Review on utilization of biochar for metal-contaminated soil and sediment remediation

Biochar is a stable carbon-rich by-product synthesized through pyrolysis/carbonization of plant- and animal-based biomass. An increasing interest in the beneficial application of biochar has opened up multidisciplinary areas for science and engineering. The potential biochar applications include carbon sequestration, soil fertility improvement, pollution remediation, and agricultural by-product/waste recycling. The key parameters controlling its properties include pyrolysis temperature, residence time, heat transfer rate, and feedstock type. The efficacy of biochar in contaminant management depends on its surface area, pore size distribution and ion-exchange capacity. Physical architecture and molecular composition of biochar could be critical for practical application to soil and water. Relatively high pyrolysis temperatures generally produce biochars that are effective in the sorption of organic contaminants by increasing surface area, microporosity, and hydrophobicity; whereas the biochars obtained at low temperatures are more suitable for removing inorganic/polar organic contaminants by oxygen-containing functional groups, electrostatic attraction, and precipitation. However, due to complexity of soil-water system in nature, the effectiveness of biochars on remediation of various organic/inorganic contaminants is still uncertain. In this review, a succinct overview of current biochar use as a sorbent for contaminant management in soil and water is summarized and discussed.

The use of renewable energy sources is becoming increasingly necessary, if we are to achieve the changes required to address the impacts of global warming. Biomass is the most common form of renewable energy, widely used in the third world but until recently, less so in the Western world. Latterly much attention has been focused on identifying suitable biomass species, which can provide high-energy outputs, to replace conventional fossil fuel energy sources. The type of biomass required is largely determined by the energy conversion process and the form in which the energy is required. In the first of three papers, the background to biomass production (in a European climate) and plant properties is examined. In the second paper, energy conversion technologies are reviewed, with emphasis on the production of a gaseous fuel to supplement the gas derived from the landfilling of organic wastes (landfill gas) and used in gas engines to generate electricity. The potential of a restored landfill site to act as a biomass source, providing fuel to supplement landfill gas-fuelled power stations, is examined, together with a comparison of the economics of power production from purpose-grown biomass versus waste-biomass. The third paper considers particular gasification technologies and their potential for biomass gasification.