To reduce the volume of sludge awannon_logot the Hamilton WRP through Biological remediation.

Project Overview

The first step in the remediation was to establish a 20 m grid over the lagoon. This work was carried out by professional surveyors.

A sludge volume determination was carried out. The determination was carried out in accordance with clause 2.5.2 in the contract. Although the contract required that only 6 samples be taken, it was decided to take 20 samples to give a comprehensive spread of results. The samples were gathered in accordance with the method as set out in the contract. The samples were numbered and the grid reference of the collection points noted.

The samples were tested by Ecowise Environmental laboratories for TS (Total solids) and VTS (Volatile Total Solids).

On the 5th of October the initial dose of BioEnergizer was applied to the surface of the lagoon. A dosing pump was calibrated and installed, attached to the wall of a small shed which is close to the secondary sedimentation tank.

A garden shed was installed to house the 1000 litre tote containing the BioEnergizer,

We chose to dose into each of the two outflows from the secondary sedimentation tank. From 6th of October, BioEnergizer was dosed into the lagoon via these outflows from the secondary sedimentation tank at the rate of 11.1 litres every 24 hours. The dose was split into 8 applications over an 8 hour period.

During the remediation the interface between the sludge surface and the water above was agitated once every two weeks. This was done by drawing a steel pipe with chains attached behind the boat.

On Thursday the 3rd April a sludge volume determination was carried out to assess the volume of sludge.

The same equipment and techniques for measurement of water and sludge depth were used as in the initial sludge volume determination. A copy is attached. 20 samples of the sludge were taken at the same points as the original samples, again using the same method. The samples were tested by Ecowise Environmental laboratories for TS and VTS. A copy of their report is attached.


It can be seen from the data that we achieved the greatest sludge reduction in the southern part of the lagoon, where the influent enters the lagoon.

During the Bioremediation there were a number of periods of heavy rain, the recorded inflows to the WRP exceeded 2.7 ML/Day for various periods. The greatest being 4 days continuously in early November, the maximum recorded was 5.553 ML/Day.

We are advised that the flow rate was on at least one day not measured due to the measuring equipment not being able to cope with the amount of inflow. In fact the WRP was effectively flooded at this time. The potential issue with the very high flow rates is that the BioEnergizer which is in the lagoon system at the time of the heavy rain will be washed through to the second lagoon and beyond. It takes some time for the BioEnergizer to re-establish in the lagoon after heavy rains.

Results of the remediation programme

Sludge Volume

The total sludge volume has been reduced by 23%. (See attached survey chart)

This includes the remediation of sludge that existed prior to the commencement of the program and the remediation of sludge that entered the lagoon during the remediation period.


There has been a significant reduction in volatile solids VTS during the remediation averaging 75.4% and an average reduction in the total solids TS of 67.7%.