Project Description

The Problem

An AD (anaerobic digestion) plant situated on a farm in Oxfordshire required confined space cleaning and the removal of solids in preparation for decommissioning.

The build-up of grits and plastics in AD plant vessels is a widespread problem.  The size of the tank can make it difficult to ensure that all solids are kept in suspension; over time the larger, heavier particles settle on the base of the tank where they become immovable.  These solids accumulate to such an extent that the volume of the tank is reduced which in turn reduces the efficiency of the treatment process. In addition, the pipe work can become blocked.  The only way to remove these “grits” as they are commonly known is to take the vessel off-line and deploy confined space cleaning options.

Grits are usually composed of unwanted waste solids from the food waste input such as glass, egg shell, seeds, hard plastics and they have little or no organic value.

AD plant before cleaning, filled with sludge and solids

Above: The AD plant before the cleaning process, showing how the sludge and particles had solidified on the base of the tank.

Pumps used to remove sludge from AD plant

Above: During the cleaning process, pumps were used to remove the sludge from the AD plant onto a tanker for removal.

The Willacy Solution

The tank contained an estimated 1,000 tonnes of liquid and semi mobile solids. Access to the tank was very restricted meaning that the cleaning process had to be carried out by a fully trained confined space operative equipped with full breathing apparatus.

In order to gain access we were able to remove part of the roof so one of our manned mini-bulldozers could be lowered in.

With this in place we used a high-pressure water cannon to liquidise all of the sludge. Using the bulldozer, our operative was then able to push the sludge toward the suction of a pump situated outside the tank which sucked the sludge out and pumped it into a waiting tanker, ready for disposal.

The project took eight days from beginning to end and the client was completely satisfied. The AD plant was left ready for decommissioning.

AD plant with all sludge and solids removed after cleaning

Above: All sludge and solids were removed, leaving the base of the tank completely clear.

AD plant with all sludge and solids removed after cleaning

Above: To the far left of this image is the hydrodozer, used to move the sludge closer to the pump for removal.

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