Removal of Nitrate Nitrogen by Rhodotorula graminis Immobilized in Alginate Gel for Groundwater Treatment

Masashi Nishida,Syuhei Matsuo,Karin Yamanari,Katsuki Kusakabe,Masayoshi Iwahara

doi:10.3390/pr9091657

Abstract

Groundwater is the source of all tap water in Kumamoto City, Japan. However, the concentration of nitrate nitrogen (NO3−-N) tends to increase every year due to the influences of overfertilization, field disposal of livestock manure, and inflow of domestic wastewater. A heterotrophic nitrification–aerobic denitrification (HN-AD) system is an attractive approach for nitrate-nitrogen removal. In this study, Rhodotorula graminis NBRC0190, a naturally occurring red yeast that shows high nitrogen removal performance in glucose, was immobilized on calcium alginate hydrogel beads. NO3−-N removal efficiency exceeded 98% in the region of NO3−-N concentration below 10 mg/L in the model groundwater. Even after the same treatment was repeated five times, the denitrification performance of the R. gra immobilized alginate hydrogel beads was maintained. Finally, when this treatment method was applied to actual groundwater in Kumamoto City, it was possible to make the water of even higher quality.

Highlights

IntroductionThe water quality of groundwater sources in the city is comparable to commercial mineral water, except for nitrate nitrogen [1]
The leakage of R. gra immobilized on alginate beads was evaluated by turbidity; the leakage increased after 50 h of incubation, but thereafter, the change in turbidity was small, indicating that R. gra was stably immobilized
The nitrate-nitrogen removal experiments were conducted at an initial nitrate-nitrogen concentration of 10 mg/L, assuming groundwater treatment

Summary

Introduction

The water quality of groundwater sources in the city is comparable to commercial mineral water, except for nitrate nitrogen [1]. Excess organic nitrogen entering the soil decomposes into ammonium, nitrite, and nitrate ions in the soil. These ions return to nitrogen molecules and organic nitrogen through denitrification and assimilation, respectively. In this way, the nitrogen cycle proceeds, but excess nitrate nitrogen pollutes groundwater. Various treatments have been applied to remove nitrate nitrogen from water sources; i.e., biological removal [2,3,4,5], ion exchange [6,7], reverse osmosis [8], and chemical reduction [9,10,11]

Methods

Results

Conclusion