Background High-sulfate mine water poses a major aquatic environmental challenge in coal mining areas across China. Accordingly, the cost-effective and efficient treatment of such water has become an urgent need for the sustainable development of the mining industry. Despite its considerable promise, microbial remediation based on sulfate-reducing bacteria (SRB) shows limited efficiency due to the scarcity of dissolved organic carbon (DOC) in mine water.

Methods The application of external slow-release carbon source (SRC) materials for SRB faces a range of challenges, such as the potentially excessive release of organic carbon in the initial stage, the unclear release mechanisms of dissolved organic matter (DOM), and the difficulty of quantifying the utilization rate of SRB. To address these issues, this study conducted experiments on three SRC materials (i.e., bagasse, corncob, and sawdust), involving their carbon release kinetics under soaking and availability for SRB. Accordingly, the carbon release patterns, DOM release mechanisms, and availability for SRB of the three SRC materials were explored.

Results and Conclusions The results indicate that the carbon release processes of the three SRC materials all followed the second-order kinetic and Ritger-Peppas equations, with rapid release occurring within 0‒8 h, followed by slow release from 8 h to 120 h. The cumulative carbon release amounts within 120 h of bagasse, corncob, and sawdust were determined at 218.44 mg/(g·L), 77.72 mg/(g·L), and 39.87 mg/(g·L), respectively. Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectra indicate that the DOM released from bagasse was dominated by fulvic-like and humic-like acids, characterized by high molecular weights. In contrast, the DOM released from corncob and sawdust consisted primarily of tryptophan-like and tyrosine-like compounds, along with products from microbial degradation, suggesting better bioavailability. Facilitated by bagasse, corncob, and sawdust, the SRB exhibited enzymatic rates for \mathrmSO_4^2- degradation of 3.88 mmol/(L·d), 3.21 mmol/(L·d), and 2.67 mmol/(L·d), respectively. Therefore, corncob exhibited appropriate carbon release capacity and high enzymatic rate, establishing it as the most suitable SRC material. The results of this study can provide a theoretical basis for both the selection of SRC materials and the microbial remediation of high-sulfate mine water.