How Sewage Waste Water Treatment Works

Sewage waste water treatment is a critical process that ensures our water resources remain safe and usable.

Each day, vast amounts of water flow from our homes, businesses, and industries, carrying waste, chemicals, and other pollutants.

If untreated, this waste water would pose serious threats to our environment, affecting rivers, lakes, and oceans, and endangering human health by spreading diseases.

Waste water treatment facilities work to remove these harmful substances, returning clean water to natural sources or making it suitable for reuse.

This article explores how sewage waste water treatment works, why it’s necessary, and how innovative processes can even generate renewable power.

What is Sewage Waste Water?

Sewage waste water is the used water that leaves homes, businesses, and industries, carrying with it a range of contaminants.

Rainwater runoff can also contribute, bringing in dirt, oils from roads, pesticides, and other pollutants from the streets and landscape.

Sewage waste water is often categorised into two types: domestic waste water and industrial waste water.

Domestic waste water originates from homes and businesses, and primarily contains organic matter, bacteria, and nutrients.

When we shower, wash dishes, do laundry, or flush the toilet, this water, mixed with human waste, food scraps, soap, grease, and various chemicals, flows into the sewage system.

Industrial waste water, however, varies widely based on the industry and can contain specialised chemicals and toxins that require unique treatment methods.

Waste water from industrial activities may contain additional pollutants, including heavy metals, oils, or harmful chemicals, depending on the processes used.

How Sewage Waste Water Treatment Works

Sewage waste water treatment is a multi-step process that removes contaminants from waste water, making it safe to release back into the environment.

The treatment process can vary in complexity depending on the facility, but most systems follow four essential stages: screening, primary treatment, secondary treatment, and tertiary treatment.

Screening

Screening is the first step in sewage waste water treatment.

During screening, large objects are removed from the incoming waste water.

These objects can include plastic, wood, rags, and other debris that can damage equipment or block pipes.

Screening is typically done using metal bars or mesh screens, which capture solid materials as the waste water flows through.

The collected waste is then removed, dried, and sent to landfills.

Screening is crucial because it protects the treatment plant’s machinery and ensures smoother processing in later stages.

Primary Treatment

After screening, waste water enters the primary treatment stage, which involves sedimentation.

In large settling tanks, waste water is held to allow solids to settle at the bottom, forming a layer of sludge.

Meanwhile, lighter substances like oils and grease rise to the surface, where they are skimmed off.

Primary treatment removes around 50% of the solid waste and pollutants from the waste water, but it doesn’t eliminate dissolved organic matter or harmful bacteria.

After this stage, the partially cleaned water moves to secondary treatment.

Secondary Treatment

Secondary treatment is a biological process that removes dissolved and suspended organic matter.

In this stage, aeration tanks are used to introduce oxygen into the water, encouraging the growth of beneficial bacteria and other microorganisms.

These microbes break down organic waste, converting it into carbon dioxide, water, and more sludge.

Once this biological breakdown is complete, the water flows into another settling tank to allow the remaining sludge to settle.

This secondary sludge is either sent back to the beginning of the process for further treatment or removed for disposal.

Secondary treatment effectively reduces most of the organic pollutants and bacteria in the waste water.

Tertiary Treatment

Tertiary treatment is the final step, which aims to remove any remaining harmful substances, such as nutrients (nitrogen and phosphorus), pathogens, and residual chemicals.

Tertiary treatment methods include filtration through sand or carbon, chemical disinfection using chlorine, or ultraviolet (UV) radiation.

Each method has its advantages; for example, UV treatment kills pathogens without leaving chemical residues.

This stage ensures the treated water is safe to release back into rivers, lakes, or oceans.

Tertiary treatment is essential for meeting strict environmental standards and protecting ecosystems from nutrient overload and harmful pathogens.

Why is Sewage Waste Water Treatment Needed?

Sewage waste water treatment is essential for protecting public health, preserving natural resources, and maintaining environmental balance.

Bacteria

Untreated waste water contains harmful bacteria, viruses, chemicals, and toxins that pose serious health risks to humans and animals.

If released directly into rivers, lakes, or oceans, this polluted water can contaminate drinking water sources, spread diseases, and harm ecosystems.

Ecosystems

Sewage waste water carries nutrients, such as nitrogen and phosphorus, which can disrupt aquatic ecosystems.

When these nutrients enter water bodies, they encourage excessive algae growth.

This process, known as eutrophication, depletes oxygen levels in the water, suffocating fish and other aquatic organisms.

In severe cases, algae blooms can release toxins that are dangerous for wildlife and people.

Contaminants

By treating sewage waste water, facilities remove contaminants, pathogens, and nutrients, ensuring the water is safe for discharge or reuse.

This process conserves water resources, making it possible to reuse treated water for agriculture, landscaping, and industrial purposes.

Waste water treatment also supports sustainable urban growth by reducing pollution and helping communities manage their waste responsibly.

Using Sewage Waste Water Treatment to Generate Power

Sewage waste water treatment can generate power by capturing and utilising energy-rich by-products from the treatment process.

Two common methods for energy generation in waste water treatment plants are biogas production and sludge incineration.

Biogas Production

During secondary treatment, sewage sludge can be sent to anaerobic digesters.

In these digesters, bacteria break down organic matter in the sludge without oxygen, producing biogas, which is primarily methane.

Methane is a potent fuel that can be captured and burned to generate electricity or heat.

This energy can power treatment plant operations, reducing reliance on external power sources.

Many modern facilities even produce excess energy, contributing power back to the grid.

Sludge Incineration

Dried sludge from the treatment process can also be incinerated to generate power.

When dried sludge is burned, it generates heat, which can produce steam to drive turbines and generate electricity.

While effective, sludge incineration requires careful management of emissions to prevent air pollution.

What are the Alternatives to Traditional Sewage Waste Water Treatment?

Alternatives to traditional sewage waste water treatment offer options that are especially useful in small communities or areas with limited infrastructure.

These alternatives include constructed wetlands, membrane filtration, septic tanks and composting toilets.

Constructed Wetlands

Constructed wetlands are engineered ecosystems that mimic natural wetlands to treat sewage waste water.

They use soil, plants, and microorganisms to filter out pollutants.

Waste water flows through the wetland, where plants and bacteria break down contaminants over time.

Constructed wetlands are a low-cost, low-energy alternative ideal for small communities or rural areas.

They can effectively remove organic matter and nutrients but require significant land space and a longer treatment time compared to conventional methods.

However, they provide an eco-friendly, visually appealing solution that supports local wildlife and restores natural habitats.

Membrane Filtration

Membrane filtration is a high-tech approach to waste water treatment, relying on semi-permeable membranes to remove impurities.

Types of membrane filtration include microfiltration, ultrafiltration, and reverse osmosis, each capable of filtering out particles, bacteria, and even dissolved chemicals.

Membrane filtration can produce high-quality water, suitable for reuse in drinking or industry.

However, it is energy-intensive and expensive, making it best suited for places needing highly purified water, such as hospitals or high-tech industries.

Although not practical for large-scale municipal use, membrane filtration is an effective alternative in specialised applications.

Septic Tanks

Septic tanks are widely used in rural or suburban areas without access to centralised sewage systems.

In a septic tank, waste water is separated: solids settle to the bottom, forming sludge, while liquid effluent flows to a drain field for further natural filtration in the soil.

They require minimal maintenance but septic tanks need periodic emptying.

They’re a low-cost alternative to full sewage treatment plants, suitable for individual homes or small groups of buildings.

However, they can pose environmental risks if improperly maintained or overloaded, as untreated effluent can contaminate groundwater.

Composting Toilets

Composting toilets treat human waste at the source by turning it into compost without using water.

These toilets rely on aerobic bacteria to break down waste, producing compost that can eventually be used as fertiliser.

Composting toilets are ideal for areas with limited water resources, and they reduce the load on centralised sewage systems.

They require regular maintenance but are low-cost, environmentally friendly, and efficient in off-grid or remote locations.

By conserving water and recycling waste, composting toilets are a sustainable option for managing waste water on a smaller scale.

Conclusion

You should now have more of an understanding of sewage waste water treatment.

Sewage waste water treatment is vital for healthy communities and ecosystems.

It involves multiple steps to remove pollutants and protect the environment.

Treatment not only cleans water but also generates energy, supporting sustainable practices.

While alternatives exist, traditional treatment remains the primary method in most cities.

By treating sewage waste water, we contribute to a cleaner, safer world.

For more information, or help with any and all of your drainage needs, get in contact with us here at KD Drainage.