Biological sulfate reduction using molasses as a carbon source

Area of Science:

• Environmental microbiology
• Wastewater treatment technologies
• Anaerobic digestion

Background:

• Sulfate reduction is crucial for treating sulfur-rich wastewater.
• Molasses offers a cost-effective carbon source for anaerobic processes.
• Upflow anaerobic sludge blanket (UASB) reactors are efficient for wastewater treatment.

Purpose of the Study:

• To assess the feasibility of a lab-scale UASB process for sulfate reduction using molasses.
• To investigate the influence of the chemical oxygen demand-to-sulfur (COD:S) ratio on microbial competition and process performance.
• To understand the impact of sulfide inhibition and granule formation on sulfate removal.

Main Methods:

• Laboratory-scale upflow anaerobic sludge blanket (UASB) reactor operation.
• Controlled variation of the feed chemical oxygen demand-to-sulfur (COD:S) ratio.
• Monitoring of sulfate removal, methane-producing bacteria (MPB) and sulfate-reducing bacteria (SRB) activity, and sulfide concentrations.

Main Results:

• Sulfate removal exceeding 80% was achieved at COD:S ratios greater than 10, favoring MPB.
• MPB and SRB activity were inhibited at dissolved sulfide concentrations around 200 mg/L.
• Lowering COD:S ratios led to intense microbial competition, sulfidogenic granule formation, and reduced COD removal (approx. 30% at COD:S < 2).
• Sulfidogenic operation achieved up to 70% sulfate removal at a COD:S of approximately 3.5.

Conclusions:

• The UASB process is feasible for sulfate reduction using molasses, with performance heavily dependent on the COD:S ratio.
• Optimizing the COD:S ratio is critical for balancing sulfate reduction and methane production while managing sulfide toxicity.
• The formation of sulfidogenic granules at low COD:S ratios impacts COD removal and substrate diffusion, affecting overall process efficiency.