Physical and chemical assessment of MSF distillate and SWRO product for drinking purpose

Abstract

The objective of this study was to evaluate the physical and chemical proprieties of desalinated seawater produced by Multi Stage Flash (MSF) and Reverse Osmosis (RO) processes for drinking purpose. The final products, after post-treatment and blending, of Kahrama MSF and Bousfer SWRO plants located in different sites were investigated in this study. Different samples were taken from raw water and product before and after post-treatments in both plants. The physical and chemical balance revealed that the desalinated water produced by MSF plant is of better quality than that produced by the SWRO plant. The Langelier Saturation Index (LSI) was used as an indicator of the aggressiveness and corrosiveness of potable water. Indeed, the LSI of the distillate was slightly positive with over 77% of the values ranging from 0 to 0.13 while about 23% of the values were negative. This is due to the increase of MSF product water temperature from 29°C to 33.82°C during the investigation period and the calcium levels which decreased to a minimum value of 45.95mg/l. On the other hand, the SWRO desalinated water had a negative LSI with values ranging from −3.27 to −1.85. These results are not within the recommended LSI values (between 0 and 0.4), which means that the product is highly aggressive and becomes improper for human consumption. These negative values are directly related to the RO product water temperature below 24.6°C and calcium concentration below 16.03mg/l as well as the lack of proper post-treatment process. From this investigation, it was recommended to improve the RO product post-treatment to make the remineralization process more effective. Some recommended guidelines suggested by the authors were presented in this paper.