The maximum solid removal was seen after one hour of the contact time in case of sewage wastewater and five hours in case of tannery effluent. The time taken for solid removal from tannery effluent was much more than that taken by sewage. This difference in treatment time is due to the higher values of zeta potential and COD of the tannery effluent than those of sewage waste. In addition to this reason, there is proteinaceous matter in tannery effluent, which surrounds the colloidal particles thus slowing down the neutralization process of zeta potential.