Production and Effectiveness of Amorphous Silica Fertilizer from Rice Husks Using a Sustainable Local Energy System

Abstract

Aims: In rice-producing countries, rice husk has long been considered a waste material. This research aimed to establish a sustainable local energy system by combustion of the rice husk, as well as to evaluate the effectiveness of the rice husk ash as silica fertilizer. Study Design: The amorphous silica in the rice husk ash was produced in an actual size (plant-scale) boiler, and the ash was used in pot and field experiments to assess its effectiveness as fertilizer for plant growth. Place and Duration of Study: This study was conducted over a period of four years (2011–2014) at the rice-processing center of a local agriculture association in the Toyama Prefecture, Japan. Methodology: The rice husk was combusted in a boiler under the conditions: 1) burning the rice husk as is, 2) incinerating in an oxygen rich atmosphere, and 3) incinerating at low temperatures of approximately 500–900°C, for heat production and the effectiveness of the rice husk ash as silica fertilizer was evaluated. Results: This study investigated the use of rice husk ash as a silica fertilizer for rice crops, and established a boiler system for rice husk combustion. As the estimated income (97,176 USD) derived from our proposed boiler system is expected to exceed the estimated expenses (81,600 USD), the system could be considered sustainable. An ideal agriculture system is proposed in this study, i.e., the rice harvest is sent to a rice-processing center for milling and the rice husk is combusted in a boiler to produce hot water. The hot water is used in the rice drying process and is piped to greenhouses for heating. Furthermore, the ash generated by the combustion of the rice husk is used effectively in the rice paddies as fertilizer. In the rice fields, the rice plants absorb the silica for growth to produce the rice crop for the next season. Consequently, this farming cycle could be expected to continue indefinitely. Conclusion: The system described in this study could be applied wherever rice is cultivated, to the considerable advantage of the producers.