Performance of a composite bioactive membrane for H2 production and capture from high strength wastewater†
In this study, a composite bioactive membrane was developed and tested to generate and capture hydrogen (H2) during the process of wastewater treatment. Hollow fiber membranes were coated with encapsulated acetogenic bacteria to simultaneously produce and capture H2 from waste feedstocks. Acetogens were encapsulated with cast poly(vinylalcohol) or electrospun microfibers. Under anaerobic conditions the poly(vinylalcohol) and electrospun composite membranes produced an average of 44.6 ± 11.3 mL H2 g−1 hexose (0.33 ± 0.08 mol H2 mol−1 hexose) and 21.2 ± 4.8 mL H2 g−1 hexose (0.16 ± 0.04 mol H2 mol−1 hexose), respectively, and captured 73 ± 12% and 57 ± 11%, respectively, of the total H2 produced in bioreactors fed synthetic high strength wastewater. The H2 capture efficiency of the electrospun composite membrane was improved by coating the modules with a thin film of polymeric silica gel, improving the H2 production to 28.3 ± 2.3 mL H2 per hexose (0.21 ± 0.02 mol H2 mol−1 hexose) and the H2 capture efficiency to 73 ± 15%. Final composite membranes were built by immobilizing bacteria directly onto the membrane surface, again improving H2 yields from high strength synthetic wastewater to a maximum of 48.4 ± 9.4 mL H2 g−1 hexose (0.36 ± 0.07 mol H2 mol−1 hexose) with a maximum H2 capture efficiency of 86 ± 9%. The optimized composite membranes were also capable of generating and capturing H2 from real wastewaters, with yields and capture efficiencies of 19.2 ± 3.0 mL H2 g−1 hexose (0.14 ± 0.02 mol H2 mol−1 hexose) and 99.1 ± 0.2%, and 46.0 ± 15.5 mL H2 g−1 hexose (0.34 ± 0.12 mol H2 mol−1 hexose) and 79 ± 19% when tested with a feed of sugar beet wastewater and dairy production wastewater, respectively. After further optimization, the composite membrane system could allow the extraction of high-quality energy from wastewater.