Effect of long-term operations on the performance of hollow fiber membrane contactor (HFMC) in recovering dissolved methane from anaerobic effluent

Various studies provide information about the high potential of using hollow fiber membrane contactors (HFMCs) for the recovery of dissolved methane from anaerobically treated wastewater effluent and the effects of different operating conditions on their performance. However, majority of those studies evaluated HFMCs at bench scale under favorable conditions, i.e. clean water as feed under short-term operations. This study evaluated the performance of porous HFMC and dense HFMC (in terms of dissolved methane removal efficiency and methane desorption flux) subjected to anaerobic feed during long-term operation of one month. The study will provide better understanding of the performance of HFMCs with conditions expected at large-scale wastewater treatment systems. From the results, the decrease in the performance of HFMCs and the increase in the mass transfer resistance per week under varying feed flux were determined. These relationships were utilized in a numerical model to incorporate the effect of long-term operation to evaluate the performance of upscaled HFMCs. The fit of the model with the experimental data with one month of operation was evaluated and the relative errors were 11.9 % and 15.3 % for porous HFMC and dense HFMC, respectively. Moreover, results showed that dense HFMC will provide better performance than porous HFMC if it were to be operated longer than two weeks before cleaning. The net energy for porous HFMC and dense HFMC were optimized to be 0.07 and 0.02 kWh·d−1, respectively. Although these results are specific to the operations and conditions used for the HFMCs in this study, the methodology established for incorporating the effect of long-term operation will be highly relevant in evaluating the performance of HFMCs in large-scale wastewater treatment applications. This will contribute to the improved recovery of dissolved methane to reduce the greenhouse gas emissions in the atmosphere and to provide additional source of clean and sustainable energy.