Start up information for sewage treatment plants after prolonged periods of inactivity


When returning to or reopening your place of business, please follow the instructions below to enable a smooth start-up and to minimise the risk of pollution when restarting your sewage treatment plant.

Firstly, make sure the area is secure and cordoned off to prevent people or animals on site from falling into the sewage treatment plant. Where possible a qualified British Water accredited engineer should be employed to carry out these procedures. This process should be undertaken by two people while observing HM Government Social Distancing (Covid-19). PPE must be worn and handwashing/sanitizing must be carried out.

When first opening the tank chambers please ensure the area is well ventilated and engineers are wearing protective face masks. Sewer gases can accumulate in sewage treatment plants, particularly Hydrogen Sulphide, which can be very dangerous even at low levels. (Sewer gas is a complex mixture of toxic and nontoxic gases produced by the decomposition of organic household or industrial components of sewage).

  • When your treatment plant is turned on, make sure the compressor/air blower is operational.
  • Inspect the air filters on the top of the compressor and remove any debris impeding the flow of air.
  • Check whether air is reaching the treatment zone of your sewage treatment plant. This can be done by checking for a mild jacuzzi effect in the middle chamber of the plant.
  • Make sure the media (golf ball sized pieces of plastic) are freely circulating in the aeration chamber within the treatment plant. These must not be accumulating at one side of the chamber or the other.
  • Ensure that the treatment plant is vented locally and that air is allowed unhindered access to the plant with no air admittance valves located on the vent.
  • Be aware that when restarting your plant after prolonged periods of inactivity, smell and odour may be generated in the initial weeks while the biomass – ‘good bacteria’ – starts to grow again on the media (Activated carbon vents are available for purchase from Marsh Industries if this is an issue).
  • Existing recirculation pipes from the final chamber to the primary chamber assist and speed up the sewage treatment process, however, a temporary submersible pump with a flow of less than 10 litres a minute can be fitted into the final humus chamber to further enhance the process. The pump must be 1m below the waterline and should discharge to the primary chamber with the hose being under the waterline to minimise the agitation of solids. The pump can be operated for 20mins in every hour for 6 hours per day for the first 4 days of start-up. After this period, the pump should be removed, cleaned and stored.

If you have concerns about restarting your sewage treatment plant, please contact the Marsh HQ on 01933 654582.

Sewage treatment plants installation and operating manual

Sewage treatment plants installation and operation


Restarting sewage treatment plants after inactivity