Iron-carbon micro-electrolysis enhances microbial sulfate reduction and sulfur recovery

Addressing the challenges of unstable activity in microbial sulfate-reducing bacteria (SRB) and the need for further recovery of sulfate reduction products, this study employed iron-carbon (Fe-C) micro-electrolysis to enhance microbial sulfate reduction (MSR) and achieve sulfur resource recovery. By comparing the synergistic effects of iron (Fe), carbon (C), and Fe/C composite systems with a polyvinyl alcohol-sodium alginate (PVA-SA) immobilization system, the key mechanisms were elucidated. The optimized Fe-C system (Fe/C mass ratio 2:1, 6 g Fe/L: 3 g C/L) reduced sulfate from 1000 mg/L to 362.9 mg/L within 5 d, while minimizing sulfide accumulation to 48.6 mg/L via in-situ generation of iron sulfides (FeS). X-ray photoelectron spectroscopy (XPS) confirmed FeS formation, validating direct sulfur recovery. Micro-electrolysis selectively enriched completely oxidizing sulfate-reducing bacteria (SRB), particularly Desulfococcus (relative abundance: 10.5 % in Fe-C group vs. 3.7 % in control), enhancing metabolic efficiency. PVA-SA hydrogel immobilization significantly improved microbial stress resistance, manifested as increased cell viability (1.21 × control) and stabilized extracellular polymeric substances (EPS). This alleviated Fe³⁺ cytotoxicity and maintained reducing conditions (ORP stabilized below -200 mV). Under the optimal Fe/C ratio, electron transfer system activity (ETSA) reached its maximum (1.4 × control). The research demonstrates that Fe-C micro-electrolysis combined with PVA-SA immobilization establishes an efficient platform for sulfate removal and sulfur resource recovery, providing a sustainable strategy for treating sulfate-laden wastewater.