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Sewage Treatment: Overview
- 1. Sewage Treatment: Overview Dr. Akepati S. Reddy School of Energy and Environment Thapar University, Patiala Punjab (INDIA) – 147 001
- 2. Sewage treatment • Why treatment? – To meet the effluent standards or to make the sewage compatible for discharge into the environment – To make sewage fit for reuse (irrigation water/reclaimed water) • Treated where? – In centralized STP (city level treatment facility) – In on-site/decentralized STP (household or colony level facility) • Treated for what? – To remove suspended solids (reduce from <400 to <100 mg/L) – organic matter (reduce BOD5 at 20°C from <350 to <30 mg/L) – Pathogens (reduce MPN from>1x108/100 mL to <1000/100 mL) – Nutrients • Reduction desired: total-N & total-P to 15/10 & 2/1 mg/L • Total-P expected: 0.16 mg/L to 12 mg/L • Total-N expected: 20 to 70 mg/L (38.7 mg/L in Thapar sewage) • Standards: 100 mg/L total-N, 50 mg/L NH3-N and 5 mg/L free NH3
- 3. Sewage treatment • Sewage is usually at some depth at the STP • Need pumping up and passing through the STP for treatment – For protecting pumps, screening and degritting is needed – Sump and pumps are required for reliable pumping • Frequently treatment units of STP can not stand sewage flow and strength fluctuations and sewage may need equalization – to avoid overloading and shock loading • Preliminary treatment – Facilitates sewage to flow through the STP – Avoid accumulation of grit in the STP in different units • Preliminary treatment: – bar screens – grit channels/chambers, aerated grit chambers, vortex type degritters and cyclone degritters – Sumps and pumps – Flow and strength equalization tanks
- 4. Sewage treatment • Primary treatment – Removal of suspended solids by design and coincidental BOD removal – removal of helminth eggs, protozoan cysts, etc. – Primary sedimentation tank – Anaerobic pond, UASB reactor, UASB pond, baffled anaerobic reactor as alternatives – Stabilization of primary sludge and/or biogas generation occurs • Secondary treatment – Removal of biodegradable organic matter by design – Coincidental removal of pathogens (MPN count) and nutrients (nitrogen and phosphorus) – Aerobic and facultative treatment – attached growth and suspended growth types – ASP and its modifications, MBR, SBR (denitrification), aerated lagoons, oxidation ponds, oxidation ditches – Facultative ponds, constructed wetlands and vegetated ponds – TFs, RBC, SAFF, FAB, MBBR
- 5. Sewage treatment • Tertiary treatment – Make the water fit for reuse (irrigation and aquaculture) – Polishing, nutrient removal and/or pathogen removal – Maturation ponds, vegetated ponds, constructed wetlands – Filtration (roughing filters) and chlorination/disinfection • Sludge handling – Primary sludge and secondary sludge • Screenings, grit and scum • Biomass from vegetated ponds and constructed wetlands – Stabilization of sludge or generation of stabilized sludge – Aerobic and anaerobic sludge stabilization – Sludge thickening, dewatering and drying • Sludge drying beds – Handling of harvested biomass in case of vegetated ponds and constructed wetlands
- 6. Grit chamber Primary clarifier Aeration tank Secondary clarifier Stabilization tank Sludge drying beds Sewage Sump & pumping Bar screen Biogas flaring unit Dried sludge for disposal Exhaust gases (CO 2 and H 2O) Filtrate to sewage sump Clarified effluent to sewage sump Treated effluent Raw sewage Screenings Biogas if not flared (supplied as fuel or emitted) Grit STP Incorporating ASP Equalization Tank air air scum
- 7. Bar screen Raw sewage Sump & pumps Raw sewage High rate Facul. pond Multistage filter Baffled anaerobic reactor Duck/fish pond sludge Twin oxide Sludge thicng. /stablng. pit backwash filtrate Stabilized sludge for disposal Treat. Effl. rechar.well Treated effluent for reuse STP at a University 1. Grit removal is not provided – might have been integrated with the raw sewage pumping 2. In place of twin oxide electro-chlorinator can also be used. 3. Excess of the treated effluent (that can not be reused) will be injected into groundwater after filtration. 4. Stabilized sludge will be dredged, once or twice a year, transported away and disposed off. Blowers for diffused air
- 8. Aerated grit chambers Bar screens Primary clarifier Constructed wetland system Treated effluent pond Sludge drying beds Thickener cum stabilizer sludge pit skims pit pumpspump Biogas flare pumps Dried sludge Exhaust LPG for ignition filtrate Harvested biomass for use as resource filtrate Treated effluent for irrigational reuse Separated grit for disposal 1:Drainage Scum for disposal Overflows into natural drain Screenings for disposal Raw sewage Filtrate & drainage pit 1:Drainage pumps 2. Filtrates & drainages 2. Filtrates & drainages Mixing with biogas Compressed air Supply for Use as fule STP proposed for a Township
- 9. Proposed STP for a Military Station Sump-1 Sump-2 pump pump Drum screen Grit chamber-1 Grit chamber-2 Anaerobic pond Compartment-1 Anaerobic pond Compartment-2 Facultative pond Facultative pond Constructed Wetland cell Constructed Wetland cell Constructed Wetland cell Recreational Fish pond Slow-sand filter sump pump Overflow to natural drain Treated effluent for reuse blower air blower blower air air Raw sewage Raw sewage
- 10. Bar screen chamber Anaerobic Pond-2 Anaerobic Pond-1 Facultative Ponds-2 Facultative Ponds-1 Natural Pond-2A Natural Pond-1A Natural Pond-2B Natural Pond-1B Natural Pond-2C Natural Pond-1C sewage pumps Raw sewage sump Raw sewage Treated effluent Bar screen STP of a Small City
- 11. Bar screen Sump & pumping Bar screen (fine) Grit chamber SBR-selector SBR- aeration Sludge sump & pumping Sludge dewatering Raw sewage Dewatered sludge Treated effluent Pumping Pumping Air from blowers for diffused aeration Screenings Grit STP at a Small City
- 12. bar screen Sludge Sump Sump & Pumps Grit Chamber UASB UASB Division Box Division Box Distribution Boxes Distribution Box Pre-aeration Unit Final Polishing Unit Sludge Sump Sludge Sump Outlet Sludge drying bed To DG set Gas Scrubber Gas Holder Gas Flaring Sewage Sludge Gas STPs for a City in Punjab
- 13. Septic tank system Septic tank output sump Aeration tank Secondary clarifier pump pump Treated effl. pond Wastewater from the complex Treated effluent for irrigation Septic sludge to the biogas plant Secondarysludge STP of an Industrial Unit Mixed liquor Sludge Nutrients Filtration & injec. well Excess treated effluent for ground water recharging Excess treated effluent