In my country, Indonesia, rice is the staple food for nearly all of the population (260 million people). I don't know how much exactly today's rice production, but the rice cultivation covered a total of around 10 million hectares throughout the country. As the by-product, the rice milling industry generates abundant husk. Nowadays, people use this husk as a fuel, such as for power generation or for paddy drying. I know this for fact, such paddy drying using rice husk as fuel is widely practiced in South Sumatera province. However, nobody knows what to do with the ash of the rice husk. Normally, people just dump them on the ground. I did googling about the rice husk ash, apparently it can be used further as a raw material in making concrete or cement. I am not sure though whether it is just in the stage of research or already in mass production. Or, whether there are other alternative use. Your thought?