Contents lists available at ScienceDirect Biomass and Bioenergy journal homepage: www.elsevier.com/locate/biombioe Research paper Effects of ammonia fiber expansion (AFEX) treated corn stover on anaerobic microbes and corresponding digestion performance Juan Pablo Rojas-Sossa a,1 , Yuan Zhong a,1 , Francesca Valenti a,b , John Blackhurst a , Terence Marsh c , Dana Kirk a , Di Fang a,e , Bruce Dale d , Wei Liao a,* a Anaerobic Digestion Research and Education Center, Department of Biosystems and Agricultural Engineering, Michigan State University, East Lansing, MI, USA b Department of Agriculture, Food and Environment, University of Catania, Via Santa Sofia, Catania, Italy c Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI, USA d Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI, USA e College of Resources and Environmental Sciences, Nanjing Agricultural University, Jiangsu, PR China ARTICLE INFO Keywords: Anaerobic co-digestion Corn stover AFEX Animal manure Microbial community ABSTRACT Dynamic changes in microbial communities and digestion performance of AFEX treated corn stover co-digestion were compared to untreated corn stover co-digestion. Even though it took longer to stabilize the AFEX treated corn stover co-digestion system than it did for the untreated corn stover co-digestion, the results show that AFEX treated corn stover is a good feedstock to enhance the archaea community and improve biogas production. In the stabilized digestion system, the AFEX treated corn stover co-digestion increased abundance of archaea com- munity (11.8%) by approximately three times compared to the untreated corn stover co-digestion (4.3%), The corresponding biogas production (213 L/kg VS loading) of the AFEX treated corn stover co-digestion was 22% higher than that (175 L/kg VS loading) of the untreated corn stover co-digestion. AFEX treatment could enable more extensive use of lignocellulosic biomass for anaerobic digestion to generate biogas and thereby provide another route for lignocellulosic biofuel production. 1. Introduction Anaerobic digestion of lignocellulosic materials has recently at- tracted increasing attention since the U.S. Environmental Protection Agency (U.S. EPA) updated the renewable fuel standard in 2017 and approved anaerobic digestion as a new fuel pathway (Pathway Q) [1]. Biogas from anaerobic digestion of lignocellulosic material is classified as a D3 renewable fuel in the cellulosic biofuel category. However, compared to cellulosic ethanol production, anaerobic digestion for biogas production consumes much less cellulose and hemicellulose (approximately 20–50% and 30–70%, respectively) [2–4]. Yue et al. [5] concluded that, under the selected digestion conditions for a manur- e:stover mass ratio of 4:1 and a hydraulic retention time (HRT) of 30 days, a semi-continuous co-digestion of corn stover and dairy manure produced 127 g methane per kg total solids (TS) loading, and the cel- lulose and hemicellulose content of the mixed manure and stover was reduced by 45% and 74%, respectively. MacLellan et al. [6] studied an anaerobic co-digestion of corn stover and swine manure at five different manure:stover mass ratios between 1:4 to 4:1 and the HRT of 20 days. The methane productivity reached 152 g methane per kg TS loading with the cellulose and xylan reduction of 42 and 40%, respectively, at the optimal manure:stover mass ratio of 3:2. Considering the recalcitrant nature of lignocellulosic materials, feedstock pretreatment is needed to improve digestion performance for cellulose/hemicellulose reduction (utilization) and biogas production. Numerous physical and chemical processes including mechanical comminution, pyrolysis, steam explosion, ammonia fiber expansion (AFEX), CO 2 explosion, acid and alkali treatment etc. have been studied to treat lignocellulosic materials [7]. Some of these have been used to pretreat lignocellulosic biomass for enhanced anaerobic digestion [8]. Chemical methods (H 2 SO 4 , HCl, CH 3 COOH, NaOH, KOH, Ca(OH) 2 , NH 3 , and H 2 O 2 etc.) are most effective at both improving methane yield and reducing cellulose and hemicellulose contents [8–10]. Jurado et al. [10] reported that aqueous ammonia soaking can increase the methane yield by 37–41%, 25–27%, and 94–162% for anaerobic digestion of wheat straw, miscanthus, and willow, respectively. Song et al. [11] https://doi.org/10.1016/j.biombioe.2019.105263 Received 12 January 2019; Received in revised form 27 April 2019; Accepted 5 June 2019 * Corresponding author. Department of Biosystems & Agricultural Engineering, Michigan State University, 524 S. Shaw Ln. Room 202, 48824-1323, East Lansing, MI, USA. E-mail address: liaow@msu.edu (W. Liao). 1 Juan Pablo Rojas-Sossa and Yuan Zhong equally contributed to this paper. Biomass and Bioenergy 127 (2019) 105263 0961-9534/ © 2019 Elsevier Ltd. All rights reserved. T