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Dissolved Methane Recovery from Novel Anaerobic Attached Growth Reactor Treating Synthetic Domestic Wastewater
Citation:
Crone, B., J. Garland, J. Pressman, H. Ryu, AND G. Sorial. Dissolved Methane Recovery from Novel Anaerobic Attached Growth Reactor Treating Synthetic Domestic Wastewater. The Ninth International Conference on Environmental Science and Technology, Houston,TX, June 25 - 29, 2018.
Impact/Purpose:
Release of methane from effluents of anaerobically treated wastewater represent both a lost energy product and the release of a green house gas. Several potential solutions have been reported in the literature including membrane based recovery. However, membrane based recovery is often operationally limited by reductions in mass transfer caused by biofouling. This presentation outlines preliminary results from a dissolved methane collection system integrated directly into the wastewtater treatment process where anaerobic biofilms are allowed to grow directly on the surface of the membrane used to collect the dissolved methane allowing for immediate recovery as methane is produced. The reactors herein described were operated for over 72 weeks without membrane cleaning and a dissolved methane recovery efficiency of greater than 80% and a total methane recovery efficiency of greater than 89%. These results contrast significantly with a control reactor that was operated without dissolved methane recovery and had a total methane recovery efficiency of 39%. Efficient recovery of dissolved methane could lead to net positive energy yield from the anaerobic treatment of domestic wastewater. These results can help advise municipalities on selecting domestic wastewater treatment technologies that reduce greenhouse gas emissions and decrease operational energy demand through the recovery of methane for subsequent use as an energy product with minimal operational maintenance.
Description:
Anaerobic Membrane Bioreactors (AnMBRs) are emerging as a sustainable option for wastewater treatment due to their production of methane through biological metabolism of Domestic Wastewater. The recovered methane can be combusted to generate electricity and offset Wastewater Plant Operational Costs. The largest technical barrier to the widespread application AnMBRs is dissolved methane losses in effluent streams which contribute to greenhouse gas emissions and result in significant reductions in energy recovery. This is exacerbated by low temperature operation, which increases methane solubility. Several authors have previously suggested in-situ degassing of the bulk reactor liquid as on option to improve COD removal, methane recovery, and increase alkalinity through the removal of carbonic acid. However, all of these improvements are reduced over time by membrane fouling. To counteract this, a novel approach was utilized which included culturing a biofilm stratified by carbon metabolism, i.e. hydrolosis, acidogenesis, acetogenesis, and methanogenesis from the outside of the biofilm to the surface of an in-situ degassing membrane in an AnMBR treating synthetic domestic wastewater. Effectiveness of this approach was evaluated by comparison of COD removal, methane yield, and stability of pH with a control reactor which contained membranes for structural support of the biomass but no active degassing. Stratification of biofilms was evaluated visually using Fluorescent In-Situ Hybridization on cross sections of membrane biofilms.