Tailoring biochar properties for anaerobic digestion: Enhancing performance under high organic loading

This study investigates the influence of biochar's physicochemical properties, along with its dosage and particle size, on anaerobic digestion of food waste at a feedstock-to-inoculum ratio of 2.4. Biochars were synthesized from spruce softwood using microwave-assisted pyrolysis at three power levels (750, 1250, and 1750 W), resulting in biochars with progressively increased carbon content, surface area, and alkalinity. Each biochar was tested at dosages of 10, 20, and 30 g/L in anaerobic digestion systems. The results showed that biochar's performance in anaerobic digestion is strongly influenced by dosage and its characteristics. The best-performing condition, biochar produced at maximum microwave power (1750 Watt) with a dosage of 30 g/L, reduced the lag phase by 59.4 % and reached 91.5 % of control's 70-day cumulative methane yield in just 35 days, effectively reducing the digestion time. The biochar produced at 750 W performed best at 10 g/L but declined at higher dosages, while the biochar produced at 1750 W improved with increasing dosage. The biochar produced at 1250 W showed the most consistent performance across all dosages, with the best performance at 20 g/L. In addition, biochar particle size significantly affected the early stage of digestion, with finer particles performing better, although its impact was smaller than that of dosage or pyrolysis conditions. These findings highlight the synergistic influence of biochar dosage and properties in enhancing anaerobic digestion performance under high organic loading conditions.