Evaluation of system performances and microbial communities of two temperature-phased anaerobic digestion systems treating dairy manure Wen Lv a , Wenfei Zhang c , Zhongtang Yu a,b,⇑ a Department of Animal Sciences, The Ohio State University, Columbus, OH 43210, United States b Environmental Science Graduate Program, The Ohio State University, Columbus, OH 43210, United States c Department of Biostatistics, Columbia University, New York, NY 10032, United States highlights  The NT-TPAD system achieved better overall performance than the AT-TPAD system.  Both digesters of each TPAD system had different roles between two TPAD systems.  Each digester harbored distinctive microbial populations.  Certain microbial groups were significantly correlated with system performance.  Methanosarcina was important in both systems but Methanosaeta only in NT-TPAD. article info Article history: Received 9 April 2013 Received in revised form 3 June 2013 Accepted 5 June 2013 Available online 13 June 2013 Keywords: Biogas DGGE Methane Methanogens qPCR abstract Two temperature-phased anaerobic digestion (TPAD) systems, with the thermophilic digesters acidified by acidogenesis products (AT-TPAD) or operated at neutral pH and balanced hydrolysis/acidogenesis and methanogenesis (NT-TPAD), were evaluated to treat high-strength dairy cattle manure. Despite similar methane productions (about 0.22 L/g VS fed), the NT-TPAD system removed significantly more VS (36%) than the AT-TPAD system (31%) and needed no pH adjustments. The thermophilic digester of the NT-TPAD system dominated the system performance and performed significantly better than that of the AT-TPAD system. The opposite held true for the mesophilic digesters. Differences of the thermo- philic digesters between two TPAD systems affected the microbial communities of both local and down- stream digesters. Each digester harbored distinctive microbial populations, some of which were significantly correlated with system performance. Methanosarcina was the most important methanogenic genus in both TPAD systems, while Methanosaeta only in the NT-TPAD system. Their populations were inversely related to VFA concentrations. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Compared to mesophilic single-stage digesters that are com- monly used in full scale (De Baere, 2000), temperature-phased anaerobic digestion (TPAD) systems are considered one of the most promising approaches that improve both efficiency and reliability of the anaerobic digestion (AD) process in renewable energy production and biomass waste management (Lv et al., 2010; Mata-Alvarez et al., 2000). Previous studies suggested that TPAD systems could achieve improved pathogen control, solid removal, and methane production compared to mesophilic single-stage digesters (Riau et al., 2010; Santha et al., 2006), and other AD systems (Kim et al., 2004; Riau et al., 2010). A TPAD system consists of a first stage thermophilic digester and a second stage mesophilic digester. The thermophilic digester can enhance hydrolysis and acidogenesis due to reduced feedstock recalcitrance and increase microbial metabolism at an elevated temperature, while the mesophilic digester provides lenient condi- tions supporting efficient and stable syntrophic acetogenesis and methanogenesis due to reduced inhibitor toxicity at a lower tem- perature (Lv et al., 2010). Depending on the pH of the thermophilic digester, a TPAD system can be categorized as either an AT-TPAD system, where the thermophilic digester is operated at acidic pH (Youn and Shin, 2005), or a NT-TPAD system, where the thermo- philic digester is operated at neutral pH (Sung and Santha, 2003). The acidic pH of the thermophilic digester in an AT-TPAD system has been shown to favor hydrolysis and acidogenesis at the ex- pense of syntrophic acetogenesis and methanogenesis (Chyi and 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.06.013 ⇑ Corresponding author. Address: Department of Animal Sciences, The Ohio State University, 2029 Fyffe Road, Columbus, OH 43210-1095, United States. Tel.: +1 614 292 3057; fax: +1 614 292 2929. E-mail address: yu.226@osu.edu (Z. Yu). Bioresource Technology 143 (2013) 431–438 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech