Evaluating Methanol and Glycerolas Alternatives to Lactate in Sulfate-Reducing Woodchip Bioreactors

Sammanfattning

Sulfate-rich mine water can cause significant environmental impacts, including acidification and metal contamination of aquatic systems. Biological sulfate reduction using sulfate-reducing bacteria (SRB) has emerged as a promising passive treatment approach. In this process, sulfate is converted to sulfide, allowing simultaneous sulfate removal and metal precipitation. However, microbial sulfate reduction requires a suitable carbon source that serves as an electron donor for SRB metabolism. In many treatment systems, this carbon is supplied through the addition of external carbon sources to sustain sulfate reduction. However, the selection of suitable low-cost carbon sources remains a major challenge for field-scale applications. This study evaluated three carbon sources for biological sulfate reduction in woodchip-based column bioreactors treating synthetic sulfate-rich mine water.The study was conducted in two phases using a laboratory-scale column experiment. In Phase 1, biochar-amended and potato peel-amended woodchip columns were compared to evaluate treatment stability and substrate suitability with lactate as the primary carbon source. Based on sulfate removal, sulfide production, alkalinity generation, and lower variability between replicate columns, the biochar-amended system was selected for Phase 2. In Phase 2, methanol and glycerol were evaluated as alternative carbon sources and compared with lactate as a control substrate.The lactate-fed columns showed the highest sulfate removal efficiencies, strongest sulfide production, highest alkalinity generation, and most stable pH conditions throughout the experiment. These results confirm that lactate remained the most effective substrate for sulfate reduction. Methanol-fed reactors showed progressively declining sulfate removal and sulfide production. This suggests poor microbial adaptation and inefficient methanol utilization under the low-temperature operational conditions. In contrast, glycerol-fed reactors showed intermediate performance and gradual recovery over time. This indicates that mixed microbial communities were able to partially adapt to glycerol metabolism. Sulfite accumulation observed during the experiment also suggested incomplete sulfur transformation pathways under some operational conditions.Overall, lactate provided the best sulfate reduction performance but may be economically limiting for large-scale passive treatment systems. Glycerol showed potential as a lower-cost alternative because of its moderate treatment performance and gradual microbial adaptation. In contrast, methanol was unsuitable under the tested conditions. The results highlight the importance of microbial acclimation, carbon-source selection, and operational conditions in optimizing sulfate-reducing bioreactor performance for mine-water treatment.