Abstract
The co-occurrence of non-toxic phytoplankton alongside cyanobacteria adds to the challenge of treating source waters with harmful algal blooms. The non-toxic species consume the oxidant and, thereby, reduce the efficacy of oxidation of both the extracellular and intracellular cyanotoxins. In this work, a 3D printed mini-hydrocyclone was used to separate a mixture of non-toxic green algae, Scenedesmus obliquus, from a toxic species of cyanobacteria, Microcystis aeruginosa. When water is pumped through the mini-hydrocyclone, cells exit through an overflow or underflow port depending on their size, shape, and density relative to the other cells and particles in the water matrix. The overflow port contains the cells that are smaller and less dense since these particles move toward the center of the hydrocyclone. In this work, the majority (>93%) of Microcystis cells were found in the overflow while the underflow contained primarily the Scenedesmus (>80%). This level of separation efficiency was maintained over the 30-min experiment and the majority of both cells (>86%) remained viable following the separation, which indicates that the pumping combined with forces exerted within the mini-hydrocyclone were not sufficient to cause cell death. The impact of free chlorine on the cells both pre-separation and post-separation was evaluated at two doses (1 and 2 mg/L). After separation, the overflow, which contained primarily Microcystis, had at least a 24% reduction in the free chlorine decay rate as compared to the feed water, which contained both species. This reduction in chlorine consumption shows that the cells separated via mini-hydrocyclone would likely require lower doses of oxidant to produce a similar level of degradation of the cyanotoxins present in either the extracellular or intracellular form. However, future work should be undertaken to evaluate this effect in natural bloom samples.
Highlights
Phytoplankton, i.e., cyanobacteria, dinoflagellates, green algae, and diatoms, in surface waters are significant contributors to the total carbon biomass pool [1]
Chlorination experiments were conducted on the mixed sample prior to separation as well as the overflow underflow samples collected after a 30-min pumping time
TheAlthough forces exerted cellsisvia the hydrocyclone did not optimization result in significant cell death with >86%. This on result promising for its potential of chlorine treatment and of all cells remaining viable after separation
Summary
Phytoplankton, i.e., cyanobacteria, dinoflagellates, green algae, and diatoms, in surface waters are significant contributors to the total carbon biomass pool [1]. T&O compounds are not a risk to human health, they cause customer complaints and lower confidence in the water treatment process [14] Both cyanobacteria and select species of dinoflagellates and green algae produce T&O compounds [15,16,17]. A prediction of which species would exit through the overflow vs the underflow was calculated using knowledge of cell density, size, and shape These predicted results were compared against the operation of the mini-hydrocyclone and the separated species were examined to determine the efficiency of the technique, the viability of the cells, and the effect on the consumption of chlorine.
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