What is rice straw?
Rice straw is a rice by-product produced when harvesting paddy. Each kg of milled rice produced results in roughly 0.7–1.4 kg of rice straw depending on varieties, cutting-height of the stubbles, and moisture content during harvest. Rice straw is separated from the grains after the plants are threshed either manually, using stationary threshers or, more recently, by using combine harvesters (Figure 1).
Figure 1. Harvesting grain and straw using the combine harvester.
Rice straw, as a lignocellulosic biomass, is comprised of three components: lignin, cellulose, and hemicelluloses. These could be fractionated through pretreatment as shown in Figure 2. Cellulose and hemicelluloses are fiber organics, whereas lignin is the cell wall (Klass 1998).
Figure 2. Major components of lignocellulosic biomass. Source: Klass 1998.
Characteristics of rice straw
Specific weight of uncompressed rice straw is about 70–80 kg/m3 at a moisture content of about 15–18%. Rice straw properties and its ash composition are summarized in Tables 1 and 2, respectively.
Table 1. Rice straw properties.
Table 2. Properties of ash from rice straw.
The characteristics of rice husk compared with other solid fuels can be summarized as follows:
Typical management options for rice straw
Traditionally, in South and Southeast Asian countries, rice straw and husk are considered as wastes, either dumped into rivers or burned in the field, causing GHG emissions, contamination, and pollution. With the development of recent technologies, rice residues can be processed and managed using better practices. Management options for rice residues can be classified as in-field and off-field management (Figure 3).
Figure 3. Options for rice straw management and use.
Guillemot A, Bruant R, Pasquiou V, Boucher E. 2014. Feasibility study for the implementation of two ORC power plants of 1 MWe each using rice straw as a fuel in the context of a public-private partnership with the institutions PhilRice and UPLB. Courbevoie, France: ENERTIME.
Jeng Shiun Lim, Zainuddin Abdul Manan, Sharifah Rafidah Wan Alwi, Haslenda Hashim. 2012. A review on utilisation of biomass from rice industry as a source of renewable energy. Renew. Sust. Energ. Rev. 16:3084–3094.
Jenkins BM. 1998. Physical properties of biomass. In: Kitani O, Hall CW, editors. Biomass Handbook Chapter 5.2. Gordon and Breach, New York.
Klass L. 1998. Biomass for Renewable Energy and Fuels. Entech International, Inc. Barrington, Illinois, United States.
Munder S. 2013. Improving thermal conversion properties of rice straw by briquetting. Master-Thesis. University of Hohenheim.