CPCB STP Outlet Parameters — Discharge & Reuse Standards Explained

Search teams and consent officers often ask for STP outlet parameters as per CPCB — the treated effluent limits your sewage treatment plant must meet before discharge to surface water, sewer, or reuse. This guide summarises commonly cited CPCB general standards, explains how state boards (e.g. MPCB) can tighten limits, and what to design into tertiary treatment when reuse is planned.

This is an engineering primer, not legal advice. Your CTO/CTE text always overrides blog summaries.

CPCB general standards for STP discharge (reference table)

Design to your consent first. The table below reflects widely referenced general parameters for treated sewage discharged to surface water — verify against current CPCB notifications and your project CTO.

Parameter	Typical general limit (surface discharge framing)
BOD₅	≤ 30 mg/L
COD	≤ 250 mg/L
Total suspended solids (TSS)	≤ 100 mg/L
pH	6.0 – 9.0
Total nitrogen (as N)	≤ 100 mg/L
Total phosphorus	≤ 5 mg/L
Fecal coliform	≤ 1,000 MPN/100 mL (tighter for reuse)
Oil & grease	≤ 10 mg/L

Reuse pathways (flushing, landscaping, cooling makeup) frequently require lower BOD/TSS and stricter coliform than secondary treatment alone achieves — budget filtration, disinfection, and monitoring accordingly.

STP outlet parameters vs reuse classes

Indian projects increasingly treat sewage for non-potable reuse. That shifts outlet parameters from “secondary effluent that looks clear” to documented quality bands with dual plumbing and signage. Read treated sewage reuse standards alongside this article.

• Landscape irrigation: often needs lower TSS and reliable disinfection.
• Flushing: coliform control and cross-connection prevention dominate audits.
• Cooling towers: adds TDS/hardness cycling concerns beyond STP biology.

Maharashtra and MPCB — layering on CPCB

MPCB consent may specify project-specific limits, sampling frequency, and reuse conditions. For Maharashtra-focused consent workflows, see STP norms in Maharashtra — CPCB & MPCB 2026. For a national compliance overview, see government norms & STP compliance in India.

Designing your STP train to hit outlet parameters

1. Pre-treatment: screening, equalization, grease control for kitchens.
2. Secondary biology: MBBR, SBR, or MBR — match automation to your O&M team.
3. Clarification / solids separation: often where TSS failures start if sludge is not wasted properly.
4. Tertiary polishing: filtration when reuse or tight TSS is required.
5. Disinfection: UV or chlorination with residual control where specified.

Sampling and proof — what auditors expect

Outlet parameters are meaningless without credible sampling: fixed points, chain-of-custody, trend logs, and calibration records for online instruments. One lucky lab report does not substitute for a monitoring programme. Sludge disposal documentation is part of the same compliance story.

Next steps

• Attach draft consent limits to your tender — not paraphrased summaries.
• Size hydraulics with our KLD calculation guide.
• Request engineering review on contact with your CTO excerpt.