Secondary treatment biological θ fv s in θ fm s in

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Secondary treatment - biological – θ, F/V = S in / θ , F/M = S in / θ X, θ C Tertiary treatment Physical / chemical Chemical precipitation - phosphorus removal Adsorption - trace organic removal Filtration - groundwater discharge or irrigation use Membrane filtration - trace everything removal Biological - N, P removal Flow sheet see Fig.11-9, p.473 in D&M Sludge treatment ( “stabilization” ) Septic tanks ( optional ) see Figure 11-3, p.466 in D&M
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Discharge Surface waters Ground water “Deep” aquifer “disposal” “Shallow” aquifer – “indirect” reuse Injection well Percolation Spray, Pond NPDES permits see Table 11-7, p.465 in D&M WATER REUSE Goal : reduce potable water use ( conserve water resources ) Most common use : irrigation Limited use on food crops fear of contamination, esp. viruses Golf courses Landscaping residential and streets, parks Different from “recycle” (direct return to potable water system) illegal Indirect Reuse discharge of waste water to source of potable water – legal Industrial cost effective (due, in part, to limited number of contaminants) STORMWATER TREATMENT OPTIONAL Retention of runoff “drainage” ponds Required whenever construction “covers” ground surface Designed primarily for solids “removal” (sedimentation) Design may facilitate or prevent percolation Number of “outfalls” makes centralized treatment impractical Sewer (collection) systems Separate sanitary, storm water Combined Non-point discharges run-off from lawns, agriculture Typical Contaminants Refuse litter Solids – erosion, accidental spills from vehicles, fibers (multiple sources) Oil, grease Metals (from vehicles, including tires) N, P fertilizer Priorities Little effect on human health Contaminants removed in potable water treatment Pathogens seldom survive “run-off” Probably less significant than airborne transport of contaminants Aesthetics - may affect “non-consumptive” use of receiving water
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