i.e. atrazine, sulcotrione, bentazone, isoproturon, diuron, glyphosate and acetochlore, were selected as the model micropollutants. Removal/degradation of these pesticides was studied by testing conventional processes employed for potable water production, i.e. adsorption, oxidation by ozone and clarification. Only partial removal of these pesticides was achieved with conventional processes. Removal of nonpolar pesticides was obtained by adsorption and rapid degradation of most of the pesticides was observed with low ozone dosages, except for atrazine and its metabolites. On the other hand, only the phosphonate-based pesticides were removed by clarification. By combining these processes, however, almost complete removal of the selected pesticides was achieved. Simultaneous ozonation and adsorption in the same reactor seems to be the most promising option for this study.

In surface water nanofiltration (NF) for drinking water production, 15 to 25% of the feed is rejected by the membranes. Two complementary approaches are investigated in order to manage concentrates. On one hand, an additional NF stage allows an increase in the yield of drinking water production from 85 to 94%. Thirty-days filtration cycles are achieved. Conductivity, natural organic matter (NOM) and micropollutant contents of permeate fully satisfy drinking water standards. On the other hand removal of phosphonates, micropollutants and NOM is investigated in order to treat the concentrate before disposal. Phosphorus is removed by adsorption on pre-treatment sludge: removal reaches 82% with 100 ppm of suspended solids. To eliminate pesticides and NOM, adsorption on granular activated carbon (GAC) is studied with pilot scale fixed bed columns. Within 20 minutes contact time, selected pesticides are completely eliminated. NOM removal is approximately 30% with wood based GAC.

A B S T R AC TIn the Nanofi ltration (NF) membrane systems utilised for river water treatment for drinking water production purposes, 15-25 % of the feed is rejected by the membrane as the concentrate. It contains natural and synthetic organic matter (COD ca. 30 mg/L) and its composition may vary with raw water quality, membrane pre-treatment and NF membrane cut-off. This study aims to achieve complete elimination of pesticides and the elimination of 60% of the natural organic matter (NOM) retained during nanofi ltration step. The investigation included testing conventional water treatment techniques-adsorption, coagulation, ozonation-and the combination of ozonation and adsorption processes. Eight pesticides detected most commonly in French surface waters were selected as model micropollutants: atrazine, sulcotrione, bentazone, isoproturon, diuron, glyphosate, amitrole and acetochlore. Simultaneous combination of ozonation and powdered activated carbon (PAC) adsorption proved to be an effi cient method for the elimination of the polar and ozone resistant pesticides at low carbon and ozone concentrations. This combination also achieved faster NOM removal than PAC adsorption only. It was observed that even with the use of high PAC concentrations, addition of low ozone dosages were necessary to degrade highly polar pesticides together with the NOM. No signifi cant modifi cation of the carbon activity and surface properties was observed at low ozone concentration levels, ca. 3 mg/L.