CHARACTERIZATION OF A BIOGAS-PRODUCING MICROBIAL COMMUNITY Buletinul AGIR, Supliment 1/2013 9 THE IMPACT OF BACTERIAL PRETREATMENT ON CORN STOVER FOR BIOGAS PRODUCTION Balázs KAKUK 1 , Orsolya STRANG 1 , Norbert ÁCS 1 , Etelka KOVÁCS 1 , Gábor RÁKHELY 1,2 , Kornél L. KOVÁCS 1,2 , Zoltán BAGI 1 1 University of Szeged, Szeged, Hungary, 2 Biological Research Center, Hungarian Academy of Sciences, Szeged, Hungary REZUMAT. Porumbul este cultivat în cantităţi semnificative cu scop nutritiv; produsele intermediare rezultate sunt planta de porumb ce este de obicei nefolosită. Datorită cantităţilor mari existente şi a conţinutului ridicat de celuloză acesta reprezintă un potenţial substrat pentru producerea de biogaz. În orice caz, această biomasă bogată în celuloză nu este utilizată în fermentatoarele anaerobe datorită insolubilităţii sale ridicate. Ea forme4ază o crustă la suprafaţa fazei lichide în reactoare ce are ca rezultat inhibarea procesului de producere a biogazului. Deoarece conţinutul ridicat de materii solide inhibă procesul formare a biogazului la scară industrială este necesară realizarea unui pretratament. Astfel, digestia anaerobă a plantei de porumb poate un mod eficient, economic şi cu impact pozitiv asupra mediului de valorificare a deşeurilor agricole pe lângă producerea unui biocombustibil regenerabil valoros. În studiul nostru, o bacterie celulozică a fost utilizată pentru pretratarea biomasei bogată în celuloză şi a fost măsurat impactul pe care îl are acest proces asupra fermentaţiei anaerobe a substratului. Cuvinte cheie: pretratament, plantă de porumb, celuloză, digestie anaerobă, biogaz. ABSTRACT: Maize is grown in large quantities for nutritional purpose; its agricultural by-product is the corn stover, which is usually unused. Because of its high abundance and high cellulose content, it is a promising substrate for biogas production. However, this cellulose-rich biomass is not used in anaerobic fermentors today, due to its insolubility. It forms a solid crust at the top of the liquid phase in the reactors, which results in the inhibition of biogas formation. Since the high solid-content inhibits the industrial-scale fermentation of corn stover, some kind of pretreatment is considered necessary. Therefore the anaerobic digestion of the corn stover could be an effective, economically profitable and environmentally friendly way of disposing agricultural wastes - besides producing a valuable renewable biofuels. In our study, a cellulolytic bacterium has been used for the pretreatment of the cellulose-rich biomass and the impact on the anaerobic fermentation of the substrate was measured. Keywords: Pretreatment; Corn stover; Cellulose; Anaerobic Digestion, Biogas. 1. INTRODUCTION Today, the most frequently used energy crop in biogas fermentors in the region is maize [1]. However, growing crops merely for biofuel production is a question under debate, considering the malnutrition of nearly 900 million people worldwide [2]. The growing price of the energy crops also pressurizes the use of alternative substrates. Fortunately biogas-technology posses a unique advantage among renewable energy producers: it can combine agricultural waste treatment, with the production of valuable green energy efficiently [3]. There are several agricultural by-products that can be utilized in biogas fermentors, including rice straw, switchgrass, wheat straw and corn stover, the latter is the most abundant in Hungary and the eastern part of Romania. With the use of these substrates, the advantages of the biogas-technology could be exploited the most. Corn stover, due to its high abundance, high cellulose and therefore energy content is a promising substrate for biogas fermentors. However, its high cellulose content also generates complications in its fermentation: the insoluble biomass usually floats on the top of the liquid phase, and forms a solid crust. This results in the inhibition of biogas formation, and other problems as well [4]. The problem is mainly due to the structural components of the plant cell wall, mainly the cellulose. Cellulose makes up most of the plant cell wall, along with the lignin and hemicelluloses [5]. It is a biopolymer, consisting of D-glucose monomers, attached to each other with ß-glycosidic bonds. Between the strands, secondary H-bonds strengthen the composition further. This arrangement results in a structure so tight that even water molecules cannot enter to the inside of the compound, thus making it insoluble [6]. To effectively digest the cellulose-rich biomass in an anaerobic fermentor, some kind of pretreat-