Eugene/Springfield Water Pollution Control Facility 1984-1991

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Section D: PLANT OPBRATiONS Page 27 PERFORMANCE: The engine genera- tors have produced gross energy savings worth about $50,000 a year. Net savings have been substantially less, about $27,000, due to maintenance and repair costs. But increasing knowledge of the equipmenthas increasedpreventive main- tenance and has reduced the number of costlyrepairs. Bothgeneratorswere sched- uledfor complete overhauls in 1991 at an estimated cost of $160,000. • Co-generation Two 420-kilowattenginegenerators use the meth- aneproduced in the digestion process to generate electricity and reduce plant power costs. The gen- erators also provide a source of hot water, which is used for sinks and showers; for heating digesters; and for heating the administration, maintenance, and facility maintenance buildings. ^ PLANT PERFORMANCE Since plant start-up, the treatment plant and its processes have consistently met the plant effluent discharge permit requirements. TSS and BOD maximum pound limits for daily and weekly maxi- mums were exceeded only three times, resulting from extremely high plant flows during prolonged periods of rainfall. INFLUENT CHARACTERISTICS Plant influent is typical of most domestic treat ment systems in the northwest. The following descriptions are limited to those characteristics that have the greatest impact on achieving pollu- tion discharge limits. • Flow Variations Annual plant flow variation range has averaged 63 to 186 percent of the average influent flow. The most extreme variation occurred in 1986, when the flows ranged from 61 to Z28 percent of the average influent flow. The higher variations re- sultedfrominflow and infiltration from the collec- tion system during periods of heavy rain. • Boiler A 1,675-horsepower boiler, rated at 5,537 MBh, has met water heating demands that could not be met by the engine generators. The boiler normally uses the methane gas produced by the digestion process for fuel and is also capable of using natural gas if the system is not able to provide enough methane to meet the needs of the heating water supply system. • Influent pH Influent pH has normally ranged from 6.9 to 8.0. The highest influent pH, recorded in March 1986, was 9.6 -the source was never identified. In June 1987, a pH of 9.0 was caused when spent caustic was wasted to the plant influent during a planned maneuver. Neither of the two instances of high pH levels upset plant processes. • Total Suspended Solids Typical of northwest facilities, the total concen- tration of suspended solids at the Eugene/Spring- fieldplant averages 141 mg/L, which is lower than the national average. The lowest monthly average of influentTSS recordedhere was 63 mg/L and the highest was 260 mg/L. Typical TSS concentration for domestic wastewater in the United States is 200 mg/L with a range of 100 to 350 mg/L. One reason the plant's averages are so low is that there are no industries that contribute large amounts of solids. (Agripac wastes are treated separately.) The high amounts of rain result in increased inflow and infiltration, which may contribute to lower con- centrations. The plant's co-generator uses digester gas to offset power costs.