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The Belgian Campine has long been the subject of multidisciplinary research into phytoremediation of a vast area of farmland that has been moderately polluted with heavy metals such as cadmium. On an experimental field in the municipality of Lommel biologists have been investigating the metal extraction potential of energy maize, rapeseed and short rotation coppice amongst others. Especially willow demonstrated some phytoextracting capacity whereas the metal extraction potential of energy maize appeared to be rather limited. From an economic point of view however, energy maize is a feasible option for generating an alternative income for the affected farmers whereas the economic potential of willow has been open for further investigation. Because willow mainly consists of lignin, cellulosis and hemicellulosis, thermochemical technologies are better suited than biological ones for the conversion of willow into valuable products. Fast pyrolysis appears to be more promising than combustion and gasification both from an ecological and an economical point of view. Due to the lower process temperature of fast pyrolysis most of the metals do not volatilize and remain in the residual char. For the small scale of operation expected in the Belgian Campine, fast pyrolysis is also preferred above combustion and gasification in terms of return on investment. However, economic risk analysis showed that even with fast pyrolysis there is a high chance of economic loss. Therefore risk reduction strategies have been identified: combined production of heat and power, fast co-pyrolysis of willow with biopolymers, and activation of the residual char show promising results.

Economic trade-offs exist between the production of biochar and bio-oil from pyrolysis of biomass. The yield of the typical fast pyrolysis products is dependent on the process temperature: maximum oil yields are obtained at temperatures between 500 and 520 °C, while the char yield decreases with temperature. Several valorization opportunities exist for these pyrolysis products: the char can be applied as a source of energy, a soil amendment or a resource for active coal production, whereas pyrolysis oil can be used for the production of heat and/or electricity and chemicals. These valorization routes influence the potential sales prices of the pyrolysis products. As a consequence, careful selection of the process temperature is required to optimize the total incoming revenues and hence the profitability of a fast pyrolysis plant. In this paper the optimal process temperature for a fast pyrolysis plant has been calculated, by elaborating Yoder’s model when biochar is used as a resource for active coal production and the pyrolysis oil is burnt in a combustion engine for the combined production of heat and power (CHP). It has been applied to the quantities of oil and char that can be expected from willow cultivation for phytoremediation in the Belgian Campine. The results indicate that the net revenues from the pyrolysis oil combustion are rather constant and hence independent of temperature, whereas the net revenues from char activation clearly decrease as temperature increases. Under current assumptions, the production of active coal apparently is more profitable than the production of oil and hence the optimal temperature equals 250 °C. However, one needs to take account of important uncertainties such as the gross revenue of active coal and the cost price of fume gas treatment. Besides, other opportunities might exist for the valorisation of the pyrolysis oil, resulting in differing optimal process temperatures for fast pyrolysis.

The value of phytoextracting crops (plants cultivated for soil remediation) depends on the profitability of the sequential investment in a conversion technology aimed at the economic valorization of the plants. However, the net present value (NPV) of an investment in such an innovative technology is risky due to technical and economic uncertainties. Therefore, decision makers want to dispose of information about the probability of a positive NPV, the largest possible loss, and the crucial economic and technical parameters influencing the NPV. This paper maps the total uncertainty in the NPV of an investment in fast pyrolysis for the production of combined heat and power from willow cultivated for phytoextraction in the Belgian Campine. The probability of a positive NPV has been calculated by performing Monte Carlo simulations. Information about possible losses has been provided by means of experimental design. Both methods are then combined in order to identify the key economic and technical parameters influencing the project's profitability. It appears that the case study has a chance of 87% of generating a positive NPV with an expected value of 3 million euro (MEUR), while worst-case scenarios predict possible losses of 7 MEUR. The amount of arable land, the biomass yield, the purchase price of the crop, the policy support, and the product yield of fast pyrolysis are identified as the most influential parameters. It is concluded that both methods, i.e., Monte Carlo simulations and experimental design, provide decision makers with complementary information with regard to economic risk.