Differences in the Effects of Calcium and Magnesium Ions on the Anammox Granular Properties to Alleviate Salinity Stress

Yeonju Kim,Soyeon Jeong,Shou-Qing Ni,Tatsuya Unno,Hyokwan Bae,Jeongmi Kim,Jaecheul Yu,Sung-Keun Rhee,Taeho Lee,Seongjae Park

doi:10.3390/app12010019

Abstract

Divalent cations were known to alleviate salinity stress on anammox bacteria. Understanding the mechanism of reducing the salinity stress on anammox granules is essential for the application of the anammox process for saline wastewater treatment. In this study, the effect of Ca2+ and Mg2+ augmentation on the recovery of the activity of freshwater anammox granules affected by salinity stress was evaluated. At the condition of a salinity stress of 5 g NaCl/L, the specific anammox activity (SAA) of the granule decreased to 50% of that of the SAA without NaCl treatment. Augmentation of Ca2+ at the optimum concentration of 200 mg/L increased the SAA up to 78% of the original activity, while the augmentation of Mg2+ at the optimum concentration of 70 mg/L increased the SAA up to 71%. EPS production in the granules was increased by the augmentation of divalent cations compared with the granules affected by salinity stress. In the soluble EPS, the ratio of protein to polysaccharides was higher in the granules augmented by Ca2+ than with Mg2+, and the functional groups of the EPS differed from each other. The amount of Na+ sequestered in the soluble EPS was increased by the augmentation of divalent cations, which seems to contribute to the alleviation of salinity stress. Ca. Kuenenia-like anammox bacteria, which were known to be salinity stress-tolerant, were predominant in the granules and there was no significant difference in the microbial community of the granules by the salinity stress treatment. Our results suggest that the alleviation effect of the divalent cations on the salinity stress on the anammox granules might be associated with the increased production of different EPS rather than in changes to the anammox bacteria.

Highlights

Saline wastewater from various industries such as food processing, petroleum, chemical, and pharmaceuticals accounts for approximately 5% of industrial wastewater [1,2,3]
The effect of the alleviation by the Ca2+ augmentation was higher than that by Mg2+. The addition of both divalent cations affected the extracellular polymeric substances (EPS) production and compositions as well as the amount of Na+ entrapped in the EPS
The increased amounts of Na+ associated with the EPS by the augmentation of divalent cations could contribute to the salinity stress alleviation for the anammox granules

Summary

Introduction

Saline wastewater from various industries such as food processing, petroleum, chemical, and pharmaceuticals accounts for approximately 5% of industrial wastewater [1,2,3]. The anaerobic ammonium oxidation process (Anammox), which is a cost-effective nitrogen removal technology, has attracted considerable attention for the treatment of saline wastewater containing a high concentration of nitrogen [1]. Anammox bacteria can be applied to saline wastewater treatment, but they have a lower salt resistance than other bacteria. The marine species have a strong tolerance to high salinity, their growth rate is slower than twice that of the freshwater species, so there is a limit to nitrogen-rich wastewater treatment [5]. Freshwater species with relatively fast growth rates are used widely for nitrogen-rich wastewater treatment. Step-by-step salt adaptation and salt stress alleviation methods are required for nitrogen-rich saline wastewater treatment, owing to their low salinity tolerance

Methods

Results

Conclusion