Biofuel production that challenges indirect land use change criticism
Human activities have led to the accumulation of toxic elements (including heavy metals) and a variety of organic contaminants in soils. These activities include long-term use of contaminated irrigation water, fertilisers, pesticides, and soil amendments (organic matter added to improve soil conditions) as well as mining. There are currently approximately 2.8 million contaminated sites in the EU-28, many of which remain unused. At the same time, biofuels are urgently needed to decarbonise transport but are facing widespread criticism, largely due to their use of arable land for feedstock production (so-called indirect land use change or ILUC). The EU-funded CERESiS project aimed to provide a win-win solution by growing energy crops that facilitate land decontamination through phytoremediation and phytomanagement and using them to produce clean biofuels. In the longer term, this will increase the land available for agriculture while producing non-ILUC biofuels.
High-yield biomass species for phytoremediation
CERESiS focused on perennial grasses and woody species with high biomass productivity and low soil contamination uptake levels. This strategy supports efficient and cost-effective large-scale processes while enabling easier biomass processing and conversion, respectively. “The high yield of these energy crops combined with their effective removal of soil contaminants incentivises farmers to plant them,” notes CERESiS coordinator Athanasios Rentizelas of the National Technical University of Athens. In addition, establishing the energy crops in highly contaminated land secures the contaminants in place, preventing their spread.
Conversion and contaminant separation approaches
CERESiS successfully adapted and optimised two thermochemical conversion methods to produce clean biofuel from contaminated feedstock while effectively retrieving the contaminants. Supercritical water gasification (SCWG) produces a gas that can be reformed into liquid biofuels. A key benefit is compatibility with wet biomass processing, eliminating the expensive and energy-demanding pre-drying process. “We modified the SCWG to recycle its process effluent stream, significantly reducing its water input requirement,” adds Rentizelas. Fast pyrolysis is a mature technology that produces liquid biofuel precursors (bio-oils). Its relatively low investment and operational cost make it well-suited to small production volumes and it produces biochar, a by-product with several applications including as a soil amendment and in metal processing. CERESiS also developed and demonstrated separation technologies to remove contaminants present in conversion products. Membrane gas absorption removed acid gas from the SCWG gas effluent. Electrocoagulation-flotation and electrochemical oxidation removed heavy metals from SCWG wastewater. Finally, microfiltration removed contaminated char particles from bio-oils.
Free online tool to support early-stage investment decisions
One of the most important outcomes was the decision support system. Growers and biofuel producers can assess combinations of biomass and conversion technologies to identify suitable biomass types for a given location and contaminant profile. “In some cases, establishing a value chain for biofuel production from contaminated land may be financially viable even without considering the benefits of land decontamination, provided that scale is large enough and high-yield biomass species are used,” Rentizelas says. In a surprising discovery with implications for the management of contaminated biomass, CERESiS found that most of the plant contamination in cases of highly contaminated soil is on plants rather than in them – in the form of dust. CERESiS has indeed delivered a successful and sustainable solution for energy and the environment with energy crops capable of phytoremediation and technologies to process them and remove their contaminants to produce clean biofuels.
Keywords
CERESiS, energy, biomass, soil, contaminants, biofuels, energy crops, SCWG, biofuel feedstocks, phytoremediation, ILUC, heavy metals
