Wetting- and fouling-resistant hollow fiber membranes for dissolved methane recovery from anaerobic wastewater treatment effluents

Abstract

Anaerobic wastewater treatment processes are becoming increasingly widespread due to their advantages in sludge management and net energy consumption. One major reason behind the energy benefit of the mainstream anaerobic processes is methane (CH4) production. Nevertheless, over one-third of the produced CH4 typically remains in effluent streams in dissolved form. To recover the dissolved CH4 (dCH4) from anaerobic effluents, the membrane contactor (MC) process enabled by porous membranes offers a promising way. However, membrane wetting and fouling issues hinder the practical implementation of the concept. Here we report a wetting- and fouling-resistant hollow fiber membrane that can operate with realistic anaerobic effluents. Coating of a highly porous (~85%) hollow fiber support with a conformal layer of polydimethylsiloxane (PDMS) provides resistance to wetting, but fouling persists. To tackle the fouling issue, we post-treated the uncured PDMS-coatings with PDMS-based amphiphilic copolymers with short (147 Da) or long (~1570 Da) side chains. Both types of post-treated membranes exhibited an improved performance when tested against effluent samples taken not only from an anaerobic membrane bioreactor but also from an upflow anaerobic sludge blanket (UASB) reactor. The membrane treated with the short-side-chain copolymer could sustain 7 days of continuous operation with UASB effluent with a performance loss of only ~10%. We observed that the fouling layers were much richer in proteins rather than subtances similar to humic and fulvic acids and microbial byproducts. Besides, we calculated that our wetting/fouling-resistant membranes provide a net energy benefit for the MC process (when the recovered CH4 is retrofitted to the process as fuel). Thus, our results suggest that the MC-based dCH4 recovery process is a viable alternative for industrial practices in case the demonstrated custom-designed membranes are employed.