Download 2017_07: Phytoremediation for Renewable Energy

2017_07: Phytoremediation for Renewable Energy:
Energy Production During Decontamination
Supervisors: Dr Jason Hallett ([email protected]), Dr Paul Fennell, and Dr
Jeremy Woods (Centre for Environmental Policy)
Department: Chemical Engineering
Increasing energy demand necessitates the development of renewable fuels. These
fuels can be made from virgin biomass, though this brings into question their
sustainability (land use, food / fuel issues) and presents a significant economic
challenge due to high feedstock prices. Simultaneously, there are currently ca.
300,000 contaminated land sites in Europe, mostly due to industrial activity. This
includes nearly 1,000 UK sites contaminated by heavy metal pollutants (Pb, Cr, Cu,
As, Ni, Zn, Cd and Hg) and therefore unsuitable for agriculture.
Phytoremediation relies on the ability of plants to remove hazardous compounds from
the soil by integrating them into plant metabolism. The most efficient method is
phytoextraction, where some plants (hyperaccumulators) can extract 1 – 10,000 mg
metal kg-1 dry mass. Phytoextraction of heavy metals is a cheap alternative to soil
removal, an in situ remediation that is aesthetically appealing and technologically
simple, while maintaining soil biodiversity without producing any waste – if the metals
are recovered and sold (phytomining) it can also provide some small revenue.
Unfortunately, neither phytoremediation nor phytomining are economically viable, as
the remediation process is slow and hyperaccumulators rarely combine significant
metal uptake with a fast growing cycle. At present, “phytominers” burn all of the
biomass to recover the metal and use the ash as fertilizer, an inefficient use of the
plant. This project aims to grow a phytoaccumulator plant with high biomass yield from
which to extract the contaminant metal using ionic liquids. We will develop
methodologies to CO2 – neutral fuels from metal contaminated biomass, fuel whose
cost is subsidized by the phytoremediation. After 4-10 years of bioenergy crop growth,
we will have produced 2nd generation bioethanol, biochar, bio-oils, metals, and new
cropland. This will increase the economic viability of both biorefining and
phytoremediation, and increase food production through biofuel production. This
requires a low-cost, low-energy process to separate lignin from cellulose, for which we
recently developed the use of novel, low-cost ionic liquids, which have high efficiency,
insensitivity to biomass inputs, and ease of product recovery.
We will contaminate soil with mine-level Ni and Zn salts to provide a synthetic
contaminated soil. We will then grow hyperaccumulating plants (willow, sunflowers)
For more information on how to apply visit us at www.imperial.ac.uk/changingplanet
Science and Solutions for a Changing Planet
for 4-12 weeks, with control plants available from Canadian remediation projects.
These will then be deconstructed using ILs that fractionate wood by extracting lignin,
leaving a cellulose pulp which is filtered and processed to bioethanol; addition of water
to the remaining IL solution precipitates lignins for pyrolysis to produce bio-oils and
biochar.
This project will focus on re-developing the IL-based pretreatment strategies used for
waste wood (with 98-99% metal removal) and virgin biomass through the incorporation
of phytoremediation. The pretreatments will be performed to determine the optimum
conditions for delignification, and understand the effect of the metals on biopolymer
quality. Key outcomes will be the amount of metal removed from soil, the amount of
sugar produced, and the chemical or energy value of recovered lignin. Finally, we will
develop high-level models to project the positive implications of this technique for land
use.
For more information on how to apply visit us at www.imperial.ac.uk/changingplanet