| Summary: | Sewage sludge is the by-product of the wastewater treatment process. Its conventional disposal methods include incineration, landfill, and agricultural land application. As populations grow, the volume of sewage sludge likewise increases. The conventional disposal methods including incineration, landfill and application to agricultural land are unsustainable and have major limitations. Therefore, a more sustainable and economical alternative is needed by converting this waste material into the resource that can enhance environmental sustainability. Due to the carbonaceous nature of sewage sludge, the aims of this research are to convert a sewage sludge sample into activated carbon, to further explore the modification of sewage sludge based activated carbon (SBAC) to improve metal sorption capacity, and to investigate the effectiveness of the modified SBACs (MSBACs) by selecting the MSBAC with best adsorption performance to compare with other adsorbents.
The SBAC was prepared through the chemical activation of ZnCl₂, followed by pyrolysis in an electric furance, and it was further modified by nitric acid. Batch sorption tests were conducted in which the SBAC and MSBACs were contacted with distilled water spiked with lead ions (Pb²⁺) to measure their adsorptivity for Pb²⁺. The Pb²⁺ sorption capacity of MSBACs was further compared with zeolite, grundite, kaolinite, and commercial activated carbon. Batch sorption tests were conducted in which MSBAC10 was contacted with natural acid rock drainage (ARD) and the ARD solution spiked with Al³⁺, Fe²⁺, Cu²⁺ and Zn²⁺ to further demonstrate its application of removing multiple-metal components.
The batch sorption tests showed the great improvement of Pb²⁺ uptake capacity of the SBAC after modification. Compared with other MSBACs and adsorbents, MSBAC10 exhibited the strongest and fastest sorption behavior. The adsorptivity for lead ions in five minutes was ranked as: MSBAC10 > illite (grundite) > zeolite > commercial activated carbon (CAC) > kaolinite > perlite, and grundite ≥ zeolite ≥ MSBAC10 ≥ CAC > kaolinite > perlite over a 24-hour period, whereas, MSBAC’s application on the natural ARD solution, removed 98.88% of Cu, 42.60% of Zn and 34.63% of Al.
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