Insights into quinone-functionalized biochar for stabilizing high-load anaerobic digestion and increasing biogas production

A high organic loading during anaerobic digestion (AD) of corn straw frequently triggers rapid volatile fatty acid (VFA) accumulation, pH decline, and process failure, partially due to inefficient syntrophic interactions and interspecies electron transfer. In this study, anthraquinone-2-sulfonate was grafted onto biochar to obtain quinone-modified biochar (QMBC), which was used to stabilize high-load AD of corn straw in a semi-continuous reactor. The results showed that during a high organic loading rate (OLR) of 2.36 g VS/L∙d, QMBC alleviated acid inhibition, reduced the total VFA concentration by 77.38 %, increased biogas production by 177.87 %, and maintained a methane concentration above 60 %. QMBC enriched electroactive bacteria, including Lentimicrobium (10.78 %) and Flexilinea (6.33 %), which were significantly and positively correlated with changes in the abundance of Methanobacterium and Methanosarcina. Functional predictions indicated significant enhancement of ccmEFGH and enzymes related to coenzyme F₄₂₀ synthesis. Overall, quinone-functionalized biochar represents a practical additive to improve the stability and biogas production of high-loading AD.