Abstract—In this study, we illustrated the performance and microbial community of single- and two-phase systems anaerobically co-digesting cassava pulp and pig manure. The results showed that the volatile solid reduction and biogas productivity of two-phase CSTR were 66 ± 4% and 2000 ± 210 ml l -1 d -1 , while those of single- phase CSTR were 59 ± 1% and 1670 ± 60 ml l -1 d -1 , respectively. Co- digestion in two-phase CSTR gave higher 12% solid degradation and 25% methane production than single-phase CSTR. Phylogenetic analysis of 16S rDNA clone library revealed that the Bacteroidetes were the most abundant group, followed by the Clostridia in single- phase CSTR. In hydrolysis/acidification reactor of two-phase system, the bacteria within the phylum Firmicutes, especially Clostridium, Eubacteriaceae and Lactobacillus were the dominant phylogenetic groups. Among the Archaea, Methanosaeta sp. was the exclusive predominant in both digesters while the relative abundance of Methanosaeta sp. and Methanospirillum hungatei differed between the two systems. Keywords—Anaerobic co-digestion, Cassava pulp, Microbial diversity, Pig manure. I. INTRODUCTION IOMASS is widely available, and its utilization for renewable energy production is becoming increasingly essential, in order to reduce emissions from fossil fuel sources and consequently to prevent global warming. Among different conversion processes for biomass, biological anaerobic digestion is one of the most economic ways to produce biogas from biomass [1]. P. Panichnumsin is with the Joint Graduate School of Energy and Environment, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand, and with Excellent Center of Waste Utilization and Management, National Center for Genetic Engineering and Biotechnology, National Sciences and Technology Development Agency, Bangkok, Thailand (e-mail: pornpan@biotec.or.th). B. K. Ahring is with AAU, Copenhagen Institute of Technology, Lautrupvang 15, 2750 Ballerup, Denmark (e-mail: bka@tricity.wsu.edu). A. Nopharatana is with Pilot Plant Development and Training Institute, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand (e- mail: annop@pdti.kmutt.ac.th). P. Chaiprasert is with School of Bioresources and Technology, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand (phone: 662-470-7525; fax: 662-452-3455; e-mail: pawinee.cha@kmutt.ac.th). Anaerobic digestion involves a series of metabolic interactions among various groups of micro-organisms. It is considered to be a complex biochemical process, comprising 4 steps including hydrolysis, acidogenesis, acetogenesis and methanogenesis. Since the acidogenic phase and methanogenic phase are greatly different in physiological and nutritional requirements, growth kinetics, and sensitivity to environmental stresses, a two-phase system takes advantage of phase separation, using separate units for acidogenesis and methanogenesis, in order to optimize environmental conditions for each phase [2, 3]. Much research has demonstrated that a two-phase system has several advantages over a conventional single-phase system, such as a higher organic degradation rate, methane production rate and process stability, as well as reducing significantly any risk of digester overloading [4-7]. Two-phase has been suggested for waste containing high amounts of readily organic compounds, in order to achieve a balanced process at a high organic loading rate [2]. In addition, results reported in the research literature have indicated that the two-phase system was able to achieve higher degradation of particulate organic compounds. The hydrolysis rate of ligno-cellulose could be enhanced by a slightly acidic pH, improving the working conditions for hydrolytic/acidogenic bacteria [8-10], and the produced VFA can improve the accessibility of hydrolytic enzymes [11, 12]. During starch production from cassava (Manihot esculenta), approximately 5.2 Mt of fresh cassava pulp is generated as a major solid waste annually in Thailand [13]. Since cassava pulp comprises 50-60% starch in dry matter and 60-70% moisture content [14], it has a major potential as raw material for biogas production. However, the low concentrations of nutrients such as nitrogen and the low buffering capacity of this waste, represent a difficulty for conversion of this material. In an anaerobic digestion process using cassava pulp, sufficient nitrogen is necessary to activate growth of microbes and to maintain buffering capacity, in order to improve process performance and stability. Generally, options to meet the above purposes are an addition of chemicals, such as urea, ammonium salt, and bicarbonate etc. or co-digestion, using waste containing high nitrogen content, which may be a more environmentally friendly alternative. In Thailand, with an average of 8 million pig produced per year, an approximate amount of 2.16 Mt of manure [13] is seen as a Comparative Performance and Microbial Community of Single-phase and Two-phase Anaerobic Systems Co-Digesting Cassava Pulp and Pig Manure P. Panichnumsin, B. K. Ahring, A. Nopharatana, and P. Chaipresert B World Academy of Science, Engineering and Technology International Journal of Agricultural and Biosystems Engineering Vol:4, No:2, 2010 162 International Scholarly and Scientific Research & Innovation 4(2) 2010 scholar.waset.org/1307-6892/10378 International Science Index, Agricultural and Biosystems Engineering Vol:4, No:2, 2010 waset.org/Publication/10378