Introduction
Cotton is a valuable industrial material. Its annual production has reached around 25.5 million metric tons worldwide (Cheng et al., 2011). Cotton exocarp (CE) and cotton seed hull are the two main by-products derived from cotton harvest and production. And more than 35 million tons of such cotton wastes could be generated per year globally (Apaydin-Varol et al., 2014). For cotton exocarp, a small amount of them are used for composting or combustion, while a large number of them are abandoned in the fields. The field operation tends to destroy soil structure and increase the risk in erosion. Cotton seed hull recovered from the oil extraction process, accounts for around 80% of cotton seed. The obtained cotton seed hull could be utilized as a medium for mushroom cultivation due to its comprehensive nutrition. However, after mushroom harvest, it is a challenge to store and dispose the spent mushroom substrate which is consisted of cotton by-products (MSC) (Phan and Sabaratnam, 2012). The residue is mainly composed of recalcitrant lignocellulose, which has a long degradation cycle naturally. Currently, most of spent mushroom substrate have been burnt for energy, which is unsustainable, environmentally unfriendly and uneconomical (Zhu et al., 2013). As lignocellulosic biomass, CE and MSC have the potential to be converted to energy, intermediate chemicals or materials via various biorefinery approaches. Their high value-added utilization can alleviate the pressure of environment pollution and extend the industrial chain of cotton production via biorefineries.