We use the term ‘biomass’ to describe living or recently dead biological material. Biomass contains stored energy from the Sun. Plants absorb the Sun’s energy through a process called photosynthesis. When we burn biomass, for example, wood in an oven, the chemical energy that was stored is transformed into heat energy.
Burning wood is not the only way to release energy, and wood is not the only type of biomass available. Typically, the term biomass is used to refer to plant material but it can also include animal matter or biodegradable wastes. Organic material that has been transformed through geological processes, as is the case for oil, for example, is not included in this description.
In New Zealand, the biomass resources can include woody resources (including leafy plants), agricultural plant resources, residue from agriculture and forestry, as well as municipal (civic waste from towns and cities) and industrial wastes (this includes liquid sewage and manure).
The biofuels most likely to be sold in New Zealand are biodiesel and bioethanol. Biodiesel is made from vegetable oils and tallow (animal fats), while bioethanol is produced from fermented sugars and starches, such as maize, dairy whey and – in the future – wood waste.
There are a number of technologies that are used to convert energy from biomass material into fuel we can use. Not all of the technologies available have been used and tested to run at a commercial level in New Zealand.
Here are examples of conversion technologies that scientists currently examine to see how useful they might be to generate fuel from biomass:
- Combustion – the burning of biomass to generate heat (for example, wood). The energy product generated is either heat or heat and electricity. Combustion technology is used to heat water, the resulting steam can drive an electricity generator and the heat that is produced can still be used. This technology is commonly used in New Zealand.
- Gasification – using partial combustion to produce gas from biomass. Usually the types of gases that are being produced are carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H) and methane (CH4), which can then be used in internal combustion engines. This technology is not yet fully commercial in New Zealand.
- Pyrolysis – using heat in the absence of oxygen to break down organic matter to its chemical components. The energy product using this technology is typically bio-oil. To produce a bio-oil, moderate temperatures are needed. The original biomass material needs to be dry for this process. There are no commercial pyrolysis systems in New Zealand – this technology is still being researched by a few labs in New Zealand and around the world.
- Anaerobic digestion – naturally degrading organic material in the absence of oxygen that produces biogas. This technology is typically used to treat wastewater sludge and organic waste. Anaerobic treatment has been applied to a wide variety of solid and liquid organic wastes, including waste from food and beverage production (sugar, soft-drink, potato, vegetable, distillery and brewery wastes); meat, dairy and wool processing; and pharmaceutical and chemical industries. The significant advantages of anaerobic processes are low energy use and reduced sludge production, generation of biogas and the ability to extract valuable fertilisers from the digested residue. This technology is well established in New Zealand.
- Chemical and mechanical processing – converting canola, waste oil and tallow from meat processing to biodiesel by pressing and or transesterification. This technology is used in New Zealand to produce biodiesel in relatively small quantities from waste cooking oil. It is most likely that canola crops may be used for the production of oil for biodiesel.
- Biochemical and enzyme technology – this technology involves biological catalysts that can be used at critical stages of the bioconversion process to replace more energy-intensive methods. Ethanol is being produced from biochemical conversions of sugars and starch, for example. The ethanol is usually blended with the petroleum fuels but they can also be used on their own. Using bioethanol or biodiesel means we don't burn quite as much fossil fuel. Bioethanol and biodiesel are usually more expensive than the fossil fuels that they replace but they are also cleaner burning fuels, producing fewer air pollutants. This technology is still being researched in New Zealand.