Phenolic acid sorption to biochars from mixtures of feedstock materials

Authors: Hall, Kathleen; CALDERON, MARIA - University Of Sevilla; Spokas, Kurt; COX, LUCIA - University Of Sevilla; Koskinen, William; Novak, Jeffrey; Cantrell, Keri

Submitted to: Water, Air, and Soil Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2014
Publication Date: 6/25/2014
Publication URL: http://handle.nal.usda.gov/10113/59585
Citation: Hall, K.E., Calderon, M.J., Spokas, K.A., Cox, L., Koskinen, W.C., Novak, J.M., Cantrell, K.B. 2014. Phenolic acid sorption to biochars from mixtures of feedstock materials. Water, Air, and Soil Pollution. 225:1-9.

Interpretive Summary: Biochar has been gaining attention, both in the public and scientific circles, as a means to combat climate change and at the same time improve soil fertility. However, there has been very little attention focused on the impact of biochar additions have on organic compounds already present in the soil system. In this research, we looked at the effect that 4 different biochars had when added to an agricultural soil (silt loam) on the changes in the sorption behavior of 3 different phenolic acids. Sorption of phenolic acids to biochars was characterized using batch equilibration. Our results support the conclusion that the properties of both the biochars and chemicals influenced sorption. Surprisingly, a majority of biochars sorbed phenolic acids less than a Minnesota agricultural silt loam soil. In addition, this study examined mixtures of feedstocks on the biochar behavior, and concluded that the sorption of the biochar could not be predicted from the biochar of the original feedstocks. In other words, a 80:20 mixture of switch grass and swine manure could not be predicted from biochars of its pure components. Thereby, this research highlights that biochar amendments need to be selected based on the desired mode of action and not all biochar types are suitable for sorbing chemicals in the soil system. Additional research is needed to fully characterize the surface chemistry responsible for these effects. These results are significant to farmers and policy makers and will assist scientists and engineers in developing improved biochars based on properties to minimize agrochemical transport and improve soil carbon management.

Technical Abstract: In an effort to customize biochars for soil amendments, multiple feedstocks have been combined in various ratios prior to pyrolysis. The resulting variation in the chemistry and structure can affect a biochar’s adsorption capacity, which influences the bioavailability of many chemical compounds in the soil system including phenolic acids. This study characterizes the sorption of 14C-labeled ferulic acid, syringic acid, and chlorocatechol to four biochars prepared from individual feedstocks and four from mixed feedstocks using batch equilibration. Pure feedstock biochar sorption followed switchgrass< swine solids< poultry litter< pine chip for both ferulic (Kd= 1.4-75) and syringic acid (Kd= 0.07-6.03), and appeared to be influenced by the properties of the biochars as well as the chemicals themselves. All biochar Kd values, except pine chip, were lower than that of the reference soil (Waukegan silt loam). The sorptive properties of the combined feedstock biochars could not be predicted from their pure feedstock components and sorption coefficients were both unexpectedly higher and lower than the individual parent materials’ biochars. Further research is necessary to understand the characteristics of these combination biochars, particularly their sorption, which this study has shown is not merely an intermediary of its components.