Performance Assessment of the Pretreatment Component of the Desalination Plants at Grünau and Bethanie in Namibia Based on Removal Efficiency

Abstract:

About a third of the world's population relies on groundwater for their water supply. However, in some cases, the quality of these sources is not suitable for human consumption. Reverse osmosis (RO) membrane technology is used in many cases to improve groundwater quality. Often, for effective performance of RO membranes pre-treatment of source water is required. This study aimed to assess the performance of the pre-treatment components of the brackish water RO desalination plants at the Grünau and Bethanie water supply areas. To assess the performance of the pre-treatment components at these two water supply areas, samples for water quality analyses like turbidity, fluoride, nitrate, and hardness were collected from the raw water and pre-treated water. The average removal efficiency of Bethanie’s sand filters was -2.14% for turbidity, hardness, nitrate, and fluoride. Sand filtration is a technology employed to reduce suspended solids (i.e. turbidity) and can improve microbiological quality. Sand filtration can also be used to remove precipitates formed after an oxidant was applied for example removal of iron and manganese. The negative value indicates that the sand filters were not effective in removing these contaminants, and in fact, they increased in concentration. The raw water was classified as group C, and the pre-treated water after sand filtration was group C as well. The average removal efficiency of Grünau’s sand filters was -43.28% for turbidity, hardness, nitrate, and fluoride. Again, this negative value indicates that the sand filters were not effective in removing these contaminants, and in fact, increased the concentrations. The raw water quality was classified as group D which remained as group D after sand filtration. The raw sources of water at both the treatment plants are groundwater abstracted from boreholes. This study demonstrated that the sand filters used in the pre-treatment at both plants provided minimal to no improvement in raw water quality and increased water losses through backwashing. Suspended solids and microbiological quality often do not require treatment with the use of groundwater, and therefore application of sand filtration technology as pre-treatment component not clearly justified. Therefore, future considerations regarding the use of these pre-treatment components in relation to raw water quality dynamics should be taken into account.

• Periodical: Engineering Headway (Volume 28)
• Pages: 47-56
• DOI: https://doi.org/10.4028/p-45Apf2
• Online since: November 2025
• Authors: Priskila Mutilifa*, Johannes Sirunda, Truddy Theron-Beukes, Kedir Bushira
• Keywords: Groundwater, Reverse Osmosis, Sand Filtration, Water Treatment

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