Water Treatment
STP for Housing Societies in Maharashtra: Complete Guide
STP guide for housing societies: why it is required, how to size it in KLD, MBBR vs SBR vs MBR, treated water reuse, running costs and common problems.
4 min read Aaradhya Enviro technical team
Quick answer
A housing society STP is sized from population × about 135 litres per person per day, with roughly 80% returning as sewage — a 200-flat society typically needs about 110–120 KLD. MBBR, SBR and MBR are common technologies. The plant must run 24 hours a day with logbooks and periodic testing.
Most large residential projects in Maharashtra are built with a Sewage Treatment Plant (STP) in the basement or a corner of the plot. Many housing societies discover only after handover that they now own a small treatment plant, with legal obligations, running costs and a committee that is expected to manage it. This guide explains what a society STP is, how it should be sized, which technology suits which project, and how to keep it running without problems.
1. Why your society has an STP
Large housing projects usually receive their approvals on the condition that sewage is treated on site and the treated water is reused. Depending on the project size and location, these conditions come from the project's Environmental Clearance, its MPCB consent and local planning rules. When the builder hands over the project, responsibility for operating the STP, and for the consent conditions attached to it, generally passes to the society.
2. How an STP should be sized
STP capacity is expressed in KLD (kilolitres per day). The basic calculation is simple:
- Population: number of flats × average occupancy (often taken as 5 persons per flat).
- Water demand: population × per-capita demand. 135 litres per person per day is the commonly used design figure for urban residential use.
- Sewage generation: roughly 80% of the water supplied returns as sewage.
- Design margin: a reasonable allowance for peak flows and future occupancy.
| Example | Calculation | Result |
|---|---|---|
| Flats | 200 flats × 5 persons | 1,000 persons |
| Water demand | 1,000 × 135 L/day | 135 KLD |
| Sewage generated | 135 × 80% | about 108 KLD |
| Design capacity | with peak allowance | about 120 KLD |
An undersized plant overflows and smells; an oversized one is hard to keep biologically stable at low occupancy. Sizing should reflect real occupancy, which is why many societies with partly occupied buildings struggle in the first few years.
3. Which technology: MBBR, SBR or MBR?
| MBBR | SBR | MBR | |
|---|---|---|---|
| Footprint | Compact | Compact | Most compact |
| Handles varying flows | Good | Very good | Good |
| Treated water quality | Good, suitable for gardening and flushing with tertiary filters | Good | Very high, best for reuse |
| Power and running cost | Moderate | Moderate | Higher (membranes, cleaning) |
| Operator skill needed | Moderate | Moderate (automation dependent) | Higher |
Whatever the core technology, a good society STP includes screening, an equalisation tank, the biological stage, a settling or separation stage, tertiary filtration (pressure sand and activated carbon filters), disinfection and sludge handling.
4. Reusing treated water
Properly treated STP water can be reused for toilet flushing, gardening, car washing and cooling. A dual plumbing line for flushing is often part of the project design. Reuse reduces the society's fresh water and tanker bills, which helps offset the cost of running the plant.
5. What it costs to run
The main running costs are electricity (blowers and pumps run continuously), operator salary or an O&M contract, chemicals for disinfection and filter backwash, periodic laboratory testing, spare parts and sludge disposal. The single biggest saving usually comes from efficient blowers and fine-bubble diffusers, which reduce aeration power.
6. The most common society STP problems
- Odour: usually caused by insufficient aeration, blower breakdown or the plant being switched off at night to save power.
- Foaming and floating sludge: often due to detergents, poor sludge wasting or an oversized plant at low occupancy.
- Turbid or smelly treated water: clogged filters, missing disinfection or a biological process that never stabilised.
- No records: without logbooks and test reports the society cannot show compliance if MPCB inspects or a resident complains.
7. A simple checklist for the committee
- Keep the consent and approvals on file and track their validity.
- Run the plant 24 hours a day; never switch off blowers to save power.
- Maintain daily logbooks: flow, running hours, power, chemicals and observations.
- Test treated water periodically through an accredited laboratory.
- Have a trained operator or a professional O&M contract.
- Plan an upgrade if the plant cannot meet norms or the society has grown.
For design, installation or a takeover audit of an existing plant, see our STP design and installation service.