Addition-specific magnetic biochar optimization enhances COD removal and microbial community dynamics in microbial electrolytic cell-anaerobic digestion (MEC-AD) system for landfill leachate treatment
Hang Yu, Jiachen Zhu, Yushan Peng, Hanbo Chen, Chongjun Chen
Abstract
Magnetic biochar (MBC) exhibits excellent electrical conductivity and biophilicity, and features magnetic materials, free radicals with long-term stability, oxygen-containing functional groups, and a graphitic structure. Seven lab-scale microbial electrolytic cell-anaerobic digestion (MEC-AD) reactors (R1-R7) with gradient MBC additions (0.5–2.5 g) were constructed to evaluate the dose-dependent COD removal efficiency in landfill leachate treatment and to analyze functional microbial community dynamics. The results showed that the R3 reactor with 1.5 g of MBC achieved the highest performance with a COD removal efficiency of 59 ± 1%, representing a 10.5% higher than that of the blank treatment without MBC. The UV–vis and EEM analyses illustrated that the MEC-AD system effectively destroyed the conjugated double bonds and aromatic compounds, with a significant reduction in the peak areas corresponding to humic acid. Additionally, GC–MS analysis provided insights into the degradation pathways of long-chain alkanes and benzenes, indicating that excess MBC in certain reactors facilitated the formation of long-chain methyl esters. The microbial community dynamics showed that MBC promoted the growth of electroactive bacteria, specifically Rhodobacteraceae (0.4% ∼ 2.7%) and Comamonadaceae (0.2% ∼ 1.4%). This promotion of key functional groups facilitated improved electron transfer, thereby enhancing the degradation of refractory organic matter within the MEC-AD system.