Characterization of Rice Husk Varieties in Uganda for Biofuels

Uganda has registered recent successes in rice production making it a potential rice basket for Eastern Africa (Africa Rice Center, 2013). The remarkable rice boom in Uganda is attributed to good farming practices, premium market prices, and favorable policies that have stimulated large private investment in the rice sector over the last few years. As a result, paddy production jumped from about 120,000 t in 2002 to more than 220,000 t in 2011 (Africa Rice Center, 2013). Rice husk (RH) is the waste generated during the milling process of rice. On average 20% of the paddy rice is husk (Giddel and Jivan, 2007), giving an annual global total production of about 144 million Mt (FAO, 2011). Several conversion techniques exist that can be utilized to extract energy from rice husks. They include thermo-chemical, bio-chemical and physico-chemical conversion techniques (Delivand et al., 2011). Besides the use of rice husk for production of biofuel, it can also be used to manufacture bio-products such as particle boards, insulation boards, ceiling boards and as a fertilizer.

Moreover, the burning of rice husk under controlled conditions generates rice husk ash (RHA) which is a valuable material for industrial applications due to its high silica content. RHA contains 87“97% silica which can serve as a source for many silicon-based materials (Rozainee et al., 2008). In addition, the ash from biomass fuel contains only trace amounts of heavy metals, which makes them fairly easy to dispose off and can also be a good fertilizer (Olanders and Steenari, 1994).

Despite the potential benefits associated with rice husk, only about 17% of the rice husk produced globally, find an application per year (Ankur, 2010), suggesting that very large quantities become a waste. The common practice of burn-ing rice husk without heat recovery and openly dumping of these wastes still prevails especially in developing countries to which Uganda is no exception (UNEP, 2009). In other places, the rice husk is left to rot in situ, subsequently emitting greenhouse gasses (GHG) and causing other environmental problems (Jeng et al., 2012). Moreover in many develop-ing countries, the utilization of rice husk is constrained by unavailability of improved technology. The chemical differ-ences between biomass components directly influence their chemical reactivities. This is why the knowledge of the total amount of each component is crucial to predict the efficiency of a biomass conversion process (Ando et al., 2000). Similarly, the utilization of RHA depends on the composition of ash which in turn depends on the plant species, growth conditions and ash fraction (Demirbas, 2005). This study therefore set out to investigate the properties of rice husk from ten selected rice varieties in Uganda. This was done so as to precisely determine the possible technologies for potential utilization of the husks from each rice variety. Additionally, an economic comparison was made to evaluate the benefits of electricity production from rice husks as opposed to diesel engine gen-erators.

Materials and methods

Sample collection and preparation

Ten varieties of rice grains were collected from one geograph-ical region in Uganda. The samples were de-husked in an identical de-husker. Approximately one kg of husk from each rice variety was carefully kept in separate sampling bags. The samples were each subsequently milled to pass through a 1 mm mesh sieve using a 1093 cyclotec sample mill for sub-sequent characterization.

Characterization of rice husk varieties

The characterization work involved bulk density, proximate analysis, ultimate analysis, lignin, hemicellulose and cellulose analyses. Three experimental runs were conducted for each parameter and then the average value obtained.

References:

Please cite this article in press as: Olupot, P.W., et al., Characterization of rice husk varieties in Uganda for biofuels and their techno-economic feasibility in gasification. Chem. Eng. Res. Des. (2015), https://dx.doi.org/10.1016/j.cherd.2015.11.010

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