# The Aerobic Denitrification Characteristics of a Halophilic Marinobacter sp. Strain and Its Application in a Full-Scale Fly Ash-Washing Wastewater Treatment Plant

## TL;DR

A salt-tolerant bacterium, Marinobacter sp. GH-1, was studied for its ability to remove nitrogen from salty wastewater and successfully applied in a full-scale treatment plant.

## Contribution

This study is the first to report full-scale application of a halophilic denitrifier in saline fly ash-washing wastewater treatment.

## Key findings

- Marinobacter sp. GH-1 has complete nitrogen metabolism pathways and strategies to tolerate high salinity.
- The strain effectively removes nitrogen under aerobic, anaerobic, and saline conditions (3–9%).
- Application in a full-scale system improved nitrate, total nitrogen, and COD removal by over 25%.

## Abstract

To date, the nitrogen metabolism pathways and salt-tolerance mechanisms of halophilic denitrifying bacteria have not been fully studied, and full-scale engineering trials with saline fly ash-washing wastewater have not been reported. In this study, we isolated and screened a halophilic denitrifying bacterium (Marinobacter sp.), GH-1, analyzed its nitrogen metabolism pathways and salt-tolerance mechanisms using whole-genome data, and explored its nitrogen removal characteristics under both aerobic and anaerobic conditions at different salinity levels. GH-1 was then applied in a full-scale engineering project to treat saline fly ash-washing leachate. The main results were as follows: (1) Based on the integration of whole-genome data, it is preliminarily hypothesized that the strain possesses complete nitrogen metabolism pathways, including denitrification, a dissimilatory nitrate reduction to ammonium (DNRA), and ammonium assimilation, as well as the following three synergistic strategies through which to counter hyperosmotic stress: inorganic ion homeostasis, organic osmolyte accumulation, and structural adaptations. (2) The strain demonstrated effective nitrogen removal under aerobic, anaerobic, and saline conditions (3–9%). (3) When applied in a full-scale engineering system treating saline fly ash-washing wastewater, it improved nitrate nitrogen (NO3−-N), total nitrogen (TN), and chemical oxygen demand (COD) removal efficiencies by 31.92%, 25.19%, and 31.8%, respectively. The proportion of Marinobacter sp. increased from 0.73% to 3.41% (aerobic stage) and 2.86% (anoxic stage). Overall, halophilic denitrifying bacterium GH-1 can significantly enhance the nitrogen removal efficiency of saline wastewater systems, providing crucial guidance for biological nitrogen removal treatment.