TASTE AND ODOR COMPOUNDS IN POTABLE WATERS: HOW TO REMOVE THEM USING OZONE-ASSISTED BIOFILTRATION?

摘要

The City of Chandler (City), Arizona, operates 45 million gallons per day water treatment plant (WTP). The City is one of the downstream users of the Salt River Project (SRP) canal water. The WTP receives waters with relatively high concentrations of taste and odor (T&O) causing compounds such as 2-methyl isoborneol (MIB) and geosmin. The MIB and geosmin are produced by blue-green algae and actinomycetes that grow in the canal. The warm climate and the plenty of sunlight create ideal conditions for algae growth. The historical concentrations of MIB and geosmin in the plant source water varied between 10 and 60 ng/L for the months of August through January. This study evaluated the potential of ozone-assisted biofiltration (OAB) for removing T&O compounds. OAB is a two-step process. In the first step, ozone is added to breakdown the natural organic matter (NOM) into bioassimilable organic carbon. In the second step, biologically active filters are used to oxidize the bioassimilable organic carbon. Pilot testing of OAB was conducted at the Chandler Water Treatment Plant as part of an American Water Works Association Research Foundation (AwwaRF) study. In these pilot studies, granular activated carbon (GAC)/sand and anthracite/sand media were evaluated parallely. To reduce removal by adsorption, exhausted GAC was used in the GAC pilot filters. The results showed higher MIB removals in filters with GAC/sand media compared to anthracite/sand. The MIB removals were a function of empty-bed contact time (EBCT); higher MIB removals were observed in filters with higher EBCTs. Most of the MIB removal occurred in the top few inches of the filters indicating predominance of biological oxidation in the upper layers of the media. Increasing ozone dose resulted in slightly enhanced MIB removal. The GAC/sand filters outperformed anthracite/sand filters in terms of TOC and UV254 reductions. Higher HPCs were observed in GAC/sand filters compared to anthracite/sand filters indicating higher bioactivity in GAC/sand filters. Both GAC/sand and anthracite/sand filters produced water with turbidities less than 0.2 NTU.