Eugene/Springfield Water Pollution Control Facility 1984-1991

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Page 20 tional cost savings have been, at least partially, offset by higher maintenance costs. The preaeration system performs well in aerating primary influent. However,175 to 220 cubic feetof rags and grit need to be removed from each preaeration channel every year. The amount of debris removed from the preaeration channels further shows that the comminutors are not effec- tive in shredding rags and other materials to the desired size. Grit pumps and related equipment have had frequent plugging problems. • Odorous Air Removal System A scrubbing system at the plant removes odors during the entire pretreatment process. The sys- tem consists of four exhaust Fans and connected duct work, which draw air from four points in the covered pretreatment structure: one in the screw pump area, two in the cornminutor area, and one in the grit handling room. The air is then blown through two vessels that contain a bed of activated carbon. The porous carbon captures and holds sulfur compounds, which are the main contributor to odors. The life of the carbon ranges from two to three years. Operators monitor the holding capacity by sampling filtered air for sulfur at several different levels. If the filter's ability to capture sulfur com- pounds is substantially reduced, the carbon bed must be replaced or regenerated. Operations has chosen to regenerate three times rather than re- place, saving approximately $35,000 each time. The regeneration process, which takes about five days, involves a series of sodiumhydroxide applica- tions of various concentxations. Spent caustic is slowly fed back into the plant influent for treat- ment. PERFORMANCE: Although the pre- treatmentprocesshas effectively handled plant flows, the protective coating for underwater concrete surfaces in the pre- treatment structures has failed. Sheets of the coating have peeled away from the concrete surfaces of the screw pump dis- charge tothe Parshallflumes. Large quan- tities of grit also have settled in these areas rather than in the grit chambers. Section D: PLANT OPERATIONS PRIMARY TREATMENT The process equipment in the Primary Treatment Complex removes the readily settleable and floatable solids from the wastewater and then transfers sludge to the digestors. The equipment includes four circular primary clarifiers, four air- operated diaphragm sludge pumps, and two air- operated diaphragm scum pumps. • Primary Clarifiers Four 135-foot-diameterclarifiersremovefloatable and settleable solids. Air-operated diaphragm pumps remove settled sludge and scum from the bottoms of the clarifiers. A solenoid activated by a timer determines the pump stroke rate. Three- way actuator valves initiate strokes and release subsequent air flow. The valves would freeze up because of the highpressure air thatwas allowed to expand through the outlet port. This caused pumps Co stop working, requiring the operators to use alternate pumps until the frozen valves thawed. The problem was improved by installing an air dryer and an oil lubrication system. Operators monitorprimary sludge thickening per- formance bysamplingthickened sludge and clari- fierblanket levels. Samples are collected once per shift and analyzed for dry weight concentration. Operators control primary sludge pump-stroke rates to maintain clarifier blanket levels and de- sired thickened sludge concentrations of five to six percent dry weight. Primary clarifiers remove scum.