What are the Principles of Sewage Treatment Plants

Overview

• Sewage treatment plants transform raw wastewater through gravity separation, biological decomposition, aeration, and flocculation to remove solids and pollutants effectively.
• The process advances via preliminary screening, primary settling, secondary microbial breakdown, tertiary polishing, and sludge management for safe effluent.
• CWS Philippines Inc. delivers expert system design, installation, optimization, and training to ensure compliant, efficient operations for industrial facilities.

Sewage treatment adheres to a straightforward, step-by-step procedure that eliminates solids, breaks down pollutants, and equips water for safe disposal or reuse. By understanding these common phases, industrial facilities can clearly see how raw wastewater becomes clean, compliant effluent.

In this guide, we explore the principles of sewage treatment plants from the contractor in the Philippines, so you can visualize what happens inside an STP, even without a technical background.

Core Concepts of Sewage Treatment Plants

Before diving into specific processes, it helps to understand the core concepts that guide every sewage treatment plant. These principles explain how wastewater is cleaned, stabilized, and made safe for discharge or reuse.

Gravity Separation

In this process, wastewater is held in a tank or basin where heavier solids naturally settle to the bottom, forming sludge, while lighter materials like oils, grease, and floating debris rise to the surface. This allows for the easy removal of both types of solids before the water moves on to more advanced treatment stages.

By relying on gravity, facilities can efficiently separate large contaminants without complex equipment, forming the foundation for subsequent biological and chemical treatment processes.

Biological Decomposition

It’s where naturally occurring microorganisms, like bacteria, break down organic matter in wastewater. These microbes consume pollutants as their food, converting harmful compounds into simpler, harmless substances such as carbon dioxide, water, and stabilized sludge.

This principle is the heart of most sewage treatment systems, as it efficiently reduces organic load and prepares the water for further polishing or discharge, all while relying on natural biological activity rather than chemicals.

Aeration

The oxygen is introduced into wastewater to support the microorganisms that break down organic matter. By supplying oxygen, aeration ensures that bacteria remain active and healthy, allowing them to efficiently decompose pollutants.

This principle not only accelerates biological decomposition but also helps prevent odors and maintains a stable, effective treatment process throughout the sewage treatment plant.

Flocculation or Coagulation

During coagulation, chemicals (called coagulants) are added to neutralize charges on particles, allowing them to stick together. Flocculation then gently stirs the water so these particles form larger clumps, or “flocs,” which can easily settle out or be filtered.

Together, these processes improve water clarity and prepare it for further treatment stages, making wastewater safer for discharge or reuse.

Stages of Treatment

Sewage treatment plants clean wastewater through a series of well-made stages, each targeting specific types of pollutants. Understanding these stages helps industrial facilities see how raw wastewater is transformed step by step into clean, safe water ready for discharge or reuse.

Preliminary Treatment (Physical)

This involves screening out items like plastics, rags, and leaves, as well as using grit chambers to settle heavy particles like sand and gravel.

By removing these materials early, this stage prevents damage or clogging in downstream equipment and prepares the water for more advanced biological and chemical treatment processes. It’s essentially the first “cleaning filter” that protects the entire system.

Primary Treatment (Physical and Chemical)

In this stage, wastewater is held in large tanks where heavier solids settle to the bottom as sludge, and lighter substances like grease and oils rise to the surface for removal.

Sometimes, chemicals are added to help small particles clump together, making them easier to separate. This stage significantly reduces the pollutant load and prepares the water for the biological treatment that follows.

Secondary Treatment (Biological)

Microorganisms, such as bacteria, consume the dissolved and suspended organic matter, converting it into stable substances like carbon dioxide, water, and sludge. This stage often involves aeration tanks or biofilm systems, where oxygen and controlled conditions help microbes work efficiently.

Secondary treatment is crucial for reducing the biological load and ensuring the water meets environmental discharge standards before further polishing or reuse.

Tertiary/Advanced Treatment (Polishing)

As the final “polishing” phase, this involves fine filtration, chemical treatment, nutrient removal (like nitrogen and phosphorus), and disinfection using chlorine or UV light. The goal is to produce water that is safe for discharge into the environment or for reuse within the facility.

This stage ensures that the treated water meets the highest quality standards and protects both the environment and public health.

Sludge Treatment

Here, thickening, stabilizing, and dewatering the sludge occur to reduce its volume and make it safer to handle or dispose of. Some facilities also use digestion processes, where microorganisms break down organic solids, producing stabilized sludge and sometimes biogas for energy.

Proper sludge treatment is essential for maintaining overall system efficiency and ensuring environmentally safe disposal or reuse.

CWS Philippines Inc.: Your Partner in Sewage Treatment Solutions

When it comes to understanding and implementing effective sewage treatment systems, CWS Philippines Inc. stands out with decades of proven experience and industry expertise. With over 20 years of serving industrial and commercial facilities, we combine technical excellence with practical solutions designed to meet your wastewater treatment needs at every stage.

We deliver comprehensive STP services that cover the full lifecycle of your sewage treatment system:

• System Design and Engineering: Customized STP layouts based on your facility’s wastewater volume, characteristics, and regulatory requirements.
• Equipment Supply and Installation: High-quality components, from screening and grit removal units to aeration systems, clarifiers, filters, and disinfection modules.
• Process Optimization: Fine-tuning your system for efficient biological treatment, oxygen management, and stable performance to achieve DENR effluent standards.
• Automation and Monitoring: Integration of control systems (SCADA/PLC) and sensors for real-time process visibility, better reliability, and reduced manual intervention.
• Maintenance, Troubleshooting, and Repairs: Preventive servicing, quick diagnostics, and responsive support to keep your STP operating smoothly with minimal downtime.
• Operator Training: Practical training sessions that empower your in-house team to confidently manage and monitor your treatment system.

Key Takeaway

Understanding the principles of sewage treatment plants is the first step for any industrial or manufacturing facility looking to manage wastewater effectively. By grasping concepts like gravity separation, biological decomposition, aeration, flocculation, and the different treatment stages, facility managers can better appreciate how wastewater is transformed into discharge-ready water.

For over 20 years, CWS Philippines Inc. has been helping facilities implement reliable and efficient STP solutions. Reach out to us today to learn how we can help your facility achieve effective and sustainable wastewater management.