Sulfate Reducing Bioreactor Longevity Estimates based on Substrate Characterization and Initial Carbon Release

摘要

Sulfate reducing bioreactors have the potential to provide treatment of mining influenced water (MIW) with low operation and maintenance requirements. However, there is a lack of validated design guidance on the specifications of the organic substrate to ensure longevity of bioreactors for metals removal. Current design criteria are based on an assumed rate of carbon release coupled to sulfate reduction from a generic substrate. Linking the specifications of the organic substrate mixtures to the rate and extent of carbon release is a first step in improving design guidance.Three 18-liter columns were filled with one of three organic materials: woodchips, sawdust or alfalfa hay, and operated for 500 days with a MIW containing Zn ≈ 170 mg/L, Sulfate ≈5000 mg/L with a pH ≈ 6. The composition of organic materials was characterized using sequential chemical extractions to operationally define carbohydrate, cellulose and lignin like fractions. The carbon released by the substrate was calculated using the effluent carbon concentration and flow plus estimated carbon utilized for sulfate removal. The potential longevity was estimated based the calculated bioavailability of the individual substrate components, the carbon released after 1.2 year of operation and two scenarios for future effluent carbon and sulfate reduction rate.Half of the bioavailable carbon in all columns was utilized in the first 1.2 years of operation and primarily was related to effluent carbon. The estimated longevity of the columns was influenced by the effluent carbon assumption. The high value of effluent carbon used (500 mg/L as COD) was the average measured value at 1.2 years from all the columns. Zero effluent carbon was used to set a theoretical maximum longevity assuming a sulfate reduction rate of 0.3 mol/m~3/d. Our data supports a conservative estimate of SRBR substrate longevity in the 2 to 5 year range.