Water Supply, Sanitary and Environmental Engineering
Scope of the domain
Water supply, sanitary and environmental engineering covers water demand, sources, treatment, distribution, sewage collection and simple disposal. The exam tests per-capita demand, treatment sequence and sanitary units.
Core rules and concepts
- Per-capita demand is expressed in litres per capita per day (lpcd); domestic demand is often taken as 135 lpcd for design in Indian practice, with public and industrial uses added.
- Sources: surface water (rivers, lakes, reservoirs) and groundwater (wells, tube wells). Treatment sequence: screening, aeration, sedimentation, coagulation-flocculation, filtration and disinfection.
- Distribution systems: dead-end, grid, ring and radial; a ring system maintains supply when one main fails.
- Sanitary terms: sullage is wastewater from sinks and baths; sewage includes sullage plus human excreta; a trap holds a water seal against foul gases.
- A septic tank combines sedimentation and anaerobic digestion; the effluent still needs a soak pit or further treatment.
Worked example
A town has 10,000 people and a design demand of 135 lpcd. Average demand = 10,000 × 135 = 1,350,000 litres/day = 1.35 million litres/day (MLD). With a peak factor of 1.5, peak demand = 1.35 × 1.5 = 2.025 MLD. Reasoning: convert litres to MLD by dividing by 10⁶; multiply by the peak factor only after finding the average.
Traps
Do not confuse lpcd with litres per day for the whole town. Do not put disinfection before filtration in the treatment train. Do not call a septic tank a complete treatment plant. Do not ignore the water seal in a trap.