IntroductionPeanut shells (PS) are abundant agro-industrial waste products that are recalcitrant to degradation under natural conditions [1]. The increasing expansion of peanut production has led to accumulation of large quantities of these shells all over the world. In the US alone, peanut production increased by 45% between 2011 and 2012, bringing production to 3.04 million metric tons [2]. Globally, 45.6 million metric tons of peanuts are produced annually [3]. It has been estimated that for every kg of peanuts produced, 230-300 g of peanut shells are generated [4]. Therefore, as much as 13.7 million metric tons of peanut shells are churned out every year, most of which are dumped into the environment or burned [5,6]. Peanut shells are a renewable resource that could be targeted for purposeful use in the food, feed, paper and bioenergy industries. However, as yet, few if any value-added uses exist for them [7].Over the years, various attempts to utilize peanut shells have been made. Small fractions were incorporated into animal feed, especially for cattle [8], while some authors have experimented on their use as dietary fiber for humans [9]. Other non-food research trials include uses in pulp production [10], feedstock for bioethanol production [11,12], particle board component [13], mulch and activated charcoal [7]. However, the major drawback to their use in large scale industrial operations is the high lignin content.Much like other agricultural lignocellulolysic biomass, peanut shells are composed mainly of lignin, cellulose and hemicellulose. Lignin, a complex polymer, is the most recalcitrant component of plant biomass [14] and binds tightly to, and provides a physical seal around, cellulose and hemicellulose [11,[15][16][17][18], thereby protecting them against attack by hydrolytic enzymes. The restricted bioavailability of these sugars and other components is thought to be largely physical, with lignin molecules reducing the surface area available to enzymatic penetration and activity [19]. In order to gain access to the sugars in cellulose and AbstractWorld consumption of peanuts has increased tremendously, resulting in abundance of peanut shell waste. The high lignin content of peanut shells limits their bioconversion to useful products or recycling. Therefore, the synergy in co-substrating peanut shells (PS) and cornstalks (CS) to enhance biodegradation was evaluated. Various compositions of peanut shells and cornstalks (% dry weight) herein called co-substrate -90PS:10CS, 75PS:25CS, 50PS:50CS, 25PS:75CS, 10PS:90CS, and two controls Cont1-100PS and Cont2-100CS were studied under solid state fermentation (SSF) with a white rot fungus, Pleurotus ostreatus for 120 days. A two-factorial experiment in a completely randomized design (CRD) was used. Results showed that substrate composition and fermentation time were important variables in substrate degradation. Lignin degradation, losses in organic matter, cellulose and hemicellulose increased with time. Increasing the composition of CS in co-substrates...