Following the successful installation of a sewage treatment plant for Camp 37 in Accra, a further contract was won for the project at Takoradi in June 1996. The two contracts involved the supply and installation of raw sewage pumping stations and Constant Transfer packaged sewage treatment plants to serve military barracks in Ghana. Each unit was designed for a population equivalent of 5000 and a daily flow of up to 1000 cubic metres.
Construction On each site, the twin 19m diameter aeration tanks and 6m diameter sludge holding tanks were constructed from glass coated steel panels. Each aeration tanks contains integral prefabricated settlement hoppers, air lift transfer and sludge return system, waste sludge removal system and aeration devices.
Access for inspection was provided by galvanised ladders and walkways across the tops of the tanks. Both plants are located in remote areas and were built by employing unskilled labour supervised by Naston engineers. Civil engineering content was kept to a minimum and limited to the construction of pump sumps, concrete bases for the tanks and the machinery houses.
Operation At both Camp 37 and Takoradi plants, waste water flows are collected at pumping stations and transferred directly to the aeration cells. The automatic balancing system designed into the aeration tanks ensures that the pumping rate does not adversely effect treatment.
The mixture of treated sewage and active bacteria is transferred at a constant rate to the integral clarifiers, thus ensuring good settlement and a high quality effluent.
Air for the process is provided by two duty and one standby blowers, each rated 18 kW and 1350 m?/h, and located in a machinery house adjacent to each plant. This building also houses the control panel which provides automatic control of each plant.
The use of twin aeration cells allows one cell to be shut down if the population falls to less than 50% of design capacity for extended periods.
Excess biological sludge produced is transferred and dewatered in the sludge holding tank. Supernatant liquor is returned to the aeration tank for further treatment. Dewatered sludge is periodically taken away by tanker.
This treatment system is simple to operate and involves no day-to-day maintenance tasks. There are no moving parts below water level and maintenance is largely limited to a standard blower service.
Ghana
