Use of biotechnological approaches to add value to rice hulls

One of the most common agricultural wastes generated in rice producing countries, rice hull (RH) is considered an environmental problem due to increased rice production and RH accumulation, especially because natural degradation in the environment is very difficult and time-consuming. Currently, RH is mostly used as bed for broiler chickens or burned for energy generation, two processes that prevent environmental accumulation in a sustainable way, without adding value to the RH. To diversificate its use and effectively add some value to the RH, a pretreatment is frequently needed, allowing the application of several biotechnological approaches. In this review, we gather information about biotechnological uses of crude and processed RH, including their use as fertilizers, filler material in natural rubber and incorporation in cement for civil construction purposes, along with their use in processes as silica extraction and adsorption/removal of environmental contaminants as heavy metals and dyes. Finally, we critically evaluate the data published in the literature, and based on our own findings, we point future directions related to RH biodegradation and further methane production.