Color removal efficiency by the biological process was low (less than 12%). Color results from the
presence of the lignin or polymerized tannins, compounds with high molecular weight, which are nontoxic
but poorly biodegradable. Typically, an activated sludge system is composed of bacteria flocs
that produce intracellular enzymes, responsible for biodegradation. This is the reason for the low
biodegradability ratio for compounds with high molecular weight [31,37].