In recent years, hydrogen (H2) has emerged as energy vector in response to the increasing global energy demand and the need to reduce carbon footprints. Among the several H2 production methods, dark fermentation has attractive operating conditions and a less dependence on natural resources. Wastewater-to-energy systems are an opportunity to close waste loops and generate additional value streams, such as biogas for electricity or heat generation, while adopting water reuse technology to achieve a more resilient water supply. Within wastewater-to-energy systems, an alternative is the composite bioactive membrane (CBMem), allowing simultaneous H2 production and separation. Its design consists of the following multiple layers: a hollow fiber membrane for gas transfer, a bioactive layer with immobilized acetogenic cells and a sealant layer. The system’s dynamic is complex due to the variety of domains and the coupling between cell metabolism and mass transfer. Modeling can improve the comprehension of phenomena, predict process performance and optimize operational and design parameters to intensify the energy recovery. In this study, a phenomenological model for a CBMem is formulated to characterize H2 production and bioactive layer behavior. The model integrates relevant biological, kinetic and mass transfer mechanisms. First, a transport model describes the velocity profiles of the permeate side, membrane and feed side. Second, a biokinetic model represents cell growth, substrate (high strength wastewater) consumption and H2 production. Third, a mass balance is given for each section of the CBMem to account for the time-based behavior of the species. The concentration of substrate, biomass and H2 are the state variables of the model. Along with the principles of conservation of mass and momentum and suitable boundary conditions, the model results to be non-linear with coupled ordinary differential equations that describe the dynamic of the state variables in the different sections. The implementation of the model could serve as guideline for further experimental design of CBMems.

Hydrogen from wastewater: a phenomenological model for a composite bioactive membrane

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