Ever wondered what happens to your toilet waste once it’s flushed away? It’s a question that often goes unnoticed, yet the answer lies at the heart of the UK's water infrastructure. This essential process first and foremost protects public health, and once treated is discharged safely back into our environment.
The water industry has been treating wastewater for centuries and sometimes doesn't always get it right as we have recently seen in the media. But since privatisation two-thirds of beaches are now classed as excellent, compared with less than a third 25 years ago, and wildlife has returned to rivers biologically dead since the industrial revolution.
Let’s go through how toilet waste is handled, from the moment you flush to when it’s returned to the environment.
The Sewer System
The backbone of the UK's waste management system is its extensive sewer network. Beneath the roads and pavements, a complex maze of pipes collects wastewater from homes, businesses, and industries, channelling it to wastewater treatment works for processing. This underground network is divided into three types:
Foul Sewers As the name suggests, carry only foul wastewater from the toilets, sinks, and baths of customer houses and from industrial effluent directly to wastewater treatment works. The pipes are designed and sized depending on the number of properties and businesses connected to the system.
Surface Water Sewers: Rainwater from roofs, driveways and roads is diverted to surface water sewers where it is transported without any treatment and discharged directly into our rivers. Any contamination from road runoff such as salts, diesel, and other fluids poured down highway drains will also directly enter rivers and can cause serious pollution. Here misconnection is a serious issue where toilets and washing machine outlets are connected to the wrong pipe.
Combined Sewers: These combined sewers collect both wastewater and rainwater. They were designed and installed at the turn of the last century and were especially popular and effective in removing waste from our cities. During heavy rainfall, water from our toilet enters the combined sewer as well as a lot of rainwater. This means the combined sewer pipe fills up and needs a quick release to reduce the pressure and its contents resulting in an overflow into the nearest river.
Combined sewer overflows (CSOs) are a feature that during heavy rainfall allow excess water, mixed with untreated sewage, to flow into rivers or seas, and are used as a protection system to prevent the backing up and causing sewage flooding into our houses. More recently, however, with significant population growth and an increased built environment including hard impermeable surfaces on driveways during moderate rainfall, the system can become overwhelmed. This can cause more frequent discharges into our rivers and seas through CSOs.
Collection and Transportation
When you flush, your toilet waste is transported through your home’s plumbing into the sewer system. The flow of wastewater typically moves downhill through gravity. In flatter areas or where wastewater needs to travel uphill, pumps are used to push it towards the wastewater treatment works. It’s a fascinating logistics process, ensuring that millions of litres of waste is constantly on the move.
Wastewater Treatment: How It’s Done
Once the wastewater reaches a wastewater treatment works, it is processed. While different wastewater treatment works may vary slightly in their methods, the generic processes are similar:
Screening: The first step involves removing large debris and grit —anything from sanitary items, plastics, to rags, wipes and even false teeth and mobile phones! Grit can seriously damage machinery such as impellors inside pumps or disrupt the treatment process if not filtered out.
Primary Sedimentation: Wastewater then flows into settling tanks, where solids sink to the bottom and fats oils and greases (collectively known as FOG) floats to the top. This phase removes a substantial amount of organic material and other suspended particles.
Secondary Treatment: Here, wonderful aerobic (oxygen loving) bacteria break down the organic matter in the wastewater. The microorganisms are very effective, quickly breaking down the contents and digesting pollutants, making the water safer for release into rivers or seas.
Tertiary Treatment: Finally, to ‘polish’ the effluent before its discharge and to ensure it is within regulatory limits, additional treatment can be included. For removal of compounds and chemicals such as phosphates, heavy metals and nitrates, natural-based solutions (NBS) such as reed beds and constructed wetlands can be used. These are a natural way to remove challenging chemicals to acceptable levels before the effluent is released back into the environment.
Sludge Management
But what happens to the solids, or sludge, that are filtered out of wastewater? In the UK, sludge isn’t wasted. Instead, it’s treated and repurposed. Through processes such as advanced anaerobic digestion, the sludge can be converted into biogas, which is a renewable energy source. The treated sludge can then be used as a fertiliser in agriculture, meeting strict environmental standards to be used on land to grow crops.
Environmental Impact
The importance of effective wastewater treatment can’t be overstated. If left untreated, wastewater would pollute our rivers, lakes, and coastal waters, threatening wildlife and causing significant public health issues. By treating wastewater, we protect both human communities and ecosystems, ensuring that our waterways remain vibrant and safe.
What’s Next for Wastewater Treatment?
One growing trend in the UK is the recycling of treated wastewater, known as recycled water or grey water. This approach offers a sustainable solution to the growing demands on water resources, especially in regions prone to shortages. While it’s not used for drinking, recycled water is highly useful for various non-potable purposes, such as:
Irrigation: Reclaimed water helps maintain parks, fields, and gardens, reducing the strain on treated drinking water supplies.
Toilet Flushing: Large institutions and commercial buildings can use recycled water for flushing, a substantial water-saving measure. The O2 arena implemented a recycling scheme and was a major opportunity for the UK water industry to showcase sustainable water management into the 21st century. In total, 692 WCs and 220 urinals were served with reclaimed water, with 277 wash-hand basins providing greywater.
Industrial Use: Some industries rely on massive amounts of water. Reusing treated wastewater in processes like cooling systems helps conserve drinking water for essential uses.
Wastewater management is continuously evolving. One of the exciting trends is the development of decentralised systems—smaller, localised treatment plants that sit closer to the source of the wastewater. These systems can potentially reduce transportation costs and energy usage, making wastewater management more efficient.
Additionally, the UK is investing heavily in infrastructure like the Thames Tideway Tunnel, a massive project designed to intercept sewage overflows before they can reach the River Thames. The tunnel will play a significant role in improving water quality across London.
Conclusion
Flushing a toilet is more than just a flush-and-forget operation. It’s a complex process involving intricate well-established infrastructure, technology, and innovation to ensure our environment is protected. From the expansive sewer networks to modern wastewater treatment facilities, each step plays a vital role in safeguarding public health and reducing environmental impact.
With the advent of new technologies, investment and sustainability efforts, such as reclaimed water systems and decentralised treatment, the future of wastewater management will continue to improve.
Projects like the Thames Tideway Tunnel represent the UK's commitment to protecting water resources, improving efficiency, and ensuring the well-being of both people and the planet. So next time you flush, you can appreciate the incredible work happening beneath your feet.
Want to learn more about wastewater management and other water-related topics? Join us for our upcoming Introduction to the UK Water Industry course, taking place on 20 – 23 January 2025. Visit our website for details and to secure your spot!
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