Reducing agitation energy-consumption by improving rheological properties of corn stover substrate in anaerobic digestion Libin Tian a , Fei Shen a,b , Hairong Yuan a , Dexun Zou a , Yanping Liu a , Baoning Zhu a , Xiujin Li a,⇑ a Centre for Resource and Environmental Research, Beijing University of Chemical Technology, 15 Beisanhuan East Road, Chaoyang District, Beijing 100029, PR China b Institute of Ecological and Environmental Sciences, Sichuan Agricultural University, Chengdu, Sichuan 611130, PR China highlights  Improving rheological properties was tried to reduce agitation energy-consumption.  Size-reduction & temperature-increase reduced shear stress by 10.4% & 11.7%.  9.2% P TS -reduction was achieved by size-reduction from 20 to 80-mesh at 35 °C.  10.3%/10 °C P TS -reduction was achieved at 20-mesh compared with 9.0%/10 °C at 80-mesh. article info Article history: Received 6 January 2014 Received in revised form 2 March 2014 Accepted 5 March 2014 Available online xxxx Keywords: Rheological properties Corn stover Anaerobic digestion Agitation energy-reduction abstract Rheological properties of corn stover substrate were investigated to explore agitation energy reduction potential for different total solid (TS) in anaerobic digestion. The effects of particle size and temperature on rheological properties and corresponding energy reduction were studied. The results indicated that corn stover slurry exhibited pseudo-plastic flow behavior at TS of 4.23–7.32%, and was well described by Power-law model. At TS of 4.23%, rheological properties were not obviously affected by particle size and temperature. However, when TS was increased to 7.32%, there was 10.37% shear stress reduction by size-reduction from 20 to 80-mesh, and 11.73% shear stress reduction by temperature-increase from 25 to 55 °C. P TS was advanced as variations of power consumption by TS-increase from 4.23% to 7.32%. There was 9.2% P TS -reduction by size-reduction from 20 to 80-mesh at 35 °C. Moreover, P TS -reduction of 10.3%/10 °C was achieved at 20-mesh compared with 9.0%/10 °C at 80-mesh. Ó 2014 Published by Elsevier Ltd. 1. Introduction The anaerobic digestion of lignocellulosic biomass is an impor- tant way to dispose agricultural residues for obtaining clean energy of biomethane. At present, anaerobic digestion of crop stalks has been paid increasing attention in China, as large amount of crop stalks such as corn stover and wheat straw is generated annually (Pang et al., 2008), serious hazy weather frequently appeared in many areas resulting from the open-field burning of crop stalks. Compared to the widely-used substrates of animal manures and food wastes with good fluidity and biodegradability, crop stalks are hard to be anaerobically converted to biogas because the com- plex chemical structure of lignocelluloses seriously hinders the effective conversion of the biomass to biogas (Shen et al., 2013). In addition, crop stalks are kinds of heterogeneous substrates with specific physical properties of heterogeneity, low density, and high water-holding capacity. Crop stalks normally need to be ground before put into digester. The ground crop stalks could not be evenly distributed inside of digester, some of them would always float on the top of digester, leading to poor heat and mass transfer and low biogas yield. Mixing is very important to solve above problems for effective anaerobic digestion of lignocellulosic crop stalks, as the improve- ment on mixing could greatly improve anaerobic digestion perfor- mances and enhance biomethane production correspondingly (Shen et al., 2013; Smith et al., 1996). Generally, mixing can be achieved by a few ways, including gas recirculation, mechanical pumping, and mechanical stirring (Karim et al., 2005). Mechanical stirring can easily achieve homogenization of substrates in digester and thereby is widely applied in industrial operations involving various solid-liquid flows (Bridgeman, 2012; Ghanimeh et al., 2012; Kowalczyk et al., 2013). Therefore, mechanical stirring is normally employed for mixing substrates of crop stalks, especially, when the total solid (TS) in the slurry is relatively high (Ward et al., http://dx.doi.org/10.1016/j.biortech.2014.03.023 0960-8524/Ó 2014 Published by Elsevier Ltd. ⇑ Corresponding author. Tel./fax: +86 10 64432281. E-mail addresses: xjlibuct@gmail.com, xjli@mail.buct.edu.cn (X. Li). Bioresource Technology xxx (2014) xxx–xxx Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech Please cite this article in press as: Tian, L., et al. Reducing agitation energy-consumption by improving rheological properties of corn stover substrate in anaerobic digestion. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.03.023