CITY OF NIAGARA FALLS CSO HIGH RATE TREATMENT ASSESSMENT
Abstract:A high rate treatment feasibility study for the Muddy Run/Central pumping station combined sewer overflow (CSO) has been recently completed at the City of Niagara Falls. In 1996, the City of Niagara Falls Sewer System Analysis and CSO Abatement Report recommended a storage facility of 24,900 m3 volume for the storage of this major overflow. Alternative CSO control options were evaluated because of the high cost of constructing a storage facility. High rate treatment by means of vortex separators was considered an attractive option after preliminary settling column tests showed that the settling characteristics of the CSO were amenable to high rate treatment. In co-operation with the Great Lakes 2000 Cleanup Fund of Environment Canada, the City of Niagara Falls commissioned a more detailed feasibility study to investigate high rate treatment in the form of vortex separators to treat the combined sewer overflow discharged from this overflow site to the Niagara River.
To characterize the settling characteristics of the overflow, settling column tests including the US EPA long column method, the Brombach method and the Naomi Tyack-Aston University rotating column method were reviewed. All three methods were compared in this study. It was found that the last two methods produced very similar settling curves. With better understanding of the methods, future settling column tests can be done with reasonable confidence.
Using the GPS-X computer model to evaluate the high rate treatment facility allowed a quick and low-cost way to analyze different combinations of influent concentrations and treatment approaches. The vortex separation model software has four sub-models that account for the intermittent nature of inflow to the high-rate treatment facility. The removal efficiency during the overflow phase is based on a relationship between the surface loading rate and the concentration-based removal efficiency. This removal efficiency curve is calibrated based on site specific settling velocity tests when treatment is applied. By accounting for both storage and concentration-based treatment efficiency, the overall effectiveness of the proposed treatment unit can be tested.
The performance of the high rate treatment facility for various size options and influent concentrations was tested and compared with regulatory guidelines. GPS-X was found to be a time and cost saving tool. Options that were considered and analyzed included: vortex underflow rate and management of underflow, number of vortex separators, the diameters of the vortex separators, chemical settling aids (for example, polymer addition), additional processes (for example, filtration), and additional first flush storage.
Document Type: Research Article
Publication date: January 1, 2000
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