Transparent exopolymer particle removal in different drinking water production centers

Abstract

Transparent exopolymer particles (TEP) have recently gained interest in relation to membrane fouling. These sticky, gel-like particles consist of acidic polysaccharides excreted by bacteria and algae. The concentrations, expressed as xanthan gum equivalents L−1 (μg Xeq L−1), usually reach hundred up to thousands μg Xeq L−1 in natural waters. However, very few research was performed on the occurrence and fate of TEP in drinking water, this far. This study examined three different drinking water production centers, taking in effluent of a sewage treatment plant (STP), surface water and groundwater, respectively. Each treatment step was evaluated on TEP removal and on 13 other chemical and biological parameters. An assessment on TEP removal efficiency of a diverse range of water treatment methods and on correlations between TEP and other parameters was performed. Significant correlations between particulate TEP (>0.4 μm) and viable cell concentrations were found, as well as between colloidal TEP (0.05–0.4 μm) and total COD, TOC, total cell or viable cell concentrations. TEP concentrations were very dependent on the raw water source; no TEP was detected in groundwater but the STP effluent contained 1572 μg Xeq L−1 and the surface water 699 μg Xeq L−1. Over 94% of total TEP in both plants was colloidal TEP, a fraction neglected in nearly every other TEP study. The combination of coagulation and sand filtration was effective to decrease the TEP levels by 67%, while the combination of ultrafiltration and reverse osmosis provided a total TEP removal. Finally, in none of the installations TEP reached the final drinking water distribution system at significant concentrations. Overall, this study described the presence and removal of TEP in drinking water systems.