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Water 2017, 9(12), 915; doi:10.3390/w9120915

200 kHz Sonication of Mixed-Algae Suspension from a Eutrophic Lake: The Effect on the Caution vs. Outbreak Bloom Alert Levels

Department of Construction Environment Engineering, University of Science and Technology (UST), Daejeon 341-13, Korea
Environmental and Plant Engineering Research Institute, Korea Institute of Civil Engineering and Building Technology (KICT), Gyeonggi-Do 102-23, Korea
Author to whom correspondence should be addressed.
Received: 23 October 2017 / Revised: 20 November 2017 / Accepted: 22 November 2017 / Published: 24 November 2017
(This article belongs to the Special Issue Eutrophication of Waterways: An Old Problem with Modern Consequences)
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For effective ultrasonic algae removal, several studies have considered the ultrasound equipment linked factors, such as power and frequency. However, studies on the response of mixed algal cultures and associated water quality parameters to ultrasound are limited. In this lab-scale sonication, the removal of cyanobacteria at a pre-set frequency of 200 kHz on mixed algae suspensions collected from a eutrophic lake was investigated. The caution (17.5 µg/L) and outbreak (1450 µg/L) alert levels in terms of chlorophyll-a (Chl-a) concentrations of the initial samples were each sonicated for 10, 15, and 20 min, and then kept in an incubator. Fifteen minutes of sonication resulted in best removal efficiency of 0.94 and 0.77, at an ultrasonic dose of 30 kWh/m3 at the outbreak and caution level concentrations, respectively. Immediately after 15 min sonication, and after standing in the incubator for a day, chlorophyll-a removal efficiencies of 0.28 and 0.90 were achieved in the outbreak level, respectively, and the matching removal efficiencies for the caution level were 0.23 and 0.64. Even though the removal was substantial in both cases, the final 147 µg/L chlorophyll-a concentration of the outbreak, which is itself still in the outbreak level range, shows that ultrasonication is not effective to satisfactorily remove algae from a concentrated suspension. Total dissolved nitrogen and chemical oxygen demand were reduced, overall, due to sonication. However, total dissolved phosphorus of the concentrated level was increased during the treatment. Although sonication needs further replicated experimental testing in whole-lake systems, our results show that 200 kHz sonication was able to reduce chlorophyll-a concentrations in small-scale laboratory tests. View Full-Text
Keywords: eutrophication; cyanobacteria; chlorophyll-a; sonication; alert level; South Korea eutrophication; cyanobacteria; chlorophyll-a; sonication; alert level; South Korea

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Tekile, A.; Kim, I.; Lee, J.-Y. 200 kHz Sonication of Mixed-Algae Suspension from a Eutrophic Lake: The Effect on the Caution vs. Outbreak Bloom Alert Levels. Water 2017, 9, 915.

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