An investigation of reliability of the water source and cost-effective chemical use at Masaka Water Treatment Works

Abstract

The challenge of providing improved and adequate water services is substantial and this study sought to determine whether the NWSC Masaka Area’s current water source is sufficient to ensure adequate water supply to meet future demands of the area. In addition, Masaka water works has the highest unit chemical cost per cubic meter of water pumped in NWSC with an average of 191Shs/m3 in comparison to the NWSC global unit chemical cost per cubic meter of 77Shs/m3. Effective management of municipal water works demands a holistic approach linking technical and economic monitoring with protection of natural eco-systems. Thus this research had the dual task of checking source adequacy as well as cost effective usage of chemicals by analysing existing data so as to determine technically the optimal way forward. River flow data for River Nabajjuzi was obtained and infilled using hot deck infilling techniques in MS EXCEL. The abstraction limit (MAM-7) of the 7-day low flow data was calculated as 8,122m3/d and was then utilized with the log Pearson Type III frequency analysis techniques to determine the yield maintainable in a once in 50 year drought of River Nabajjuzi. This was calculated as 13,478m3/d. The abstraction limit and safe yield were both higher than the highest abstraction rate during the period 2006-2008 of 4733m3/d and the plant design capacity of 8000m3/d implying adequacy of the source currently for Masaka area. However, the calculated future and ultimate years’ demands of 11,552m3/d by 2018 and 19,791m3/d by 2028, were significantly higher than the abstraction limits for River Nabajjuzi implying that it would not be an adequate source for the area in the near future. Explorations for a new source should begin soon for future planning. In addition, the water quality results for River Nabajjuzi indicate that it is characterized by low pH of average range 5.8-6.1, high colour with an average of 206Ptu, high iron content with an average 2.4mg/l and high turbidity with an average of 38.8NTU. All these parameters were observed to increase significantly during the dry seasons and reduce in the wet seasons. The analysis of the water pumped and chemical consumption records showed greater chemical consumption and cost along the Boma treatment line than the Bwala treatment line for chlorine with averages of 1022kg/month and 688kg/month respectively and Soda ash with averages of 2016kg/month and 981kg/month respectively. However, the Aluminium Sulphate consumption was greater along the Bwala treatment line with an average of 2212kg/month compared to 1838 kg/month for Boma treatment line. This was in contrast to the fact that more water on average was pumped from Boma treatment plant than from Bwala treatment plant i.e. 60,920m3/month compared to 55,878m3/month respectively. As both plants have the same water source, it implies that this anomaly could be due to operational inefficiencies and inadequate design of some of the process units. It can thus be concluded that River Nabajjuzi is still a valid current source of water for Masaka Municipality in the short term but not for the long term. In addition, the chemical consumption at the Masaka water works are higher during the dry season than the wet season due to the variation in the characteristics of the raw water but with some anomalies caused by operational and design handicaps. Exploration for new water source while incorporating the Integrated urban water management principles needs to be undertaken in the very near future to provide continuous water supply for Masaka town.