Abstract:

To address the escalating sulfate pollution in groundwater (primarily from mining, chemical industries, and agricultural non-point sources), this study developed and validated a closed-loop treatment strategy integrating iron-carbon micro-electrolysis with PVA-SA immobilization for sulfur reduction, fixation, and resource recovery. An up-flow packed column simulating aquifer conditions was constructed to compare the long-term sulfate removal and sulfur fixation performance of three fillers: quartz sand (Control), PVA-SA-embedded maifanite (Ma), and PVA-SA-embedded iron-carbon-maifanite (FeC-Ma). Key results demonstrated: (1) The effluent sulfate concentration in FeC-Ma stabilized at 136.1 mg/L (average removal: 90%), significantly outperforming the Control (230.3 mg/L, 80.4%); (2) Iron-carbon micro-electrolysis effectively fixed sulfides as FeS precipitates within the gel matrix, reducing effluent sulfide to 2.1 mg/L (Phase I, HRT=2 d; Control: 182.5 mg/L) with 70% fixation efficiency sustained for 40 days; (3) Metagenomic analysis revealed that during sulfate reduction, FeC-Ma enriched complete-oxidizing sulfate-reducing bacteria (e.g., Desulfococcus), upregulated dissimilatory reduction genes (aprA/B-dsrA/B), and suppressed competitive methanogens (Methanothrix decreased by 52%), jointly driving sulfur precipitation; (4) Independent sulfur-autotrophic denitrification using fixed sulfur as electron donor achieved efficient nitrate reduction (effluent ${\mathrm{NO}}_{3}^{-}$-N<5 mg/L) with 82.1% sulfur recovery. This technology provides an efficient solution for groundwater sulfate remediation and sulfur resource recovery.

Key words: iron-carbon micro-electrolysis, PVA-SA gel, sulfur recovery, groundwater remediation, sulfate-reducing bacteria