Biochar Metal Sorption and Effect on Microbial Sulfate Reduction

Abstract

Biochar is a stabilized, recalcitrant carbon compound, created when biomass is heated to temperatures between 300-1000°C, under low oxygen concentrations. It can be produced from a variety of biomass feedstock, such as agricultural residues, wood chips, and manure. Recently, biochars have found several applications in environmental remediation. This study evaluated the effect of biochar on microbial sulfate reduction in cell suspension assays and batch growth experiments, as well as the potential of biochar to remove heavy metals from aqueous solution. Irrespective of dosage (0.5 – 10 g/L), biochar increased the extent of sulfate reduction by Desulfovibrio alaskensis G20 up to 4-fold in suspension assays. Batch growth experiments demonstrated that biochar concentrations up to 10 g/L have no inhibitory effects on microbial sulfate reduction and cell growth. We further compared the sorptive properties of different biochars for copper and nickel. Biochars were pyrolyzed in the presence of magnesium hydroxide (Mg(OH)2) or magnesium chloride (MgCl2) and sorption isotherms for copper and nickel were compared to unmodified biochar. Copper and nickel sorption capacities were greatly improved for the magnesium-enhanced biochars, indicating that biochar mineral supplementation can increase the efficiency of metal adsorption and removal from solution. Ongoing research under this theme aims at the development of a biochar-mineral composite material that promotes biological sulfate reduction and heavy metal adsorption in order to provide an efficient, low-cost, environmentally-friendly absorbent material that can be used for mine water treatment in bioreactors and/or permeable reactive barriers.