Table of Contents
India faces a silent crisis with over 72,000 million litres of sewage generated daily, of which 70% flows untreated into rivers, lakes, and farmland. This discharge loads soil with 10–20 kilograms of organic matter per kilolitre and leaches pathogens into groundwater, threatening 60% of the population reliant on borewells.
The role of STP plant in pollution prevention is indispensable—transforming sewage into safe effluent while protecting ecosystems and public health. SKF Elixer’s Vulcan STP, built with AABR technology in stainless steel, ensures 95%+ pollutant removal, enabling reuse and compliance in capacities from 5–500 KLD.
This blog explores untreated sewage impacts, contamination pathways, STP mechanisms, and regulatory frameworks. Whether you manage a 200-unit society in Bengaluru or a factory in Coimbatore, understand how sewage treatment benefits extend far beyond compliance to safeguard soil, water, and future generations.
Impact of Untreated Sewage on Environment
River and Lake Eutrophication
Untreated sewage introduces 5–10 grams of phosphorus and 30–50 grams of nitrogen per kilolitre, nutrients that accelerate algal growth at rates of 10–100 times normal in stagnant water bodies. Detergent-derived phosphates (average 8 mg/L in influent) create foam layers 2–3 metres high during monsoons, blocking sunlight and oxygen exchange across 500–1,000 square metres of surface daily. This leads to fish mortality of 50–100 tonnes annually in the 900-acre lake, valued at ₹50 crore in lost fisheries and tourism revenue.
Downstream, dissolved oxygen drops below 2 mg/L for 10–15 kilometres, suffocating macroinvertebrates and collapsing the food chain that supports 20–30 bird species.
Soil Salinization and Structure Damage
Each kilolitre of sewage contributes 0.5–1.5 kilograms of dissolved salts (primarily sodium chloride and bicarbonates from detergents and human waste). When used for irrigation at 5,000 KL per hectare annually, this adds 2,500–7,500 kilograms of salts, raising soil electrical conductivity (EC) from a baseline of 0.5 dS/m to 2–4 dS/m within 3–5 years. At EC >2 dS/m, osmotic stress reduces water uptake in wheat and rice by 15–25%, translating to yield losses of 1–1.5 tonnes per hectare—equivalent to ₹15,000–₹25,000 per hectare at MSP rates.
Simultaneously, excess organic carbon (200–400 grams per KL) creates hydrophobic coatings on soil aggregates, dropping infiltration from 50 mm/hour to 10 mm/hour and causing waterlogging in 30–40% of lowland fields during monsoon.
Biodiversity Loss
Fecal coliform levels of 10^7–10^9 MPN/100 mL in raw sewage eliminate sensitive macroinvertebrates like mayflies and stoneflies within 1–2 kilometres of discharge points, reducing species diversity by 50–70% in polluted streams.
Chromium from mixed industrial sewage (1–10 mg/L) bio-accumulates in fish tissue to 0.5–2 mg/kg, exceeding FSSAI’s 0.1 mg/kg limit and entering human diets through consumption of 100–200 grams of fish daily, increasing cancer risk by 1 in 10,000 over a lifetime.
Air Quality Degradation
Anaerobic decomposition in open drains releases 50–100 litres of methane per kilolitre of sewage—equivalent to 1–2 kilograms CO₂e in global warming potential. In unsewered urban clusters housing 1 lakh residents, this contributes 10–15% of local greenhouse gas emissions, or 5,000–7,500 tonnes CO₂e annually, exacerbating urban heat islands and respiratory issues in densely populated areas.
Mechanism of Soil and Groundwater Contamination
Surface Runoff and Leaching
A 1 cm rainfall event over a 1-hectare sewage-saturated plot mobilizes 100 kilolitres of runoff, carrying 20–40 kilograms of total suspended solids (TSS) into nearby drains or water bodies. In loamy soils with hydraulic conductivity (K) of 10⁻⁵ m/s, vertical percolation allows 1 kilolitre of sewage to infiltrate 1–2 metres in 24 hours, reaching shallow aquifers (5–15 metres depth) within 3–7 days during monsoon.
Groundwater Recharge Pollution
E.coli migrates 50–100 metres horizontally in 30 days through soil macropores and cracks, with certain groundwater studies showing 40% of borewells within 500 metres of open drains exceeding 10,000 MPN/100 mL—rendering water non-potable without boiling or filtration costing ₹5,000–₹10,000 per household annually.
Nitrate at 50 mg/L leaches 1 metre per year in clay loam; cumulative loading over 10 years elevates baseline levels from 5 mg/L to 45 mg/L, triggering methaemoglobinaemia in infants consuming 0.5–1 litre daily.
Soil Microbial Imbalance
Anaerobic pathogens outcompete nitrogen-fixing rhizobia, reducing biological nitrogen fixation by 30–50 kilograms per hectare annually—equivalent to ₹10,000–₹15,000 in urea fertilizer replacement at current rates. Heavy metals like chromium adsorb onto clay particles at 70–90% efficiency initially, but soil saturation after 5–7 years releases 0.1–0.5 mg/L into the root zone, stunting plant growth by 20–30%.
Long-Term Accumulation
Irrigation with 500 KL of sewage per year on 0.1 hectare adds 250–750 kilograms of salts, increasing EC by 1 dS/m every 2–3 years and rendering land saline within a decade. Organic carbon loading of 10–20 tonnes per hectare over 5 years forms water-repellent layers, reducing soil water holding capacity by 20% and increasing irrigation demand by 300–500 KL per hectare annually.
How STP Systems Prevent Ecological Degradation
Physical Screening and Settling
Bar screens with 6–10 mm spacing remove 2–5 kilograms of TSS per kilolitre, while primary clarifiers with surface loading rates of 1–2 m³/m²/hr settle 50–60% of suspended solids—preventing 1,000–2,000 kilograms of debris from entering soil or water bodies annually in a 100 KLD plant.
Biological Treatment (AABR Core)
Synthetic media with 200–300 square metres per cubic metre surface area supports stable biofilms that degrade 95%+ of BOD (from 200–400 mg/L to below 10 mg/L) and achieve 80–90% nitrogen removal through simultaneous nitrification-denitrification in a single tank. Pathogen reduction reaches 6-log (99.9999%) via extended hydraulic retention (12–18 hours) and optional UV disinfection.
Tertiary Polishing
Dual media filters (sand-anthracite) reduce TSS to below 5 mg/L, while activated carbon adsorption removes residual organics and odour compounds. Chlorine or UV dosing ensures zero viable pathogens in effluent.
Sludge Management
Filter presses dewater sludge to 70–75% solids, producing 30–50 kilograms of cake daily from a 100 KLD plant—composted into 10–15 tonnes of nutrient-rich manure annually, preventing 10–15 tonnes of raw sludge from leaching into soil.
Government Norms and Green Building Compliance
CPCB Effluent Standards
Discharge requires BOD ≤20 mg/L, TSS ≤50 mg/L, pH 6.5–9; reuse demands BOD ≤10 mg/L, TSS ≤10 mg/L, fecal coliform ≤100 MPN/100 mL—Vulcan AABR consistently achieves BOD below 8 mg/L.
State Pollution Control Boards
Consent to Operate is mandatory with online continuous effluent monitoring systems (OCEMS) for plants above 50 KLD. Non-compliance triggers ₹1–5 lakh fines and operational closure until rectification.
Jal Jeevan Mission
UrbanTargets 100% sewage treatment by 2026 with 30–50% capital subsidies for STPs in residential and institutional projects.
Green Building Norms
IGBC awards 4 points for 50% wastewater reuse and 6 points for 75%; GRIHA mandates dual plumbing and on-site treatment for 3+ star ratings, adding 5–8% to property resale value (₹8–12 lakh per flat in premium segments).
Swachh Bharat Integration
Encourages co-treatment of faecal sludge in existing STPs, with guidelines for 20–30% capacity allocation in urban plants.
SKF Elixer’s AABR STP exceeds all norms with <10 mg/L BOD and IoT compliance reporting.
Conclusion
The role of STP plant in pollution prevention is foundational to India’s environmental security. By intercepting 95%+ pollutants, enabling 90% water reuse, and generating compost, SKF Elixer’s Vulcan AABR STP protects soil fertility, groundwater purity, and community health.
Invest in proven sewage treatment benefits for compliance, cost savings, and sustainability. Contact SKF Elixer today.
FAQs
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1. How does untreated sewage affect soil fertility?
1 KL adds 0.5–1.5 kg salts and 200–400 g organics; over 5 years, raises soil EC 1–2 dS/m, reduces infiltration 50%, and kills beneficial microbes—dropping crop yields 20–30% (₹15,000–₹25,000/ha loss).
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2. What is the pathway of groundwater contamination from sewage?
Pathogens travel 50–100 m horizontally in 30 days; nitrate leaches 1 m/year. 100 KLD untreated discharge contaminates 1 crore litres aquifer yearly.
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3. How does AABR STP prevent river pollution?
Removes 95% BOD (<10 mg/L), 80–90% nitrogen, and 6-log pathogens—preventing 7–8 tonnes BOD and 10¹² coliforms from entering rivers annually (100 KLD plant).
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4. What are CPCB reuse standards for treated sewage?
BOD ≤10 mg/L, TSS ≤10 mg/L, fecal coliform ≤100 MPN/100 mL, pH 6.5–9—Vulcan AABR achieves <8 mg/L BOD, enabling flushing/gardening.
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5. How does STP help achieve green building certification?
90% reuse (90,000 litres/day from 100 KLD) earns 4–6 IGBC points; zero discharge + compost = GRIHA mandatory criteria—adding 5–8% property value (₹8–12 lakh/flat).
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