Performance evaluation of the Kpong water treatment plant

The Kpong Water Treatment Plant, located 54km to the north of Tema with a capacity for producing 182000m3/d of water is one of the two plants serving the Accra Tema Metropolitan Area. The plant is limited by the capacities of the low-lift and high-lift pumping stations and currently produces about 170000m3/d. The plant was initially designed as a conventional treatment plant with full facilities for aeration, coagulation, flocculation, sedimentation and rapid sand filtration. Presently however, no coagulation is carried out due to improved quality of raw water abstracted as a result of the construction of the Akosombo Dam upstream and the Kpong Dam downstream of the plant. As expansion works are to be carried out in the near future the plant was evaluated to determine its performance with respect to the current treatment process employed. The availability of good raw water quality also makes the use of slow sand filters an attractive treatment option at the plant. The evaluation of the performance of the plant was carried out by determining the efficiency of pollutant removal (turbidity, colour, suspended solids, settleable solids, iron and coliform bacteria) and the removal efficiency of the whole plant, determining the efficiency and level of production, comparing the final water quality to WHO Guidelines and Ghana Standards for drinking water quality, performing percentile analysis on the final water to determine percentage achievements of targets set by the utility for final water quality and also assessing the major unit processes and operations. Water quality data and production records for the most recent twelve months were used for the evaluation. It was found out that all the time, the final water quality met WHO Guidelines and Ghana Standards for drinking water quality. Percentile analysis showed that the plant met its targets for final water turbidity of ≤ INTU 93% of the time, colour of ≤ 5 PtCo 95% of the time, residual chlorine of 0.5 - 1.0mg/l 70% of the time and pH of 8.0 - 9.0 87% of the time. Targets for bacteriological quality were met 100% of the time. A comparison of final water from the plant to selected brands of bottled water- Voltic, Yes, Okay and Aqua fill revealed that the final water closely compares to Yes bottled water. Trend charts revealed that the plant performance is affected by raw water quality. The clariflocculators were found to have poor removal efficiencies with respect to turbidity, colour and suspended solids. Removal of iron and coliform bacteria was good. This is however due to the pre-chlorination process. The filters were found to be efficient in the removal of colour, turbidity, iron and coliform bacteria. The plant was thus found to be performing well with regards to removal of pollutants. An assessment of blackened filter media revealed that the media is coated with small amounts of manganese and iron. The average production efficiency of the plant was found to be about 98% and the level of production 93%. Evaluation of the feasibility of the use of slow sand filters as an option to a conventional treatment plant for expansion works at the plant revealed that, although the slow sand filters treat water from the Volta Lake adequately, they are not the best option as the large scale of plant required makes their use more expensive than rapid sand filters. It is recommended that measures to prevent pollution of the raw water source be instituted and enforced. The capacity of the low-lift and high-lift pumping stations should be increased. The blackening of filter media should be investigated further and the filtered water sampling point relocated to a point before the addition of lime. The feasibility of the use of dual media filter beds with high filtration rates as a treatment option for expansion works should also be investigated.

Source: KNUST