Spent Mushroom Substrate- Prospects and Challenges of Agro-waste Management into Sustainable Solutions: A Review

India being an agrarian country produces huge amount of agro-wastes which can be sustainably bio converted through mushroom cultivation. It entails minimum investment for a small scale enterprise and ameliorate income of rural households of India to combat poverty. As a by-product of mushroom production, the Spent Mushroom Substrate (SMS) is generated which consists of unused fungal parts, semi mineralized lignocellulosic waste and retrievable mineral nutrients. The genesis and application of SMS comprises an integrated approach of rural bio-entrepreneurship because it can be converted into several aspects supporting circular economy. The semi fermented biomass can be re-utilized as source of compost, bio fertilizer, or as substrate for a fresh or 2^nd cycle of mushroom production. Plant pathogens can be minimized by SMS derived bio pesticides. SMS can be used as an amendment of livestock and aquaculture feed thus reducing the cost of procuring commercial foods. Biofuels can be extracted from SMS and various bioremediation processes can be achieved by its Biochar. Industrially important lignocellulosic enzymes are retrieved from SMS and used in various applications minimizing agro-wastes from the field. With such versatile benefits at hand, no critical review was observed addressing the challenges and constraints associated with SMS application like standardization steps, toxicity concerns and commercial feasibility. Thus, this review article focusses to abridge various aspects of SMS utilization with the technical pros and cons to reduce and safeguard environmental consequences.