By integrating biochar into semi-continuous reactors operating for 100 days, the research shows notable gains in gas yield, stronger resistance to acidification, and more resilient microbial communities.
Food waste continues to rise worldwide, placing pressure on waste-management infrastructure and increasing greenhouse gas emissions. Anaerobic digestion (AD) is widely used to convert organic waste into biogas, yet conventional one-phase digesters often struggle with poor stability, high CO₂ content, and sensitivity to microbial shifts. TPAD—which separates hydrogen and methane production—provides improved efficiency but remains limited by acid build-up and low tolerance for high organic loading rates. Chemical buffers can stabilise pH but add cost and may disrupt microbial activity. Given these challenges, exploring sustainable additives such as biochar is essential to improving TPAD performance and enabling wider industrial adoption.
A study (DOI:10.48130/een-0025-0010) published in Energy & Environment Nexus on 21 October 2025 by Yusron Sugiarto's team, The University of Western Australia, highlights how biochar enables TPAD systems to operate at loading levels previously associated with failure, offering a practical strategy to enhance renewable gas recovery from food waste.
The study evaluated the role of biochar in a TPAD system treating food waste by operating paired semi-continuous stirred-tank reactors—with and without biochar—over 100 days across seven stages of increasing organic loading rates (0.5–6.0 g VS/(L·d)). In both the hydrogen-producing first reactor (R1) and the methane-producing second reactor (R2), the team monitored gas production rates (H₂ and CH₄), pH dynamics, volatile fatty acid (VFA) profiles, and microbial community composition to link process performance with underlying biochemical and microbial mechanisms. In R1, hydrogen production started on day 2 and increased as loading and dilution rates were adjusted, but reactors amended with biochar consistently showed higher H₂ production, with gains of 45–88% over controls and no decline even at the highest loading of 6.0 g VS/(L·d). These improvements were associated with more stable pH (≈5.5 versus 4.5–5.0 in controls) and moderated VFA accumulation, particularly reduced propionic acid build-up at high loadings. In R2, biochar likewise enhanced methane production: CH₄ appeared earlier, CH₄ content increased, and the CH₄ production rate remained stable at ~1,900 mL/d, whereas controls declined by ~12% at the highest loading as pH fell and VFAs accumulated. Throughout both phases, biochar-treated reactors maintained higher pH (around 5.5 in R1 and 7.2–7.3 in R2) and lower inhibitory VFA levels, confirming its buffering and metabolic support functions. Microbial analyses showed that biochar substantially enriched Clostridiaceae in both phases and promoted the growth of key methanogenic archaea, especially Methanosarcinaceae and Methanobacteriaceae, fostering stronger syntrophic networks and facilitating direct interspecies electron transfer. Together, these method–result linkages demonstrate that biochar stabilises semi-continuous TPAD and enables sustained hydrogen and methane production under loading conditions that destabilise conventional systems.
The findings demonstrate that biochar is a practical and cost-effective additive for stabilising TPAD systems treating food waste. By preventing acidification, enhancing microbial resilience, and enabling high-rate digestion at OLRs up to 6.0 g VS/(L·d), biochar allows TPAD systems to match or exceed the throughput of conventional anaerobic digesters while producing a higher-quality renewable gas mixture. Municipal waste facilities, agricultural biogas plants, and decentralised food-waste-to-energy systems could adopt this approach to increase renewable energy recovery, lower reliance on chemical buffers, and improve operating reliability. The study also provides a microbial basis for designing future biochar-enhanced digestion technologies.
