Use of reverse osmosis for the removal of coliform bacteria from brackish water in the dairy industry

A limiting recovery rate strategy has been established for completely eliminating pathogenic bacteria as total coliforms by reverse osmosis (RO) spiral membrane during hard and non-organic brackish water treatment for the manufacture of reconstituted powder-based milk in the dairy industry. The physicochemical quality of brackish water showed that the total hardness and conductivity, around 600 mg L-1 as CaCO3 and 2,300 mu S cm(-1) respectively, were significantly higher than World Health Organization (WHO) and European directive drinking water standards. Similarly, the microbiological quality did not meet regulatory standards because of the high number of pathogenic microorganisms as total coliforms present in the feed water of the RO process. CaCO3 scale has been found to be the major constituent of brackish water highlighting the absence of organic compounds, which weakens the thickness of the membrane fouling layer and therefore the limiting flux cannot be reached. So, the limiting recovery rate has been found as an alternative solution to the limiting flux in which the limiting conditions of RO filtration were conserved. Indeed, it was found that the retention is more efficient at the limiting recovery rate revealing the limiting transmembrane pressure (TMPlimiting). Furthermore, the pH of permeate water decreased with the increase of TMP until a constant value (pH5.6) was achieved at the limiting recovery rate corresponding to the TMPlimiting (11 bar). Total retention (100%) of total hardness and total coliforms from 11 bar was achieved for a limiting recovery rate value of about 72%. The remaining bacteria are non-pathogenic as aerobic mesophiles (total bacteria) which can be removed or reduced by pasteurization of reconstituted milk.