Increased methane solubility associated with operational temperatures below traditional mesophilic and thermophilic regimes reduces the potential Obatoclax produced by the system due to the energy expenditure required to recover dissolved methane from the effluent. Membrane recovery of methane is further complicated by increased membrane resistance at lower temperatures due to decreased permeability and increased liquid boundary layer resistance caused by higher fluid viscosity and the resulting decrease in diffusivity in the boundary layer. Membrane permeability is predicted to change with temperature according to the Arrhenius equation (Raharjo et al., 2007).equation(5)P=P0e−EpRTwhere P0, is a pre exponent factor, T is the temperature in Kelvin, R is the universal gas constant and Ep is the activation energy of permeability (Raharjo et al., 2007). Bandara et al. (2011) evaluated the effect of temperature on membrane-based dissolved methane recovery by maintaining a constant membrane module HRT of 8.5 h and 80 kPa transmembrane pressure (assuming a feed side pressure of 101.3 kPa and permeate pressure of 21.3 kPa) while operating a UASB at 35 °C, 25 °C, and 15 °C (Bandara et al., 2011). The concentration of dissolved methane leaving the UASB reactor was 15.8 ± 1 mg CH4/L, 20.6 ± 1.8 mg CH4/L, and 26.1 ± 1.3 mg CH4/L while the concentration of dissolved methane leaving the degassing membrane reactor was relatively constant at 3.8 ± 1.3 mg CH4/L, 3.3 ± 1 mg CH4/L, and 3.5 ± 0.5 mg CH4/L at 35 °C, 25 °C, and 15 °C, respectively. These similar concentrations leaving the degassing module suggest Interallelic complementation dissolved methane recovery was limited by the partial pressure of methane in the permeate stream. This, in combination with the fact that there was no temperature measurement or control reported for the membrane module, may have masked some temperature effects including decreased permeability with decreasing temperature. The authors reported dissolved methane recovery of 77 ± 7% at 35 °C, to 85 ± 4% at 25 °C, and 86 ± 2% at 15 °C due to increased partitioning into the dissolved phase as temperature decreased while the total methane recovery, including headspace and dissolved methane, remained at 97 ± 1% at all temperatures (Bandara et al., 2011).
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