Domestic Sewage Treatment Plants

Design and sizing of a Domestic Sewage Treatment Plant

A domestic sewage treatment plant should be sized in accordance with the British Water code of practice ‘Flows and Loads – Sizing Criteria, Treatment Capacity for Sewage Treatment Systems’.

A domestic dwelling will produce a flow (in litres) and BOD and Ammonia (in grams) per person – calculated to the maximum number of residents. A flow of 180 L/day, BOD of 60 g/day (75g/day for mobile homes) and Ammonia of 8g/day. The treatment plant is then sized and designed based on these figures.

Why Sample a domestic sewage treatment plant?

Most owners of a domestic sewage treatment plant have an agreement with a tankering company to de-sludge the tank on a regular basis. But how do you know if the plant is performing as designed? Is the discharged effluent being treated to within the required standard?

Regular sampling of the final effluent will determine whether the tank is working within limits or if the treatment plant is polluting.

There are many causes of a plant not working as expected. See our post Potential reasons for my package Sewage Treatment Plant not meeting consent for more information.

Sampling and testing of the final effluent can help to pinpoint the reason behind a failure.

Maintenance of Domestic Sewage Treatment Plants

As a normal part of the operation of a package Sewage Treatment Plant (STP), solids (also referred to as sludge) are produced. The sludge will build up over time and the depth will exceed the manufacturer’s guidelines. At this point, the tank will need to be desludged.

If the tank is not desludged, the treatment plant will work less efficiently. The quality of the treated effluent will decrease beyond the allowable limits (the consent to discharge permit). STP sampling chamber

If the effluent quality is worse than permitted, the environment could potentially be polluted. In addition, damage could be caused to the soakaway system. Non-compliance of the permitted consent to discharge issued by the Environment Authority, the environmental regulatory governing body, will place the owner of the installation at a potential risk of prosecution.

Frequency of Maintenance

The normal recommended desludging interval for domestic sewage treatment plants is generally every 6 months. The actual required de-sludge period can be less or more than 6 months.

The Sewage Treatment Plants will be sized in accordance with the British Water Code of Practice. But depending upon the current loading into each system, the final discharge properties and quality, the frequency of desludging may need to be adjusted.

Benefits of Sampling and Testing

Regular sampling and testing of the treated effluent (sample taken from the sampling point of the installation) will help to determine the following:

  • If the plant is more heavily loaded than designed. The condition of the effluent may indicate a more frequent emptying schedule is required. Conversely a lighter loading may require a less frequent emptying schedule
  • The compilation of an historical sample analysis record can show evidence of compliance
  • Highlight issues with the plant. Sampling can help determine what is affecting the quality of the final effluent

Our Sampling and testing service for Treatment Plants

We work with owners of individual properties with an STP and multiple properties that share a sewage treatment plant that need to ensure that their package treatment plant is operating within the specified limits. TSC also are employed by property owners who have issues with their plants. We can provide independent testing and analysis to determine if there is a problem.

See our case studies page for examples

Please Contact The Tank Sampling Company to discuss your requirements…