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B-2 <br />only O.lt pollutants which need to be removed. Wastewater treatment is <br />difficult because it is necessary to maintain a very hi/jh removal efficiency <br />while dealing with large volumes of water. <br />The O.lf in wastewater that must be removed or modified consists mostly of <br />organic material, bacteria, and nutrients. The organic material, which is <br />sometimes called the "biochemical oxygen demand" (BOD), comes from a variety of. <br />sources in a domestic wastewater system. Food preparation, dish and clothes <br />washing, and wastes from the relatively inefficient human digestive system all <br />discharge into the domestic sewage system. Table B.1. shows the concentration <br />of BCD, suspended solids, and other materials in raw sewage and in septic tank <br />effluent. BOD and suspended solids are measures of the percentage of organic <br />material found in wastewater. <br />Pathogens are microorganisms which cause disease and are usually present in <br />domestic sewage. Fecal conforms are indicators of the presence of pathogens <br />and Table B.1. shows that in 100 ml (about 1/2 cup) of septic tank effluent, <br />there are between 1,000 and 1 million. There are about the same number of <br />viruses in this quantity of effluent. <br />Nutrients are part of the materials in septic tank effluent and are of concern <br />because of possible eutrophication of ground or surface waters and possible <br />contamination of water supply wells. Nitrogen and phosphorus are the nutrients <br />of major concern in sewage tank effluent. Quantities of these nutrients are <br />listed at various locations in the soil treatment system in Table B.1. <br />Table B.1. Treatment Efficiencies of Soils <br />Parameter <br />Raw <br />Waste <br />Septic Tank <br />Effluent <br />One Foot <br />Below Trench <br />Bottom <br />Three Feet <br />Below Trench <br />Bottom <br />BOD- (rag/1) <br />0 270 - HOO 140 - 175 0 0 <br />TSS (mg/1)300 - 400 45 - 6*?0 0 <br />Fecal Conform <br />(MPN/100 ml) <br />1 million to <br />100 million <br />1 thousand to <br />1 million <br />0 - 100 0 <br />Viruses <br />(PFU/ml) <br />(Unknown)100 thousand to <br />10 million <br />0 - 1000 0 <br />Nitrogen <br />Total (mg/1)100 - 150 <br />1 <br />50 - 60 <br />• <br />-- <br />NH^j (mg/1)50 - 120 30 - 60 •B - 60 B <br />NO^ (tug/]) <br />Total Pho3~ <br />< 1 < 1 B - 40 B - 40 <br />phorus (mg/1)10 - 40 10 - 30 B - 10 B - 1 <br />‘ B s Background <br />% <br />r <br />( <br />vmni'r i