STP Cost for a Factory: Capacity, Technology Choice and What Drives It

There is no honest per-factory price for an STP, because the cost follows five things: the daily sewage flow in KLD, the strength of the sewage, the quality you must reach, the technology and civil route you choose, and how long you must operate it. Fix those five, ask bidders to price civil, mechanical, electrical and operation separately, and the quotes become comparable.

Why a factory STP has no standard price

Two factories with the same headcount can need very different plants. One discharges to a municipal sewer and needs only a modest treatment train. The other must reuse the water for flushing and gardening, has a canteen that sends grease and high organic load into the sewage, and sits on a plot with a high water table. The first plant is a tank and a blower. The second is a plant, a tertiary filter, a reuse line and an operator.

We do not publish a rupee-per-KLD figure for STPs, and we would be wary of any page that does without asking about your site. What we can publish is the method and the questions that move the number. An STP also treats only domestic sewage. Process wastewater from the factory goes to an effluent treatment plant, which is designed from the process and not from headcount. Our guide on STP versus ETP for an industrial expansion explains where the line falls.

Step one: fix the flow

Capacity is the daily sewage flow the plant must handle, expressed in kilolitres per day. The usual route is headcount multiplied by a per-head water demand from the National Building Code, multiplied by the share of that water that returns to the sewer. Add the canteen separately, and add growth if the factory will expand. Where the factory already runs, use water-meter readings instead of a code value. A measured flow is always better than a calculated one.

Flow has two numbers, and both cost money. The daily volume sets the tank volume and the biological capacity. The hourly peak sets the sewers, the lifting pump, the screens and the equalisation tank. A factory with three shifts has a gentle peak. A factory where everyone eats in the same half hour has a sharp one. Our STP capacity calculator shows the daily mean and the peak separately and states what it assumes, and the guide to STP sizing mistakes lists where industrial plants go wrong.

Step two: fix the quality you must reach

The target is the biggest single lever, because every extra step of treatment adds a unit process. Discharge to a sewer, to a drain, to land and to reuse are four different targets. The consent from the State Pollution Control Board sets yours, and the board can ask for more than the national minimum.

At national level, the National Green Tribunal's order of 30 April 2019 in OA 1069/2018 set tighter limits for treated sewage. CPCB's compliance filings to the Tribunal assess plants against BOD below 10 mg/l and total suspended solids below 20 mg/l, with limits also on COD, nitrogen, phosphorus and faecal coliform. Sources differ on the exact faecal coliform figure and on how the order applies to older plants, so read the numbers in your own consent and not in a summary. A plant designed to an older, looser limit will not meet a 10 mg/l condition, and retrofitting a tertiary stage costs more than building it in. See the CTE and CTO consent guide for how the board looks at it.

Step three: choose the process, and price it as a package

Four process families cover most factory STPs. None has the lowest cost in every case. They trade capital, footprint, power and the skill needed to run them.

Vendors will tell you their own process is the right one, and trade sources disagree on energy use and flow tolerance, so we do not rank them here. Ask each bidder for the design basis (flow, peak factor, influent BOD and COD, target) and the power rating of the installed blowers and pumps. A quote that does not state its design basis cannot be compared with one that does.

Step four: count what sits outside the tank

The items that surprise budgets are rarely inside the treatment train.

• Civil work: RCC tanks, excavation in poor soil, dewatering where the water table is high, waterproofing. At larger capacities civil work is a large share of the job, so ask whether the quote includes it.
• Collection and lifting: sewers from every block, manholes, a sump and lifting pumps where the plant is uphill of the building.
• Reuse piping: a separate treated-water line to flushing, gardens or cooling make-up, with a storage tank. This can cost as much as part of the plant.
• Sludge handling: drying beds or a mechanical dewatering unit, and a disposal route.
• Power, controls and monitoring: the panel, a standby supply, flow meters, and any online monitoring the consent requires.
• Odour and landscape screening when the plant sits near a gate or office.
• Operation: operator, power, chemicals and spares. For a plant that runs for fifteen years, operation can outweigh the purchase price.

The MEPF cost calculator can place the STP inside the budget for the whole building, which is where it belongs. A water system is easiest to cost when the demand, the plumbing and the reuse lines are designed together, so ask the design team to share one water balance with every bidder.

How Secured Engineers helps

Plumbing and public health is one of the disciplines we design and build, together with the STP, water treatment and effluent plants described on our STP, WTP and ETP page. Design is done in-house, and Fire NOC, CEIG and DISCOM net-metering applications are filed in-house, so the STP's power supply, the pump room and the building services are coordinated by one team. Mechanical, electrical, plumbing, fire and solar work can sit under one contract. We work from offices in Noida (Delhi NCR) and Ludhiana, with 535+ projects across 18+ states and 89.77% repeat clients.

If you already hold an STP quotation or a budget, send it. We will check the design basis, the scope split and the missing items, and tell you what to ask each bidder. Start from our plumbing and public health service, message us on WhatsApp, call +91 70099 85817, or ask for a free proposal with your drawings.