SANITARY ENGINEERING Planning, designing and installation of system for the collection, conveyance, treatment and disposal of the waste

Definitions Refuse: Any waste matter lest as waste or worthless Sewage: includes all types of liquid wastes from latrines urinals, storm water, industrial wastes etc… Sullage: Liquid discharge from bathrooms, kitchens, wash basins etc… Garbage: Dry refuse including decayed fruits, leaves, paper pieces Sewer: closed drain through which drainage is conveyed Chemical oxygen demand: the amount of oxygen required to oxidize (chemically decompose) the given quantity of sewage is called COD Bio chemical oxygen demand: the amount of oxygen required for biological decomposition of waste matter

SEPTIC TANK Water tight single storied sedimentation tank where the sewage undergoes anaerobic decomposition BIOLOGICAL ACTION Sewage is retained for specific period- suspended solids settle down – sludge Sludge and the liquid undergo anaerobic decomposition – gets digested and reduces itself – sludge formed is removed at frequent intervals – effluent treated properly – either to soak pit or dispersion trenches Grease and fat rise to the surface of the sewage as scum

DESIGN ASPECTS For treatment of human excreta and urine Minimum diameter of pipes – 100 mm Volume septic tank depends on quantity of flow and the detention period Detention period – 24 hours ( may vary from hours ) Rectangular in shape – length is usually 2-4times breadth Grease, detergents, disinfectants- should not be allowed to the tank Minimum free board is 300mm

Construction details Two compartments- seperated by baffle walls Rectangular tank with brick or concrete Brick walls – 200mm, Concrete walls – 150 mm Plastering – 12 mm thick ( 1:3) Flooring – M15 concrete; 1:10 slope towards sludge outlet RCC or cast iron covers are provided over the tank Ventilation pipes – 50mm dia., taken to a height of 2m minimum, covered with mosquito nets

SEPTIC DON’TS Eliminate anti-bacterial cleaners. Don’t use detergent with bleach. Don’t do excessive cold water washing. Septic tank bacteria needs a warm climate. No water softeners into tank.

SOAK PIT Effluent from septic tank – fed to soak pit Soil absorption method Liquid effluent- soaks the soil Covered pit Rectangular in shape Minimum lateral dimension -atleast 1 m Filling-brick bats or broken stones Lining above inlet level is plastered Pit is covered with RCC slab

DISPERSION TRENCH Trenches of depth 50 to 100 cm and 30 to 100 cm excavated to a slight gradient Bottom layer – washed gravel / crushed stone Rest layers – coarse aggregates Length of trench - 30 m with a min. spacing of 1.8 m Covered with ordinary soil and the top surface is turfed ( 15 cm above ground level)

Water is our most precious resource. We can live without oil or gas We cannot survive without clean and safe water

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