Woodchips
[3] They may also be used as an organic mulch in gardening, landscaping, and ecosystem restoration; in bioreactors for denitrification;[4] and as a substrate for mushroom cultivation.
[12] There are four potential methods to move woodchips: pneumatic, conveyor belt, hopper with direct chute, and batch system (manual conveyance).
The blade rotation is set parallel to the opening so wood is pulled into the chipper by the spiral motion.
Screw-type, also called high-torque rollers, are popular for residential use due to being quiet, easy to use and safer than disk and drum types.
In industry, processing of bark chips is often separated after peeling the logs due to different chemical properties.
[citation needed] Woodchips are also used as landscaping and garden mulch, for water conservation, weed control, and reducing and preventing soil erosion.
[20][21][22][23] It is a subsurface system where denitrification by micro-organisms utilizing a carbon source (as electron donor) reduces the nitrate into a harmless nitrogen gas.
[21] Denitrifying woodchip bioreactor have a low construction and operational costs with a comparatively long lifespan going up to 15 years.
[25][26] A 2013 experiment showed that after 70 days of startup, a woodchip pile loaded with liquid pig manure at 5 L/m2/day removed an average of 90% of nitrate after one month.
If the trees are taken down in the winter and left to dry for the summer (with teas in the bark and covered so rain can't reach to them), and is then chipped in the fall, the woodchips' moisture content will be approximately 20–25%.
[32] Compared to the solid waste disposal problems of coal and nuclear fuels, woodchip fuel's waste disposal problems are less grave; in a study from 2001 fly ash from woodchip combustion had 28.6 mg cadmium/kg dry matter.
[36] When wood burning is used for space heating, indoor emissions of 1,3-butadiene, benzene, formaldehyde and acetaldehyde, which are suspected or known carcinogenic compounds, are elevated.
[38] Unlike the smooth, uniform shape of manufactured wood pellets, woodchip sizes vary and are often mixed with twigs and sawdust.
While avoiding the costs associated with refinement, the lower density and higher moisture content of woodchips reduces their calorific value, substantially increasing the feedstock needed to generate an equivalent amount of heat.
Greater physical volume requirements also increase the expense and emissions impact of trucking, storing and/or shipping the wood.
On the other hand, woodchip systems are typically designed to cleanly and efficiently burn "green chips" with very high moisture content of 43–47% (wet basis).
[39] If woodchips are harvested as a by-product of sustainable forestry practices, then this is considered a source of renewable energy.
[41] Woodchips and bark chips can be used as bulking agents in industrial composting of municipal biodegradable waste, particularly biosolids.
Undergrowth coppice is ideal for chipping, and larger trees may be left in place to shade the forest floor and reduce the rate of fuel accumulation.
[citation needed] Woodchip costs usually depend on such factors as the distance from the point of delivery, the type of material (such as bark, sawmill residue or whole-tree chips), demand by other markets and how the wood fuel is transported.
[44] In the 20 years leading up to 2008, prices have fluctuated between US$60–70/oven-dry metric ton (odmt) in the southern states, and between US$60/odmt and US$160/odmt in the Northwest.
[45] Wood chips have been used as a source of single-dwelling heating in Canada since the early days of settling but the development of oil and natural gas has dramatically decreased its usage.
Prince Edward Island (PEI) has the most wood-chip plants due to high electricity rates and subsidies from the federal government.
The European Union is promoting woodchips for energy production in the EU Forest action plan 2007–2011.
Large supplies of softwood chips are imported from countries such as the United States and Australia for this purpose.
