Production of Activated Carbon from Sewage Sludge for the Removal of Lead from Water

Abstract

Different activated carbons were produced from sewage sludge taken from Sharjah waste water treatment plant. Carbonization and activation were carried out in steam environment without an external flowing inert stream or in nitrogen environment. Sewage sludge was dried under sun before carbonization and solid KOH was added in between carbonization and activation steps. Maximum temperature reached for carbonization and activation was 700°C. In post treatment activated carbons were either washed directly with acid solutions (5M HCl or 5M HNO3), or were rinsed in soxhlet. Activated carbons were analyzed by sorption of nitrogen, Boehm titrations, pH measurement, thermal analysis (DTA and DTG analysis), ash content, scanning electron microscope and energy-dispersive X-ray spectroscopy mapping and adsorption of lead isotherms. In production of activated carbons from sewage sludge a total mass loss of 81 to 83 percent was observed. Nitrogen adsorption / desorption curves showed that most of the surface area was possessed by micro and meso pores with an average pore size of 25 Å. Carbonized samples possessed surface area less than 4 m2/g. Sewage sludge based activated carbons produced under nitrogen environment and steam environment exhibited surface area 1019 and 838m2/g respectively. pH experiments showed that carbonized samples were basic, activated carbons post treated with acid were acidic and activated carbon rinsed in soxhlet is basic. Boehm titration results were consistent with pH results and revealed the presence of high amount of surface functional groups in all sludge based carbons, 4 to 6 mmol/g. Carbonized samples possessed high ash contents up to 50 percent. Activation processes under steam and nitrogen environments reduced the ash contents to 14 and 30 percent respectively. Elemental analysis revealed the presence of a wide distribution of up to 12 elements in all sludge based activated carbons. Equilibrium time for adsorption for sludge based activated carbons was estimated to be 48 hours. Carbonaceous material that was activated under nitrogen environment showed higher adsorption capacity 75mg/g than that activated under steam environment 50mg/g. Search Terms: sewage sludge, activated carbon adsorbent, lead removal