Comparison of SHF and SSF processes from steam-exploded wheat straw for ethanol production by xylose-fermenting and robust glucose-fermenting Saccharomyces cerevisiae strains

In this study, bioethanol production from steam-exploded wheat straw using different process configurations was evaluated using two Saccharomyces cerevisiae strains, F12 and Red Star. The strain F12 has been engineerically modified to allow xylose consumption as cereal straw contain considerable amounts of pentose. Red Star is a robust hexose-fermenting strain used for industrial fuel ethanol fermentations and it was used for comparative purposes. the highest ethanol concentration, 23.7 g/L, was reached using the whole slurry (10%, w/v) and the recombinant strain (F12) an an SSF process, it showed an ethanol yield on cunsumed sugars of 0.43 g/g and a volumetric ethanol productivity of 0.7 g/l h for the first 3 h. Ethanol concentrations obtained in SSF processes were in all cases higher than those from SHF at the same conditions. Furtermore, using the whole slurry, final ethanol concentration was improved in all tests due to the increase of potential fermentable sugars in the fermentation broth. Inhibitory compounds present in the pretreated wheat straw caused a significantly negative effect on the fermentation rate. However, it was found that the inhibitors furfural and HMF were completely metabolized by the yeast during SSF by metabolic redox reactions. An often encountered problem during xylose fermentation is considerable xylitol production that occurs due to metabolic redox imbalance. However, in our work this redox imbalance was counteracted by the detoxification reactions and no xylitol was produced

Battles over Biofuels in Europe: NGOs and the Politics of Markets

In this paper, we argue that a consortium of NGOs has played a significant role in shaping the market for, and restricting the use of, biofuels as an alternative to conventional fuels for road transport in Europe. This paper considers why a number of NGOs (Greenpeace, Oxfam, WWF, RSPB, Friends of the Earth) have chosen to enter the biofuels debate, and how they have variously developed policy, agreed a political campaign, and exercised political influence, in a key area of the world's response to major global climate change: how to reduce the carbon footprint of transport. We found that in many cases the development of NGO policy has been driven more by narrow political opportunities for influence than by broader and more coherent policy responses to global climate change or economic development, or indeed rigorous assessment of the scientific evidence. The research provides evidence of how NGO policies and lobbying significantly affected biofuel policy changes, review processes, target reductions, and sustainability regulation in the UK and in Europe. We consider that politically instituted markets, such as the one for biofuels, are examples of the emergence of new forms of governance of capitalist political economies facing a novel and pressing combination of drivers (climate change, energy security, resource constraints, and sustainable land-use). Politically instituted markets open up possibilities for political intervention from non-governmental or party-political actors, in ways that other markets do not. If political shaping of markets by NGOs becomes more widespread, issues of democratic legitimacy and public scrutiny will become ever more pressing. The paper is based on in-depth interviews with senior scientific directors and policy-makers in five NGOs, and of senior officials in UK government departments and the European Commission (DG Environment and DG Transport and Energy). It forms part of a wider ESRC research project in Brazil, the USA and Europe on the Transition to Sustainable Bioeconomies. </jats:p