At this optimum pH, the particles surface charge is reduced or neutralized and the suspen-sion is destabilized. CR is an anionic dye; therefore, the neutralizingof negatively charged CR molecules at acidic pH, leads to theirdestabilization and flocculation. Furthermore, at acidic pH, nega-tively charged groups on the polysaccharide are protonated andneutralized. However, in acidic pH lower than the optimal value,the solubility of freshly formed sludge could increase which leadsto the decrease in dye removal (Patel and Vashi, 2012). It seemsthat changes in the pH is more effective on the removal of resid-ual moieties of the dye molecules than the color producing part,therefore its effect on COD reduction is more significant than colorremoval