Pilot study: Impact of suspended solids removal technology on subsequent ozonation for sewer overflow treatment

Approximately 3.2 billion cubic meters of untreated sewer overflow water is discharged into U.S. lakes and rivers every year during high-intensity precipitation events posing both environmental and public health challenges. A decentralized, end-of-pipe sewer overflow treatment system would eliminate detrimental overflow effects by handling peak wet-weather flow and associated pollutant loadings. In this study, an overflow treatment system comprised of suspended solids removal followed by chemical oxidation was assessed. Three different suspended solids removal technologies were employed to determine their compatibility with subsequent ozonation and to estimate the treatment cost to meet Clean Water Act discharge permit requirements for biochemical oxygen demand (BOD), total suspended solids (TSS), and Escherichia coli (E. coli) in approximately 30 minutes of total treatment time. Both cloth media filtration with ozonation and chemically enhanced primary treatment with ozonation met permit limits for BOD, TSS, and E. coli, while conventional primary treatment only met permit limits for BOD and TSS, ostensibly due to lower TSS removal by conventional primary treatment. Initial suspended solids removal was a key parameter for effective, subsequent ozonation to remove BOD, achieve disinfection, and decrease operating costs. The estimated, simple operating cost was competitive with conventional activated sludge ($0.10/m³ water treated, 2022 dollars). A full-scale decentralized, end-of-pipe treatment system could be operated as a “peaker facility” to handle large flows during storm events but remain idle during dry weather periods.