Improving biodegradability of dissolved organic matter (DOM) in old landfill leachate by electrochemical pretreatment: The effect mechanism of polarity

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Enhancing the biodegradability of old landfill leachate is vital for the efficient treatment or resource utilization of municipal solid waste. Electrochemical pretreatment emerges as a promising technology for transformation of refractory dissolved organic matter (DOM). However, the specific impact of polarity on improving biodegradability of DOM remains unclear. In this study, a divided electrolyzer was used to explore the changes in the biodegradability of DOM in old landfill leachate during electrolysis. Meanwhile, the correlation mechanism between BOD5 variation and DOM evolution was explored by spectroscopy and Maldi-TOF-MS analysis. Results shown that different polarities all have positive effect on enhancing the biodegradability of DOM, while the structural changes related with BOD5 are depending on the polarity. In the anode chamber, electrochemical oxidation (EO) generates and eliminates carboxyl groups. Additionally, EO concurrently eliminates humic-like substances, which are challenging for microorganisms to degrade, and protein-like substances, which are easily degradable by microorganisms. This creates a competitive mechanism that coexist the promotion and inhibition for biodegradability. In the cathode chamber, electrochemical reduction (ER) transforms DOM components, accumulating easily useable protein components for microorganisms. Kinetic studies show that EO related BOD5 changes are aptly described by a competition model, considering both generation and removal of bioavailable components. ER related BOD5 changes suit a pseudo-first-order kinetic model. These insights into the transformation of old leachate DOM support the development of methods predicting BOD5 evolution, crucial for future process optimization.