Specific Denitrifying and Dissimilatory Nitrate Reduction to Ammonium Bacteria Assisted the Recovery of Anammox Community From Nitrite Inhibition

Abstract

The anaerobic ammonium oxidation (anammox) by autotrophic anaerobic ammonia-oxidizing bacteria (AnAOB) is a biological process used to remove reactive nitrogen from wastewater. It has been repeatedly reported that elevated nitrite concentrations can severely inhibit the growth of AnAOB, which renders the anammox process challenging for industrial-scale applications. Both denitrifying (DN) and dissimilatory nitrate reduction to ammonium (DNRA) bacteria can potentially consume excess nitrite in an anammox system to prevent its inhibitory effect on AnAOB. However, metabolic interactions among DN, DNRA, and AnAOB bacteria under elevated nitrite conditions remain to be elucidated at metabolic resolutions. In this study, a laboratory-scale anammox bioreactor was used to conduct an investigation of the microbial shift and functional interactions of AnAOB, DN, and DNRA bacteria during a long-term nitrite inhibition to eventual self-recovery episode. The relative abundance of AnAOB first decreased due to high nitrite concentration, which lowered the system’s nitrogen removal efficiency, but then recovered automatically without any external interference. Based on the relative abundance variations of genomes in the inhibition, adaptation, and recovery periods, we found that DN and DNRA bacteria could be divided into three niche groups: type I (types Ia and Ib) that includes mainly DN bacteria and type II and type III that include primarily DNRA bacteria. Type Ia and type II bacteria outcompeted other bacteria in the inhibition and adaptation periods, respectively. They were recognized as potential nitrite scavengers at high nitrite concentrations, contributing to stabilizing the nitrite concentration and the eventual recovery of the anammox system. These findings shed light on the potential engineering solutions to maintain a robust and efficient industrial-scale anammox process.

Nitrite deteriorates bioreactor performance by reducing growth ofCa.Brocadia sapporoensis instead of inhibiting the anammox activity

“…In this study, a continuous flow complete-mix MBR system with a 1.5 L effective volume was utilized to conduct the experiments. The detailed configuration and operations of the MBR were reported previously 6 . In summary, seed sludge was obtained from a laboratory-scale anammox reactor that had been operating for two years at a nitrogen loading rate (NLR) of 2 g N/L/d.…”

“…Sludge samples were collected at 22 time points during the experiment from MBR for DNA extraction using the DNeasy PowerSoil Pro Kit (QIAGEN, Germany). Sequencing of DNA followed the methods described in our previous study 6 . In brief, the hypervariable V4 region of the bacterial 16S rRNA gene was amplified using primers 515F (5′-GTGCCAGCMGCCGCGGTAA-3′) and 806R (5′-GGACTACHVGGGTWTCTAAT-3′).…”

“…Metagenomic analysis was conducted based on our previous study 6 . Briefly, clean reads were assembled using MEGAHIT version 1.2.2 29 .…”

“…Anammox finds wide application in treating high-concentration ammonium (400 -6000 mg/L) wastewater including landfill leachate and pharmaceutical, hospital, and livestock wastewater [3][4][5] . Maintaining an optimal nitrite concentration is essential for stable nitrogen removal in the anammox process 6 . When using anammox process to remove ammonia from wastewater, careful control is needed to oxidize roughly 50% of the ammonia load to nitrite without being further oxidized to nitrate, which has no use to AnAOB 7,8 .…”

An integrated meta-omics approach reveals the different response mechanisms of two anammox bacteria towards fluoroquinolone antibiotics

“…Metagenomic analyses were conducted based on our previous studies [19]. Details are provided in Text S3.…”