LEACHING BEHAVIORS OF HEAVY METALS ON PETROLEUM SLUDGE WASTE TREATMENT BY USING SOLIDIFICATION/STABILIZATION (S/S) METHOD WITH PALM OIL FUEL ASH AS PARTIAL CEMENT REPLACEMENT NOORAFIZAH BINTI MURSHID A thesis submitted in fulfillment of the requirement for the award of the Master’s Degree in Civil Engineering TITLE Faculty of Civil and Environmental Engineering Universiti Tun Hussein Onn Malaysia OCTOBER 2018