A PIB backgrounder of 21 October 2026 sets out the sewage treatment technologies used under the Namami Gange Programme, and it reads as a field guide to how a river gets cleaned. The programme has taken up 199 sewerage infrastructure projects worth about ₹31,327 crore, of which 116 are complete. They are meant to create 5,270 million litres per day (MLD) of new sewage treatment capacity, of which 2,237 MLD has been created, and to rehabilitate 925 MLD of existing capacity, of which 873 MLD has been done.
Those two pairs of numbers tell different stories, and they are the first thing to notice. Rehabilitation is about 94% complete. New capacity is about 42% complete. Repairing old plants is faster than building new ones, and the gap between sewage generated and sewage treated in the Ganga basin depends on the new ones.
What a sewage treatment plant does, in three stages
The science here is NCERT Class XII Biology (Microbes in Human Welfare), and every technology in the backgrounder is a variation on it.
Primary treatment is physical. Screening and sedimentation remove floating debris, grit and settleable solids. What settles is primary sludge; what flows on is the primary effluent, still carrying dissolved and suspended organic matter.
Secondary treatment is biological. The effluent goes into aeration tanks, where air is pumped in and aerobic microbes grow as flocs — masses of bacteria bound with fungal filaments. The flocs consume the organic matter, and the effluent's biochemical oxygen demand (BOD) falls. The effluent then passes to a settling tank, where the flocs settle out as activated sludge. Part of it is pumped back to the aeration tank as inoculum; the rest goes to anaerobic sludge digesters, where methanogenic bacteria break it down and produce biogas — methane, carbon dioxide and hydrogen sulphide.
Tertiary treatment removes what biology leaves behind — nutrients such as nitrogen and phosphorus, and pathogens — commonly ending with disinfection by chlorination.
BOD, the number that measures pollution
BOD is the amount of oxygen that microorganisms would consume in breaking down the organic matter in a litre of water. The more organic pollution, the higher the BOD. It is the single most useful number in this topic because it connects the plant to the river: sewage discharged with high BOD drains dissolved oxygen from the river as it decomposes, and fish and other aquatic life suffocate.
The National Green Tribunal's 2019 order set treated-effluent norms of BOD below 10 mg/l, total suspended solids below 20 mg/l and COD below 50 mg/l, with limits on faecal coliform, total nitrogen and total phosphorus. It replaced a 2017 Environment Ministry relaxation that had allowed a BOD of 30 mg/l. These are the "NGT norms" the backgrounder refers to.
The technologies, grouped by how they work
The backgrounder describes Namami Gange's approach as technology-neutral — the process is chosen to suit the site rather than the site being forced to suit one process. The list looks long, but it sorts into six families.
1. Aerobic suspended growth: the activated sludge family
- Conventional Activated Sludge Process (ASP) — the textbook process above.
- Sequential Batch Reactor (SBR) — a cyclic version of activated sludge in which aeration, settling and decanting happen in sequence in the same tank. The backgrounder describes it as offering the highest treatment efficiency possible in a single-step biological process.
2. Aerobic attached growth: microbes on a surface
- Moving Bed Biofilm Reactor (MBBR) and Fluidised Aerated Bed (FAB) — microbes grow as a biofilm on small plastic carriers kept moving in the tank, which packs more biomass into a smaller volume.
- Food Chain Reactor (FCR) — introduced in India through Namami Gange. It adds fixed artificial media and plant roots to the activated-sludge principle, so that a whole food chain of organisms, not only bacteria, works on the waste. Advantages: smaller footprint, lower power use and nutrient removal. Five FCR plants operate — two at Bhatpara (West Bengal) and three at Prayagraj — and one is under construction at Bhagalpur, at about 175 square metres per MLD.
3. Aerobic granular sludge: NEREDA
NEREDA, a technology developed at Delft University of Technology, uses the same bacteria as activated sludge but grows them as dense aerobic granules that settle much faster than flocs. Faster settling means smaller tanks. The 60 MLD NEREDA plant at Pahadi, Patna, needs a bioreactor of about 1,900 square metres, against about 5,400 for the SBR alternative cited, and the backgrounder records power savings of about 50% over ASP and 20% over SBR.
4. Anaerobic treatment: UASB
Upflow Anaerobic Sludge Blanket (UASB) reactors send sewage upward through a blanket of anaerobic sludge granules without air, producing biogas. UASB was developed in the Netherlands and came to India in the late 1980s under the Ganga Action Plan, first at Kanpur; under the first Yamuna Action Plan it became the dominant choice. Its known weakness for municipal sewage is that the effluent usually needs post-treatment — polishing ponds or aerated lagoons — to meet BOD norms, which is why the backgrounder lists "UASB and its combinations with aerated lagoons".
5. Non-biological processes
- Electrocoagulation and electro-oxidation — an electric current and a sacrificial metal anode release coagulating ions that destabilise suspended and emulsified pollutants. No microbes are involved, so the process does not slow down in the cold — the reason it suits Uttarakhand, at Badrinath and in Chamoli, with 17 installations.
- Advanced Oxidation Process (AOP) — a pilot at Varanasi's Assi drain treats wastewater on site instead of laying long interception sewers. Its financing is the notable part: no upfront capital payment, with payment linked to the quantity of water treated and to performance indicators.
6. Nature-based and decentralised systems
- Constructed wetlands — engineered beds of water, plants, substrate and microorganisms. At Bithoor (Uttar Pradesh), a town of about 20,000, six wetlands built directly on drains treat about 2 MLD, bringing BOD from about 75 mg/l to below 10 mg/l.
- Soil Biotechnology — a constructed soil filter developed at IIT Bombay that combines sedimentation and infiltration with biochemical processes in a mineral bed with native microflora and plants, with very few moving parts. A 1.2 MLD plant at Devprayag uses it.
- Johkasou — a Japanese prefabricated, plug-and-play treatment unit for domestic sewage, used where sewer networks cannot be built. Six installations in Uttarakhand.
The land problem, and the four-storey answer
Land is the binding constraint for treatment plants in hill towns and old river cities. The 7.5 MLD multi-storey plant at Muni Ki Reti, upstream of Rishikesh's Triveni Ghat, is the country's first four-storey municipal STP under the programme. It occupies about 900 square metres — about 120 square metres per MLD, against about 400 for the conventional alternative cited.
Set beside the NEREDA and FCR figures, the comparison is the most useful analytical thread in the backgrounder. Every newer technology in it is, among other things, a way of treating more sewage on less land.
Sludge, septage and energy
A treatment plant produces a second waste stream: sludge. The backgrounder treats it as a resource.
- Anaerobic digestion of sludge produces biogas for power. At Varanasi's 140 MLD Dinapur STP, biogas meets about 52-72% of the plant's power use; at the 80 MLD Naini STP in Prayagraj, about 50%. A 220 MLD STP at Meerut is identified for Bio-CNG.
- Dewatering, using a volute press at the 50 MLD Ramana STP, reduces the volume of sludge to be handled.
- Faecal Sludge and Septage Management (FSSM) covers homes with septic tanks rather than sewer connections. A Faecal Sludge Treatment Plant (FSTP) treats septage brought by tankers — the 10 KLD pilot at Chunar is the example — and does not replace an STP. Co-processing lets tankers discharge septage into a city STP for treatment alongside sewage.
- On-site solar at the 42 MLD Naini STP generates about 3,850 units a day against a requirement of about 5,700, and Meerut is proposed as a fully solar-powered Green STP.
How the programme is financed, and why that matters
The early Ganga clean-up plans built plants that then performed poorly, because the contractor's interest ended at construction. Namami Gange changed the contract. Under the Hybrid Annuity Model (HAM), the government pays up to 40% of capital cost during construction and the remaining 60% as annuities over 15 years, together with operation and maintenance — and both are linked to the plant's performance. The first HAM agreements were signed in October 2017 for Haridwar and Varanasi. One City One Operator extends the principle by giving a single operator responsibility for all the treatment assets of a city, new and old. The AOP pilot at Assi carries the logic to its end point: no payment until the water is treated.
The institutional lineage
| Year | Step |
|---|---|
| 1985-86 | Ganga Action Plan approved in 1985, launched January 1986 — the first river action plan |
| 1993 | GAP Phase II, extending to tributaries; later merged into the National River Conservation Plan |
| 2008 | Ganga declared India's National River |
| 2009 | National Ganga River Basin Authority constituted |
| 2011 | National Mission for Clean Ganga (NMCG) registered as a society |
| 2014 | Namami Gange launched as an integrated conservation mission |
| 2016 | National Ganga Council, chaired by the Prime Minister, replaces the NGRBA |
Namami Gange's eight pillars, in the backgrounder's list: sewerage treatment infrastructure, river-front development, river-surface cleaning, biodiversity, afforestation, public awareness, industrial effluent monitoring and Ganga Gram. Sewage infrastructure is at the centre because untreated municipal sewage is the largest source of the river's organic load. The programme's planning has since moved towards the city and the drain as the unit, through urban river management plans, and the same plant-by-plant logic drives the Yamuna rejuvenation programme in Delhi. Industrial effluent — dyes from textile clusters, for instance — is a separate chemistry problem; a recent laboratory approach to it is the piezo-photocatalytic removal of dye from wastewater.
🔑 Revision block
- Progress: 199 projects, ₹31,327 crore, 116 complete; new STP capacity 2,237 of 5,270 MLD (about 42%); rehabilitation 873 of 925 MLD (about 94%).
- Three stages: primary = physical (screening, sedimentation); secondary = biological (aeration, flocs, BOD falls, activated sludge partly recycled as inoculum); tertiary = nutrients and disinfection (chlorination).
- Sludge digesters: anaerobic; methanogens produce biogas (CH₄, CO₂, H₂S).
- BOD: oxygen microbes need to decompose organic matter; NGT 2019 norms: BOD < 10, TSS < 20, COD < 50 mg/l.
- Aerobic: ASP, SBR (cycles in one tank), MBBR, FAB, FCR (introduced in India through Namami Gange; Bhatpara, Prayagraj).
- NEREDA: aerobic granular sludge; 60 MLD at Pahadi, Patna; about 50% power saving over ASP.
- UASB: anaerobic, Dutch-developed, introduced under GAP at Kanpur in the late 1980s; needs post-treatment.
- Others: electrocoagulation (works in cold; Uttarakhand), AOP pilot at Assi drain (pay-for-performance), constructed wetlands (Bithoor), Soil Biotechnology (IIT Bombay; Devprayag), Johkasou (Japan).
- Muni Ki Reti: first four-storey municipal STP; about 120 m² per MLD vs 400.
- Financing: HAM = 40% capital in construction + 60% annuity over 15 years, performance-linked; first deals Oct 2017 (Haridwar, Varanasi); One City One Operator.
- Lineage: GAP 1985-86 → National River 2008 → NGRBA 2009 → NMCG 2011 → Namami Gange 2014 → National Ganga Council (PM) 2016.
🎯 Practice MCQs
Q1. In a sewage treatment plant, the stage in which aerobic microbes reduce the organic content of the effluent is: (a) primary treatment (b) tertiary treatment (c) secondary treatment (d) preliminary screening
→ (c) Secondary (biological) treatment takes place in aeration tanks, where microbial flocs consume organic matter.
Q2. The gases produced by methanogenic bacteria in anaerobic sludge digesters include: (a) methane, carbon dioxide and hydrogen sulphide (b) oxygen, nitrogen and methane (c) ozone, carbon monoxide and hydrogen (d) chlorine, ammonia and oxygen
→ (a) Methanogens are obligate anaerobes; they produce biogas that is mainly methane, with carbon dioxide and hydrogen sulphide.
Q3. A high biochemical oxygen demand (BOD) in a water sample indicates: (a) a high concentration of dissolved oxygen (b) a high level of organic pollution (c) the absence of microorganisms (d) a high concentration of heavy metals
→ (b) BOD measures the oxygen microbes need to decompose organic matter, so it rises with organic pollution.
Q4. NEREDA, used at a 60 MLD plant at Pahadi, Patna, is based on: (a) anaerobic sludge blankets (b) electrocoagulation (c) constructed wetlands (d) aerobic granular sludge
→ (d) It uses the same bacteria as activated sludge but grows them as dense granules that settle quickly, cutting tank size and power use.
Q5. Which of the following sewage treatment processes works without a supply of air? (a) Upflow Anaerobic Sludge Blanket (b) Sequential Batch Reactor (c) Activated Sludge Process (d) Moving Bed Biofilm Reactor
→ (a) UASB is anaerobic and produces biogas; the other three are aerobic processes.
Q6. Electrocoagulation-based plants were installed in Uttarakhand mainly because: (a) they need no electricity (b) they produce more biogas than other processes (c) they do not depend on microbes and so suit cold, hilly locations (d) they are the cheapest option for large cities
→ (c) Biological processes slow down in the cold; electrocoagulation uses an electric current and a metal anode instead.
Q7. Under the Hybrid Annuity Model adopted for sewage projects under Namami Gange: (a) the private operator bears the entire capital cost and recovers it through user charges (b) up to 40% of capital cost is paid during construction and the rest as performance-linked annuities (c) the State government funds the entire project upfront (d) the operator's payments are fixed regardless of plant performance
→ (b) The remaining 60% is paid as annuities over 15 years with O&M, both linked to the plant's performance.
Q8. Johkasou, used for decentralised sewage treatment in Uttarakhand, is a technology from: (a) Japan (b) the Netherlands (c) Germany (d) Israel
→ (a) It is a Japanese prefabricated, plug-and-play unit for treating domestic sewage where sewer networks are impractical.
Q9. The National Ganga Council, which oversees the rejuvenation of the Ganga, is chaired by the: (a) Union Minister of Jal Shakti (b) Union Minister of Environment (c) Chief Minister of Uttar Pradesh (d) Prime Minister
→ (d) The Council was constituted in 2016 and replaced the National Ganga River Basin Authority.
Q10. The Ganga was declared India's National River in: (a) 1986 (b) 2008 (c) 2011 (d) 2014
→ (b) It was declared the National River in 2008; the NGRBA followed in 2009 and NMCG was registered in 2011.
📋 How this gets asked (PYQ pattern)
Sewage treatment sits where the CDS paper's Biology and Environment sections overlap, and the questions follow two well-worn tracks.
The first is the NCERT process question. Which stage is biological; what flocs are; what activated sludge is and why part of it is recycled; which bacteria produce biogas and which gases they produce. These come straight from Microbes in Human Welfare and are set almost every few years in one form or another. The aerobic-versus-anaerobic distinction is the commonest trap — a statement that the sludge digester is aerobic, or that methanogens need oxygen, is false.
The second is the BOD question: what a high BOD means. The trap is to equate BOD with dissolved oxygen; they move in opposite directions, because the more organic matter there is, the more oxygen microbes consume.
The third, from the Environment side, is the institutional chain — the year of the Ganga Action Plan, the year the Ganga became the National River, who chairs the National Ganga Council. Pairs of years and a chairperson are easy to set and easy to confuse.
A fourth, rarer but now well supplied, is the technology-match question: UASB with anaerobic, NEREDA with granular sludge, Johkasou with Japan, electrocoagulation with cold climates.
For a written answer on river pollution, the proposition worth making is that India's earlier river plans built plants without ensuring they ran, and that the decisive reform was contractual rather than technical. Lay out the treatment stages, note that technology choice now follows the site, state the capacity gap honestly, and argue that performance-linked payment is what makes a sewage treatment plant clean a river rather than merely exist beside one.
Preparing for CDS/OTA? In Biology, the NCERT chapter on microbes in human welfare is a reliable source of questions — learn the treatment stages and the aerobic-anaerobic split cold. Start with our CDS/OTA study material, follow the daily CDS current affairs, and prepare with our faculty in the upcoming Cavalier courses in Delhi.
✍️ Written by Col D.N. Sharma — Science & general-studies faculty at The Cavalier. Reviewed by the Cavalier Faculty Desk.