The controversial debate over the sustainability and "green-ness" - of biofuels has been re-ignited by research from Swiss-based institute Empa. While the study maintains that biofuels can be sustainable, depending on certain conditions and the technology involved, only a few are more environmentally friendly than petrol.Gizmag reported on the study entitled 'Harmonisation and extension of the bioenergy inventories" and an assessment carried out by the Swiss Federal Laboratories for Materials Science and Technology (Empa) in conjunction with the Institute Agroscope Reckenholz-Tänikon and the Paul Scherrer Institute. DIFFERENT POLLUTIONIt is an update of a first-of-a-kind report compiled in 2007 that has been made more relevant for the present with new energy plants, manufacturing processes and updated assessment methods. Yet, the researchers arrived at a similar conclusion... although biofuels can have a smaller carbon footprint than fossil fuels, they produce other types of environmental pollution, including soil acidity and excessive levels of fertilisers in lakes and rivers.More alarmingly, biofuels from deforested areas have a bigger greenhouse gas footprint than fossil fuels. This is also true of indirect land usage, Gizmag reports: if existing agricultural land is used for the first time for a biofuel crop, new areas will have to be cleared to make up for displaced food and animal feed crops.Empa researcher Rainer Zah said: “Most biofuels just deflect the environmental impact: fewer greenhouse gases, thus more growth-related pollution for land used for agriculture.”The Gizmag report says biogas made from residues and waste materials performs particularly well in terms of reducing emissions, having as much as half the environmental effect of petrol. Ethanol-based fuels tend to be greener than those biofuels with an oil base. Nevertheless, any environmental advantage or disadvantage depends on how the fuel is made and the technology involved.POSITIVE NOTEBesides the methodological updates, the new report also fixed some "weaknesses" of the previous report, where the researchers underestimated how many changes to natural areas, such as rain forest destruction, afftected the greenhouse gas balance.On a positive note, biofuel crops can increase the carbon content of soil. As examples, the report cites the cultivation of oil palms on unused grazing land in Colombia or jathopha plantations in India and east Africa where desertified land has been transformed into arable areas. However, Gizmag says, the report's authors warn that all these benefits depend on the type of agriculture being practiced and the land’s previous use, with each biofuel type needing to be analysed individually.The report also included some general advice on what to do to avoid the most adverse ecological results from biofuel production. Clearing forests and bush areas is an obvious no-no. In the case of agricultural land, indirect change of land is also bad practice. Finally, second-generation biofuels, based on residues such as straw, garden and timber waste, can be environmentally sound if they are not being diverted from other uses and if their extraction does not compromise soil fertility and biodiversity.