Lustleigh WwTW

Bere Alston WwTW

CASE STUDY

Project Details
Client: South West Water (SWW)
Location: Devon, England
Category: retrofitmbbr

Project Description

Bere Alston is situated on a peninsula created by the rivers Tamar and Tavy in an area of outstanding natural beauty. With a population of about 2000, the village lies in the Bere peninsula. Bere Alston is about 12 km north of the centre of Plymouth as the crow flies, but the road trip requires either a long detour via Tavistock or else negotiating narrow lanes and a narrow bridge.

The village of Bere Alston has grown in population since the original CB750 SAF plant was installed on the site. Our client, South West Water (SWW), decided to take pro-active action and reduce the ammonia (NH3) to ensure the site stayed within its discharge consent.

SWW working with Advanced Solutions and Technologies Ltd (AS&Tech) identified a period where the NH3 was typically at its lowest level. AS&Tech had advised SWW that the conversion would take 5 days, so the SAF plant was turned off on day 1 and AS&Tech began by removing the top covers on the SAF plant, so access could be gained to remove the existing fixed film media. AS&Tech completed the removal of the top covers on the day 1. On day 2 the existing fixed film media was removed and then the 4 off internal cells were cleaned down and a start was made on fitting the new 4 off square stainless-steel mesh floor grids.

On day 3 AS&Tech finished off the fitting of the square stainless-steel mesh floor grids (see photo). The mesh ensures the new media cannot reach the diffusers located at the bottom of each cell. SWW decided the diffusers which were around 10 years old needed to be replaced. This was done on a cell by cell basis in conjunction with the fitting of the mesh floors. On day 3 the internal cell screens which can be removed if needed, were installed using a sliding system (see photo).

Day 4 was spent filling each cell with the new media, a 50% fill of each cell was determined to be the correct amount for the treatment required at the site. The top covers were re-instated and the unit was then filled with effluent. The blowers were switched into manual mode and each cell was checked for its aeration pattern. Following a successful check, the unit was then switched to full auto mode. As the unit was effectively a new unit it would take two to three weeks for the media to begin to reduce the BOD/NH3 and it would be fully operational after 6 to 8 weeks (temperature dependant).

Since the conversion, the MBBR unit has ensured the site stays within its discharge consent and no further work has been carried out on the unit. The project went smoothly and it was down to the good planning on the part of SWW and AS&Tech prior to reaching the site. The conversion was completed at the end of day 4, one day ahead of the planned time frame.