Sewage Treatment Plant (STP Plant) – Working Process, Benefits, Cost & Installation Guide

A Sewage Treatment Plant (STP Plant) is an advanced wastewater treatment system designed to treat domestic and commercial sewage before discharge or reuse. With rising urbanization, water scarcity, and strict environmental norms from the Central Pollution Control Board, installing an STP plant has become mandatory for residential societies, commercial buildings, hotels, hospitals, and industries.

Today, businesses are actively searching for “STP plant cost,” “sewage treatment plant installation,” “commercial STP plant manufacturer,” “STP plant working process,” and “industrial wastewater treatment solutions.” This guide explains everything you need to know about sewage treatment plants, including process, technologies, benefits, and FAQs.

What is a Sewage Treatment Plant?

A sewage treatment plant is a system that removes contaminants such as organic waste, suspended solids, oil & grease, chemicals, and harmful microorganisms from wastewater. The treated water can be reused for:

Toilet flushing

Gardening and landscaping

Cooling towers

Industrial processes

Construction use

The main goal of an STP plant is to reduce:

BOD (Biochemical Oxygen Demand)

COD (Chemical Oxygen Demand)

TSS (Total Suspended Solids)

Pathogens and harmful bacteria

STP Plant Working Process

The STP plant working process is divided into three major stages:

1. Primary Treatment

Screening removes plastic, paper, and large solids

Grit chamber removes sand and heavy particles

Primary clarifier separates settleable solids

This stage removes physical impurities from sewage.

2. Secondary (Biological) Treatment

Aeration tank introduces oxygen

Microorganisms break down organic matter

Secondary clarifier separates sludge

This stage significantly reduces BOD and COD levels.

3. Tertiary Treatment

Pressure sand filter removes fine particles

Activated carbon filter removes odor and color

UV or chlorination for disinfection

Treated water now meets discharge norms set by pollution cont