Performance of a composite bioactive membrane for H2 production and capture from high strength wastewater

Abstract

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.