The Potential of Biochar
Amendments to Remediate
Contaminated Soils
Jose L. Gomez-Eyles,
* Luke Beesley,
Upal Ghosh
and Tom Sizmur
1 The Remediation of Soils Contaminated with Organic Pollutants
using Biochars
1.1 Introduction
1.2 Mechanisms for Biochars’ Sorption of Organic
1.3 Optimizing Biochar Production for Organic Contaminant
Department of Chemical, Biochemical, and Environmental Engineering, University of Maryland
Baltimore County, Baltimore, Maryland 21250, United States; E-mail: jlge@umbc.edu
The James Hutton Institute, Craigiebuckler, Aberdeen, AB15 8QH, UK;
E-mail: Luke.Beesley@hutton.ac.uk
Department of Agricultural Chemistry, Universidad Autónoma de Madrid, 28049 Madrid,
Spain; E-mail: eduardo.moreno@uam.es
Department of Chemical, Biochemical, and Environmental Engineering, University of
Maryland Baltimore County, Baltimore, Maryland 21250, United States;
E-mail: ughosh@umbc.edu
Department of Materials Science and Engineering, Iowa State University, 2220 Hoover Hall,
Ames, Iowa 50010, United States; E-mail: tosizmur@mail.iastate.edu
*Corresponding author
The Potential of Biochar Amendments to Remediate Contaminated Soils 101
1.4 Possible Complications
1.4.1 Long Term Effectiveness
1.4.2 Reduced Herbicide Ef ciency
1.4.3 Reduced Contaminant Degradation
1.4.4 Possible Toxic Effects to Soil Fauna
2 The Remediation of Soil Contaminated with Inorganic Pollutants
using Biochars
2.1 Introduction
2.2 Mechanisms for Biochars’ Immobilization of Metals
2.2.1 Increase in Soil pH
2.2.2 Ion Exchange
2.2.3 Physical Adsorption
2.2.4 Precipitation with Mineral Ash
2.2.5 Improvement of Soil Properties
2.3 Possible Complications
2.3.1 Increase in Soil pH
2.3.2 Application of Organic Matter
2.3.3 Changes in Redox Conditions
2.3.4 Phosphorus Supply
2.3.5 Summary of Complications
2.4 Impregnating Biochars with Iron Oxides
There is a legacy of polluted soils worldwide, contaminated with a variety
of different chemicals from a wide range of industrial (e.g., electricity
generation, oil refi ning, mining), agricultural (e.g., pesticide application)
and urban (e.g., waste disposal, motor vehicle discharges) sources. Soils are
considered polluted when they have an excess of an element or compound
which, through direct or indirect exposure, causes a toxic response to
biota resulting in unacceptable risks to the environment or human health
(Adriano 2001, Abrahams 2002, Vangronsveld et al. 2009). This is a cause for
concern in many countries such as the U.S where over 100,000 contaminated
sites have been identifi ed (Connell 2005), or the E.U. member states that
102 Biochar and Soil Biota
have reported 250,000 polluted sites that need urgent remediation (Mench
et al. 2010). The remediation of contaminated soils is therefore receiving
increasing attention from governments, legislators, industries and the
general population. Due to the wide range and dispersive nature of many
contaminant sources, soil contamination is often too widespread for
ex situ remediation options (e.g., excavating and burying polluted soils in
landfi ll sites) to be practically, environmentally or fi nancially viable. This
has resulted in the development of more sustainable, in situ remediation
treatments that, in many cases, involve the application of amendments directly
to contaminated soils. For soils contaminated with inorganic pollutants
like heavy metals, these amendments include clay minerals, zeolites, lime
or composts (Simon 2000, Mench et al. 2003, Vangronsveld et al. 2009),
whereas for organic contaminants like polycyclic aromatic hydrocarbons
(PAHs), or polychlorinated biphenyls (PCBs), activated carbons have been
favored (Brändli et al. 2008, Ghosh et al. 2011). The application of this kind
of in situ amendments does not remove the contaminants from the soil, so
their success is based on a reduction in the bioavailability and/or mobility
of the contaminants in question. This reduction is achieved by altering
the physico-chemical and biological characteristics of the soil, ultimately
reducing the risk of contaminant uptake by fauna and fl ora, or leaching into
waters. Biochars have received interest recently as an amendment for soil
remediation purposes due to their potential to reduce the bioavailability of
organic contaminants (Gomez-Eyles et al. 2011, Hale et al. 2011), inorganic
contaminants (Beesley and Marmiroli 2011), and both organic and inorganic
contaminants simultaneously (Cao et al. 2009, Beesley et al. 2010b). This
is demonstrated by a rapid increase in the number of studies published
featuring, within their title, the words ‘biochar’, ‘soil’, and ‘contaminated’
or ‘polluted’ from just 1 in 2007 to almost 30 in 2011 (Fig. 1).
This increase refl ects a growing awareness and use of biochars for the
remediation of contaminated soils. In this chapter the effi cacy of biochars
for contaminant mitigation in soils is examined, describing the mechanisms
by which biochars can reduce contaminant mobility and bioavailability.
We also identify possible complications that could arise from amending
contaminated sites with biochars and discuss new developments in biochar
technology and production to overcome these complications.

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