According to DEFRA (Department for Environment, Food and Rural Affairs) there are approximately 330,000 kilometres of public sewers in England and Wales in 2020 and this is the most common way to deal with sewage and wastewater. However, many rural locations do not have access to the mains and require another system to manage their waste which is the responsibility for all building owners. It is becoming increasingly common with new builds on green sites to install a treatment plant or septic tank. Although they are more frequently used, we regularly see the wrong terminology used for different management system and people can be confused with what they are called and how they work. So, we have decided to provide a breakdown to simplify and understand each approach/ system.

Main Sewers

Mains sewers are an underground network of pipes that are designed to carry wastewater from homes, businesses, and other buildings to sewage treatment plants. The wastewater that enters the sewer system can come from a variety of sources, including toilets, sinks, showers, and washing machines.

The wastewater travels through the pipes by gravity, and as it moves, it combines with other wastewater from other buildings. The pipes that make up the sewer system are typically made of durable materials such as concrete or PVC plastic, and they are designed to withstand the weight of the wastewater and any other debris that may be present.

As the wastewater travels through the pipes, it is carried to a sewage treatment plant, where it undergoes a series of processes to remove contaminants and other harmful substances. These processes may include physical, biological, and chemical treatment methods, such as sedimentation, filtration, and disinfection.

Once the wastewater has been treated, it is typically released into nearby bodies of water, such as rivers or oceans, where it can be safely diluted and dispersed. In some cases, the treated wastewater may be reused for certain purposes, such as agricultural irrigation or industrial cooling.

Pro’s

  • Easy to connect to
  • A monthly/ annual fee paid to the Wastewater Management company for maintenance and service

Con’s

  • Not available throughout the country
  • System is old and will often take rainwater which risks overflooding and untreated water releasing in the sea

Cesspits

A cesspit is an underground tank that is designed to hold untreated sewage and wastewater.

Cesspits are usually made of concrete, brick, or plastic, and they are designed to be watertight to prevent leakage of sewage and other contaminants into the surrounding soil and groundwater. The size of the cesspit will depend on the number of people using it and the amount of wastewater that is generated.

Wastewater from toilets, sinks, and other sources is collected in the cesspit and stored until it is full. At this point, a licensed waste contractor must be called to empty the cesspit and transport the sewage to a treatment plant for proper disposal or treatment.

Cesspits require regular maintenance and cleaning to prevent overflowing and to ensure that they are functioning properly. If a cesspit is not properly maintained, it can lead to unpleasant odours, health hazards, and environmental pollution.

Overall, cesspits are a basic and temporary solution for managing sewage and wastewater in areas without access to a mains sewer. However, they are less convenient and more expensive to maintain, and they pose a greater risk to public health and the environment if they are not properly maintained.

Pro’s

  • Solution for when mains connection, or septic tank or treatment plant are not allowed
  • Suitable for contaminated waste

Con’s

  • Very expensive to maintain and need to be regularly emptied
  • If not maintained and tank is damaged can be a huge environmental risk

Septic Tanks

A septic tank is a type of underground tank that is used to treat and dispose of household wastewater in areas where a connection to a mains sewer is not available or practical, such as in rural areas.

Septic tanks are typically made of concrete, fiberglass, or plastic, and they are designed to hold untreated wastewater and allow it to separate into three layers. The top layer is a layer of scum that consists of oils, grease, and other floating substances. The middle layer is a layer of clarified wastewater, which is also known as effluent. The bottom layer is a layer of sludge that consists of heavy solids and other materials that settle to the bottom of the tank.

As wastewater enters the septic tank, it undergoes a natural process of decomposition by bacteria that are naturally present in the wastewater. The bacteria break down and digest the organic materials in the wastewater, producing a layer of sludge at the bottom of the tank and releasing gases such as methane into the air.

The effluent layer in the septic tank is then discharged into a drain field or leach field, which is a network of perforated pipes or chambers that allow the effluent to slowly percolate into the surrounding soil. The soil acts as a natural filter, removing harmful bacteria and other contaminants from the effluent before it is returned to the groundwater.

Septic tanks require regular maintenance and pumping to remove the accumulated sludge layer and prevent overflow. If a septic tank is not properly maintained, it can lead to unpleasant odours, health hazards, and environmental pollution.

Pro’s

  • Great solution for sites without mains

Con’s

  • Limits what can go into wastewater as bleach and other household items can kill off the required bacteria which breakdowns the matter.
  • Cannot be installed in a flood risk zone
  • Requires highly permeable ground for the drainage field
  • Only removes 30% of pollutants

Sewage Treatment Plants

Sewage treatment plants are designed to treat and dispose of wastewater from individual households. The system typically consists of several components, including a septic tank, a treatment unit, and a drainage field.

Wastewater from toilets, sinks, and other sources enters the septic tank, which is an underground tank designed to hold the wastewater. Once inside the tank, solid matter settles to the bottom of the tank, forming a layer of sludge. Grease, oils, and other floating substances form a layer of scum on the top of the wastewater. The effluent, which is the liquid layer between the sludge and scum, then moves to the treatment unit, which is typically a bio-filter or a treatment chamber. In the treatment unit, microorganisms break down the remaining organic matter and pollutants in the effluent. After being treated, the effluent moves to the drainage field, which is a network of perforated pipes or chambers that allow the effluent to slowly percolate into the surrounding soil. The soil acts as a natural filter, removing any remaining contaminants and pollutants. Once the effluent has been treated and filtered by the soil, it is safely returned to the groundwater.

Pro’s

  • The wastewater is treated safely and can prevent environmental damage
  • A great solution when septic tanks aren’t suitable

Con’s

  • Requires power

If you require an alternative sewage and wastewater management system to the mains sewers then it is important to seek professional advice and a licence from the Environment Agency must be obtained to allow any wastewater to enter the waterways.

We had Paul Howe and Will Hadler from Kingspan at our office in Hove for a presentation on ‘Old Cesspits, Septic Tanks & Environmental Regulations’. Kingspan are one the largest manufacturers for treatment plants and septic tanks and provide an excellent design service to ensure you install the right type of kit. Visit their website here.