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

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.

A microsieve-based filtration process for combined sewer overflow treatment with nutrient control: Modeling and experimental studies.

Combined sewer overflows contain a highly variable, wide range of contaminants, both in particulate and soluble form, making conventional water treatment processes unable to offer adequate public health protection. In this study, an integrated treatment process designed to simultaneously remove typical combined sewer overflow pollutants (suspended solids, chemical oxygen depends, turbidity) in conjunction with nutrient (nitrogen and phosphorus), was developed. The removal of particulates as well as dissolved nitrogen and phosphorus was achieved by first adsorbing soluble pollutants on zeolite and powdered activated carbon, and subsequently applying filtration carried out by polymer-enhanced microsieving. Laboratory experiments were designed using design-of-experiment techniques and carried out to assess the effects of the various treatment variables (cationic polymer, zeolite, powder activated carbon and microsieve size) in the designed combinations. A response surface model was fitted to the experimental dataset in order to capture and describe the non-linear relationships between treatment variables and treatment objectives. Finally, an optimization study was carried out using Pareto analysis showing that cationic polymer, zeolite, and powdered activated carbon, followed by fine mesh microsieving, worked synergistically in the integrated treatment process. Several optimal process conditions emerged, in particular, a treatment combination consisting of 1.1 mg/L of the cationic polymer, 250 mg/L of zeolite, 5 mg/L of powdered activated carbon, and a 370 µm mesh size. Under this condition, expected performance would be reductions of 72%, 56%, 35%, and 75% for turbidity, total Kjeldahl nitrogen, total chemical oxygen demand, and total phosphorous, respectively. The findings presented in this paper demonstrate the possibility of achieving multiple treatment objectives in a single and integrated treatment step, hence providing municipalities with viable treatment options where the issues of combined sewer overflow and nutrient management are simultaneously tackled.