Statistical analyses (Mann–Whitney U test) indicate that bentonite, activated clay and Macrosorb addition made no or little difference in effluent total colors when compared to biological treatment without additives. Statistical analyses also indicate that the addition of DEC and PAC into the activated sludge system were more effective than the other treatments. When the DEC and PAC additions were compared in terms of effluent total color removal efficiency, DEC was similar to 100 mg/L PAC addition and 200 mg/L PAC addition. The main disadvantage of PAC addition was the concurrent increase of TSS concentration in activated sludge. It can be noted that 100, 200 and 400 mg/L PAC additions had similar effluent total color values. However, 400 mg/L PAC addition gave the best color removal efficiency.
The effect of the TSS concentration and the influent color to the effluent color was also investigated using multiple linear regression analysis. As a result of multiple linear regression analysis, (with DEC and PAC addition) no statistically significant relationship has been established between effluent color/influent color and TSS concentrations (p>0.05). On the other hand, when only bentonite, activated clay and Macrosorb were added, the effluent color was primarily dependent on the influent color and the TSS concentration had little effect.