Pyrolysis of biosolids with waste cardboard: effect of operating parameters, feedstock size and blending ratio

Global waste is a rising problem that requires attention. Pyrolysis is a process that converts waste into valuable products like biochar, bio-oil, and gas by heating feeds above 300 °C. Pyrolysis studies mostly concentrate on fuel production and characterization, while biochar studies lack parametric analysis, especially for co-pyrolysis. Little attention is given to the effects of blending ratio and particle size on biochar yield. This research focuses on the pyrolysis of biosolids obtained from gas-to-liquid wastewater treatment, waste cardboard, and co-pyrolysis of blended samples. Pyrolysis was performed using a muffled furnace at temperatures ranging from 350–850 °C , heating rates of 3–10 °C /min, and residence times of 30–180 min to examine biochar yield and properties. Particle sizes and blending ratios were also studied. Proximate and ultimate analyses, metal composition, surface area, and surface charge studies were conducted on biochar samples utilizing analytical instruments. Biosolids had the highest yield followed by mixed samples and cardboard for all conditions, with temperature and blending ratio having the greatest impact on yield. Regarding surface area, the maximum was found to be at 650 °C revealing 10.34, 170.4, and 124.8 m2/g for biosolids, cardboard, and mixed samples, respectively. A significant effect with change in blending ratio and a minimal effect by varying particle size was observed on the biochar yield. For future applications, temperatures below 550 °C can be considered in terms of biochar yield, ash, and metal contents; as heating rate and residence time showed minimal effects on yield, lower points are preferred to conserve energy during pyrolysis. Overall, mixing waste improved quality and yield, making it environmentally beneficial for applications. Graphical abstract