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. . B-� �Vastcwater, which enterti the soil in tt sewa��e treatmen[ system, becomes food and water for the biolo;�ical community. Domestic What /s w�lstewater is 99.9�/o wtiter and only 0.1% pollutants that need to be (/1/aSteWater? removed. Wastewater trecitment is difficult because it is necessary ro maintairl a very high removal efficiency while dealing with lar�e volumes of water. The U.1% in wastewater that must be removed or modified consists mostly of organic material, bacteria and nutrients. The organic rn�iterial, which is sometimes called the "biochemical oxygen demand" (BOD), comes from a variety of sources in a domestic wastewater system. Food preparation, dish washing and clothes washin��, and wastes from the relatively inefficient hunrin digestive system all disch.trge into the doi»estic sewabe system. Figure B-4 shows the concentration of BOD, suspended solids, and other materials in raw sewa��e and in septic tank eftluent. BOD and suspended solids are r»easures of the percent.iy�e of or;_;anic �n.iterilll tOUf1CI lIl W�istewater. P,ithoy�ens are microorganisms th�tt cause disease and are usually present in domestic sewa��e. Fecal coliforins are indicators of the pl�esence of pathobei�s. Fi��ure B-4 shows that in 100 ml (about 1/2 cup) of septic tank ef�fluent, the►•e ai'e between 1000 and 1 million fecal colifoiz»s. "I'here are about the stui�e nun�ber ot�viruses in this quantity of efflui;nt. Figure B-4: Treatment Efficiencies of Soils One foot Three feet Raw Septic tank below trench below trench Parameter waste effiuent bottom bottom BODS(mg/I) 270-400 140-175 0 0 TSS (mg/I) 300-400 �5-65 0 0 Fecal coliform 1 miliion to 1 thousand to 0-100 0 (MPN/100 ml) 100 million 1 million Viruses (Unknown) 100 thousand to 0-1000 0 (PFU/ml) 10 million Nitrogen Total (mg/I) 100-150 50-60 --- --- NH4 (mg/I) 60-120 30-60 'B-60 B NO3 (mg/I) less than 1 less than 1 B-40 B-40 Total phosphorus (mg/I) 10-40 10-30 B-10 B-1 'B = background Figurc B-�