How Does A Sewage System Work: Sewer System & Septic System

Sewage systems, also known as sewer systems or wastewater systems, are essential for transporting the wastewater from homes, businesses, and industries to treatment plants. These intricate systems work 24/7 to remove contaminants and make the wastewater safe before releasing it back into the environment. From the toilet to the treatment plant, sewage undergoes an elaborate process to protect water sources and public health.

In this blog post, we will walk through how different types of sewage systems work, from small septic systems to complex urban wastewater treatment plants. We will look at what happens during each step of wastewater treatment and how the various components fit together to form a functioning whole. Understanding what goes on behind the scenes can help us appreciate these often overlooked infrastructure systems.

How Does A Septic System Work?

Many homes and businesses, especially in rural areas, use decentralized septic systems to treat wastewater onsite. Septic systems provide a low-cost, low-maintenance option where municipal sewer systems are not available. But how do they turn household wastewater into harmless effluent?

A septic system has four main components:

  • Septic Tank: This watertight container collects all wastewater from the home, including from sinks, showers, washing machines, and most importantly, toilets. Inside the tank, heavier solids settle to the bottom to form a sludge layer, while lighter fats and oils float to the top as scum.
  • Distribution Box: This box divides the liquid effluent flowing out of the septic tank and distributes it evenly into the leach field.
  • Drainfield/Leach Field: Perforated pipes buried in gravel-filled trenches disperse the effluent from the distribution box into the surrounding soil. As the wastewater percolates down through the soil, further treatment occurs.
  • Soil: The soil provides final filtration and treatment as natural physical, biological, and chemical processes remove pathogens, nutrients, and other contaminants. Ultimately, the water is absorbed into the deeper groundwater.

Here is a simplified step-by-step overview of how a typical septic system works:

  1. All wastewater from the home flows into the septic tank. Here solids settle out as sludge, while fats and oils float to the top as scum.
  2. The liquid effluent in the middle layer flows out of the tank into the distribution box.
  3. The distribution box divides and spreads the effluent evenly into a network of perforated pipes that make up the leach field.
  4. The wastewater trickles out of the pipes and percolates down through layers of soil and gravel.
  5. As the effluent filters through the soil, remaining impurities are removed and disease-causing pathogens are destroyed.
  6. Finally, the water is absorbed into the deeper groundwater to replenish the local water table.

With proper design, installation, and maintenance, septic systems offer an effective, environmentally-friendly, small-scale option for treating household wastewater. The combined treatment processes eliminate bacteria and contaminants, and allow the safe return of water to the environment.

How Urban Sewer Systems Work

In urban areas, homes and buildings are usually connected to a municipal sewage system that transports wastewater long distances to a centralized treatment plant. Compared to individual septic systems, these public sewer systems have larger-scale, more advanced treatment methods to handle huge volumes from entire cities.

While sewer system configurations vary based on geography, some common components are:

  • Sewer Main: The main underground pipe collects wastewater from smaller lateral pipes running under streets. Manholes provide periodic access to the main sewer for inspections and maintenance.
  • Lift Stations: Since sewage flows downhill by gravity, pump stations are placed where needed to pump it over hills.
  • Treatment Plant: giant facilities clean and remove contaminants from the wastewater at industrial scales before discharging into water bodies.

Here are the key steps in how municipal wastewater systems work:

  1. After using the toilet, shower, or sink, the wastewater flows out of homes/buildings into lateral sewer pipes running beneath streets.
  2. The smaller lateral pipes connect with larger underground main sewer lines.
  3. The sewage flows downhill by gravity through this network, passing through access manhole covers when needed.
  4. At low points where gravity alone cannot move the wastewater, lift stations pump it to higher elevations.
  5. The main sewers carry all the sewage from the urban area to the wastewater treatment plant.
  6. Here the wastewater undergoes primary treatment to filter out solids, secondary treatment by microbes to remove organics, and sometimes additional advanced treatment and disinfection.
  7. After treatment and testing, the cleaned effluent is discharged to a local body of water under strict regulations.

Modern municipal sewage systems are engineering marvels that use smart pipe networks and treatment technology to eliminate pollution and protect community health. Keeping these intricate systems running requires ongoing maintenance and upgrades as cities grow.

How Do Treatment Plants Clean Wastewater: Urban Wastewater Systems

The end goal of both septic tanks and municipal sewers is to pipe all the wastewater to a treatment plant for intensive cleaning. But what goes on inside these facilities to transform raw sewage into crystal clear effluent?

In general, plants use a multi-stage treatment process to remove solids, dissolve organics, kill pathogens, and extract excess nutrients. The cleaned water can then be safely discharged back to environmental waters or reused.

Here is an overview of the key phases:

Primary Treatment

  • Solids and grit are physically filtered out by screens and gravity settling tanks. This removes about 25-50% of solids and organics.

Secondary Treatment

  • Remaining organics are digested by oxygenation and microbial action, removing up to 90% of impurities. Common methods are trickling filters and activated sludge tanks.

Tertiary Treatment

  • Advanced technologies like filters, chlorine, UV, ozone or membrane filtration further polish the effluent to meet strict discharge limits.

Throughout the process, the removed screenings, grit and sludge undergo separate treatment to render them safe for disposal or reuse. Some is further processed into products like fertilizer.

Sophisticated instrumentation also carefully monitors flow rates, storage tanks levels and water chemistry to optimize the purification process.

When functioning properly, the successive stages act as a complex treatment train that thoroughly cleans the wastewater before releasing it back to replenish water bodies. Modern plants are fine-tuned to remove specific pollutants affecting the local watershed.

Upgrading aging infrastructure and adapting to new water quality challenges are constant goals. More cities are also building water reuse capabilities to protect ecosystems from drought and overuse.

How Can Sewage Systems Fail?

Sewage systems are amazing engineering feats central to public health, but age, accidents and disasters can still cause severe failures. Some common issues include:

  • Pipe blockages and leaks due to tree roots, grease buildup and ground shifts.
  • Rust and cracks degrading concrete tanks and steel pipes over decades.
  • Heavy rainfall and flooding overwhelming system capacity.
  • Power outages knocking out pumping stations and treatment plants.
  • Toxic industrial discharges killing microbial treatment cultures.
  • Earthquakes breaking pipes, tanks, and vital system components.

When parts of the sewage network break down, overflows of raw, untreated sewage can occur. These unfortunate releases pose major health hazards and ecosystem damage if not contained quickly.

Cities work hard to prevent these incidents through staff training, emergency plans, infrastructure upgrades and proactive maintenance. But as climate change fuels more extreme weather, keeping sewage from spilling into streets and waterways is an increasing challenge.

Investing to expand system capacity and improve component resilience is crucial. New smart sensors and remote operation technology also help operators detect issues faster when they arise.

Staying on top of sewage infrastructure saves cities from literal drowning in wastewater.

The Future of Sewage Treatment

While the basics of collecting wastewater for centralized treatment have remained similar for decades, innovation is now taking sewage systems into the future.

  • Cities are decentralizing systems with smaller localized plants to reuse water locally while reducing pumping costs.
  • Improved filtration methods allow effluent recycling for irrigation, industry and even drinking water augmentation.
  • Intelligent sensors monitor system health in real time, enabling faster leak detection and preventive maintenance.
  • New membranes, nutrient recovery reactors and disinfection processes target emerging contaminants of concern.
  • Treatment byproducts like biosolids and biogas are becoming renewable energy sources.
  • Computer-optimized treatment combinations and operational settings save chemical, energy, staff and infrastructure expenses.

Sewage systems are also vital players in the global challenges of water scarcity, nutrient pollution, urban resilience, and climate change adaptation.

As population growth further strains aging infrastructure, optimizing treatment plants and pipes with technology-rich upgrades provides sustainability and public health wins. Exciting innovations lie ahead to keep these critical systems functioning into the next century.


In conclusion, a sewage system is a vital component of urban infrastructure, responsible for managing and treating wastewater to protect public health and the environment. By understanding the main entities and terms related to sewage systems, you now have a comprehensive overview of how this essential system works. The next time you flush your toilet or take a shower, you’ll have a deeper appreciation for the complex yet effective process that ensures our communities stay clean and healthy.

For septic tank pumping and sewage cleanup around Atlanta Georgia, contact Southeast Water Restoration!