Environmentally Friendly Silica Extraction from Rice Husk

In Thailand, rice husk is abandoned agricultural waste generated from rice milling. Even though it was commonly used as a fuel in household and biomass powerplant, there is still a lot of rice husk that is not utilized properly and disposed in landfills, leading to environmental problems. Previous studies found that rice husk contains up to 21-25 %wt of silica (SiO2) which can be extracted by several methods such as hydrolysis with acids or bases and burning method. Hydrolysis with acid is a conventional method for silica extraction from rice husk. Hydrochloric, nitric, sulfuric acid are mostly used for digesting organic contents in rice husk. However, the process of acid extraction produces acid wastewater that is toxic to the environment. Thus, alternative method for silica extraction should be investigated. This research aims to study a green silica extraction from rice husk using microbial fermentation, instead of using acid in conventional hydrolysis method. The microbial inoculum is the Microbial Activators (super LDD1) produced from the Land Development Department, Thailand. The super LDD1 is a group of microbes (Actinomyces and fungi) that has a high ability to produce cellulase enzyme for degradation of agricultural waste materials to a compost in a short period of time. The condition of fermentation such as amount of super LDD1 and fermentation time were investigated. The result indicated that the fermentation of rice husk with 0.1% (super LDD1) for 10 days was a promising method. No chemical was used in the process and the wastewater could be reused in the process.