The secondary sludge from the sludge holding tank will be fed to a sludge thickener (for secondary) which further increases the concentration of the solids. The thickener shall be made of an RCC structure. The sludge thickener will have circular geometry and has a drive mechanism, access platform, rake arm mechanism mounted on it. The supernatant rises in the thickener and flows over the overflow weir and gets collected into the equalization cum neutralization tank. The underflow of thickener contains thickened sludge which will be collected into the centrifuge feed tank by gravity.