One-stage hollow-fiber membrane bioreactor for wastewater treatment and resource recovery through hydrogen-driven mixotrophic nitrogen assimilation

In this study, a one-stage, H2-fed hollow-fiber membrane bioreactor (HFMBR) was developed and investigated for the treatment of synthetic wastewater and the simultaneous upcycling of waste reactive nitrogen into microbial protein through a mixed hydrogen oxidizing bacteria (HOB) culture. The effect of different hydraulic retention times, H2:O2 and CODH2:CODacetate ratios were investigated to obtain the best results in terms of ammonium nitrogen removal and assimilation, soluble chemical oxygen demand (sCOD) removal, CO2 release, biomass concentration, and protein content. The use of membrane technology leverages the bubble-less diffusion of gaseous substrates in the liquid medium, improving gas delivery to microbial cultures by enabling a direct biological uptake and avoiding gas loss and accumulation through bubbles. The microbial community composition and evolution under mixotrophic and heterotrophic conditions was also monitored and evaluated.