Biogas clean-up using a novel hollow fibre membrane bioreactor for end-use applications
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The aim of this research was to develop a novel hollow fibre membrane bioreactor (HFMB) that can be used for H2S laden waste gas treatment and biogas desulfurization. In addition, the aim was to utilize the HFMB for simultaneous removal of H2S and NH3 from raw biogas. Prior to study the HFMB, recent advancement of biological biogas purification technologies was reviewed including the challenges and future scope of these technologies. In the first phase of this PhD research, the feasibility of the polyethersulfone based HFMB configuration was established for biological removal of gas-phase H2S (up to ~ 650 ppmv) employing three lab-scale HFMBs. In the second phase, resilience of the HFMB was tested under different operating conditions including H2S concentrations (up to ~ 3600 ppmv), empty bed residence time (EBRT, up to 62 s), famine period, shock loads, pH and different biomass types. The HFMB achieved ~ 100% removal efficiency (RE) with an elimination capacity (EC) of 30-34 g m-3 h-1 at ~ 20°C under steady-state operation. The critical loading rate of H2S was ~ 135 g m-3 h-1 under transient-state operation. In the third phase, the HFMB was tested for simultaneous removal of H2S (up to ~ 1850 ppmv) and NH3 (up to ~ 1030 ppmv) from raw biogas at different EBRT. The HFMB achieved ~ 100% RE for both H2S (up to ~ 1850 and 1200 ppmv at an EBRT187 and 46 s, respectively) and NH3 (up to ~ 460 and 750 ppmv at an EBRT 187 and 46 s, respectively). At an EBRT of 46 s, the RE of both H2S and NH3 varied in the range of 85-97 and 73-95%, respectively, when the inlet biogas laden with ~ 1200-1700 ppmv of H2S and 750-1050 ppmv of NH3. The critical loading rates of H2S and NH3 were ~ 150 and 40 g m-3 h-1, respectively. This study confirms that the HFMB can be useful for H2S and NH3 laden waste gas treatment and biogas purification.