ReviewOverview of biochar production from preservative-treated wood with detailed analysis of biochar characteristics, heavy metals behaviors, and their ecotoxicity
Graphical abstract
Introduction
Wood is one of the most valuable natural resources and is used traditionally in outdoor applications and building interiors. On the other hand, wood is an organic material composed of cellulose, hemicellulose, and lignin, which are is prone to biological/chemical corruption by both living organisms and abiotic components. Ross reported that 10% weight loss from fungal attack could reduce the strength of wood by almost 50% (Ross, 2010). Consequently, many studies have been performed to develop wood preservatives focusing on durability improvement and replacement cost reduction (Teng et al., 2018).
Chromated copper arsenate (CCA)-treated wood impregnated with hexavalent chromium (Cr), copper (Cu), and pentavalent arsenic (As) is a representative preservative wood used widely in the industrial field, and is classified into three types depending on the metal content (Ohgami et al., 2015). Humar et al. reported that the disposal amount of CCA-treated wood will reach about 16 × 106 m3 in 2020 (Humar et al., 2004). Because CCA is a water-soluble heavy metal, soil and ground water can be polluted because of their leaching by exposure to rainwater (Aceto and Fedele, 1994). In particular, it has been reported that As can cause lung cancer in humans (Taylor et al., 1989). In addition, Cr can increase the risk of lung cancer (Luippold et al., 2003). Accordingly, CCA-treated wood was regulated in several countries approximately 30 years ago, which led to a rapid worldwide shift to copper-based wood preservatives (Hingston et al., 2001a).
Non-chromated arsenical water-borne preservatives, such as alkaline copper quaternary (ACQ), copper azole, copper citrate, and copper ethanolamine, have been used in numerous timber applications over the past decade (Bolin and Smith, 2011). Among them, ACQ, a mixture of quaternary ammonium compounds (QACs) and copper oxide, is commonly used because of its great biocidal activity against fungal or insect attack (Hata et al., 2003). Despite its relative environmentally friendly properties compared to CCA, it will eventually be thrown away at the end of its life time and its waste management will become a major issue in the near future. Hasan et al. reported that the amount of leached metals was proportional to the degree of retention of the treated wood with higher retention degrees resulting in higher quantities in leachates and more mass of metals lost. Accordingly, Cu leached from the ACQ-treated wood is up to 15 times higher than the Cu leached from CCA-treated wood, which might result in soil and water pollution by eluted copper (Hasan et al., 2010).
Preservative-treated wood waste can be recycled as an energy source or other valuable products via a thermochemical conversion process. Pyrolysis is a thermochemical conversion process performed near 400–500 °C under limited oxygen conditions, which generates bio-oil as the main liquid product along with biochar (solid) and non-condensable gas (Li et al., 2018). Various types of biomass, including wood waste, agricultural residues, forestry residues, municipal solid waste, and animal manures, have been used as feedstock for biochar production (Duku et al., 2011). Preservative-treated wood waste, such as CCA- and ACQ-treated wood, has been suggested as an alternative feedstock for bio-oil and biochar production (Koo et al., 2014; Kim et al., 2012). Recently, there has been increasing interest in understanding biochar as a whole, particularly its prospects and applications to environmental management as well as valuable products because it is a multifunctional material related to greenhouse gas reduction, carbon sequestration, soil fertilization, contaminant immobilization, and water filtration (Ok et al., 2015). According to previous research, the physicochemical characteristics of biochar are clearly influenced by the pyrolysis variables, including the feedstock type, temperature, residence time, and atmosphere (Li et al., 2018). Among them, the feedstock characteristics and temperature are the main parameters affecting the biochar yields and characteristics (Enders et al., 2012; Bird et al., 2011).
The environmental issues resulting from preservative-treated, wood-based biochar production should be considered because trace amounts of heavy metals, particularly As, can volatilize into the atmosphere when pyrolyzed. Most heavy metals are retained in biochar at even higher concentrations than in general soil or contaminated soil (Huang et al., 2018). Therefore, heavy metals can leach into the soil and affect the ecosystem, particularly biomass growth (Li et al., 2019a). When heavy metals are absorbed and transferred into biomass, they can cause metabolic disturbances, arrest cell division, cell death, or alter the structure and functions of various membranes or enzymes (Dadrasnia and Emenike, 2013; Singh et al., 2013).
Biochar application into valuable products, such as adsorbents, catalyst support, and batteries, has undergone rapid development recently (Gu et al., 2015; Mohan et al., 2014; Lee et al., 2017; Qian et al., 2015; Li et al., 2019b). Nevertheless, few review papers have introduced the behavior of heavy metals in preservative wood during biochar production as well as efficient methods to handle these metals. This paper introduces the state-of-the-art knowledge of the fate of heavy metals in preservative-treated wood during biochar production, including (1) the feedstock characteristics, (2) catalytic effect of heavy metals on the thermal degradation behavior of preservative-treated wood, (3) biochar characteristics from preservative-treated wood, (4) risks that heavy metals pose when they escape into the ecosystem during the biochar production process, and (5) heavy metal removal method from biochar. Furthermore, the challenges and future prospects for the efficient and eco-friendly utilization of biochar are discussed. This report is expected to offer easy accessibility to an extensive readership and will be an influential reference for future directions of eco-friendly biochar production from preservative-treated wood.
Section snippets
Chemical composition of preservative-treated wood
All woody biomass is composed of holocellulose (cellulose and hemicellulose) and lignin. Cellulose is a homogeneous polysaccharide comprised of ringed glucose through covalent bonding between the oxygen of the C1-hydroxyl group of glucose and the C4 of the adjoining glucose, called a β-1,4 glycosidic bond and is a major constituent of the primary cell walls of lignocellulosic biomass (Jarvis, 2003). Hemicellulose is heterogeneous polysaccharide with diverse structures composed of xyloglucans,
Thermochemical conversion process for biochar production
Biochar can be produced from a range of thermochemical processes, involving fast/slow pyrolysis and gasification. Each process is distinguished by different reaction temperatures, heating rates, residence times of the volatiles, and atmosphere (N2, O2, and air) (Meyer et al., 2011). Hydrochar is another carbon-rich material possibly produced from lignocellulosic biomass or agricultural residue via a hydrothermal carbonization process (HTC) (Oliveira et al., 2013). This process uses water as the
Fate of heavy metals and their ecotoxicity
Generally, biochar could improve the soil quality and reduce soil ecotoxicity by adsorbing potentially toxic trace elements (As, Cd, Cr, Cu, Hg, Ni, and Zn) and organic contaminants (agro-chemicals, antibiotics, and other hydrocarbons) from soil or water (Palansooriya et al., 2019; Ahmad et al., 2012; Inyang et al., 2016; Liang et al., 2017; Beesley et al., 2011; Tang et al., 2012; Yang et al., 2015; Wang et al., 2015, 2017). Environmentally persistent free radicals (EPFRs), which have an odd
Heavy metal removal process from biochar
As mentioned above, heavy metals, which are generally used in wood preservatives, exhibit ecotoxicity and have a high boiling point. Cu or Cr are inevitably retained in biochar (small amounts of As can be volatilized) (Kim et al., 2012; Jones and Quilliam, 2014). In particular, according to a previous study, liquefaction effectively removes most of the metals (98% As, 92% Cr, and 83% Cu) from the CCA-treated wood, with only approximately 2, 6, and 7% of As, Cr, and Cu, respectively, remaining
Challenges and future perspectives
Recently, biochar obtained from HTC or pyrolysis has been studied widely because pyrolysis or incineration is effective in generating energy (Lucchini et al., 2014). The physical (e.g., water holding capacity, O2 content, and moisture level), chemical (e.g., pollutant immobilization and carbon sequestration), and biological (e.g., microbial abundance, diversity, and activity) properties of the soils can be improved synergistically by adsorbing various toxic compounds by biochar (Gul et al., 2015
Conclusions
The disposal of spent preservative-treated wood becomes more expensive because of strict regulations. Therefore, an economical way to recycle waste preservative-treated wood should be investigated. Generally, carbonaceous biochar, which is produced from pyrolysis, can adsorb heavy metals leached in soil or water, and reduce the ecotoxicity of contaminated sites, simultaneously enhancing the bioavailability of contaminated sites. On the other hand, when the preservative-treated wood is
Acknowledgements
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2018R1A2B2001121).
References (210)
- et al.
Mechanisms of silicon-mediated alleviation of heavy metal toxicity in plants: a review
Ecotoxicol. Environ. Saf.
(2015) - et al.
Effects of pyrolysis temperature on soybean stover-and peanut shell-derived biochar properties and TCE adsorption in water
Bioresour. Technol.
(2012) - et al.
A review of biochars’ potential role in the remediation, revegetation and restoration of contaminated soils
Environ. Pollut.
(2011) - et al.
Fate of arsenic before and after chemical-enhanced washing of an arsenic-containing soil in Hong Kong
Sci. Total Environ.
(2017) - et al.
Chelant-enhanced washing of CCA-contaminated soil: coupled with selective dissolution or soil stabilization
Sci. Total Environ.
(2018) - et al.
Algal biochar–production and properties
Bioresour. Technol.
(2011) - et al.
Remediation of heavy metal(loid)s contaminated soils – To mobilize or to immobilize?
J. Hazard. Mater.
(2014) - et al.
Life cycle assessment of ACQ-treated lumber with comparison to wood plastic composite decking
J. Clean. Prod.
(2011) - et al.
Preparation and characterization of a metal-rich activated carbon from CCA-treated wood for CO2 capture
Chem. Eng. J.
(2017) Review of fast pyrolysis of biomass and product upgrading
Biomass Bioenergy
(2012)
Electrokinetic remediation of wood preservative contaminated soil containing copper, chromium, and arsenic
J. Hazard. Mater.
CO2 adsorption on chemically modified activated carbon
J. Hazard. Mater.
Palladium nanoparticles supported on amine-functionalized SiO2 for the catalytic hexavalent chromium reduction
Appl. Catal. B
Release and transformation behavior of Cl during pyrolysis of torrefied rice straw
Fuel
Rapid determination of environmentally persistent free radicals (EPFRs) in atmospheric particles with a quartz sheet-based approach using electron paramagnetic resonance (EPR) spectroscopy
Atmos. Environ.
Arsenic toxicity, health hazards and removal techniques from water: an overview
Desalination
Improving the two-step remediation process for CCA-treated wood: part II. Evaluating bacterial nutrient sources
Waste Manag.
Pilot-scale investigation of the robustness and efficiency of a copper-based treated wood wastes recycling process
J. Hazard. Mater.
Antioxidant enzyme activities as affected by trivalent and hexavalent chromium species in Fontinalis antipyretica Hedw
Chemosphere
Formation and stabilization of persistent free radicals
Proc. Combust. Inst.
Risk analysis of pyrolyzed biochar made from paper mill effluent treatment plant sludge for bioavailability and eco-toxicity of heavy metals
Bioresour. Technol.
Metal loss from treated wood products in contact with municipal solid waste landfill leachate
J. Hazard. Mater.
Biochar production potential in Ghana—a review
Renewable Sustainable Energy Rev.
Partial dissolution of ACQ-treated wood in lithium chloride/N-methyl-2-pyrrolidinone: separation of copper from potential lignocellulosic feedstocks
Chemosphere
Characterization of biochars to evaluate recalcitrance and agronomic performance
Bioresour. Technol.
Effect of essential inorganic metals on primary thermal degradation of lignocellulosic biomass
Bioresour. Technol.
The effect of alkali metals on combustion and pyrolysis of Lolium and Festuca grasses, switchgrass and willow
Fuel
The effect of lignin and inorganic species in biomass on pyrolysis oil yields, quality and stability
Fuel
Understanding the pyrolysis of CCA-treated wood: part I. Effect of metal ions
J. Anal. Appl. Pyrolysis
Removal copper, chromium and arsenic from CCA-treated yellow pine by oleic acid
Build. Environ.
Physico-chemical properties and microbial responses in biochar-amended soils: mechanisms and future directions, Agriculture
Ecosystems & Environment
Field-scale leaching of arsenic, chromium and copper from weathered treated wood
Environ. Pollut.
Electron microscopic study on pyrolysis of CCA (chromium, copper and arsenic oxide)-treated wood
J. Anal. Appl. Pyrolysis
Ozone regeneration of granular activated carbon for trihalomethane control
J. Hazard. Mater.
Review of disposal technologies for chromated copper arsenate (CCA) treated wood waste, with detailed analyses of thermochemical conversion processes
Environ. Pollut.
Total recycling of CCA treated wood waste by low-temperature pyrolysis
Waste Manag.
Low-temperature pyrolysis of CCA-treated wood: thermogravimetric analysis
J. Anal. Appl. Pyrolysis
Leaching of chromated copper arsenate wood preservatives: a review
Environ. Pollut.
Leaching of chromated copper arsenate wood preservatives: a review
Environ. Pollut.
Effect of carbonization temperature on the structural changes of woodceramics impregnated with liquefied wood
Carbon
Effect of pyrolysis temperature on chemical form, behavior and environmental risk of Zn, Pb and Cd in biochar produced from phytoremediation residue
Bioresour. Technol.
Fungal bioremediation of copper, chromium and boron treated wood as studied by electron paramagnetic resonance
Int. Biodeterior. Biodegradation
Leaching of chromated copper arsenate (CCA)-treated wood in a simulated monofill and its potential impacts to landfill leachate
J. Hazard. Mater.
Optimization of a chemical leaching process for decontamination of CCA-treated wood
J. Hazard. Mater.
Application of a CCA-treated wood waste decontamination process to other copper-based preservative-treated wood after disposal
J. Hazard. Mater.
Metal contaminated biochar and wood ash negatively affect plant growth and soil quality after land application
J. Hazard. Mater.
Two possible pathways for the release of arsenic during pyrolysis of chromated copper arsenate (CCA)-treated wood
J. Hazard. Mater.
A comparative review of biochar and hydrochar in terms of production, physico-chemical properties and applications
Renewable Sustainable Energy Rev.
Do the unique properties of nanometals affect leachability or efficacy against fungi and termites?
Int. Biodeterior. Biodegradation
Bioremediation and decay of wood treated with ACQ, micronized ACQ, nano-CuO and CCA wood preservatives
Int. Biodeterior. Biodegradation
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These authors equally contributed to this study.