QUALITY IMPACTS OF RECYCLE STREAMS   Environmental Engineering & Technology, Inc. evaluated a number of American Water Works Services Company=s water treatment plants throughout the country to determine the water quality impact of recycle streams. EE&T was selected to perform this work by the AWWA Research Foundation. AWWARF recognized that with more stringent turbidity, disinfection and organic regulations of the Surface Water Treatment Rule and Amendments to the Safe Drinking Water Act, more attention must be paid to contaminants potentially present in recycled streams. The streams could represent a major addition to the level of contaminants present in raw water. Additional attention may need to be given to treatment of recycle streams, point of addition in the primary treatment train, and equalization and thereby maximum dilution of the return flow. A sampling program was developed for twelve plants using various forms of recycle. This program was designed to determine whether the quality impacts of the recycle streams were significant and to quantify these impacts. Based on these data and on the operational data of the plants, six plants were chosen for in-depth sampling. The sampling protocol for the chosen six plants included testing for a number of parameters: Turbidity, Solids, Iron and Manganese, THM (Instantaneous and Formation Potential), TOC, AOC, Aluminum, Heterotrophic Plate Count, Giardia Cysts, Cryptosporidium Cysts, and Particle Counting. This in-depth sampling program, conducted over a seven month period, characterized the waste streams in terms of important biological, organic, and inorganic parameters. It was determined that in some cases, there was a beneficial effect of recycle, such as a reduction in the required coagulant dose. In other plants, however the potential for water quality was undesirable. It was found that some wastewater and washwater process streams contained high levels of AOC, THMFP, manganese, cysts, and particle counts. Laboratory investigation and more in-depth full scale testing was undertaken to assess conditions that contributed to the build-up of contaminants or promoted their release from solids. Treatment methods and operational control procedures were investigated to reduce the contribution of the various organics, inorganics, and cysts from the return flows. Treatment strategies investigated included sedimentation, coagulation, oxidation, filtration and combinations of the above. For all six plants, recommendations were developed for operational changes based on the findings of the sampling and evaluation program.