Environmental Engineering Reference
In-Depth Information
in areas with an excess of nutrients. In such situations, the use of digestate
for energy purposes, such as co-combustion for power generation, can be a
option. Further energetic use will normally involve additional treatment
such as fiber separation, drying and even pelletizing. The high ash, sulfur
and nitrogen content of digestate will necessitate emission control.
12.4.4 Other uses of digestate
An uncommon yet increasing use of the solid fraction of digestate is as
bedding material in animal breeding stables, substituting for straw.
Research on construction materials from dried manure fibers of AD-
processed animal manure carried out by Winandy and Cai (2008) and
Spelter et al. (2008) showed that the solid fraction of digestate can also be
used to make low-grade building products such as fiberboards or composite
materials. According to Rigby and Smith (2011), it would be possible to
produce medium density fiberboards (MDF) and wood-plastic composites
(WPC) from digestate resulting from food waste. The fibers of this digestate
are dried and blended with liquid resin and then pressed and formed into
panels, which is the same process as for treating wood to produce panels.
Another potential opportunity to use solid digestate is as raw material for
bio-pesticide production, specifically for the cultivation of Bacillus
thuringiensis, which is needed for the production of many bio-pesticides
(Rigby and Smith, 2011). In this case, the composition and the C/N ratio of
digestate have to be suitable and detailed investigation of the suitability of
digestate as a growth medium is required. A niche product for the use of
digestate may be the preparation of activated carbons by phosphoric acid
activation, as investigated by Yuan et al. (2010).
Digestate can be also used for vermiculture, producing high-quality
earthworm compost. Surplus earthworms can be then fed to chickens. In
countries such as China, digestate has been used as an additive to animal
feed for pig, chicken, fish and shrimp production; this option is limited by
national legislation and public acceptance.
12.5 Conclusion
Increasingly strict environmental legislation in most countries is aimed at
the avoidance of pollution of all kinds and losses of biodiversity, as well as
the prevention of any potential toxic effects and health risks for living
organisms. Producing digestate of high quality is part of the overall demand
for quality in today's society and is an integral part of biogas technologies,
providing more than just renewable energy. Besides renewable energy,
biogas from AD has the potential to deliver environmentally sound and
veterinary-safe solutions for the treatment of animal manure and suitable
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