A UASB bioreactor using silage as a carbon source to reduce sulfate

Low cost-treatment for sulfate removal is required in many areas where potable water is scarce. The biggest challenge in biological treatment is finding an abundant low or no-cost carbon source. This work demonstrated for the first time that leachate from the agricultural byproduct silage can be used in an upflow anaerobic sludge-bed bioreactor to reduce sulfate for on-farm water treatment. The reactor ran continuously for approximately one year with an average silage leachate feed COD concentration of 4,471 ± 857 mg L⁻¹, and sulfate feed concentrations varying from 1,253 to 2,081 mg L⁻¹. The maximum sulfate reduction rate (SRR) of 9.75 ± 0.23 mmol (L day)⁻¹ was achieved at the high sulfate influent concentration and the amount of organics consumed was between 80–90%. Sulfide levels in the UASB bioreactor were consistently high for most of the experiment, averaging 516.6 ± 188.5 mg L⁻¹. Interestingly, during the last month of operation when sulfide concentrations were highest the SRR continued to increase. It was estimated that 36% of the silage leachate carbon was used directly for sulfate reduction.