The limits a treatment plant is actually designed to. General standards under the Environment (Protection) Rules, sewage treatment plant norms, and how to read them against your consent to operate.
Your consent to operate from the State Pollution Control Board is the legal document — it may impose limits tighter than the national standards below, and it decides which discharge mode applies. The tables here are the national general standards (Environment (Protection) Rules, Schedule VI) and the sewage treatment plant standards, presented the way a designer uses them: parameter, limit, discharge mode. All values in mg/L unless stated.
Standards are amended from time to time and some limits are under litigation or revision. Verify against the current gazette notification and your consent before finalising a design. KK Enviro Engineers can do this check for you as part of a proposal.
| Parameter | Inland surface water | Public sewer | Land for irrigation | Marine / coastal |
|---|---|---|---|---|
| pH | 5.5–9.0 | 5.5–9.0 | 5.5–9.0 | 5.5–9.0 |
| Suspended solids (TSS) | 100 | 600 | 200 | 100 |
| BOD (3 days, 27 °C) | 30 | 350 | 100 | 100 |
| COD | 250 | — | — | 250 |
| Oil & grease | 10 | 20 | 10 | 20 |
| Total dissolved solids (inorganic) | 2,100 | 2,100 | 2,100 | — |
| Ammoniacal nitrogen (as N) | 50 | 50 | — | 50 |
| Total Kjeldahl nitrogen (as N) | 100 | — | — | 100 |
| Free ammonia (as NH₃) | 5 | — | — | 5 |
| Phosphate (as P) | 5 | — | — | — |
| Chloride | 1,000 | 1,000 | 600 | — |
| Sulphate | 1,000 | 1,000 | 1,000 | — |
| Fluoride | 2 | 15 | — | 15 |
| Phenolic compounds | 1 | 5 | — | 5 |
| Sulphide (as S) | 2 | — | — | 5 |
| Cyanide (as CN) | 0.2 | 2 | 0.2 | 0.2 |
| Hexavalent chromium | 0.1 | 2 | — | 1 |
| Total chromium | 2 | 2 | — | 2 |
| Copper | 3 | 3 | — | 3 |
| Zinc | 5 | 15 | — | 15 |
| Nickel | 3 | 3 | — | 5 |
| Lead | 0.1 | 1 | — | 2 |
| Cadmium | 2 | 1 | — | 2 |
| Arsenic | 0.2 | 0.2 | 0.2 | 0.2 |
| Mercury | 0.01 | 0.01 | — | 0.01 |
| Temperature | ≤ 5 °C above receiving water | 45 °C at outlet | — | 45 °C at outlet |
| Colour and odour | see note | — | — | — |
Colour and odour: all efforts to remove colour and unpleasant odour as far as practicable. Bio-assay test: 90 % survival of fish after 96 h in 100 % effluent. Industry-specific standards (textile, pharma, tannery, distillery, refinery, dairy, etc.) override these where notified.
| Parameter | Metropolitan / state capitals (2017 notification, tightened for new STPs) | Other areas (2017 notification) | Older / general discharge norm |
|---|---|---|---|
| pH | 6.5–9.0 | 6.5–9.0 | 5.5–9.0 |
| BOD | 10 | 20 (30 elsewhere) | 30 |
| COD | 50 | — | — |
| TSS | 20 | 50 (100 elsewhere) | 100 |
| Total nitrogen (as N) | 10 | — | — |
| Ammoniacal N | 5 | — | 50 |
| Faecal coliform (MPN/100 mL) | < 100 (desirable), 230 (permissible) | < 1,000 | — |
The 2017 MoEF&CC notification set BOD 20 / TSS 50 for metros and 30 / 100 elsewhere; subsequent NGT directions (2019) require new and upgraded STPs to achieve BOD 10, COD 50, TSS 20, TN 10 and faecal coliform below 230 MPN/100 mL in most states. Reuse for flushing, gardening and construction generally requires the tighter set plus disinfection. Design new STPs to the tighter column unless your consent says otherwise.
| Use | Typical requirement |
|---|---|
| Toilet flushing, landscaping | BOD ≤ 10, TSS ≤ 10, turbidity ≤ 2 NTU, faecal coliform ≤ 100 MPN/100 mL, residual chlorine 0.5–1 mg/L |
| Cooling tower make-up | As above plus TDS/hardness within cooling programme limits; often UF + partial RO |
| Construction / dust suppression | BOD ≤ 30, TSS ≤ 30, disinfected |
| Industrial process reuse | Process-specific; usually UF + RO permeate (TDS < 100–300 mg/L) |
| Irrigation (treated sewage) | BOD ≤ 100 (land discharge standard); tighter where crops are eaten raw |
A plant is designed backwards from the limit that binds. For most industrial ETPs discharging to inland water, COD 250 and BOD 30 bind, with an industry-specific parameter (colour, ammonia, chromium, TDS) usually deciding an extra stage. For STPs, the tight BOD 10 / TSS 20 / TN 10 set forces nitrification–denitrification and tertiary filtration — which is why a modern STP is bigger than a 2010 one of the same capacity. Where TDS 2,100 binds and there is no CETP or sewer, ZLD follows. Run the calculators, or send your consent and inlet analysis and we will tell you which limit drives your plant.
Send your consent to operate and inlet analysis — we reply with the binding parameters and the treatment stages they require.