Table of Contents
Every minute, 50,000 litres of raw sewage—thick with human waste, detergents, and kitchen scraps—slip untreated into India’s rivers, lakes, and soil. Scaled across 1.4 billion people, this amounts to 45,000 million litres daily, enough to fill 19,000 Olympic pools. Sewage water pollution now contaminates 70% of surface water and 60% of groundwater sources, turning lifelines like the Ganga, Yamuna, and Cauvery into toxic corridors.
The Central Pollution Control Board (CPCB) labels 351 river stretches “critically polluted,” with Biochemical Oxygen Demand (BOD) exceeding 30 mg/L—ten times the safe bathing limit. As urban India swells by 2.5 crore residents annually, untreated sewage emerges as the single largest driver of water contamination in India.
SKF Elixer’s modular Vulcan STP systems, powered by Attached Growth Bioreactor (AABR) technology, offer a scalable countermeasure, treating sewage at source in compact basement units and returning clean water to the cycle.
Sources and Composition of Untreated Sewage
Sewage originates from three primary domestic streams, amplified by commercial and institutional contributors.
1. Blackwater (Toilets & Urinals)
- Volume: 40–50% of total sewage
- Per capita: 40–50 litres/day
- Composition: Faecal matter (200–300 g wet/person), urine (1.0–1.3 litres), toilet paper, pathogens (10⁷–10⁹ faecal coliforms/100 mL), nitrogen (10–12 g as NH₄-N), phosphorus (1.5–2 g).
- A 1,000-resident apartment generates 40–50 KLD blackwater with BOD 400–600 mg/L.
2. Greywater (Kitchens, Bathrooms, Laundry)
- Volume: 50–60%
- Per capita: 80–100 litres/day
- Composition: Food particles, oils (5–15 g/person), detergents (surfactants 2–5 g/L), suspended solids (150–250 mg/L), COD 500–800 mg/L.
- Food courts in malls add 300–500 mg/L FOG (fats, oils, grease).
3. Institutional & Commercial Inputs
- Hospitals: 450 litres/bed/day, antibiotics, disinfectants, X-ray chemicals.
- Hotels: 300 litres/room/day, high organic load from laundries.
- Hostels/Schools: 50–80 litres/student/day.
Composite Sewage Profile (Urban India)
- Flow: 135 litres per capita per day (lpcd)
- BOD: 250–350 mg/L
- COD: 600–900 mg/L
- TSS: 300–500 mg/L
- Total Nitrogen: 40–60 mg/L
- Total Phosphorus: 8–12 mg/L
- pH: 6.8–7.8
- Temperature: 25–32 °C
In rural areas, pit latrines and soak pits contribute 10,000–12,000 MLD, often leaching into shallow aquifers.
How Sewage Contributes to River and Groundwater Contamination
River Contamination Pathways
Untreated sewage enters water bodies via three routes:
- Direct Discharge: 22 major cities dump 12,000 MLD raw into rivers. Delhi alone releases 2,500 MLD into the Yamuna via 18 drains—70% of river flow in dry season.
- Nallah Interception Failure: 60% of open drains meant for stormwater carry sewage. Monsoon dilution masks pollution temporarily; post-rain BOD surges to 100 mg/L.
- Sewer Overflows: Aging pipelines (40–50 years old) crack under traffic load. A 1 mm crack in a 300 mm pipe leaks 500 litres/hour.
Impact Metrics
- Dissolved Oxygen Depletion: BOD >30 mg/L consumes all DO within 5–10 km downstream. Yamuna’s 22-km Delhi stretch records 0 mg/L DO for 300 days/year.
- Eutrophication: Phosphorus triggers algal blooms. Vembanad Lake (Kerala) sees 50–70% surface covered by water hyacinth, reducing fish catch from 15,000 tonnes (1990) to 3,000 tonnes (2023).
- Pathogen Load: Faecal coliform >10 lakh MPN/100 mL at Kanpur, Varanasi, Kolkata. Bathing in such water carries 1 in 3 infection risk.
Groundwater Contamination Pathways
- Septic Tank Leakage: 40% of urban households use septic tanks; 50% are poorly designed (no lining, <1 m from well). Nitrate leaching reaches 150–300 mg/L in tubewells.
- Sullage Infiltration: Kitchen and bathroom greywater poured into open plots percolates 1–2 m to shallow aquifers.
- Flood Plain Encroachment: Yamuna floodplains in Delhi host 5 lakh slum residents; open defecation contaminates recharge zones.
Impact Metrics
- CGWB reports 1,085 blocks with nitrate >45 mg/L—60% linked to sewage.
- Arsenic and fluoride co-mobilization in Bihar, UP due to anaerobic conditions created by organic load.
35% of Delhi’s 15,000 tubewells show E. coli; 20% exceed WHO limits
Effects on Ecosystems and Human Health
Ecosystem Damage
- Fish Kills: DO <2 mg/L suffocates carp, catfish. Ganga lost 50 native species since 1980.
- Biodiversity Loss: Wetland birds abandon polluted lakes. Chilika Lake (Odisha) saw 30% decline in migratory birds.
- Coral Bleaching in Coastal Zones: Sewage-laden rivers reduce salinity in estuaries, stressing corals in Gulf of Mannar.
Human Health Impact
- Waterborne Diseases: 1.5 lakh diarrhoeal deaths annually; 70% sewage-linked.
- Antibiotic Resistance: Hospital sewage introduces resistant bacteria; 58% of Delhi’s sewage carries ESBL genes.
- Cancer Clusters: Nitrate >50 mg/L linked to gastric cancer; Bihar’s 12 districts report 2x national average.
- Economic Cost: ₹3.6 lakh crore/year in treatment, lost wages (NITI Aayog, 2023).
Lack of Treatment Infrastructure in Urban Areas
Capacity vs Reality
- Urban sewage: 62,000 MLD
- Installed STP capacity: 26,879 MLD (43%)
- Functional capacity: 17,326 MLD (28%)
- Gap: 44,674 MLD untreated daily
Infrastructure Deficits
- Incomplete Sewer Networks: Only 40% of urban wards have underground drainage. Open drains carry 60% sewage.
- Land Constraints: Conventional STP needs 0.2 m²/litre/day. A 100 MLD plant requires 20 acres—unavailable in cities.
- Power & Maintenance: 40% STPs face 4–8 hour power cuts. Operator salary ₹15,000/month; turnover 60%.
- Funding: Municipal sewerage budget <5% of total. User charge recovers 20% O&M.
Tier-wise Breakdown
- Metro cities (8): 36% treated
- Tier-2 (100+): 25% treated
- Tier-3 (4,000+): <10% treated
Role of Modern STPs in Reducing Water Pollution
Modern Sewage Treatment Plants (STPs) intercept, purify, and recycle sewage at source, breaking the pollution cycle.
Key Features of Next-Gen STPs
- Compact Footprint
SKF Elixer’s Vulcan STP uses Attached Growth Bioreactor (AABR)—synthetic media with 220 m²/m³ surface area. A 100 KLD unit fits in 80 m² (basement-friendly). HRT: 5–6 hours vs 16–24 in ASP. - High Treatment Efficiency
- BOD reduction: 250 mg/L → <10 mg/L (96%)
- TSS: 300 mg/L → <5 mg/L
- Total Nitrogen: 50 mg/L → <10 mg/L (nitrification-denitrification in single tank)
- Pathogens: <100 MPN/100 mL (UV disinfection)
- Energy Optimization
- Fine bubble diffusers: 28% OTE
- VFD blowers: 0.6 kWh/m³
- Solar integration: 50–70% power offset
- A 200 KLD plant consumes 120 units/day (₹1,000 at ₹8/unit)
- Automation & Remote Monitoring
- PLC + SCADA: Auto-adjusts aeration based on DO (2 mg/L setpoint)
- Mobile app: Alerts for pH drift, pump failure
- OCEMS integration: Real-time CPCB reporting
- Modularity & Relocatability
- 25 KLD skids; add parallel units in 45 days
- Dismantle in 21 days, recommission in 28 days
Reuse Applications
- Flushing: 40 litres/person/day saved
- Landscaping: 10,000 m² park irrigated
- Cooling Towers: 30% makeup reduction
- Construction: Dust suppression
Sludge Management
- 30% less sludge than ASP
- Anaerobic digestion → biogas (0.8 m³/kg VS destroyed)
- Compost: ₹3/kg sale to nurseries
Cost-Benefit (200 KLD Plant)
- Capex: ₹75–85 lakh
- O&M: ₹2.2 lakh/month
- Savings: ₹3.5 lakh/month (water + sewer charge)
- Payback: 24–30 months
- 20-year NPV: ₹4.8 crore savings
Modern STPs transform sewage from pollutant to resource. A single 100 KLD plant prevents 36.5 million litres of raw sewage from entering rivers annually—equivalent to protecting 100 km of river stretch.
As India aims for 100% treatment by 2030, decentralized, efficient systems like Vulcan STP offer the only viable path. From basement bioreactors to rooftop solar, technology exists. The challenge lies in deployment—at every apartment, office, and institution—before the next drop of untreated sewage claims another life, livelihood, or lake.
FAQs
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1. How much untreated sewage enters the Ganga daily?
6,000 MLD across Uttar Pradesh, Bihar, and West Bengal. Kanpur (400 MLD), Varanasi (300 MLD), and Patna (250 MLD) are major contributors.
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2. What is the safe BOD level for river water used for bathing?
CPCB mandates BOD ≤3 mg/L for bathing. Most urban river stretches exceed 30 mg/L due to sewage.
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3. How does sewage affect groundwater in cities without sewer networks?
Septic tank leakage and open drain infiltration raise nitrate to 100–300 mg/L and introduce pathogens. 35% of urban tubewells show E. coli.
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4. Can a 50 KLD Vulcan STP fit in an apartment basement?
Yes, footprint 40 m², height 3.8 m. Treats sewage from 350–400 residents, recycles 40,000 litres/day for flushing.
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5. What is the annual water saving from a 300 KLD mall STP?
What is the annual water saving from a 300 KLD mall STP?
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