Energy crop clean-up: Breathing new life into contaminated land

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More than 400 million hectares of land around the world has been left contaminated and abandoned because of the lack of a financial incentive to pay for the clean-up writes Dr Phil Longhurst. In the UK, just 18% of contaminated land – most commonly by toxic forms of metals – has been recovered, remaining a hazard to the environment and public health.

New research has demonstrated the combined benefit of growing crops on contaminated land (just common plants such as willow, elephant grass and sunflowers) to both remediate land to make it safer for agriculture and development, and provide a payback in terms of energy.

If all the contaminated land stock was used to produce energy crops in this way it would provide 10% of the world’s energy needs – around 2,000 million tonnes of oil equivalent fuels.

Using plants to uptake environmental contaminants from soil (known as ‘phytoremediation’) is not new, but more recent research to exploit the plant uptake of elements, thermochemical biomass conversion, the emission of contaminants during energy production processes, and better recovery of metals, transform the idea into an approach with major benefits.

One of the major advantages of phytoremediation is low cost. According to a study across Europe the average cost for on-site phytoremediation is 122 Euros per m3 compared with 231 Euros per m3 for traditional excavation and off-site landfilling. There’s also better performance compared to the conventional approach, with the scope for permanent removal of contaminants with minimal disturbance and low energy input to the site. There’s then the energy produced to be considered. The quantities of biomass produced during phytoremediation are a mixture of high concentrations of hemicellulose, cellulose, lignin which have a calorific value. Treated thermochemically the biomass becomes a fuel gas that can be used for heat and electricity generation. The metals retrieved during the thermochemical process are concentrated, making it easier to recover.

Many of the metals that contaminate soils are also valuable and scarce natural resources, dispersed throughout the environment via industrial and commercial activities. It’s already been recognised that the recovery of these elements is critical for the sustainability of a number of industries. Arsenic, for example, is predicted to run out sometime in the next five to 50 years if consumption continues at present rates – and is an essential part of the production of transistors and LEDs. Nickel (used for anything involving stainless steel) and platinum group metals (used in catalytic converters, fertilisers etc.) are also identified as critical materials to the UK economy at risk of depletion in the Resource Security Action Plan (RSAP). However, despite increasing demand, none of this supply is supported by recycling due to the high cost of recovery from low concentrations when compared to conventional mining.

Initial pilots are underway. Currently, the Chinese Government’s Ministry for Land Resources is working with the Chinese Academy of Sciences and international partners including ourselves at Cranfield to investigate the potential for widespread application of this approach.

Next week sees the first major event dedicated to the science behind the approach. The first international Symposium on Phytoremediation for Energy & Element Developments (SPEED 2016), organised by Cranfield University (www.cranfield.ac.uk/SPEED2016), brings together researchers and policy-makers to discuss the current state-of-the-art and futurevision for the technologies involved.

The aim of the conference, taking place on 19 April 2016 at the Royal Institution of Chartered Surveyors in London, is to understand better the research challenges, economic and policy drivers and scope for low cost contaminated land remediation using bioenergy production and metal(loid) element extraction, promoting the collaboration between industry and land management developments, linking research with policy initiatives. The event will review the most recent scientific opportunities and consider the contribution and  development challenges to achieving low cost, low energy soil treatments that recover valuable resources for future use.

Dr Phil Longhurst, Reader in Environmental Technology, Cranfield University, www.cranfield.ac.uk

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