Potential Impact of Biochar Water-Extractable Substances on Environmental Sustainability

Abstract

Application of biochar as a soil amendment could be a significant approach for carbon sequestration to possibly control climate change for energy and environmental sustainability. However, more studies are needed in a number of research areas, including the development of clean biochar materials free of any harmful substances, before this approach could be implemented at a global scale. In this study, biochar water-extractable substances were tested for their potential harmful effects on the growth of aquatic photosynthetic microorganisms including both blue−green alga (cyanobacteria Synechococcus) and eukaryotic green alga (Desmodesmus) that represent the primary photosynthetic producers of the aquatic environment. The water extracts from three different biomass-derived biochar materials varied widely in their dissolved organic and inorganic contents, as well as in their characteristics including their pH values. Bioassays with pinewood-derived biochar water extract showed a significant inhibitory effect on aquatic photosynthetic microorganism growth in a dose-dependent manner, while chicken litter and peanut shell-derived biochar water extracts showed no signs of growth inhibition. The pinewood-derived biochar water-extracted substances were further separated into three fractions based on their molecular sizes and electric charges through an electrodialysis separation process using a cellulose− acetate membrane with a 500-delta cutoff pore size. Our analysis showed that the active component of pinewood-derived biochar water-extracted substances that are toxic to both blue−green alga (cyanobacteria Synechococcus) and eukaryotic green alga (Desmodesmus) is likely a 500-delta (or smaller) organic chemical species that carries at least one carboxyl group. This finding is important to engineering a high-tech biochar that can be free of any undesirable substances for its soil applications toward agricultural and environmental sustainability.

Biochar and Manure Effects on Net Nitrogen Mineralization and Greenhouse Gas Emissions from Calcareous Soil under Corn

“…An inhibitory effect of biochar on microorganisms has been observed by others (Dempster et al, 2012) and attributed to water-soluble, low molecular-weight (<500 Da) organic species (Smith et al, 2012), volatile organic compounds , or ethylene (Spokas et al, 2010) released from the biochar. Biochar additions have also been shown to alter the composition of soil bacterial populations, increasing those of families involved with reduction of NO 3 to NH 4 , N 2 fixation, and denitrification but decreasing those involved in nitrification of NH 4 to NO 2 Khodadad et al, 2011;Lehmann et al, 2011;Ducey et al, 2013).…”

Molecular characterization of the thermally labile fraction of biochar by hydropyrolysis and pyrolysis-GC/MS

“…In fact, the microorganisms can utilize a number of labile biochar constituents as an energy source [22]. While some biochar associated labile components have biocidal activity [54], which may increase its stability against biotic decomposition. For instance, previous studies have shown that the inhibitory component of deleterious some biochars is likely to be low molecular weight organic acids and phenols [55,56].…”

Biochars in Soils: Towards the Required Level of Scientific Understanding

“…Recent studies focusing on soil-biochar-biota interactions in both terrestrial and aquatic ecosystems suggest potential impacts regarding the application of some biochars to soil on the activity and structure of edaphic and freshwater biological communities (due to leaching and potential transport of biochar particles into watercourse), their trophic relationships, and the processes they mediate. The extent and pattern of biological responses and/or observed toxicity can be assigned to bioavailable biochar fractions and appear to depend mainly on the target species and exposure scenarios, as well as on biochar physico-chemical properties and application rates (Busch et al 2012;Oleszczuk et al 2013;Smith et al 2012;Bastos et al 2014;Marks et al 2014;Domene et al 2015;Jaiswal et al 2015). A number of different mechanisms may play a role in determining biological responses to biochar amendment.…”