Adaptive routing behaviors between “touch-go” and direct electron transfer of pyrogenic carbon to promote phosphorus recovery as vivianite

• Biochar as electron transfer station enhanced vivianite recovery rate and efficiency • The redox cycle of quinone C=O formed “touch-go” indirect electron transfer pathway • The colonization of cell and Fe 3+ on biochar established new redox balance • Graphitization of carbon matrix offered direct electron transfer for vivianite recovery Microbial extracellular electron transfer (EET) driven by dissimilatory iron reduction bacteria is considered integral to elemental cycles and biochemical transformations, which involves the synthesis of the phosphate mineral vivianite in both natural aqueous systems and wastewater treatment plants (WWTPs). Exogenous conductive mediators have been investigated to facilitate EET and iron respiration. Herein, sufficient biochar (>5 g·L −1 ) served as electron-transfer-station established new redox balances for iron reduction, which kinetically promoted vivianite recovery. The average iron reduction rate was increased by 107%, leading to a 105% enhancement of vivianite yield mediated by Geobacter sulfurreducens PCA in the presence of biochar. The O-H groups as stable electron donor contributed 14%-19% for vivianite recovery regardless of electron exchange capacity of biochar. As the pyrolysis temperature increased from 300 to 600 ℃, quinone C=O facilitated electrons reversibly touch-go on biochar, with its contribution rising from 47% to 66%. Subsequently, an alternative direct electron transfer route was adaptively constructed in biochar matrix with high temperature, which dominated 52% for vivianite recovery at 900 ℃. This study demonstrated the mechanisms of EET promoted by biochar in vivianite recovery, offering insights into biochemical electron flux and conductive networks in the coupling of iron and phosphorus recycling.