AWWA ACE63252

This paper discusses a bench-scale study performed to evaluate coagulation, oxidation and adsorption treatment processes for improving filtered water UV transmittance (UVT) at the Southeast Water Purification Plant (SEWPP) for the city of Houston, Texas prior to UV disinfection. The objectives of the UVT Improvement Study were to: evaluate various coagulants at bench-scale for improving filtered water UVT prior to UV disinfection; evaluate various oxidants and adsorbents at bench-scale for improving filtered water UVT prior to UV disinfection; evaluate the benefit-cost tradeoffs associated with implementing upstream UVT- improvement treatment processes to reduce capital and operating costs of the new UV disinfection system. The finished water produced by the SEWPP is of high quality and meets all federal and state drinking regulatory requirements, as well as voluntary treatment performance standards established under U.S. Environmental Protection Agency's Partnership for Safe Water. The paper presents a summary of raw and finished water quality for the period 1996-2001. The water quality during the bench scale tests was challenging when compared with historical average water quality data. Raw water UVA was substantially higher during the bench tests. While TOC was comparable, raw water turbidity values were lower during the bench tests. Overall, the bench-scale treatment results should provide a conservative indication of full-scale treatment performance under more typical raw water quality conditions. UV transmittance (UVT) is the most critical water quality parameter for designing UV disinfection systems. Consequently, the design of the UV system should be based on long-term UVT data trends to capture seasonal variations in water quality. The paper presents an eight-year UV 254 absorbance trend for the SEWPP for the period 1996-2004 based on biweekly sampling of raw and finished water. The raw water UVT varies markedly from less than 20% to greater than 90%, reflecting seasonal changes in the organic characterization of the raw water. The lowest UVT values (< 50%) typically occur in the summer months and the highest values (>60%) in the winter months. Filtered water UVT values are more consistent than raw water values, but nonetheless, varied from around 75 to 90% over the 8-year period. Procedures for jar testing and related laboratory studies for evaluating alternative coagulants and oxidants for UVT improvement are given and include: coagulant stock solution preparation; sampling procedures; oxidant/adsorbent tests; and, quality control procedures. Includes tables, figures.