Combined sewer overflow treatment: Assessing chemical pre-treatment and microsieve-based filtration in enhancing the performance of UV disinfection

Abstract

Disinfection of combined sewer overflow (CSO) is necessary to reduce the amount of microorganisms discharged into surface waters. In this study, an efficient and cost-competitive treatment for CSO, employing UV disinfection, was developed. High suspended solids content in CSO poses a significant challenge for UV disinfection so laboratory experiments were carried out to asses the effect of chemical pre-treatment followed by micro-sieve filtration on the reduction of total suspended solids (TSS) and the increase of UV transmittance (UVT). The efficiency of UV, with and without pre-treatment, was investigated and a microbial inactivation model was developed to describe the fecal coliforms (FC) inactivation kinetics. Finally, the environmental impacts of the proposed treatment were simulated at the large-scale by stormwater management model (SWMM), and the cost of the proposed treatment train was evaluated and compared with current CSO treatment strategies.Experimental results showed that UV alone achieved 3.6-log reduction of FC at a UV fluence of 80 mJ/cm2, while a 4-log reduction of FC was achieved at a much lower UV fluence of 10 mJ/cm2, when the UV disinfection was preceded by chemical pre-treatment and microsieving filtration using a 32 μm mesh. Under these conditions, the TSS removal achieved was 73%, and the UVT increased from 14% to 32%.The SWMM showed that the proposed CSO treatment achieved a reduction in TSS by one order of magnitude and a decrease in number of FC from 1.05 × 1014 to 1.24 × 1010 CFU. The cost analysis performed herein suggests that the proposed treatment train is competitive to current CSO treatment strategies in terms of cost-effectiveness.The study demonstrates the potential of the innovative CSO treatment scheme to quickly and effectively treat a large amount of wastewater flow thus providing municipalities with a low footprint treatment unit for CSO.