Enhancement of liquid flow through a leach bed reactor for anaerobic digestion of high solids cattle manure
Date
2017
Authors
Wu, Rongxi, author
Sharvelle, Sybil, advisor
De Long, Susan, committee member
Butters, Greg, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Due to animal production waste increases in Colorado, anaerobic digestion (AD) has become increasingly considered as a technology to convert organic solid waste (OSW) into renewable energy. The arid climate with water resource limitation in Colorado results in high solids cattle manure (HSCM) production, containing between 50% and 90% total solids (TS). Conventional AD for animal manure is best option to treat manure with less than 20% TS, but limited feasibility for conventional anaerobic digesters treats manure in Colorado. The multi-stage anaerobic digester (MSAD) investigated in this study can digest HSCM. An integral part of the MSAD is the Leach Bed Reactor (LBR), which is loaded with HSCM (up to 90% TS). A small quantity of water percolates into the LBR and is recirculated through the LBR where hydrolysis occurs until a large amount of organic material is solubilized into the leachate. A review of the literature has indicated that clogging can be an issue in operation of manure LBRs. Since sustaining liquid flow through LBRs can be a challenge, research was conducted to better understand how to use this technology to treat HSCM. The objectives of this research were to 1) assess the performance of the LBR component of the MSAD technology with different top layer materials and flow regimes to enhance duration of sustained flow, 2) assess the ability of varying top layer materials and flow regimes to enhance hydraulic conductivity of the manure bed in the LBR to maximize hydrolysis in the LBR. For this study, downward flow and upward flow LBR configuration experiments were conducted. The combination of a sand layer on top of the manure beds and an improved top filter for the LBR was added in the upward flow LBR configuration. HSCM samples from each stage of the experiment were analyzed for TS, fixed solids (FS), and volatile solids (VS), and the leachate samples were analyzed for chemical oxygen demand (COD). The leachate outflow rate and column pressure head were also measured daily. Due to failure of all downward flow experiments, the upward flow LBR configuration was evaluated. The clogging issues and leachate flow through the LBR improved by changing to the upward flow LBR configuration. The average operation time of the upward flow experiment was prolonged to 21 days comparing with downward flow experiment, which operated for an average of only 7 days. The percentage reduction of VS in upward flow experiments was on average above 40% indicating successful hydrolysis in the LBRs, comparable to VS reduction observed by other researchers (Uke and Stentiford, 2012). The COD concentration of the upward flow experiments started at an average of 45 g COD/ L and approached the LST's COD concentration of 10 g COD/L at day 10. This indicates that the MSAD was effectively degrading the HSCM throughout the batch digestion period. The constant pressure head of upward flow experiments indicated that no pressure built up inside the LBRs resulting in improved flow through the manure in these systems. In summary, this research showed that the upward flow LBR configuration with the combination of a sand layer on top of the manure bed and improved top cap filter can sustain leachate flow through the LBR for 21 days of operation.