Mini-Hydrocyclone Separation of Cyanobacterial and Green Algae: Impact on Cell Viability and Chlorine Consumption

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.

A Novel Bioflocculant Produced by Cobetia marina MCCC1113: Optimization of Fermentation Conditions by Response Surface Methodology and Evaluation of Flocculation Performance when Harvesting Microalgae

“…Microalgal biomass is critical in biofuel research, with biomass harvesting as a critical step in achieving high biofuel efficiency. Compared to traditional techniques such as gravity filtration or centrifugation, the flocculation-based technique for algal cell harvesting is more convenient because a large amount of culture is available for treatment (Moradinejad et al 2019). However, due to the problematic application, high cost (physical flocculation), and virulence (chemical flocculation) of the flocculation technique in microalgal biomass harvesting, the physical and chemical approaches of the flocculation technique are rendered inadequate (Cerff et al 2012).…”

Optimization of the Outlet Flow Ratio of Mini-Hydrocyclone Separators Using the Full Factorial Design Method to Determine the Separation Efficiency

“…Manufacturing minihydrocyclone separators using conventional methods is highly complicated and difficult, as they are fabricated using the 3D printing method [10]. Notably, 3D-printed minihydrocyclones have been recently optimized to separate fine particles with low flow rates [11,12].…”