Rice Hulls for Composites - Introduction to Polymeric Composites with Rice Hulls - page 64

Nature also helps by way of worms in the soil, which can play a key part in rice-
hull decomposition because rice hulls can be difficult to compost due to their high
content of cellulose and lignin. Their waxy surface cover also impedes microbial
attack due to their low capacity to absorb water. Using composts made by mixing
rice hulls with manure greatly contributes to micronutrient content and improves the
soil structure because of greater retention of water and air. This is a good example
of utilisation of crop residue and its transformation into a resource. Rice hulls with
their high contents of lignin and cellulose are a source of the precursor of humus
(the organic-matter component with the greatest stability and nutrient availability).
Researchers have developed composting practices of rice hulls to obtain fertilisers
that are suitable for use in other applications (e.g., public and domestic gardens).
These ready-to-use organic fertilisers are also sold in bags made from recycled paper
or plastics.
5.4.9 Rice Hulls in Cement Bricks
Traditionally, most rice hulls have been disposed of as waste. However, for some
time, the practical possibilities of such agricultural waste have been emerging in
applications, particularly in building construction. Two significant factors to promote
the search for alternate materials are (i) environmental concerns, and (ii) the shortage
and increasing costs of traditional materials used for particular applications. Examples
include cement bricks or clay bricks for building construction.
Many manufacturers of cement and clay bricks are now mixing in a high proportion
of rice hulls in the form of ash or in its natural state to produce excellent bricks.
According to reports from researchers and actual users of these bricks, they perform
well against the elements, vermin and mould, and could easily replace the part of
natural sand (silica) because rice hulls (especially in the form of ash) are high in silica.
Reduced material costs are also a significant factor.
5.4.10 Rice Hull Briquettes
Briquettes have been in place for a long time as a cheap source of fuel for many
applications. Growing environmental concerns have prompted people to look for
alternate solutions for heating and ambiance fires that result in minimal environmental
pollution. The economic aspects of alternate fuels to replace traditional fuels are also
significant. Traditionally, petroleum-based fuels had taken precedence and this trend
will probably continue for some time, especially where large industrial applications
are concerned.