18 April 2005 OZONATION-BIOFILTRATION FOR NOM REMOVAL FROM SURFACE AND GROUND WATERS Sudha Goel 1 , Raymond M. Hozalski, and Edward J. Bouwer 2 1 Dept. of Civil Engineering, IIT Kharagpur, Kharagpur 721 302 2 Dept. of Geography and Environmental Engineering, The Johns Hopkins University, Baltimore, MD 21218 Natural Organic Matter (NOM) is present in all drinking water sources and is typically quantified in terms of Total Organic Carbon (TOC). The presence of NOM in drinking water sources can lead to problems like bacterial regrowth in water distribution systems, formation of carcinogenic disinfection by-products (DBP) during disinfection with chlorine, color, taste and odor problems, and reduced activated carbon (AC) adsorber bed life [Bouwer and Crowe 1988]. Further, higher levels of NOM require higher chlorine doses due to the higher chlorine demand exerted by NOM. Legislation to reduce the maximum allowable total trihalomethan (THM) concentration in finished drinking waters from 100 µg/L to 80 µg/L was passed in 1998 and more halogenated compounds were brought under the purview of this rule [USEPA 2005]. TOC action levels at a concentration of 4 mg/L with a long-term target concentration of 1 mg/L have also been proposed. Therefore, a major concern for water utilities is finding suitable cost-effective treatment strategies for reducing TOC levels in finished drinking waters. A possible treatment strategy for reducing all the above-mentioned problems especially bacterial regrowth is removal of the biodegradable fraction of TOC (designated BTOC) using biofiltration processes. European experience with biofiltration processes has demonstrated that TOC removals of 5 to 75 % can be achieved [Bouwer and Crowe 1988]. The wide range in TOC removal efficiencies is attributed to differences in composition of TOC source, variation in biofilm media, and use of pretreatment processes like ozonation that can enhance biodegradation. Many US water utilities are committed to using ozone as a primary disinfectant or oxidant in response to recent regulations regarding DBP and TOC levels. Limited information was available about differences in biodegradation potentials of different NOM sources, effect of ozonation on NOM biodegradation, the potential for BTOC removal in a biofilter, factors affecting BTOC removal in a biofilter, and the potential of ozonation-biofiltration treatment in reducing TOC, BTOC and DBP levels in finished drinking waters. This project was conducted to resolve some of these questions and provide basic design and operational guidelines for biofiltration. Water utilities that want their treated water to be biologically stable (by removing BTOC) and reduce TOC and DBP levels in their finished waters without compromising its quality may find this information useful. OBJECTIVES The general objective of this project was to investigate the combined use and effectiveness of ozonation and biofiltration as a treatment strategy for reducing TOC levels in finished drinking waters. Four NOM sources were selected to represent a broad spectrum of compositions that might be encountered in drinking water supplies. Specific objectives of the project included: (1) measure BTOC levels for different NOM sources, (2) determine the effect of ozone dose on the biodegradability of each NOM source, and (3) investigate factors controlling TOC biodegradation (BTOC and TOC removal) in sand biofilters under conditions simulating conventional water treatment. Batch biodegradation and biofiltration studies were conducted with different NOM sources to address these objectives. MATERIALS AND METHODS Sources of NOM NOM composition depends on its origin. Four NOM sources were chosen for this study to represent a wide spectrum of compositions that may be encountered in drinking water treatment: 1) Dismal Swamp Water (DSW) from the Great Dismal Swamp Natural Wildlife Refuge in southeastern Virginia. TOC in this water is mostly peat-based fulvic acids and is representative of soil-based materials washed off into streams. 2) Florida Ground Water (FGW): Florida Cities Water Co. treats and supplies water obtained from a shallow, unconfined aquifer to a community in Florida. Page 1 of 18