Fuels derived from biomass
Biofuels are made from renewable sources or from the byproducts of waste streams. There is an ongoing argument about the sustainability of biofuels. Opponents say biofuels are not ‘clean’ and they use land that could be used for food. In some places growing biofuels has caused deforestation, soil erosion and water degradation. Proponents say it is renewable and can be grown sustainably on marginal land or made from waste ‘streams’. Studies have reported that New Zealand has enough marginal land to become self-sufficient in transport fuels.
Plants use photosynthesis to grow and produce biomass. Biomass can be used directly as fuel or to produce liquid and gas biofuels.
All biofuels, being carbon-based, create CO2 emissions when used. However if the biomass is regrown the CO2 emitted gets reabsorbed from the atmosphere and there is little/no net effect.
Liquid biofuel is usually either a bio-alcohol such as ethanol or a bio-oil such as biodiesel. Biodiesel can be used in modern diesel vehicles with little or no modification to the engine and can be made from vegetable as well as from animal oils and fats (both recycled and new). Biodiesel creates 20-40% less emissions than petrol.
In New Zealand ethanol and biodiesel are are being phased in as blends with petrol and diesel.
Solid biofuels are used directly usually in the form of combustible solids – wood, solid municipal biogenic waste, combustible field crops and agricultural waste. Most sorts of biomass can be burnt to heat water and to drive turbines. Solid biomass can also be gasified and used as below.
Biogas can easily be produced from current waste streams, such as: paper production, landfills, sewage and cattle effluent (good news for the dairy industry!). These wastes are slurried and allowed to naturally ferment, producing methane gas which can be burnt or converted into higher grades of gas.
The remaining waste after biogas extraction is often more suitable as fertilizer than the original biomass.