Bioresource Technology 124(2012)379-386 Contents lists available at SciVerse ScienceDirect 88恶 Bioresource Technology ELSEVIER journal homepage:www.elsevier.com/locate/biortech Comparison of solid-state to liquid anaerobic digestion of lignocellulosic feedstocks for biogas production Dan Brown,Jian Shi,Yebo Li* Department of Food,Agricultural,and Biological Engineering.The Ohio State University/Ohio Agricultural Research and Development Center,1680 Madison Ave,Wooster, OH 44691-4096.United States HIGH LIGH TS Solid state anaerobic digestion(SS-AD)of eight types of lignocellulosic biomass. Liquid anaerobic digestion (L-AD)of eight biomass feedstocks was compared with SS-AD. No significant difference in methane yield between SS-AD and L-AD. Volumetric biogas productivity of SS-AD was 2-to 7-fold greater than that with L-AD. Methane yields from crop residues were higher than those from woody biomass. ARTICLE IN FO ABSTRACT Article history: Lignocellulosic biomass feedstocks (switchgrass,corn stover,wheat straw,yard waste,leaves,waste Received 20 April 2012 paper,maple,and pine)were evaluated for methane production under liquid anaerobic digestion(L- Received in revised form 11 August 2012 AD)and solid-state anaerobic digestion(SS-AD).No significant difference in methane yield between L- Accepted 13 August 2012 Available online 22 August 2012 AD and SS-AD.except for waste paper and pine,were found.However,the volumetric productivity was 2-to 7-fold greater in the SS-AD system compared with the L-AD system,except for paper.Methane yields from corn stover,wheat straw,and switchgrass were 2-5 times higher than those from yard waste. Keywords: Solid-state anaerobic digestion maple,and pine biomass.Waste paper had a methane yield of only 15 L/kg VS caused by souring during Biogas SS-AD due to organic overloading.Pine also had very low biogas yield of 17 L/kg VS,indicating the need Corn stover for pretreatment prior to SS-AD.The findings of this study can guide future studies to improve the Switchgrass efficiency and stability of SS-AD of lignocellulosic biomass. Lignocellulosic biomass 2012 Elsevier Ltd.All rights reserved. 1.Introduction methanogenic bacteria involved in AD have a low growth rate and are sensitive to inhibitors such as low pH caused by excessive Anaerobic digestion (AD)is a naturally occurring phenomenon concentrations of volatile fatty acids (VFAs).Thus,maintaining a in which organic matter is decomposed by an assortment of mi- balance of the four phases (hydrolysis,acidogenesis,acetogenesis crobes in an oxygen-free environment to produce biogas,composed and methanogenesis)of the AD process is essential.The effect of primarily of methane(CH4)and carbon dioxide(CO2)(Frigon and composition of lignocellulosic biomass on methane yield has al- Guiot,2010).Although the initial applications of AD were for stabil- ready been studied extensively:however,most of these studies ization and treatment of waste sludge,AD can also be a source of were limited to liquid AD (L-AD)which operates at a total solids renewable energy (Yu and Schanbacher,2010).AD not only (TS)content of 15%or less even though solid-state AD (SS-AD). provides an alternative source of energy but is also an alternative which is generally operated at a TS content of 15%or higher route to divert organic wastes and reduce greenhouse gas emissions (Guendouz et al.,2010),would be ideal for feedstocks such as agri- from landfills(Mata-Alvarez et al.,2000;Frigon and Guiot,2010). cultural and municipal solids wastes due to their availability and The presence of lignin,the crystallinity of cellulose,and limited low moisture content(Yu and Schanbacher,2010).SS-AD has many surface availability reduce the biodegradability of lignocellulosic advantages over L-AD including a smaller reactor volume for the biomass,making the hydrolysis step one of the bottlenecks that same solids loading;fewer moving parts:lower energy input for limit the production of methane (Frigon and Guiot,2010).The heating and mixing:easier to handle end product;and a greater acceptance of inputs containing glass,plastics,and grit (Li et al.. Corresponding author.Tel.:+1 330 263 3855. 2011).Problems in L-AD,such as floating and stratification of fats, E-mail address:li.851@osu.edu (Y.Li). fibers,and plastics,are not present in SS-AD(Chanakya et al.,1999). 0960-8524/-see front matter2012 Elsevier Ltd.All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.08.051Comparison of solid-state to liquid anaerobic digestion of lignocellulosic feedstocks for biogas production Dan Brown, Jian Shi, Yebo Li ⇑ Department of Food, Agricultural, and Biological Engineering, The Ohio State University/Ohio Agricultural Research and Development Center, 1680 Madison Ave., Wooster, OH 44691-4096, United States highlights " Solid state anaerobic digestion (SS-AD) of eight types of lignocellulosic biomass. " Liquid anaerobic digestion (L-AD) of eight biomass feedstocks was compared with SS-AD. " No significant difference in methane yield between SS-AD and L-AD. " Volumetric biogas productivity of SS-AD was 2- to 7-fold greater than that with L-AD. " Methane yields from crop residues were higher than those from woody biomass. article info Article history: Received 20 April 2012 Received in revised form 11 August 2012 Accepted 13 August 2012 Available online 22 August 2012 Keywords: Solid-state anaerobic digestion Biogas Corn stover Switchgrass Lignocellulosic biomass abstract Lignocellulosic biomass feedstocks (switchgrass, corn stover, wheat straw, yard waste, leaves, waste paper, maple, and pine) were evaluated for methane production under liquid anaerobic digestion (L￾AD) and solid-state anaerobic digestion (SS-AD). No significant difference in methane yield between L￾AD and SS-AD, except for waste paper and pine, were found. However, the volumetric productivity was 2- to 7-fold greater in the SS-AD system compared with the L-AD system, except for paper. Methane yields from corn stover, wheat straw, and switchgrass were 2–5 times higher than those from yard waste, maple, and pine biomass. Waste paper had a methane yield of only 15 L/kg VS caused by souring during SS-AD due to organic overloading. Pine also had very low biogas yield of 17 L/kg VS, indicating the need for pretreatment prior to SS-AD. The findings of this study can guide future studies to improve the efficiency and stability of SS-AD of lignocellulosic biomass. 2012 Elsevier Ltd. All rights reserved. 1. Introduction Anaerobic digestion (AD) is a naturally occurring phenomenon in which organic matter is decomposed by an assortment of mi￾crobes in an oxygen-free environment to produce biogas, composed primarily of methane (CH4) and carbon dioxide (CO2) (Frigon and Guiot, 2010). Although the initial applications of AD were for stabil￾ization and treatment of waste sludge, AD can also be a source of renewable energy (Yu and Schanbacher, 2010). AD not only provides an alternative source of energy but is also an alternative route to divert organic wastes and reduce greenhouse gas emissions from landfills (Mata-Alvarez et al., 2000; Frigon and Guiot, 2010). The presence of lignin, the crystallinity of cellulose, and limited surface availability reduce the biodegradability of lignocellulosic biomass, making the hydrolysis step one of the bottlenecks that limit the production of methane (Frigon and Guiot, 2010). The methanogenic bacteria involved in AD have a low growth rate and are sensitive to inhibitors such as low pH caused by excessive concentrations of volatile fatty acids (VFAs). Thus, maintaining a balance of the four phases (hydrolysis, acidogenesis, acetogenesis and methanogenesis) of the AD process is essential. The effect of composition of lignocellulosic biomass on methane yield has al￾ready been studied extensively; however, most of these studies were limited to liquid AD (L-AD) which operates at a total solids (TS) content of 15% or less even though solid-state AD (SS-AD), which is generally operated at a TS content of 15% or higher (Guendouz et al., 2010), would be ideal for feedstocks such as agri￾cultural and municipal solids wastes due to their availability and low moisture content (Yu and Schanbacher, 2010). SS-AD has many advantages over L-AD including a smaller reactor volume for the same solids loading; fewer moving parts; lower energy input for heating and mixing; easier to handle end product; and a greater acceptance of inputs containing glass, plastics, and grit (Li et al., 2011). Problems in L-AD, such as floating and stratification of fats, fibers, and plastics, are not present in SS-AD (Chanakya et al., 1999). 0960-8524/$ - see front matter 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.08.051 ⇑ Corresponding author. Tel.: +1 330 263 3855. E-mail address: li.851@osu.edu (Y. Li). Bioresource Technology 124 (2012) 379–386 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech