Sustainable paddy cultivation through effective waste management

By Ishara Wijesinghe
Uva Wellassa University

The map of Sri Lanka shows a large number of blue colour reservoirs and channels against a greenish background. This is because of the well-distributed irrigation system and the availability of agricultural and forest lands. Ancient kings who ruled Sri Lanka gave priority to agriculture and irrigation because paddy cultivation was one of the most vital sectors in the country. At present, the government of Sri Lanka offers fertilizer subsidies, agricultural loans at low-interest rates and good quality seed to the farmers while assuring that the harvest is purchased by the government at good price margins. Not only the government but also some reputed private organizations are engaged in paddy cultivation in various ways.

Paddy cultivation was an art and culture in earlier days, now it is purely a business which always combines with science and technology. Therefore, the stakeholders in the paddy sector invest a considerable amount of money, time and manpower focusing a big volume of quality paddy harvest. According to the Central Bank Report 2019, among all the agricultural lands, paddy had been cultivated in about 1.12 million hectares during both Yala and Maha seasons and harvested 4.6 million metric tons of paddy. On an average, 20-25% by weight of the paddy is the husk which gives an annual total production of about 1 million metric ton of husk according to the annual paddy production of Sri Lanka in 2019. But the methods to manage and use the paddy husk waste innovatively is lacking though it represents some part of the investment. In another way, the accumulation (large heaps of husks) and mismanagements (open burning) of paddy husk waste cause a big environmental issue. The emission of carbon dioxide and other volatile compounds during burning is a big issue once open burning takes place everywhere in the country. As a country which has an agriculture-based economy, to what extent the people know about the value of this waste is problematic. Therefore, this effort is, to discuss the importance and management of paddy husk waste and to make aware of how society should think of waste material.

Why is paddy husk important?

Simply, it is a waste material which has an economic value. Also, it contains various natural compounds like silica and lignocellulose. The composition of paddy husks shows that it contains approximately 15−30% of silica, 70−85% of lignocellulose (35−40% of cellulose, 15−20% of hemicellulose and 20−25% lignin) and trace amounts of metal ions. These lignocellulosic materials and silica should have a monetary value because the inputs of the paddy production have converted into these forms through a natural process. In terms of energy, this material has high heat value which is sufficient to use as a renewable raw material to generate energy. From an economical point of view, this is a conversion of the investment and on the other hand, a loss of money if it is not utilized for any beneficial uses. Thus, the given facts indicate how important the paddy husk and how diverse the potential uses of it.

How can the paddy husk be used?

To generate energy…

It can be used in different applications as a bulk i.e. paddy husk is largely used as a fuel on a small scale, and on a large scale for electrical power and thermal energy generation. In some occasions, it is used as a fertilizer in agricultural fields. The high heat value (15MJ/kg) of paddy husk facilitates the use of it to generate electrical and thermal energy. Once the energy is generated, it can be used for heating and drying purposes i.e. the fossil fuel in industrial boilers can be substituted by paddy husks.

Some countries make briquettes and pellets of paddy husk by pressing at high pressure. This facilitates more efficient transportation compared to that of loose bulk. The use of paddy husk briquettes having comparatively high density (550kg/m3) can efficiently be used for energy production and this is a growing business in some paddy cultivating countries. For example, these briquettes and pellets are used in Myanmar and Cambodia to generate electricity. They have supplied the power generated through paddy husk to operate their rice mills while cutting down the amount of fossil fuel used for the same purpose earlier. Therefore, the paddy husk can be identified as a renewable and eco-friendly material which is efficient in generating energy.

In agriculture…

Soil properties in agricultural lands are important for the growth of crops and to receive high yield. But with the time, the physical and chemical properties of soil are reduced due to intensive agricultural practices. Therefore, the conditioning of soil in agricultural lands is required. In some countries, the paddy husk is usually used as a fertilizer in the same fields. However, biochar can be made by burning paddy husk with a limited supply of oxygen at temperatures less than 700°C. This biochar can be used as a conditioner of soil, storage of carbon, and filter for percolating water through the soil. Further, the biochar can increase the water-holding capacity, aeration and stimulate growth activity of plants while increasing the organic carbon, nitrogen, phosphorus and potassium levels in the soil. According to one author, the sequestration of carbon by biochar can help to mitigate climate changes. Likewise, paddy husks itself and as biochar have a number of benefits when considering the soil properties and climate change.

A combined approach to manage paddy husk waste; an example from the construction and tyre industries…

Complete combustion of paddy husk facilitates extraction of silica from it with simple chemical reactions. The concentration of silica in paddy hush ash is more than 90% by weight. This silica can be used as an additive in cement production, a green filler for rubber components, i.e. tyres, an absorbent material, a drug carrier and a medical additive, etc. Compared to other industries, more volume of silica is consumed in rubber and construction industries. In construction industries silica is used as an additive in cement, but synthetic silica is commonly used. So, there is a possibility to replace synthetic silica in cement with paddy husk ash silica. This can be a long term solution for managing paddy husk waste because most of the cement-based structures are built for a long period. Apart from this, the silica extracted from paddy husks can be used in rubber products at large volumes. Usually, rubber products are reinforced with carbon black, that is why people see them in black. However, in the recent past, the silica made of synthetic roots was used to improve the properties of rubber components. Now, silica-reinforced tyres which give low fuel consumption are highly used in vehicles. Therefore, this provides two advantages such as replacement of carbon black which causes various environmental issues and opening a new window to replace synthetic silica with silica extracted from natural sources such as paddy husks. Interestingly, the construction industry is now seeking methods to use waste tyres (in powder form) in cement composites to improve the shock absorbance and comfortability like properties. Thus, this provides a green light for tyre waste management also.

All in all, if technologies for extraction of silica like material from agricultural wastes (paddy husk, wheat straw) are scaled up to industrial level, these materials will effectively be utilized in different industries, meanwhile integrating the technologies and industries for sustainable economic development conserving the environment for future.

How should we think of wastes?

Before that, what does the term ‘waste materials’ stand for? The common understanding is, it is a material that has to be discarded with no use or a byproduct of a particular production process which cannot be used further or a thing has no value and use. All of these opinions are negative and this is a good platform to change the attitudes of the community. I also have heard such negative answers for the same question even from undergraduates who are considered as the cream of knowledge of the society. I believe that this is not a problem of their knowledge but the attitude of the society has gone into their minds. However, if we define the waste as a ‘valuable resource at a wrong place in a wrong form or wrong media’ it will imply that there are a number of uses of it as well as how the waste is converted into an effective form of use.

Changing of such established traditional attitudes of a society is big business, but top to bottom approach (from leaders to general society) can trigger such changes. There is enough number of acts, regulations and conventions in the world to manage the wastes. However, until we reach a philosophical change, the management of wastes will be a dream. Thousands of scientific research studies are going under the theme of waste management and effective findings are being used in various applications. The collaboration between researchers and the industry is vital to attain the goals of research and development. In Sri Lanka, the Universities and Research Institutes have established units to collaborate with the industry and this is a good approach to take the society towards an innovative direction. The waste management principles and methodologies like ‘Cleaner Production’ approach and ‘3R’ (Reduce, Recycle and Reuse) concept, etc., should go to the grass-root level of the society. The general community should be enlightened on the new concepts through extension services. If not the gaps between the expected goals of the country and the actual situation will increase and the development of the country will only be stagnated to concepts and policies printed on the papers. Overall, it is obvious that the integration of the whole society with positive attitudes is essential to accomplish the development of the country through knowledge and skills.

(The writer is a lecturer in Rubber Processing Technology, Department of Export Agriculture, Faculty of Animal Science and Export Agriculture, Uva Wellassa University, Badulla)