Denitrification-Potential Evaluation and Nitrate-Removal-Pathway Analysis of Aerobic Denitrifier Strain Marinobacter hydrocarbonoclasticus RAD-2

Dedong Kong,Yunjie Ruan,Wenbing Li,Yale Deng,Guangsuo Chen,Fucheng Lin,Jianhai Yu

doi:10.3390/w10101298

Dedong Kong, Yunjie Ruan + Show 5 more

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https://doi.org/10.3390/w10101298

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Abstract

An aerobic denitrifier was isolated from a long-term poly (3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV-supported denitrification reactor that operated under alternate aerobic/anoxic conditions. The strain was identified as Marinobacter hydrocarbonoclasticus RAD-2 based on 16S rRNA-sequence phylogenetic analysis. Morphology was observed by scanning electron microscopy (SEM), and phylogenetic characteristics were analyzed with the API 20NE test. Strain RAD-2 showed efficient aerobic denitrification ability when using NO3−-N or NO2−-N as its only nitrogen source, while heterotrophic nitrification was not detected. The average NO3−-N and NO2−-N removal rates were 6.47 mg/(L·h)and 6.32 mg/(L·h), respectively. Single-factor experiments indicated that a 5:10 C/N ratio, 25–40 °C temperature, and 100–150 rpm rotation speed were the optimal conditions for aerobic denitrification. Furthermore, the denitrifying gene napA had the highest expression on a transcriptional level, followed by the denitrifying genes nirS and nosZ. The norB gene was found to have significantly low expression during the experiment. Overall, great aerobic denitrification ability makes the RAD-2 strain a potential alternative in enhancing nitrate management for marine recirculating aquaculture system (RAS) practices.

Highlights

Recirculating aquaculture systems (RAS) are a potential alternative to traditional aquaculture systems due to their intensive production and environmental sustainability [1]
Marinobacter hydrocarbonoclasticus strain RAD-2 was isolated from a denitrifying reactor using PHBV as the carbon source and biofilm carrier
A 5:10 C/N ratio, 25–40 ◦ C temperature, and 100–150 rpm rotation speed were the optimal conditions for aerobic denitrification (Table 2)

Summary

Introduction

Recirculating aquaculture systems (RAS) are a potential alternative to traditional aquaculture systems due to their intensive production and environmental sustainability [1]. RAS mainly use biological filters to oxidize ammonium to nitrate through nitrification, with nitrite as the intermediate product since ammonium and nitrite have direct toxicity to most fish species [2]. The heterotrophic denitrification process depends highly on sufficient organic substances as electron donors, which inhibit its application under the circumstances of a low C/N ratio, such as groundwater or RAS effluent treatment [4,7]. An interesting alternative that uses biodegradable polymers as simultaneous biofilm carriers and carbon sources was proposed and demonstrated as feasible for nitrate removal in many solid-phase denitrification reactors [6,7,8,9,10,11,12]

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