Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci Performance of a polypropylene membrane contactor for the recovery of dissolved methane from anaerobic effluents: Mass transfer evaluation, long- term operation and cleaning strategies María Henares, Pablo Ferrero, Pau San-Valero, Vicente Martínez-Soria, Marta Izquierdo ⁎ Research Group GI 2 AM, Department of Chemical Engineering, University of Valencia, Avda. Universitat s/n, 46100 Burjassot, Spain ARTICLE INFO Keywords: Anaerobic reactor Fouling Mass transfer Membrane contactor Methane degassing ABSTRACT A polypropylene membrane contactor was used for the recovery of dissolved methane from an anaerobic reactor effluent. Effect of operational parameters, operation mode and fouling on long-term operation was studied using vacuum pressure or N 2 as sweep gas. Results were analyzed based on the mass transfer estimations. Lower performance was observed in the shell-side mode due to the lower liquid velocity and the probable channeling. Membrane pore wetting was observed with the increase in Q L in the vacuum-pressure mode. This was confirmed with mass transfer resistance analysis, resulting in an estimated wetted pore fraction of between 0.25 and 0.53. The highest removal efficiencies were obtained with the liquid flowing in the lumen side and sweep-gas op- eration (between 98% and 67% for Q L between 4.1 and 27.2 L h –1 ), with negligible effect of the N 2 flow rate. In the long-term operation, the impact of membrane fouling was less intense in the lumen side, with longer op- eration time and more reversible fouling. A complete characterization of the fouling based on water sample analysis concluded that both inorganic and organic foulants were present, probably with higher biofouling presence. A combination of water and chemical cleanings resulted in a recommended protocol based on daily water cleaning. 1. Introduction Anaerobic reactors for the wastewater treatments generate a me- thane-rich biogas, which can be used in combustion for the production of heat and/or electricity. Even though the low solubility of methane in water, residual dissolved methane (D-CH 4 ) is often present in the final water effluent, especially in anaerobic treatments at sub-mesophilic and psychrophilic temperatures (< 25 °C) due to the increase in gas solu- bility at low temperatures [1]. Increase in greenhouse gas diffuse emissions, loss of energy source and generation of potential explosive atmospheres when discharged into closed vessels or sewers are the main problems when managing these effluents. Thus, its recovery/removal is necessary for economic, environmental and security reasons. The treatment technologies for gas desorption from anaerobic waters in- clude spray aeration, packed towers, tray aerators, diffuse aeration, and membrane contactors [2]. The use of membrane contactors is a com- mercially available mature technology for applications such as O 2 or CO 2 removal, among others [3]. However, its application for the re- moval D-CH 4 from anaerobic effluents is still at research/pilot level. From the first promising results [4–8], the number of published papers has grown in recent years [9–14], demonstrating the interest of scien- tific community in this technology. However, some practical implica- tions, such as the long-term stability of membrane contactors and the optimum driving force (vacuum/sweep gas) are still scarcely studied, and further research is needed. Membrane contactors offer many advantages over conventional technologies [2]; however, the presence of the membrane introduces an additional mass transfer resistance. Depending on membrane material, the nature of the liquid phase and transmembrane pressure, the mem- brane pores may be occupied by liquid, corresponding to the so-called wetted operation, which strongly decreases the permeate flux. Mea- sures to prevent the wetting problem may include the increase in the hydrophobicity of the membrane by increasing the contact angle be- tween the liquid and the membrane [14]. The surface tension of the liquid phase also plays an important role. The presence of organic compounds may decrease the surface tension of solutions, which de- creases the breakthrough pressure, leading to a rapid increase in membrane wetting. The wetting phenomenon is an effect widely stu- died in the CO 2 absorption using organic absorbents [15,16], and water-based absorbents [17–19]. In the application of membrane https://doi.org/10.1016/j.memsci.2018.06.045 Received 14 April 2018; Received in revised form 7 June 2018; Accepted 22 June 2018 ⁎ Corresponding author. E-mail address: marta.izquierdo-sanchis@uv.es (M. Izquierdo). URL: http://giam.blogs.uv.es/ (M. Izquierdo). Journal of Membrane Science 563 (2018) 926–937 Available online 25 June 2018 0376-7388/ © 2018 Elsevier B.V. All rights reserved. T