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CHLORINE DISINFECTION OF BLENDED WASTEWATER EFFLUENTS I
Citation:
RHODES, E., L. A. BOCZEK, AND M. C. MECKES. CHLORINE DISINFECTION OF BLENDED WASTEWATER EFFLUENTS I . Presented at WEFTEC 2007, SAN DIEGO, CA, October 14 - 18, 2007.
Impact/Purpose:
to inform the public
Description:
During wet weather events collected water can exceed the capacity of a wastewater treatment plant (WWTP) and alternate flow management techniques must be employed. One technique is to treat influent flows through primary clarification and limit the flow to the secondary treatment units. Excess flow from the primary clarifiers, which by-passes secondary treatment, is then recombined or “blended” with secondary effluents and disinfected. During the blending process particulate matter, ammonia or other organic compounds within primary effluent will reduce the disinfection effectiveness. Samples of primary and undisinfected secondary effluents were collected from a local WWTP. These effluents were then mixed thoroughly at three different ratios to produce blended effluents. Samples of each of these blended products were assayed for indicator organisms (fecal coliforms, enterococci, total heterotrophs and somatic and male specific coliphage), suspended solids, turbidity, total organic carbon, ammonia, redox potential, and pH. Blended effluents were then mixed with a dilute sodium hypochlorite solution to a final total chlorine residual concentration of approximately 2.0 mg/L and sampled after 30 minutes of contact time. Samples were dechlorinated and assayed for microorganisms as described above. Preliminary results show that the total suspended solids for the 5:5, 3:7, and 1:9 blended samples were 28.1, 14.9, and 9.5 mg/L, respectively. The addition of sodium hypochlorite reduced fecal coliforms and enterococci by 99.99% in all blended samples, while heterotrophic bacteria were reduced by 99.1% in all blended samples. The coliphage were only reduced 65.5% in the 5:5 blended samples but were reduced 98.7% in the 1:9 samples. This data suggests that the increased amount of primary effluent reduces the disinfectant¿s ability to kill or inactivate the coliphage population while numbers of conventional indicator bacteria were effectively reduced.