‘Floc and Sink’ Technique Removes Cyanobacteria and Microcystins from Tropical Reservoir Water

Abstract

Combining coagulants with ballast (natural soil or modified clay) to remove cyanobacteria from the water column is a promising tool to mitigate nuisance blooms. Nevertheless, the possible effects of this technique on different toxin-producing cyanobacteria species have not been thoroughly investigated. This laboratory study evaluated the potential effects of the “Floc and Sink” technique on releasing microcystins (MC) from the precipitated biomass. A combined treatment of polyaluminium chloride (PAC) with lanthanum modified bentonite (LMB) and/or local red soil (LRS) was applied to the bloom material (mainly Dolichospermum circinalis and Microcystis aeruginosa) of a tropical reservoir. Intra and extracellular MC and biomass removal were evaluated. PAC alone was not efficient to remove the biomass, while PAC + LMB + LRS was the most efficient and removed 4.3–7.5 times more biomass than other treatments. Intracellular MC concentrations ranged between 12 and 2.180 µg L−1 independent from the biomass. PAC treatment increased extracellular MC concentrations from 3.5 to 6 times. However, when combined with ballast, extracellular MC was up to 4.2 times lower in the top of the test tubes. Nevertheless, PAC + LRS and PAC + LMB + LRS treatments showed extracellular MC concentration eight times higher than controls in the bottom. Our results showed that Floc and Sink appears to be more promising in removing cyanobacteria and extracellular MC from the water column than a sole coagulant (PAC).

Incorporating Microbial Species Interaction in Management of Freshwater Toxic Cyanobacteria: A Systems Science Challenge

“…Physical control entails the mechanical inhibition, removal, or elimination of toxic cyanobacteria [23]. The use of plankton nets, hand-removal, and coagulants falls within this category [24,25], as do dam operations in reservoirs (hydrologic control, flushing [20,26]). Physical control methods also include alteration of the habitat to make it unfavorable for cyanobacterial survival and proliferation.…”

Advances in Sustainable Strategies for Water Pollution Control: A Systematic Review

“…Nutrients [31] Green liver system Cyanotoxins Wastewater from aquaculture [32] Floc and sink Cyanobacteria [33] Lanthanum-modified bentonite (LMB-sink/lock)…”

Removal of Cyanobacteria and Cyanotoxins in Waters

“…Worldwide, the most widely applied water treatment technology at water treatment plants involves a combination of coagulation, flocculation, sedimentation, filtration, and disinfection to treat water. Herein, five papers focus either directly or indirectly on coagulation and its alternatives or on the potential impacts of conventional water treatment technologies on drinking water containing cyanobacteria and/or cyanotoxins [2]. Arruda et al [2] have demonstrated that the so-called "floc-and-skin" technique, based on the combination of a ballast (i.e., natural soil or modified clay) and a coagulant, can effectively remove cyanobacterial biomass comprised of Dolichospermum circinalis and Microcystis aeruginosa, depending on the ballast's capacity to adsorb microcystin.…”

“…Herein, five papers focus either directly or indirectly on coagulation and its alternatives or on the potential impacts of conventional water treatment technologies on drinking water containing cyanobacteria and/or cyanotoxins [2]. Arruda et al [2] have demonstrated that the so-called "floc-and-skin" technique, based on the combination of a ballast (i.e., natural soil or modified clay) and a coagulant, can effectively remove cyanobacterial biomass comprised of Dolichospermum circinalis and Microcystis aeruginosa, depending on the ballast's capacity to adsorb microcystin. At the laboratory scale, the authors studied the effect of the floc-and-skin technique on the release of microcystins from cyanobacterial biomass in real water from the Funil Reservoir, a eutrophic system in southern Brazil.…”

“…At the laboratory scale, the authors studied the effect of the floc-and-skin technique on the release of microcystins from cyanobacterial biomass in real water from the Funil Reservoir, a eutrophic system in southern Brazil. Their results demonstrate that the technique is more effective than using a sole coagulant (i.e., polyaluminum chloride) to remove cyanobacteria and extracellular microcystins from water [2]. Next, Mucci et al [3] studied the effect of using chitosan as a coagulant to remove cyanobacteria from the water column.…”