Nitrate Removal and Dynamics of Microbial Community of A Hydrogen-Based Membrane Biofilm Reactor at Diverse Nitrate Loadings and Distances from Hydrogen Supply End

Minmin Jiang,Haixiang Li,Hua Lin,Yuchao Chen,Yuanyuan Zhang,Xuehong Zhang,Junjian Zheng,Yuhang Yuan

doi:10.3390/w12113196

Abstract

The back-diffusion of inactive gases severely inhibits the hydrogen (H2) delivery rate of the close-end operated hydrogen-based membrane biofilm reactor (H2-based MBfR). Nevertheless, less is known about the response of microbial communities in H2-based MBfR to the impact of the gases’ back-diffusion. In this research, the denitrification performance and microbial dynamics were studied in a H2-based MBfR operated at close-end mode with a fixed H2 pressure of 0.04 MPa and fed with nitrate (NO3−) containing influent. Results of single-factor and microsensor measurement experiments indicate that the H2 availability was the decisive factor that limits NO3− removal at the influent NO3− concentration of 30 mg N/L. High-throughput sequencing results revealed that (1) the increase of NO3− loading from 10 to 20–30 mg N/L resulted in the shift of dominant functional bacteria from Dechloromonas to Hydrogenophaga in the biofilm; (2) excessive NO3− loading led to the declined relative abundance of Hydrogenophaga and basic metabolic pathways as well as counts of most denitrifying enzyme genes; and (3) in most cases, the decreased quantity of N metabolism-related functional bacteria and genes with increasing distance from the H2 supply end corroborates that the microbial community structure in H2-based MBfR was significantly impacted by the gases’ back-diffusion.

Highlights

Nitrate (NO3 − ) contamination of surface and groundwater has become a significant challenge due to the uncontrolled discharge of wastewater and the intensive use of fertilizers [1,2]
Concerning the microbial communities at diverse locations of the biofilm fed with influent containing 30 mg N/L NO3 −, Hydrogenophaga, was always the primary genus regardless of the distance from the H2 supply end, where its relative abundance was dramatically increased from 13.1% at the distance of 5 cm to 21.7% at the distance of 35 cm
Metabolism was increased from 0.83% in the upside to 0.88% in the downside of the biofilm; this mirrored the variation tendency in the abundance of the genes involved in membrane transport with changing distance from the H2 supply end

Summary

Introduction

Nitrate (NO3 − ) contamination of surface and groundwater has become a significant challenge due to the uncontrolled discharge of wastewater and the intensive use of fertilizers [1,2]. As an emerging autotrophic denitrification approach, H2 -based membrane biofilm reactor (H2 -based MBfR), has gained widespread popularity in recent years for the purification of NO3 − -contaminated surface and groundwater, mainly attributed to the unique advantages, namely, allowing efficient and cost-effective NO3 − elimination with minimal bio-sludge yield and without. Water 2020, 12, 3196 allowing efficient and cost-effective NO3− elimination with minimal bio-sludge yield and without needfor forexternal externalcarbon carbonsource source[5,6,7]. 2-concentration gradient across the walls of the hollow-fiber membranes (HFMs), driven by the H2 -concentration gradient across the walls of the hollow-fiber membranes (HFMs), diffusespassively passively from intramembrane the HFMs-attached. In the Hbiofilm, H2 is diffuses from the the intramembrane to thetoHFMs-attached biofilm.biofilm

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