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Dissolved biomethane in anaerobic effluents has long been a hurdle for energy harvesting through anaerobic wastewater treatment processes. Here, we present a novel membrane process for dissolved methane recovery through the normal range of domestic wastewater temperatures by utilizing an omniphobic (nonwetting) microporous membrane. In a process driven by a solubility gradient, dissolved methane is extracted from a methane-rich aqueous solution (feed), transported across the omniphobic membrane, and absorbed into a nonpolar organic solvent (draw) that has a high solubility for methane. We fabricated the omniphobic membrane by coating a microporous polymeric membrane with silica nanoparticles, followed by surface fluorination. Using the omniphobic membrane, we demonstrate that nearly ≥90% of dissolved methane is recovered from methane-saturated feedwater at 15, 25, and 35 °C, simulating anaerobic effluents produced in the psychrophilic to mesophilic temperature range, while negligible transport of water is observed. Further measurements and comparative energy analysis suggest that this novel process can enable net energy production, with a higher value at a lower temperature, which outperforms other dissolved methane recovery techniques.

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There is considerable interest in recuperative thickening (RT), the recycling of partially digested solids in an anaerobic digester outlet stream back into the incoming feed, as a 'high-performance' process to increase biogas production, increase system capacity, and improve biosolids stabilization. While polymer flocculation is commonly used in full-scale RT operations, no studies have investigated the effect of flocculation conditions on RT process performance. Our goal was to investigate the effect of polymer type and dosage conditions on dewatering performance and biogas production in a lab-scale RT system. The type of polymer flocculant significantly affected dewatering performance. For example, the 440 LH polymer (low molecular weight (MW) polyacrylamide) demonstrated lower capillary suction time (CST) and filtrate total suspended solids (TSS) values than the C-6267 polymer (high MW polyacrylamide). An examination of the dewatering performance of RT digesters with different polymers found a strong correlation between CST and filtrate TSS. The type of polymer flocculant had no significant effect on biogas productivity or composition; the methane content was greater than 60% in good agreement with typical results. The optimization of the polymer flocculation conditions is a critical task for which the lab-scale RT system used in this work is ideally suited.

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