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

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.

Simultaneous Partial Nitrification and Denitrification Maintained in Membrane Bioreactor for Nitrogen Removal and Hydrogen Autotrophic Denitrification for Further Treatment

“…The population of Hydrogenophaga exhibited low relative abundances in our study compared with previous work [42,43]. The possible explanations for the lack of Hydrogenophaga in the present study are as follows: (1) the successful PN-D process brings about the accumulation of NO − 2 in the MBR effluent; the presence of NO − 2 has a toxic effect on Hydrogenophaga, and the reproduction of Hydrogenophaga is sensitive to its presence [17]. (2) The MBfR influent contained synthetic wastewater and domestic wastewater with COD, NO − 3 , and NO − 2 , and other nitrogen compounds.…”

“…Here, nitrate and nitrite diffuse from water into biofilm being reduced [14,15]. The advantages of this hydrogenotrophic denitrification compared with conventional heterotrophic denitrification technology include the utilization of nontoxic and inexpensive H 2 as electron donors, no requirement for the addition of external organic carbon, a small footprint, relatively low cost, and low production of biological sludge [16,17]. Promising outcomes have been reported with MBfR for treating nitrate-and nitrite-contaminated water for research and commercial applications.…”

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

“…Pseudomonas is a hydrogen autotrophic denitrifier and a nitrate-reducing taxa that has been shown to play a key role in hydrogen autotrophic denitrification during removal ( Zhang et al, 2015 ). Hydrogenophaga is a well-known, but uncultured, hydrogen-oxidizing bacterial genus that characteristically reduces and can play a large role in H 2 -based MBfR functioning ( Jiang et al, 2020 ). In addition, Thauera have been previously considered the most active denitrifying bacteria in sewage treatment systems, and were the primary contributor to nitrogen wastewater denitrification in a previous study ( Dong et al, 2021 ).…”

Characteristics of denitrification and microbial community in respect to various H2 pressures and distances to the gas supply end in H2-based MBfR

“…In the sealed gas supply mode of the H 2based MBfR, the diffusion flux of the effective gas at the end of the HFM to the biofilm is usually low, which can prevent many fiber membranes from operating and decreasing the utilization efficiency, ensuing in the waste of the membrane material and reactor volume. Jiang et al (2020) also showed that most of the functional genes associated with the microbial metabolism and denitrification processes in microbial communities on HFM in closed operation mode showed a weakening trend as they moved away from the gas supply side, under the influence of gas counter-diffusion. Therefore, this back-diffusion reduced the total effectiveness of the biofilm and the average denitrification efficiency.…”