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WATER MANAGEMENT
SEWAGE TREATMENT (DOMESTIC WASTEWATER TREATMENT)
 process of removing contaminants from waste water and household sewage, both runoff (effluents) and domestic.
 Process of producing an environmentally-safe fluid waste stream (or treated effluent) and a solid waste (or treated sludge) suitable for disposal or reuse (usually as farm fertilizer).
SEWAGE TREATMENT INVOLVES THREE STAGES
 Primary treatment
 Secondary treatment
 Tertiary treatment
PRE-TREATMENT
 Removes materials that can be easily collected from the raw waste water.
 The waste may damage or clog the pumps and skimmers of primary treatment clarifiers (trash, tree limbs, leaves, etc.)
SCREENING
sewage water is screened to remove all large objects carried in the sewage stream.
GRIT REMOVAL
 Grit channel or chamber where the velocity of the incoming wastewater is adjusted to allow the settlement of sand, grit, stones, and broken glass.
 Grit removal is desirable for larger plants
FAT AND GREASE REMOVAL
 Fat and grease is removed by passing the sewage through a small tank where skimmers collect the fat floating on the surface.
 Air blowers in the base of the tank may also be used to help recover the fat as a froth.
PRIMARY TREATMENT
 Sewage flows through large tanks, commonly called "primary clarifiers" or "primary sedimentation tanks."
 Grease and oil from the floating material can sometimes be recovered for saponification.
 sedimentation tank may remove from 60 to 65 percent of suspended solids, and from 30 to 35 percent of biochemical oxygen demand (BOD) from the sewage.
SECONDARY TREATMENT
 To substantially degrade the biological content of the sewage which are derived from human waste, food waste, soaps and detergent.
 The majority of municipal plants treat the settled sewage liquor using aerobic biological processes.
 The bacteria and protozoa consume biodegradable soluble organic contaminants and bind much of the less soluble fractions into flock.
SECONDARY TREATMENT
Fixed-film or attached growth systems
 include trickling filters and rotating biological contactors.
Suspended-growth systems
 include activated sludge, where the biomass is mixed with the sewage and can be operated in a smaller space than fixed-film systems that treat the same amount of water