title: Suitability of marginal biomass-derived biochars for soil amendment.
abstract: The term "marginal biomass" is used here to describe materials of little or no economic value, e.g. plants grown on contaminated land, food waste or demolition wood. In this study 10 marginal biomass-derived feedstocks were converted into 19 biochars at different highest treatment temperatures (HTT) using a continuous screw-pyrolysis unit. The aim was to investigate suitability of the resulting biochars for land application, judged on the basis of potentially toxic element (PTE) concentration, nutrient content and basic biochar properties (pH, EC, ash, fixed carbon). It was shown that under typical biochar production conditions the percentage content of several PTEs (As, Al, Zn) and nutrients (Ca, Mg) were reduced to some extent, but also that biochar can be contaminated by Cr and Ni during the pyrolysis process due to erosion of stainless steel reactor parts (average+82.8% Cr, +226.0% Ni). This can occur to such an extent that the resulting biochar is rendered unsuitable for soil application (maximum addition +22.5 mg Cr kg(-1) biochar and +44.4 mg Ni kg(-1) biochar). Biomass grown on land heavily contaminated with PTEs yielded biochars with PTE concentrations above recommended threshold values for soil amendments. Cd and Zn were of particular concern, exceeding the lowest threshold values by 31-fold and 7-fold respectively, despite some losses into the gas phase. However, thermal conversion of plants from less severely contaminated soils, demolition wood and food waste anaerobic digestate (AD) into biochar proved to be promising for land application. In particular, food waste AD biochar contained very high nutrient concentrations, making it interesting for use as fertiliser.
authors.affiliation: UK Biochar Research Centre, School of Geosciences, University of Edinburgh, Crew Building, Alexander Crum Brown Road, Edinburgh EH9 3FF, UK.
authors.forename: Wolfram
authors.initials: W
authors.lastname: Buss
authors.affiliation: School of Geosciences, University of Edinburgh, Crew Building, Alexander Crum Brown Road, Edinburgh EH9 3FF, UK.
authors.forename: Margaret C
authors.initials: MC
authors.lastname: Graham
authors.affiliation: UK Biochar Research Centre, School of Geosciences, University of Edinburgh, Crew Building, Alexander Crum Brown Road, Edinburgh EH9 3FF, UK; School of Geosciences, University of Edinburgh, Crew Building, Alexander Crum Brown Road, Edinburgh EH9 3FF, UK.
authors.forename: Jessica G
authors.initials: JG
authors.lastname: Shepherd
authors.affiliation: UK Biochar Research Centre, School of Geosciences, University of Edinburgh, Crew Building, Alexander Crum Brown Road, Edinburgh EH9 3FF, UK. Electronic address: ondrej.masek@ed.ac.uk.
authors.forename: Ondřej
authors.initials: O
authors.lastname: Mašek
mesh_terms: D001673:Biodegradation, Environmental; D018533:Biomass; D002244:Carbon; D002606:Charcoal; D052918:Environmental Restoration and Remediation / Q000379:methods*; D005308:Fertilizers; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis / Q000737:chemistry; D013696:Temperature; D014934:Wood
chemical_list: D005308:Fertilizers; D012987:Soil; D012989:Soil Pollutants; C540010:biochar; D002606:Charcoal; D002244:Carbon
keywords: Biochar; Contaminant; Marginal biomass; Nutrient; Potentially toxic element; Pyrolysis