The site for the new sludge dewatering plant at the Mossel Bay Municipality regional sewerage works at Hartenbos was recently handed over to the civil subcontractor for the project.

The project, with a total value of R18 million, entails the construction of the plant at which waste-activated sludge will be dewatered and treated to improve the quality of the water that will be discharged from the plant.

It will also have facilities to facilitate the disposal of the dewatered sludge.

The municipality is at present using drying beds to dry the sludge but the existing drying beds are approaching maximum capacity.

“There is no space on the property to build additional drying beds and for this reason we have decided to build the new plant which will be an improvement on the current processes and will lead to increased productivity,” said a municipality spokesperson.

When the new plant is commissioned, the waste-activated sludge will be pumped to the existing sludge holding ponds from where it will gravitate via two waste-activated sludge pipelines to the dewatering facility.

One line will feed the belt press, to be installed under this contract, and the other line will feed a second future press to be installed at a later date. From here, the flow of sludge onto the press will be controlled.

Polyelectrolyte, together with dilution water, will be added to the stream of sludge and the sludge will be dewatered by the linear screen/filter belt press equipment (dewatering process train) with a design load of 420 kg per hour per press.

The dewatered cake will then be transferred to a sludge silo. From there it will be collected and removed.

The filtrate (as well as filtrate collected from the existing dewatering facility via a new gravity line to be installed under this contract) and wash water will be pumped to the nearest drying bed located approximately 40m away.

The main contractor on the project is PCI South Africa and the sub-contractor (civil) is Khubeka Construction. The electrical sub-contractor is Electron and the engineers are Worley Parsons RSA. Lyners Consulting Engineers are the project managers.

The project is scheduled for completion in November 2015.