Domestic Sewage Treatment Plants: Your Questions Answered

Posted On: 15 June 2024

Domestic Sewage Treatment Plants: Your Questions Answered

Posted On: 15 June 2024

Understanding and managing domestic sewage treatment plants can be complicated. These systems, essential for treating wastewater from homes and small-scale commercial environments, are pivotal to maintaining ecology and sustainability.

Understanding their mechanics, regulations, and impact on both our homes and the broader ecosystem is crucial. This blog delves into the workings of a domestic sewage treatment plant, answering the most common questions you might have.

How Does a Domestic Sewage Treatment Plant Work?

A domestic sewage treatment plant treats wastewater from domestic settings or small-scale commercial settings. Here’s a brief overview of how they operate.

  • Primary Settlement Zone – Wastewater from the property feeds directly into the primary chamber of the treatment plant. Solid matter settles at the bottom of this tank and begins to biodegrade as part of the aerobic process. Effluent from the primary settlement zone then flows into the reactor zone.
  • Reactor Zone – A bubble air diffuser is positioned at the bottom of the reactor zone which ensures that the media is always moving freely. As the effluent passes over the media, it is purified by microorganisms growing on the surface. The circulation of the media and the liquids are made possible by a small air compressor and housing at ground level.
  • Final Settlement Zone – Finally, the treated effluent flows into the final settlement zone where very small levels of remaining solids settle to the bottom, after which the final effluent is suitable to discharge to a watercourse or drainage field.

While this gives you an insight into the workings of a domestic sewage treatment plant, the design of these plants may vary based on the product type, size and regulations including Part H of the Building Regulations, General Binding Rules and British Water Codes of Practice – Flows & Loads 4.

Where Does Domestic Waste Go After a Sewage Treatment Plant?

After being processed in a sewage treatment plant, human waste is separated into liquid and solid components, each with its own path of disposal, via a soakaway or drainage field. When the treated water is allowed to be discharged into a watercourse, the process typically involves the following steps:

Treated Effluent (Liquid Part)

The treated liquid, which has undergone primary, secondary, and sometimes tertiary treatment, is released into a river or stream. This discharge is regulated to ensure the effluent meets environmental standards laid out by the Environment Agency that protect aquatic life and preserve water quality.

The treated water is significantly cleaner than when it enters the plant, it is intended to integrate harmlessly with the natural water in the environment, contributing to the water cycle without adversely impacting the ecosystem.

Biosolids (Solid Part)

The solid waste, which is now converted into biosolids, is treated further to reduce pathogens and contaminants. These biosolids can then be used as fertiliser or soil conditioner in agricultural settings, given their nutrient-rich composition.

In cases where land application is not feasible or the biosolids are not suitable for agricultural use, they may be disposed of in landfills or incinerated. Incineration, particularly, reduces the volume of waste and can sometimes be used for energy recovery.

The goal of a sewage treatment plant process is to safely reintegrate human waste back into the environment, either by returning treated water to the natural water cycle or by municipal works or sewage treatment plant emptying services. The entire process is conducted under strict environmental guidelines to ensure that both the effluent and biosolids do not harm the ecosystem or public health.

What Are The Sewage Treatment Plant Regulations 2020?

As of January 1, 2020, regulations for private sewage treatment plants, including septic tanks, were implemented in the UK. These regulations apply mainly to systems that discharge wastewater directly into a watercourse and emphasise the need for systems to be properly maintained and not cause pollution.

Here’s an overview:

Upgrading Septic Tanks Systems

Existing septic tanks that discharge directly to surface water must be upgraded. This upgrade is essential to prevent environmental contamination and ensure compliance with current regulations.

This upgrade could involve connecting the property to mains sewers, installing a small sewage treatment plant where only treated sewage is discharged, or installing a drainage field.

Regulatory Compliance

All systems must comply with the ‘general binding rules’ set by the Environment Agency. Regular maintenance and emptying of the system is legally required every 12 months, in addition to;

  • Using a registered waste carrier for system maintenance.
  • Limits on the volume of treated sewage discharged (2000 litres per day into a drainage field or 5000 litres per day into flowing water).

Building Regulations for Sewage Treatment Plants

Any new installation or significant changes to existing systems require building regulations approval. Planning permission may also be necessary in some cases.

When selling a property with a private sewage system, it’s required to upgrade the system before completing the sale, and full details of the septic tank or sewage treatment plant must be provided to the buyer.

Sewage Treatment Plant Distance From House UK

These regulations emphasise environmental protection and the need for property owners to responsibly manage their private sewage systems. The location and siting of the plant are crucial, requiring adherence to guidance outlined in Part H of the Building Regulations, General Binding Rules, and British Water Codes of Practice – Flows & Loads 4.

For detailed guidance and specific inquiries, it is advisable to consult with professionals, such as Harlequin. For further assistance, please visit our contact page. Additionally, you can access a detailed presentation on the regulations here.

Does a Sewage Treatment Plant Need a Drainage Field?

Whether a sewage treatment plant requires a drainage field depends on the ground conditions and site restraint. In general, sewage treatment plants are designed to treat wastewater to a level where it can be safely discharged into the environment. This discharge can occur in different ways:

Discharge to Surface Water: Advanced sewage treatment plants can clean the wastewater to a level that allows it to be discharged directly into surface water (like a river or stream). In this case, a drainage field may not be necessary.

Discharge to Groundwater: If the treated effluent is to be discharged into the ground, such as in a garden or field, a drainage field or a soakaway is required. These installations must be designed in accordance with percolation tests to ensure proper filtration and avoid contamination. For a comprehensive understanding of the relevant regulations, visit our detailed presentation on septic tank regulations here.

The need for a drainage field also depends on the Environment Agency regulations. In the UK, for instance, the Environment Agency’s regulations determine the appropriate method of discharge based on factors like the volume of effluent, the sensitivity of the local environment, and the proximity to a water source.

How Much Electricity Does a Domestic Sewage Treatment Plants Use?

The electricity consumption of a domestic sewage treatment plant can vary depending on the type and size of the system. A typical sewage treatment plant, which runs continuously, consumes energy based on the size of the air blower used.

For instance, a system serving up to 6 people with a 50-watt blower consumes about 1.2 kWh per day, resulting in an annual consumption of 438 kWh, costing approximately £127.02 annually at an average 2024 UK electricity price of 29.0p/kWh. Systems for larger populations, such as up to 10, 15, or 20 people, will have higher consumption and costs due to larger blowers and higher energy use​​.

It’s important to note that these figures are estimates and actual costs can vary depending on specific circumstances such as the type of system installed, electricity prices, and the actual usage of the sewage treatment plant.

Domestic Sewage Treatment Plants

Domestic sewage treatment plants balance the demands of modern wastewater management needs with the responsibility to protect and manage the environment.

Their ability to efficiently process wastewater while adhering to stringent environmental regulations ensures that domestic wastewater is safely reintegrated into the ecosystem.

The detailed guidelines for their installation, operation, and maintenance underline a commitment to environmental safety and public health. By understanding the electricity requirements, regulatory compliance, and the importance of proper installation and maintenance, homeowners and property managers can make informed decisions that align with both environmental and practical needs.

Should you require further information, expert advice, or wish to discuss specific requirements for a domestic sewage treatment plant, please feel free to contact us.

Our team of specialists, with 100 years of experience, is on hand to provide you with the guidance and support you need to make informed decisions about your sewage treatment solutions.

Check out our case studies to find out more about sewage treatment plants: CAP 12 Installed at a Large Country Home | CAP6&9 back in action | Harlequin CAP9 perfectly replaces a failed septic tank.