AUTHOR=Dong Kun , Feng Xinghui , Yao Yi , Zhu Zongqiang , Lin Hua , Zhang Xuehong , Wang Dunqiu , Li Haixiang 

TITLE=Nitrogen Removal From Nitrate-Containing Wastewaters in Hydrogen-Based Membrane Biofilm Reactors via Hydrogen Autotrophic Denitrification: Biofilm Structure, Microbial Community and Optimization Strategies

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.924084

DOI=10.3389/fmicb.2022.924084

ISSN=1664-302X

ABSTRACT=<p>The hydrogen-based membrane biofilm reactor (MBfR) has been widely applied in nitrate removal from wastewater, while the erratic fluctuation of treatment efficiency is in consequence of unstable operation parameters. In this study, hydrogen pressure, pH, and biofilm thickness were optimized as the key controlling parameters to operate MBfR. The results of 653.31 μm in biofilm thickness, 0.05 MPa in hydrogen pressure and pH in 7.78 suggesting high-efficiency <inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi mathvariant="normal">NO</mml:mi><mml:mn>3</mml:mn><mml:mo>−</mml:mo></mml:msubsup><mml:mo>−</mml:mo><mml:mi mathvariant="normal">N</mml:mi></mml:math></inline-formula> removal and the <inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi mathvariant="normal">NO</mml:mi><mml:mn>3</mml:mn><mml:mo>−</mml:mo></mml:msubsup><mml:mo>−</mml:mo><mml:mi mathvariant="normal">N</mml:mi></mml:math></inline-formula> removal flux was 1.15 g·m<sup>−2</sup> d<sup>−1</sup>. 16S rRNA gene analysis revealed that <italic>Pseudomonas</italic>, <italic>Methyloversatilis</italic>, <italic>Thauera</italic>, <italic>Nitrospira</italic>, and <italic>Hydrogenophaga</italic> were the five most abundant bacterial genera in MBfRs after optimization. Moreover, significant increases of <italic>Pseudomonas</italic> relative abundances from 0.36 to 9.77% suggested that optimization could effectively remove nitrogen from MBfRs. Membrane pores and surfaces exhibited varying degrees of calcification during stable operation, as evinced by Ca<sup>2+</sup> precipitation adhering to MBfR membrane surfaces based on scanning electron microscopy (SEM), atomic force microscopy (AFM) analyses. Scanning electron microscopy–energy dispersive spectrometer (SEM–EDS) analyses also confirmed that the primary elemental composition of polyvinyl chloride (PVC) membrane surfaces after response surface methodology (RSM) optimization comprised Ca, O, C, P, and Fe. Further, X-ray diffraction (XRD) analyses indicated the formation of Ca<sub>5</sub>F(PO<sub>4</sub>)<sub>3</sub> geometry during the stable operation phase.</p>