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The current WQCF is a combined biofilter-activated sludge plant which treats wastewater by mechanical <br /> screening,primary treatment, and secondary aeration and settling. Solids are thickened and biologically <br /> decomposed, and then trucked to a landfill.Within the cities of Manteca and Lathrop,wastewater is collected in <br /> buried pipelines and conveyed to the WQCF for treatment and disposal. Flows enter the plant at the influent pump <br /> station,pass through two mechanical screens to separate out large debris, and then move to the grit structures for <br /> primary treatment. <br /> PRIMARY TREATMENT <br /> Once screened for large debris,the influent enters aerated grit tanks where air is injected into the influent <br /> wastewater to separate solids from liquid. The purpose of the grit tanks is to remove relatively high-density <br /> inorganic particles from the wastewater stream. Flows from the grit chambers then enter the primary <br /> sedimentation basins to remove settleable solids and floatable scum such as oil and grease. Here,remaining solids <br /> are allowed to settle to the bottom of the basin where they are collected and then pumped to the digesters. <br /> SECONDARY TREATMENT <br /> Primary effluent is then sent through a biofilter feed pump station and two biotowers with high-rate plastic media. <br /> The plastic media serves as a base for fixed-film treatment that removes solids and organics from the wastewater. <br /> From the biotowers,wastewater flows into five fine-bubble activated sludge aeration basins where the effluent is <br /> infused with oxygen to provide a food source for microscopic organisms (which break down the effluent). <br /> Oxygen helps to speed up natural processes and causes the organisms to multiply, enlarge, and settle more <br /> quickly. From the activated sludge basins, flows are conveyed to three secondary clarifiers where suspended <br /> matter is removed by gravity while the effluent becomes clearer. Solids removed from the clarifiers are returned <br /> to the aeration basins or wasted to the solids handling facilities. <br /> DISINFECTION AND DISCHARGE <br /> Following secondary treatment,undisinfected secondary effluent is used to irrigate approximately 190 acres of <br /> City-owned cropland surrounding the WQCF. Effluent not used to irrigate cropland is directed to on-site <br /> chlorination and dechlorination facilities, and is subsequently discharged to the San Joaquin River via an existing <br /> side bank outfall. <br /> As a result of the Phase III Schedule B improvements(discussed above), effluent is nitrified and denitrified to <br /> address low dissolved oxygen concentration concerns.Ammonia generated by the digestion process reduces <br /> dissolved oxygen in water,which leads to aquatic toxicity problems. To reduce ammonia,nitrification, or the <br /> process of converting nitrogen compounds(primarily ammonia)to nitrates and nitrites(from NH3 to NO or NOA <br /> is utilized. To control nitrates, denitrification, or the process of converting the nitrate/nitrite to free nitrogen <br /> (nitrogen gas)is utilized. Although not normally harmful,the nitrate/nitrite compounds can be harmful to fish in <br /> high concentrations. By decreasing effluent ammonia levels,nitrification-denitrification thus increases dissolved <br /> oxygen concentrations in receiving waters to non-toxic levels. The specific process currently employed at the <br /> WQCF should allow the plant to avoid future ammonia toxicity problems. <br /> Secondary effluent discharged to the San Joaquin River is only allowed when the river has a certain downstream <br /> flow condition. To address this operational constraint, Schedule D disinfected effluent off-line storage <br /> improvements will allow the WQCF to store effluent during certain river flow conditions. River flow data from an <br /> existing real time in-stream flow meter located at the Mossdale Bridge monitors the flow within the river. <br /> SOLIDS HANDLING <br /> Sludge removed in the secondary treatment process is thickened in two dissolved air flotation units,where air is <br /> injected into the activated sludge to separate the solids from the liquid. The sludge is then sent to two anaerobic <br /> digesters where organic constituents within the solids are broken down("digested") in the absence of oxygen <br /> City of Manteca WQCF and Collection System Master Plan 2005 Update <br /> May 2006 5 Notice of Preparation <br />