COMPLIANCE INFO_1991-2006 - Laserfiche WebLink

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Technical Memorandum -2- March 31, 1992 • Based upon cumulative metals loadings the projected future capacity of the 303 acre site is estimated at approximately 35 years. BACKGROUND ORATION Description of Treatment Process The City of Manteca's Wastewater Quality Control Facility (WQCF) is a 5.45 mgd (ADWF) secondary treatment facility that treats domestic wastewater from the City of Manteca (City) and the City of Lathrop. A pending expansion of the WQCF will increase the capacity to 6.95 mgd. The WQCF is located on a 243 acre site owned by the City, of which 19 acres are occupied by the treatment facilities and another 14 acres are used as pasture land. At this time, the pasture land is not used for effluent or sludge disposal. The City also leases an additional 93 acres of farm land. Therefore, a total of 303 acres is available for disposal of treated effluent. Since 1988, a portion of the effluent has been discharged in the winter months to the San Joaquin river. A site plan of the treatment plant layout is shown in Figure 1. The liquid treatment process consists of screenings and grit removal, primary sedimentation, intermediate biological treatment using biotowers, followed by conventional activated sludge treatment. The sludge treatment process consists of dissolved air flotation thickeners, anaerobic digesters, and sludge drying beds. A schematic of the sludge treatment process is presented in Figure 2. The secondary effluent is used for crop irrigation on the 303 acre agricultural land. Sludge application has been designated for only the City-owned 210 acre site. SLUDGE MANAGEMENT Sludge Production Data A historical summary of the annual sludge production is shown in Table 1. The year 1989 was the fust full calendar year for which complete sludge data is available which does not reflect the impact of the start-up of the new wastewater treatment and sludge handling facilities. Due to lack of adequate data prior to 1989, sludge production for these years was calculated based on the yearly average annual flows and total suspended solids (TSS) concentration of 200 mg/L. A TSS of 200 mg/L was used assuming an influent and effluent concentration of 230 mg/L and 30 mg/L, respectively. This analysis assumes that no solids reduction is achieved in the liquid treatment process. The 1989 and 1990 sludge production data were calculated assuming a 50 percent solids reduction in the digester and the drying bed. The 1990 sludge production is 3,720 lbs/day. As a check for data accuracy, sludge production calculated from 1990 land application records is 4,188 lbs/day. Sludge Characteristics Sludge from the drying beds is tested semi-annually for total metals. A summary of the Total Threshold Limit Concentration (TTLC) for Manteca's sludge is presented in Table 2.