Sewage Treatment Plants

Specialists in sewage treatment plant installation, maintenance & repair.


Independent Drainage specialises in sewage treatment plant installation, maintenance and repair.


As the leading off-mains drainage specialist in the south of England, we bring years of expertise in sewage treatment. As well as sewage treatment plant installation, maintenance and repair, we conduct drainage surveys for insurance claims and homebuyer surveys – to help homeowners get the cost of fixing their off-mains drainage system covered by their building insurance.


To prevent harmful runoff, solid waste buildup and odours, regular maintenance and servicing of your sewage treatment plant is essential. Our sewage treatment specialists will ensure that your sewage treatment plant is always in good working order, in full compliance with legislation.

Sewage Treatment Plant Diagram


Sewage Plant Treatment

Not every home or business has access to mains drainage for sewage, relying instead on a sewage treatment plant installed on the property. Sewage treatment plants process waste to a standard that can be discharged directly into a watercourse, drainage field or (with a permit) to a soakaway – causing no harm to the environment or to public health.


Sewage treatment plants have many advantages over alternative sewage processing systems: they can be used in areas where ground conditions are unsuitable to receive waste from a septic tank, in a high water table or in a groundwater protection zone. The discharge from a sewage treatment plant doesn’t need any further filtration and can be run off safely.


Unlike a septic tank, the outflow from a sewage treatment plant will not contaminate a drainage field with suspended solids or anaerobic bacteria – prolonging the life of a drainage field and the surrounding area.


As sewage treatment specialists, Independent Drainage helps residents and business owners to establish long-term sewage treatment solutions, with sewage treatment plant installation and ongoing servicing.



Our team of sewage treatment specialists works with all types of sewage treatment plants, and can install systems tailored to your situation. The following are some of the most common installations we come across and carry out.



Activated sludge process (ASP) systems use electricity to blow air into raw, unsettled sewage. This smashes the solids to develop a biological 'soup'. Aeration allows the naturally occurring bacteria in waste to digest any organic content, reducing the overall pollutant level. ASP sewage treatment plants don’t have a primary settlement chamber, which means less frequent emptying and fewer unwanted odours.


Once the sewage has been aerated for long enough, excess liquid is discharged into a clarification chamber, where live bacteria settle to the bottom. Dead bacteria rise to the top, leaving clean water in the middle – which can then be discharged safely into either a watercourse, drainage field or soakaway.



In a submerged aeration filter, a primary settlement chamber holds solid material. This is where anaerobic digestion by bacteria takes place. Clarified water then passes into a second chamber containing a submerged media – and here, the water is treated to remove dissolved constituents by aerobic bacteria, supported by diffused air. This process ensures that full treatment is achieved before the material flows to a final settlement chamber. The final, treated wastewater is discharged to the drainage field, watercourse or soakaway.


In a trickle filter sewage treatment plant, a primary settlement chamber holds solids where anaerobic digestion takes place. Clarified water is lifted through by the free passage of air through the filter media, and distributed evenly over the surface. Material is digested by aerobic bacteria before entering a third and final chamber. The final product is then safely discharged to the drainage field.



Sequencing batch reactors are a type of activated sludge process for the treatment of wastewater, which treat sewage in batches. The installation consists of multiple tanks, or a single, chambered tank with a flow through system. While one tank or chamber is in settling and decanting, the other is aerating and filling. Oxygen is passed through the wastewater to encourage anaerobic bacteria to consume the nutrients in the waste, which speeds up the sewage treatment process.

South of England Map
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