# Removal of Chemical Oxygen Demand (COD) from Swine Farm Wastewater by Corynebacterium xerosis H1

## TL;DR

This study isolates and characterizes Corynebacterium xerosis H1, a bacteria that efficiently degrades chemical oxygen demand in swine wastewater without needing immobilization.

## Contribution

The discovery of a carrier-free, efficient COD-degrading strain of Corynebacterium xerosis H1 for swine wastewater treatment.

## Key findings

- Corynebacterium xerosis H1 achieved a 27.93% COD degradation rate in swine wastewater.
- The strain reduced nitrogen-containing compounds, proteins, and lipids while increasing lignins in wastewater.
- SBR with H1 improved COD removal and reduced fluorescence intensity of organic pollutants.

## Abstract

Swine wastewater (SW) has a high chemical oxygen demand (COD) content and is difficult to degrade; an effective strategy to address this issue is through biodegradation, which poses negligible secondary pollution risks and ensures cost-efficiency. The objectives of this study were to isolate an effective COD-degrading strain of SW, characterize (at the molecular level) its transformation of SW, and apply it to practical production. A strain of Corynebacterium xerosis H1 was isolated and had a 27.93% ± 0.68% (mean ± SD) degradation rate of COD in SW. This strain precipitated growth in liquids, which has the advantage of not needing to be immobilized, unlike other wastewater-degrading bacteria. Based on analysis by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), this bacterium removed nitrogen-containing compounds in SW, with proteins and lipids decreasing from 41 to 10% and lignins increasing from 51 to 82%. Furthermore, the enhancement of the sequencing batch reactor (SBR) with strain H1 improved COD removal in effluent, with reductions in the fluorescence intensity of aromatic protein I, aromatic protein II, humic-like acids, and fulvic acid regions. In addition, based on 16S rRNA gene sequencing analysis, SBRH1 successfully colonized some H1 bacteria and had a higher abundance of functional microbiota than SBRC. This study confirms that Corynebacterium xerosis H1, as a carrier-free efficient strain, can be directly applied to swine wastewater treatment, reducing carrier costs and the risk of secondary pollution. The discovery of this strain enriches the microbial resource pool for SW COD degradation and provides a new scheme with both economic and environmental friendliness for large-scale treatment.