Abstract

In developing countries like Botswana, addressing leachate treatment presents considerable difficulties, especially regarding the management of sewage sludge (SS). This research evaluated the capacity of activated biochar, derived from sewage sludge, to adsorb Total Organic Carbon (TOC). Biochar was produced under conditions with limited oxygen, by placing approximately 50 grams of dried sewage sludge in sealed porcelain crucibles and heating them at a rate of 10°C per minute to 400°C for four hours. The resulting biochar (WWSBC400) was then stored in plastic bags in a dry environment. The pyrolysis yield was calculated as the ratio of the weight of the produced biochar to the initial weight of the dry sewage sludge. The study identified the maximum adsorption capacities (qm) for TOC in landfill leachate solutions, highlighting surface precipitation as a key adsorption mechanism for WWSBC400. Additionally, the removal of carbon ions using biochar produced from sludge at Gaborone's wastewater treatment facility was investigated. Continuous adsorption columns were utilized to demonstrate TOC solution adsorption, with performance evaluated in a fixed-bed column through model simulation. The Thomas model was used to compare experimental kinetic data, with the experimental data generally aligning well with the Thomas model, achieving a correlation coefficient (R²) of 0.9114 for the first round of activated biochar removal. The adsorption capacity of the biochar was recorded at 389.265 mg/g after 14.5 hours of column adsorption, with regeneration studies showing varying adsorption capacities of 742.82 mg/g, 875.47 mg/g, 682.13 mg/g, and 735.21 mg/g for successive rounds. Surface precipitation was found to be a vital process for carbon adsorption onto WWSBC400. In conclusion, using sewage sludge biochar for co-contaminated soil shows potential for heavy metal immobilization, presenting a viable option for environmental rehabilitation.