Dutch design treatment for Ghanaian waterworks

Rising demand for water in the Ghanaian town of Kwanyaku means that the waterworks need upgrading and the distribution system extending. Fred de Bruijn and Peter Tienhooven of Dutch consultant Witteveen+Bos outline the plans.

The existing waterworks in the town of Kwanyaku in southern Ghana have proved to be inadequate to satisfy the increasing water demand. Moreover, Ghana Water Company (GWC) is keen to expand the Kwanyaku distribution system to provide drinking water to adjacent towns and villages.

Belgian-Dutch contractor Denys has been awarded the contract to upgrade both the Kwanyaku waterworks and the main distribution network. Dutch consultant Witteveen+Bos has provided study, design and engineering assistance to the project.

Kwanyaku abstracts its water from the rain-fed Ayensu River where a dam for impoundment is in place. A recent study has confirmed that increased abstraction to 35,000m3/d will meet demand up to 2020 if river discharge is maintained at adequate capacity to supply, for instance, Winneba city, which is abstracting its drinking water downstream.

In the Witteveen+Bos design scheme, the river water will be coagulated with alum dosing, and flocculation and clarification will be achieved in combined, circular basins. The clarification sludge, which in Ghana is usually discharged into the river, will be treated on sludge-drying beds for subsequent land disposal.

The clarified water will be polished by rapid gravity sand-filtration. The filtered water will be disinfected by gas chlorination while being contained in contact chambers, prior to supply into the treated water reservoirs.

The technology adopted in the treatment works is common to Ghanaian practice, however technical design has been modernised compared with previous installations. The on-site handling of sludge and washwater is relatively new to Ghana, and was particularly attached to Dutch funding conditions in an effort to raise the standard of GWC's environmental conduct.

Furthermore, GWC and Denys agreed that the existing distribution network should be upgraded at the same time. In this way leakage can be reduced, and revenues can increase both from the existing customer base and from the new towns and villages that will be connected to drinking water.

In total, 25km of mains transportation pipelines will be constructed within the project, and about 50,000 additional households should be supplied. Also, the existing network is undergoing review and all valve chambers will be retrofitted under the project.

The project is now under construction, well ahead of schedule. Overall project commissioning is scheduled in the first half of 2007.

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