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Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/29/2012 Publication Date: 11/11/2012 Citation: Loughrin, J.H., Cook, K.L., Lovanh, N.C. 2012. Recirculating waste through a silicone membrane in an aerobic chamber improves biogas quality and wastewater malodors. Transactions of the ASABE. 55(5):1229-1237. Interpretive Summary: Swine manure was circulated through silicone hosing located in an external tank to which aeration was supplied. The silicone hose allowed for the passage of small molecules such as methane and malodorous compounds so that bacteria in the aeration tank could degrade them. A reduced nutrient medium was supplied to the bacteria in the aeration tank to enhance their degradation of the swine waste compounds. In a first experiment, silicone rubber was added to the aeration tank to act to absorb potentially toxic compounds and thereby protect bacterial growth. Concentrations of malodorous compounds were greatly reduced in treated swine waste as compared to untreated waste. Similarly, methane and carbon dioxide concentrations in the atmosphere of the treated slurry were also reduced, especially in the case for carbon dioxide where concentrations of this important greenhouse gas were reduced by almost 80 percent. This seemed to be largely because treated waste slurry had less acidity than did the control. This resulted in treated slurry having more bicarbonate buffering than the control slurry. In treated and control swine waste bacterial populations were similar with Bacteroides comprising over 50% of the total. In a second experiment, the supplemental silicone was omitted from the aeration tank. In this experiment, carbon dioxide concentration was again greatly reduced while methane concentration was not. This result indicates that a system such as this could enhance the quality of biogas produced by anaerobic digesters resulting in cleaner burning gas. Technical Abstract: Wastewater from swine waste slurry was circulated through silicone hosing located in an aeration tank. The silicone hose acted as a membrane allowing for the passage of low molecular weight compounds such as methane and malodorous compounds. The aeration tank employed a minimal medium for microbial growth and finely chopped silicone rubber to absorb potentially toxic compounds that could slow bacterial growth. Concentrations of malodorous compounds were greatly reduced in treated waste slurries as compared to control waste slurries. Similarly, methane and carbon dioxide concentrations in the atmosphere of the treated slurry were also reduced, especially in the case for carbon dioxide where headspace concentrations of this important greenhouse gas were reduced by almost 80 percent. This seemed to be largely because treated waste slurry had a higher pH resulting in more bicarbonate buffering. In control and treated slurries, bacterial populations were similar with Clostridia and Bacteroides comprising over 50% of the total population. In subsequent experiments in which the silicone rubber buffer was omitted from the aeration tanks, malodorous compounds were removed from the wastes as efficiently as in the first experiment. Carbon dioxide concentration in treated slurry headspace was again greatly reduced but methane concentration was not. These results suggest the possibility that this system could enhance the quality of biogas produced by anaerobic digesters. |
