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Primary Treatment <br /> Primary treatment in the NSF and the SSF is identical.Wastewater flows from the preliminary treatment system to <br /> the primary treatment system,where it undergoes a series of steps to remove solids from the wastewater stream. <br /> Once screened for large debris,the influent enters two aerated grit tanks,where air is injected into the influent to <br /> separate solids from the liquid. The purpose of the grit tanks is to remove relatively high-density inorganic particles <br /> from the wastewater stream.Twelve diffusers installed in each tank are supplied by low-pressure air blowers. Once <br /> separated from the wastewater,grit settles into the hoppers in the bottom of the grit tanks,where it is collected and <br /> periodically hauled to a landfill for disposal. <br /> Flows from the grit chambers then enter the three,parallel,primary, sedimentation basins to remove settleable <br /> solids (primary sludge) and floatable scum such as oil and grease. Here,remaining solids are allowed to settle to <br /> the bottom of the basin,where they are collected,thickened, and then pumped to the anaerobic digesters. <br /> Secondary Treatment <br /> For the NSF,primary effluent is then sent through a biotower feed pump station and two biotowers with high-rate <br /> plastic media. The plastic media serves as a base for fixed-film treatment that removes solids and organics from <br /> the wastewater. From the biotowers,biotower effluent then flows to five aeration basins with parallel plug flow, <br /> each with a volume of approximately 300,000 gallons and equipped with fine bubble diffused air systems. In the <br /> basins,the effluent is infused with oxygen to provide a food source for microscopic organisms (which break down <br /> the effluent). Oxygen helps to speed up natural processes and causes the organisms to multiply, enlarge, and settle <br /> more quickly. The diffused air network is supplied by four multivane centrifugal blowers. <br /> Within the aeration basins,removing additional organics is accomplished in a conventional activated-sludge <br /> process that is downstream of the plant's biotowers. Mixed liquor from the aeration basins is settled in three 85- <br /> foot diameter, 12-foot-deep secondary clarifiers,where suspended matter is removed by gravity and the effluent <br /> becomes clearer. Solids removed from the clarifiers are returned to the aeration basins or wasted to the solids <br /> handling facilities. <br /> A similar arrangement exists for the SSF, although no biotowers are utilized. Five larger aeration basins, each <br /> with a volume of 420,000 gallons provide equivalent treatment to the NSF. Secondary clarification is <br /> accomplished in two 110-foot-diameter by 16-foot-deep secondary clarifiers. <br /> Secondary effluent from both the NSF and SSF is routed by gravity toward the chlorine contact tanks while return <br /> activated sludge(RAS)and waste activated sludge(WAS)are pumped to the aeration basins and dissolved air <br /> flotation(DAF)thickeners,respectively. <br /> Effluent Disinfection, Storage, and Disposal <br /> Following secondary treatment,undisinfected secondary effluent is used to irrigate approximately 190 acres of <br /> City-owned cropland surrounding the WQCF. Secondary effluent not used to irrigate cropland is disinfected with <br /> chlorine gas and dechlorinated with sulfur dioxide, and then is 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 in wastewater reduces dissolved oxygen in <br /> water,which leads to aquatic toxicity problems. To reduce ammonia,nitrification, or the process of converting <br /> nitrogen compounds(primarily ammonia)to nitrates and nitrites(from ammonia to nitric oxide or nitrogen <br /> dioxide), is used. To control nitrates, denitrification, or the process of converting the nitrate/nitrite to free nitrogen <br /> (nitrogen gas)is used. Although not normally harmful,in high concentrations,the nitrate/nitrite compounds can <br /> Manteca WQCF and Collection System Master Plans EIR EDAW <br /> City of Manteca 3-13 Project Description <br />