Biocel Sewage Treatment Plant Problem & Solution

Failed soakaway
Biocel Sewage Treatment Plant
Colchester, Essex, CO7
13 November, 2014
Dry, Poor Ground drainage, Clay Soil
6 Person


Septic tank problems in Essex are common due to much of the county having a clay sub-strata.  Clay is mainly impermeable and as a result the effluent discharged to the receiving soakaway from a septic tank cannot drain away, resulting in the soakaway and septic tank having problems with surcharging.

The owners of this property, which is located on the outskirts of Colchester in Essex, had experienced septic tank problems since they moved into the dwelling in March 2014.  Unlike functioning septic tanks, it had been necessary to empty this tank on a monthly basis.

To determine the cause for the septic tank problems Mantair engineers carried out an internal inspection of the tank and conducted percolation tests to determine the porosity of the sub-strata.  The results of the inspection showed that the septic tank was in good structural condition with both inlet and outlet ‘dip pipes’ located.  The results of the percolation test showed that the sub-strata was unsuitable for a soakaway; this being the cause of the problems being experienced.

With the property having a watercourse on the boundary of the rear garden, Mantair engineers recommended that the septic tank be upgraded into a sewage treatment plant by installing a Biocel on the outlet of the existing tank.  Manufactured by Tricel, the Biocel septic tank conversion unit is designed to treat the receiving effluent from a septic tank and provides a treated effluent suitable for discharge direct to a watercourse.


The Biocel uses the existing septic tank as a primary settlement chamber whereby solids and floating matter are retained.  The remaining effluent passes from the septic tank and into the Biocel tank.  Within the Biocel are aeration and final settlement chambers.  The aeration chamber uses a Submerged Aerated Filter process whereby aerobic micro-organisms develop through the use of fine bubble aeration and plastic media.  Air is continuously supplied to the aeration chamber by a small air compressor (blower), which is housed remote from the Biocel tank.

Within the final settlement chamber fine solids are separated from the liquids.  The resulting treated effluent conforms to the required standard to be discharged to a natural watercourse.

The scope of the installation works included:

  • Installation of the Biocel within a suitably sized excavation, including for a concrete base and backfill;
  • Exposing the outlet from the existing septic tank and connecting this using drainage pipework to the Biocel sewage treatment unit;
  • Locating the air blower within a remote blower housing and provision of an RCD protected power supply to this point;
  • Installation of a new 110mm diameter discharge drain to the boundary watercourse;

On completion of the ancillary works, Mantair engineers commissioned the Biocel system.


Mantair provides a comprehensive septic tank and sewage treatment plant service throughout Essex and other Counties. This includes free site inspections, guidance and advice on the most suitable system for the client’s requirements, complete installation, commissioning and full after sales care.

Did you know that the cost to resolve your septic tank problems may be covered by your existing buildings insurance policy?

Mantair works in partnership with the UK’s leading drainage insurance claims management company to offer our customers a unique insurance claims management service. Providing expertise in managing insurance claims for the costs of repairing or replacing damaged drainage systems, we work on behalf of property owners helping them to save thousands of pounds in resolving their septic tank problems. Read more…

Call our team today to find out more about how we can help solve your septic tank problems on 01255 853890.