INCREASING TREATMENT PLANT WET WEATHER FLOW CAPACITY WITH COARSE MONOMEDIA FILTRATION: A CASE STUDY AT TWO NEW YORK WASTEWATER TREATMENT PLANTS

Coarse Monomedia Filtration (CMF) is a proven treatment technology for tertiary treatment of wet weather flows. Utilizing a deeper filtration bed than standard tertiary filters, two Western New York facilities in the Town of Tonawanda and Niagara County were able to double their filtration capacities during wet weather events. Additionally, CMF produced significant savings in energy costs and chemical costs, which continue today.In addition to the deep bed, CMF features a large (3mm), spherically-shaped, uniformly sized media throughout the bed. The sphericity of the particles allows a greater flow volume to pass through the media. As the surface pore spaces restrict from solids adsorption, the velocity increases through the bed allowing solids capture deep throughout the filter.In 2004, the Erie County Department of Environment and Planning's Southtowns Treatment Plant finished retrofitting their conventional filters to CMF. In a unique application, the CMF will accept flow from the Southtowns Plant's Overflow Retention Facility (ORF). This primary treated stormwater effluent will be blended with secondary treated effluent before filtration. The blended effluent is expected to meet and/or exceed permit limits.In another unique application of CMF, the City of Geneva, New York has pilot tested CMF at its 4 MGD wastewater treatment plant (WWTP). In the Geneva application, CMF was used to process preliminarily treated influent wastewater during wet weather events through the CMF before blending it with secondary treated effluent prior to disinfection and discharge.One of the foremost challenges facing publicly and privately operated wastewater systems in the next several years will be complying with regulations governing combined sewer overflow (CSO) and sanitary sewer overflow (SSO) treatment under Environmental Protection Agency policy initiatives. Most systems have begun identifying and quantifying CSO's/SSO's, and decisions regarding cost-effective methods for minimizing and treating CSO/SSO flows will have major economic impact on most sewered communities. Coarse monomedia holds the promise of being a cost-effective unit process for the treatment of CSO/SSO flows at remote locations in wastewater collection systems.During the Geneva Pilot Study, 40 samples for total suspended solids (TSS) analysis were collected. Of these, 39 are considered valid. One was eliminated due to pilot plant upset.The influent TSS concentrations ranged from 46 to 210 mg/L, with an average concentration of approximately 94 mg/L.The effluent TSS concentrations ranged from 4 to 61 mg/L, with an average concentration of approximately 19 mg/L. 16 of the 19 effluent samples, approximately 83 percent, were below the 30-day discharge limitation of 30 mg/L TSS, and 18 of the 19 samples, approximately 95 percent, were below the 7-day discharge limitation of 45 mg/L TSS.The percent removal of TSS ranged from 49.2 percent to 95.7 percent, with an average removal of 79.1 percent. 6 of the 19 samples, approximately 32 percent were above the required 85 percent removal.Biochemical oxygen demand (BOD) analysis is a more complicated procedure than TSS analysis. As a result, the laboratory deemed fewer results acceptable. Of the 40 BOD samples submitted for analysis, 5 results were eliminated because of significant non-conformances, and one was eliminated due to the pilot plant upset. Four (10 percent) of the valid results are estimated values because of slight deviations from acceptance criteria.The influent BOD concentrations ranged from 36 to 290 mg/L, with an average concentration of approximately 149 mg/L.The effluent BOD concentrations ranged from 14 to 140 mg/L, with an average concentration of approximately 41 mg/L. 7 of the 14 effluent samples, 50 percent, were below the 30-day discharge limitation of 30 mg/L BOD, and 11 of the 14 samples, approximately 79 percent, were below the 7-day discharge limitation of 45 mg/L BOD.The percent removal of BOD ranged from 12.5 percent to 94.4 percent, with an average removal of 61.7 percent. 3 of the 14 samples, approximately 21 percent were above the required 85 percent removal.Though conclusions from the Southtowns Plant Demonstration Project for the use of CMF on ORF effluent are not available at this time, the results of the Geneva pilot study for preliminarily treated wastewater are promising. The filters proved able to reduce the TSS and BOD concentrations in the wastewater to acceptable levels for blending. The greatest obstruction in the use of CMF to process preliminarily treated wastewater was found to be the presence of a relatively small percentage of large particles. This is not expected to be an issue at the Southtowns WWTP due to the higher level of treatment prior to CMF and demonstrates the potential for CMF as a wet weather treatment tool at many other sites throughout the country.