Low Dose Coagulant and Local Soil Ballast Effectively Remove Cyanobacteria (Microcystis) from Tropical Lake Water without Cell Damage

The combination of a low dose of coagulant with a ballast, also known as “flock and sink,” has been proposed as a lake restoration and cyanobacteria bloom management strategy. The effectiveness of this technique using aluminum sulfate (alum) as a coagulant and a local soil (LS) from Thailand as a ba...

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Bibliographic Details
Published in:	Water (Basel) Vol. 13; no. 2; p. 111
Main Authors:	Thongdam, Somjate, Kuster, Anthony C., Huser, Brian J., Kuster, Anootnara T.
Format:	Journal Article
Language:	English
Published:	Basel MDPI AG 01-01-2021
Subjects:	Alum Aluminum Aluminum sulfate Ballast Cellular structure Chlorophyll Climate change Coagulants Cyanobacteria Environmental Sciences Eutrophic environments Eutrophic waters Eutrophication Experiments flock and sink Laboratories Lake restoration Lake sediments Lakes Microcystis Miljövetenskap Nutrient release Oceanografi, hydrologi, vattenresurser Oceanography, Hydrology, Water Resources Phosphorus scanning electron microscope Scanning electron microscopy Tropical lakes Water circulation Water column Water damage Water quality Zeta potential Thailand
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Summary:	The combination of a low dose of coagulant with a ballast, also known as “flock and sink,” has been proposed as a lake restoration and cyanobacteria bloom management strategy. The effectiveness of this technique using aluminum sulfate (alum) as a coagulant and a local soil (LS) from Thailand as a ballast in eutrophic water dominated by positively buoyant Microcystis colonies collected from a tropical lake was investigated by measuring changes in chlorophyll-a (chl-a), pH, and zeta potential. Cell integrity was also evaluated using scanning electron microscopy. Results showed that alum alone could reduce chl-a (up to 60% to 83%) at doses (higher than 3 to 6 mg Al/L) dependent on the initial pH (7.6 to 8.2) and initial chl-a concentration (138 to 615 µg/L) of the lake water but resulted in morphological changes to cellular structure and generally required a dose that reduced pH to <7. LS ballast alone was able to reduce chl-a concentrations (up to 26% at highest dose of 400 mg/L) and caused no significant changes to pH or zeta potential. Combining a low dose of alum (2 mg Al/L) with some amount of LS ballast (50 to 400 mg/L) created an interaction effect that resulted in 81 to 88% reduction in chl-a without changes to zeta potential or morphological changes to cellular structure. Flock and sink may serve a niche role in lake restoration when positively buoyant cyanobacteria are present in the water column during time of treatment. This research showed that an 800% increase in ballast dose resulted in about an 8% reduction in chl-a when combined with 2 mg Al/L of alum. Therefore, it is recommended that ballast dose should be determined by considering its phosphorus sorption capacity and the potentially releasable phosphorus in the lake sediment in order to realize long-term reductions in sediment nutrient release.
ISSN:	2073-4441 2073-4441
DOI:	10.3390/w13020111