Biomass Depolymerization projects
Mesophilic and Thermophilic Bioconversion of Stillage Derived from Lignocellulosic Biomass-to-Ethanol Fermentation to Methane
This project examines the chemical and nutrient composition of two potential sources (corn stover and energy cane) of lignocellulosic stillage residues from bioenergy crops. These stillage sources form the substrate for anaerobic digestion studies. Anaerobic digestion is carried out at mesophilic (40°C) and thermophilic temperature (60°C) in a Conventional Stirred Tank Reactor (CSTR) and Hybrid reactor (combining an Upflow Anaerobic Sludge Blanket (UASB) and anaerobic filter). Benchtop fermenters are used to study fundamental aspects of microbial ecology and performance characteristics in the system. Molecular microbial ecology and deep sequencing approaches focus on key functional groups involved in the hydrolysis of polymers, production and utilization of hydrogen (interspecies hydrogen transfer) and acids (acid oxidation) and methanogenesis (terminal carbon and electron flow). Started in 2012.
The goal of this project is to chemically characterize bioethanol stillage, to convert it to methane and understand the microbial community responsible for this process. We have analyzed 3 different batches of the acidic thin stillage (pH 4.2). Six hybrid reactors (3 mesophilic and 3 thermophilic) and 2 conventional reactors (thermophilic) are capable of utilizing 91 to 94% and 77% of the soluble carbon. Methane production improves when decreasing the organic strength of the feed, with longer turnover times and with lower sulfate concentration. The microbial communities are dominated by Euryarchaeota, Synergistetes and Firmicutes in mesophilic reactors and by Euryarchaeota, Firmicutes and Thermotogae in thermophilic reactors.
Two anaerobic mesophilic (40 oC) hybrid reactors have been running stably for over one year converting lignocellulosic bioethanol stillage to methane. These reactors have been monitored daily for pH, COD depletion, methane and total gas production, and structure of the microbial community responsible for degradation of the components of the stillage to methane. At full strength influent concentration (40 g COD per L) and 34-hour hydraulic retention time they are generating 350ml CH4 per hour with 85 percent reduction in COD. We have successfully inoculated thermophilic (55 °C) bioreactors with sludge from municipal wastewater treatment plants. After chemical analysis of the new batch of stillage obtained from sugarcane bagasse treatment, mesophilic and thermophilic reactors will be switched to new stillage source derived from sugarcane bagasse.
One of the largest remaining hurdles in the production of bioethanol from lignocellulosic biomass is the stillage generated in the process. The goal of this project is to convert bioethanol stillage to methane and understand the microbial community responsible for this process. We have analyzed the chemical composition of the thin stillage produced by lignocellulosic ethanol production and show that the Chemical Oxygen Demand (COD) or strength of the waste stream is 42 g/l and 96% soluble. Many of the key components of the stillage, including lactate, ethanol, acetate, and multiple sugars, are easily degradable by anaerobic bacteria. Two mesophilic anaerobic reactors were inoculated from a stable cattle waste fermenting anaerobic community. These lab-scale hybrid reactors have a 1.1L working volume and retention time of 54 hours. These reactors have been running stably for 170 days and are capable of utilizing 84% of the soluble carbon in the stillage from lignocellulosic ethanol production. The current methane production rate is 0.49 liters of methane per gram of COD (a measure of organic carbon). Performance of the reactors is not impacted by stress such as increased organic loading rates and decreased pH. Initial analysis of the microbial communities by 16S ribosomal RNA sequencing showed that the reactors are dominated by members of the phyla: Firmicutes, Bacteriodetes, Protobacteria, and Spirochaetes. The dominant methane producing archaea are members of Methanosarcinaceae and Methanobacteriaceae.
Published in 2014
Functional Potential of Soil Microbial Communities in the Maize Rhizosphere, X. Li, J. Rui, J. Xiong, J. Li, Z. He, J. Zhou, A. C. Yannarell, R. I. Mackie, PLoS One, doi: 10.1371/journal.pone.0112609, November 10, 2014.