) both used vacuum and were able to achieve a methane concentration of up to 27% in the recovered gas phase (Bandara et al., 2011) with the authors indicating that higher concentrations were achievable [4,12]. However, low operating vacuum pressures are necessary to ensure that vacuum does not impose gas phase controlled mass transfer. To illustrate, Ito et al. (1998) achieved 17% dissolved oxygen removal at a vacuum pressure of 52 kPa which increased to 80% when vacuum was increased to 4 kPa [23]. This is analogous to the effective operating vacuum pressure reported by Cookney et al. (2012) for dissolved methane removal from wastewater which is energetically constraining and when applied to microporous HFMC, such vacuum pressures are also likely to promote pore wetting [4]. Importantly, in this study, a microporous HFMC operated in sweep-gas mode has been demonstrated to recover methane in usable form using only short residence times which establishes the practical viability of recovery. Both the treatment objective (i.e. greater than 88% removal efficiency) and the recovery of methane for reuse can be achieved under gas phase controlled conditions through placing HFMC in series which has been shown to remain economically viable despite the increase in pressure drop and necessary membrane area [1].
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