of the equilibrating solution but the observation showed that the
net reduction in the COD and color of the leachate by the soil for the
sake of economic point of view and obtained the positive result.
Additionally, the removal of COD of the leachate decreases when
the pH of the solution exceeds pH 2.00 might be due to deprotonation
of the hydroxyl groups at mineral surfaces in soil decreases
the positive net surface charge plus organic molecules turn into
more electronegative. The organic materials and mineral surfaces
repel each other and limit the surface complex formation, releasing
the organic materials into the soil solution and thus increase the
COD of the soil solution (Grybos et al., 2009).