Effects of Aloe Vera and Algae-Derived Biochars and Hydrochars on Mesophilic Anaerobic Digestion of Food Waste

Biochar (BC) and hydrochar (HC) are carbon-rich materials derived from organic wastes through pyrolysis/gasification and hydrothermal carbonization (HTC), respectively, offering promising pathways for waste valorization and resource recovery within a circular economy framework. Owing to their porous structure and surface functionality, these materials have gained attention as additives in anaerobic digestion (AD), where they may enhance the microbial activity, improve the buffering capacity, and facilitate direct interspecies electron transfer (DIET), resulting in greater process stability and higher methane (CH4) yields. This study evaluated the effect of BC and HC derived from aloe vera leaves and algae on methane production during the AD of food waste (FW). Batch experiments were conducted under mesophilic conditions (37 °C) for 60 days, using a 1:1 inoculum-to-substrate ratio and a dosage of 10 g L−1 of each carbonaceous material. The results show that adding BC increased cumulative biogas production by 10–14%, while HC led to an 18–35% increase compared with the control. Additionally, dissolved chemical oxygen demand (d-COD) removal improved by up to 30%, and volatile solids (VSs) removal rose by 31% in the FW and aloe HC reactors, highlighting the greater enhancement potential of HCs in methane production. Overall, the findings demonstrate that integrating carbonaceous materials derived from organic residues into AD systems can enhance bioenergy recovery while reducing environmental impacts, supporting more sustainable and circular waste-to-energy processes.