Biochar Types from Latrine Waste and Sewage Sludge Differ in Physico-Chemical Properties and Cadmium Adsorption

Pyrolysis of latrine fecal waste could produce valuable products for minimizing environmental contamination with heavy metals. The objective of this study was to determine yields, characteristics and cadmium (Cd) sorption of biochar from latrine fecal waste and sewage sludge, as affected by pyrolysis temperature. Slow pyrolysis at 350, 550 and 650°C, was used to produce the biochar. In addition to proximate and ultimate analysis, surface area, porosity and functional groups were analyzed. A batch sorption study was conducted to determine the cadmium sorption capacity of the biochar. Biochar from latrine waste had higher yield, ash content, surface area and pore volume and lower total and fixed carbon (C) and volatile matter than from sewage sludge. Yield, volatile matter, total C, nitrogen (N) and hydrogen (H) decreased with pyrolysis temperature, while ash content, surface area and porosity increased. Surface functional groups of the biochar also varied with feedstock and pyrolysis temperature. The Cd sorption capacities were higher for biochar from latrine waste than from sewage sludge. The findings indicated that characteristics of biochar from latrine waste differ from that of sewage sludge origin and has greater potential as an adsorbent for removal of Cd from wastewater.