Journal of Bacteriology & Parasitology

Micro - Nano Bubble Technology- An In-Situ Treatment for Microbial Community Changes in Urban River

Toshiyuki Tony^* Department of Microbiology, Kyoto University, Kyoto, USA
^*Correspondence: Toshiyuki Tony, Department of Microbiology, Kyoto University, Kyoto, USA, Tel: +81-91-1656-5994, Email:

Received: 01-Dec-2020 Published: 22-Dec-2020, DOI: 10.35248/2155-9597.20.S6.005

Introduction

These black-odor rivers flows through the cities affect residents’ life and pose a serious threat to human health. Thus, treating the polluted urban rivers and recovering their ecological function have attracted much attention in China. It is well known that microbes play an important role in biogeochemical cycling of aquatic ecosystem, which could decompose, transform and mineralize organic or inorganic matters in urban rivers [1].

Additionally, microbes are the first that interacted with dissolved substances and severely impacted by perturbations of the water quality. Previous study showed that although microbes could adapt to the environment fluctuation to some extent, the microbial structure will shift significantly with intensive change of the ambient. Thereby, microbes could be used to monitor and evaluate the pollution of water, and increasing the concentration of dissolved oxygen in the water body is the primary method to alleviate the pollution of urban streams. Many physiochemical or biological treatment methods which involve plants aeration, chemical agents and bacterial inoculation exclusively or in combination to remove or metabolize the pollutants mitigate the pollution in different extents. Lately, the Micro-nano Bubble Technology (MBT) has been applied in water treatment, resulting in good effects [2].

Micro-nano bubbles are small bubbles with diameters of several micrometers and nanometers, with high self-pressurization and longer lifetime, which have recently been explored as promising candidates for aeration [3]. The primary application of micronano bubble was focused on activating the microorganisms, flotation, water treatment, and aeration. Unlike the normal macro bubbles (with diameter 1-10 mm), the micro-nano bubbles would swell and burst in liquid with high mass transfer, and significantly increase the concentration of Dissolved Oxygen (DO) in water, reaching to the possible oversaturation. For these excellent properties, MBT would resolve the problem of hypoxia in polluted river efficiently. Recently, micro-nano bubbles were used to mitigate the pollution by enhancing the concentration of DO and eliminating the impurities in the river.

Water Quality Improvement of Black-Odor River

Selected water physicochemical indexes, such as DO, ORP, COD and so on, were used to evaluate the river condition and impact assessment. The result showed that the river was polluted with low DO (0.60 mg/L-1.02 mg/L) and ORP (around-140.00 mV) levels before treatment, and then the DO and ORP values were significantly increased during MBT treatment and stabilizes gradually. During the continuous aeration period, the DO increased to 4.00 mg/L-7.50 mg/L, and then was stable around 4.00 mg/L during intermittent aeration. In like manner, the ORP value increased from negative values to around 130.00 mV during continuous aeration period, and then stable. The sharp decreasing of DO and ORP values might be due to the discharge of waste-water when sampling. Meanwhile, the pH was around 7.00 during the treatment, which was not affected by MBT. In addition, the micro-nano bubbles could combine the impurities in the river, then float upon water and been eliminated, for which, the turbidity of the river was decreased from 148.00 NTU to around 21.00 NTU [4].

The Alphaproteobacteria, Betaproteobacteria, Deltaproteobacteria, Epsilonproteobacteria, Gammaproteobacteria, Flavobacteria, Actinobacteria, Clostridia, Sphingobacteria, and Bacteroidia were dominant microbes at class level. The Alphaproteobacteria, Gammaproteobacteria and Deltaproteobacteria are usually abundant in marine environment. The tidal water brought seawater and marine microbes, affecting the microbial community structure in the river. For other microbes, though they were still abundant after treatment, the relative abundance was changed. The relative abundance of Actinobacteria, Cytophagia and Sphingobacteria were increased significantly after MBT treatment, which were found in oligotrophic aquatic environment and able to degrade biopolymer. Furthermore, it was reported that Actinobacteria and Verrucomicrobiae are more abundant in sediment samples than water [5]. The increased abundance of Actinobacteria and Verrucomicrobiae indicated that MBT might encourage the microorganisms migrated with nutrients from sediment to water. The Bacteroidia, Clostridia, Deltaproteobacteria, Flavobacteria and Synergistia were decreased after MBT treatment, most of which were reported as potential opportunistic pathogens or nutrient-loving microbes under anaerobic condition. For example, Bacteroidia and Flavobacteria were reported as potential fecal indicator bacteria, Deltaproteobacteria could metabolize sulfate in anaerobic environment [6,7].

Discussion and Conclusion

The decreased trend of these microbes suggests that after MBT treatment, the aquatic environment was not suitable for these microbes. In all, the result showed that MBT would influence the abundance of microbes, which was mainly related to the concentration of DO and organic matters.

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