Lesser known options for the use of sawings and sawdust
Small sized sawmill residues such as sawings and saw dust in many part of the world are simply dumped or burned. In Germany more than half of this material is being used for the production of wood based panels, mainly particle board. Actually (2007) a growing percentage becomes pressed to pellets or briquettes for energy use and so the resources are becoming scarce! In addition to this well known products there is a surpringly broad variety of other uses for small sizes wooden particles:
|Sawdust in many countries still is regarded as a troublesome by-product of sawmilling operation and often disposed of as landfill or incinerated, thus causing environmental problems.
In central Europe cattle are usually kept in stalls with slatted floors. In comparison with straw sawings offer definite advantages as bedding material. They can be easily be disposed as part of liquid manure, moreover, the do not block the spaces between the slots. Certain disadvantages have been reported: especially as far as dairy cows are concerned. Sharp pointed sawings can cause injury to cows´ teats and lead to streptococcal infections. It is therefore recommended that only softwood sawings/ shavings may be used, which is dry and lacking splinters.
Like straw, sawings are also widely used in horse stables. Of particular importance is the high level of absorbency provided by dry shavings; furthermore as they can be pressed into bundels, they require less storage space than straw. (Example) They are, however, somewhat more expensive and the waste disposal can cause problems since farmers and mushroom growers are often hesitant to accept such“wooden” manure.
Pet litter is a product of special importance not only on the German market. In addition to straw, both sawings and shavings are used. The number of small mammals (guinea pigs, rabbits etc.) in German households rose from 4 million in 1996 to 5.7 million in 2000. 59% of these households have children. Current demographic trends show that these numbers can decrease. They might be compensated for through a rising interest for pets among elder people.
|Pet litter from shavings is widely used. Wooden cat litter newly is competing with mineral based products.
In Germany in 2001 there were a total of 6.9 million cats, making them the most popular pet. This number is still growing. In the year 2002 cat litter with its 189 million € in sales holds the largest market share among “commodities” for pets . This market is dominated by mineral based materials, however manufacturers have noted a tendency toward the use of wood based products which are said to be more “ecological”. (Example)
|Through mushroom production low value wood (residues) can be transformed into high value food.
2. Mushroom Production
Through the production of edible fungi low value wood material (sawdust, small pieces of stems) can be transformed into high value food. This can be done in a very efficient way: When growing shiitake (Lentinula edodes) intensively under controlled conditions (defined substrate composition, temperature, humidity, light) the fresh weight of mushrooms produced can reach 70– 100 % of the dry mass of the wood comsumed.
A detailed description on the cultivation of shiitake (Lentinula Edodes) on synthetic logs you can find here: http://www.mushroomcompany.com/200108/shiitake.pdf
Large increases can be expected because it has only been possible to cultivate a few basidiomycetes (mainly Agaricus, Lentinus, Pleurotus, Auricularia, Volvariella, Flammulina and Tremella) up to now. In many cases it is still not known how the fruiting body development can be induced. When this question is solved, more species can be used and the overall production will further increase.
3. Wood as Food and Feed
About 200 years ago it was found that the large molecular carbohydrates in wood, namely cellulose and hemicellulose, can be fractionised by acid treatment into simple sugars (glucose, hexose and pentose) and thus converted to food. Because of the huge investments necessary to build production facilities, this has only made sense economically in times of need . But as ruminants are able to utilise cellulose through encymatic solubilisation, studies have been carried out to establish whether wood products could be used in addition to grass and other feeds. Experiments with fermented or acidified wood flour (see 7.) have been successful. In India, for example, a suitable solid state fermentation process has been developed to enhance the biological composition and nutrition value of sawdust using Pleurotus sajor-caju (springerlink). Cellulose made from sawdust can possibly be used as feed if it is carefully derived and finely ground .
Among the wood flour products shown in Table 1 feed extender is mentioned. This is a fine wood meal obtained from so called fat trees (softwoods and“smooth” hardwoods which contain a fatty oil, e.g. birch (1.5– 3.3%) and lime (6.3- 9.2%)). In times of need this has been added to normal feed, it is partially digestable.
For human consumption wood meal can be used as an extender in cereal flours; in addition, spruce meal can be used to coat baking trays to prevent the dough from sticking.
|For smoking often sawdust is being used.
4. Food Processing
Sawmill by-products have not only been used directly and indirectly for the production of food stuffs but have, for centuries, also been used to help conserve them and to improve their taste.
Smoking is a traditional method of food conservation for meat and fish. This is usually done by smouldering of hardwoods such as beech, oak and maple or juniper in the form of sawings, shavings or split wood. The smoke has a germicidal and drying effect on the food. Depending on the temperature it can be categorized as cold, warm or hot smoke .
Oak wood chips from wood barrel production are used to improve the taste of red wine during fermentation in steel containers. Just as wooden barrels are toasted so too are the chips. This makes them an important factor in the development of aromatic substances in red wine which determine its taste and color .
|Ceiling boards and tiles made from sawdust and cement have been presentend on the World Exposition EXPO 2000 by Nigeria. (Report: PDF 810 kB)
5. Building Products
An interesting use of sawmill by-products in construction is demonstrated by wall form units made of low-density cement-bonded wood fiber composite. "It is composed of specially graded recycled waste wood (100% clean, natural softwood lumber) that is neutralized and mineralized and then bonded together with Portland cement. This material is lightweight with an adequate carrying capacity, porous, thermal insolating and very durable. It does not rot nor decay. It is vermine, termite and insect proof and does not support fungus growth. It is accepted as environmentally friendly and does not contain nor emit any toxic elements." (source; other example) When producing this material it care has to be taken that the wood being used is compatible with cement. If its sugar content is too high, it can be reduced by first subjecting the sawdust to fermentation. - The use of a mixture of sawdust, sand and cement for making wall panels has been fairly common in parts of Australia and other countries for many years.
6. Environmental protection
One possibility for using sawings and sawdust for environmental protection purposes is to mix it with materials which are to be composted, e.g. manure. In the composting of sewage sludge wooden particles serve as structural material. Its main function is to help adjust the water content of the rotting mixture to an optimal value and to increase the volume and stability of the pores.
|Not only living trees but also chipped wood can care for clean air and water!
A mixture of wood chips and compost can be used as biofilter to treat odorous air. A well-managed biofilter can reduce odor emissions by 85%, hydrogen sulfide by 90% and ammonia by around 60%.(source)
Modified sawdust can be used for filtering:
- Chemical modification of sawdusts with fatty acylazides was carried out in order to obtain new materials for the removal of organic pollutants, e.g., fats, among others, from water. The wood thus modified presented higher affinities than unmodified wood for oleic acid and olive-oil chosen as representative compounds of fats and allowed their elimination from water. (springerlink)
- In another case the reaction of succinic anhydride with wood meal from Picea abies was studied in a search for low cost materials usable in the removal of heavy metals. Three more or less modified sawdust samples were used after activation with NaHCO3 for the removal of cadmium(II) from water. (springerlink)
- In contrast, trials with untreated sawdust from different tree species resulted in a relatively low degree of filtering of Cd (II), but displayd much higher rates for copper (II) and zinc (II). In these trials sawdust from hardwood species such as oak and black locust was more efficient as an absorbent than sawdust from the poplar, willow and fir .(springerlink)
A Japanese company is offering a fast fermentation system for sewage sludge using wood chips as a kind of catalyst. To reduce the consumption of water and the production of sewage sludge sawdust toilets can be helpful.
Researchers in Iowa (U.S.A.) have found that lining underground drainage tiles with wood chips can filter out about 70 percent of the nitrates stemming from dead plants, human waste and crop fertilizers. As the wood decomposes, bacteria transform the nitrates into nitrogen gas. Lab tests have shown that all nitrates could be effectively removed if the water is held within the system long enough .(source)
residues can be used for soil
On the other hand a recent study of DŁnisch
et al. (2007), conducted in Germany and Brazil,
demonstrated the potential of wood residues (chips
and flour from Pinus sylvestris, Pinus
taeda and Cordia goeldiana) as
suitable raw materials for the development of
new products for soil amelioration. Pellets
containing a mixture of solid wood, ash, and
charcoal residues impregnated with nutrients
could be developed to increase the cation
exchange capacity and thereby the efficiency of
the application of mineral fertilizers. So waste
from wood processing and burning facilities
could be be used to reduce leaching of nutrients
into the groundwater and to stabilize the chemical soil conditions in long
An indirect way of environmental protection is if sawdust substitutes for sphagnum peat in horticultural applications (example 1, example 2). Generally there is an ongoing research on the potential of wood/ charcoal residues for soil amelioration (springerlink).
7. Wood Flour Products
For approximately 100 years wood flour has been produced by either sieving sawdust and/or finely grinding sawings, shaving or pieces of wood. Because of the very high standards which have to be met in the production of wood flour products, the raw material must be carefully selected and processed according to strict guidelines.
A fundamental factor with regard to the quality of wood flour is the original tree species; the size and form of the grit also plays a role although with decreasing size the influence of the species and the form becomes less relevant. Other important properties include the degree of purity, moisture and resin content, colour, type of chemical reaction, ash content and the iodine-potassium-starchgrade.
Table 1: Variety of possible uses of wood flour as described by Vorreiter (1960)
|Filler for batteries
|Putty and adhesives
|Filler for paper and cardboard
|Cleaning and polishing agents
|Coating for baking trays
|Wood plastic composites
|Explosives and fuses
|Medical dressing material
A more extensive publication on this topic you can download: Manuscript.
In 1969 John M. Harkin from the Forest Products Laboratory of the U.S. Forest Service published a very substantial paper with 221 references on "Uses of Sawdust, Shavings and Waste Chips". (If not available for download anymore, ask Wood Report!). At the end it provides a table on the uses based on special physical properties!