Biochar and earthworms working in tandem: research opportunities for soil bioremediation

Authors: SANCHEZ-HERNANDEZ, JUAN - University Of Castilla-La Mancha(UCLM); Ro, Kyoung; DIAZ, FRANCISCO - University Of La Laguna

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2019
Publication Date: 6/15/2019
Citation: Sanchez-Hernandez, J.C., Ro, K.S., Diaz, F.J. 2019. Biochar and earthworms working in tandem: research opportunities for soil bioremediation. Science of the Total Environment. 688:574-583. https://doi.org/10.1016/j.scitotenv.2019.06.212.
DOI: https://doi.org/10.1016/j.scitotenv.2019.06.212

Interpretive Summary: Intensive use of agrochemicals is considered one of the major threats for soil quality. The use of biochar, a carbonaceous material produced from pyrolysing biomass, represents an attractive option enhancing both remediation and soil carbon storage potentials. Currently, activation of biochar with chemical or physical agents seeks for improving its remediation potential, but most of them have some undesirable drawbacks such as high costs and generation of chemical wastes. This paper briefly introduces current biochar bioactivation methodologies and the mechanisms underlying the coating of biochar with enzymes mostly utilizing laboratory microbial cultures. We then propose a new conceptual model using earthworms to activate biochar with extracellular enzymes. This new technique can be used to produce a new material called vermichar, vermicompost mixed with bioactivated biochar. The vermichar can be used to improve soil quality and remove pollutants from soil.

Technical Abstract: Intensive use of agrochemicals is considered one of the major threats for soil quality. In an attempt to mitigate their side-effects on non-target organisms and soil functioning, many engineering and biological remediation methodologies are currently available. Among them, the use of biochar, a carbonaceous material produced from pyrolysing biomass, represents an attractive option enhancing both remediation and soil carbon storage potentials. Currently, activation of biochar with chemical or physical agents seeks for improving its remediation potential, but most of them have some undesirable drawbacks such as high costs and generation of chemical wastes. Alternatively, the use of biological procedures to activate biochar with contaminant-degrading enzymes is gaining popularity mainly due to its eco-friendly nature and cost-effectiveness. In these strategies microorganisms play a key role as a source of extracellular enzymes, which are retained on the biochar surface. Recently, several studies point out that soil macrofauna, particularly earthworms, may act as a biological vector facilitating and increasing the adsorption of enzymes on biochar. This paper briefly introduces current biochar bioactivation methodologies and the mechanisms underlying the coating of biochar with enzymes mostly utilizing laboratory microbial cultures. We then propose a new conceptual model using earthworms to activate biochar with extracellular enzymes. This new earthworm-biochar model can be used as a theoretical framework to produce a new product "vermichar", vermicompost mixed with bioactivated biochar that can be used to improve soil quality and remove pollutants in soil, or to develop innovative in-situ "vermiremediation" technologies utilizing the beneficial effects of both earthworms and biochar. Since biochar may contain toxic chemicals, this paper also highlights the need for an ecotoxicological knowledge around earthworm-biochar interaction in order to stimulate further discussion on suitable procedures for assessing the environmental risk of using this conceptual model in bioremediating contaminated soils.