Satisfactory quartz7/31/2023 Besides, as a polymeric coagulant, the bridging action of PAFC is also benefit for the coagulation. The cationic Al and Fe ion of these coagulants could coagulate negative charged algal cells through charge neutralization. AlCl 3, FeCl 3 and PAFC are the most widely used traditional organic coagulants in drinking water treatment. Therefore, studying traditional inorganic coagulants combined with ballast to remove harmful algae is more meaningful in drinking water plant. Although the removal efficiency was remarkable, the high-cost and increase of natural organic matter (NOM) would restrict the application of organic coagulants in drinking water treatment. Those researchers mainly combined organic coagulants (especially chitosan) with ballast to removal harmful algae. Besides, the ballast should not accelerate algal cell lysis and algal toxin release during floc storage, which would degrade the quality of the water obtained upon dewatering the flocs ( i.e. Therefore local soils are not suitable, because the metal ions and organic matter in soils may be released into drinking water. For example, the ballast must not cause secondary pollution in drinking water. More issues need to be considered for application in drinking water treatment. Until now, most researchers have focused on the use of ballast coagulation to remove harmful algae from natural water, rather than use in drinking water treatment. Ballast particles, such as clay, soil and sand, serve as seed grains when coagulation proceeds, while accelerating the sedimentation through increasing floc density 13. Compared to soils and clays, sands are more commercially viable and completely harmless to water quality. The strong removal of harmful marine algae using chitosan mixed with sand has also been reported 12. For example, the combination of chitosan with local soils and clays achieved higher removal efficiencies of cyanobacteria in Taihu Lake 8, 9, 10. It is a gravity-based physicochemical separation process involves the injection of a ballasting agent, typically microsand, to increase the floc density and size 11. Recently, the application of ballast coagulation to control HABs has been extensively studied 8, 9, 10. However, due to the buoyancy of algal cells 7, the flocs cannot be completely settled, which will reduce the removal efficiency. In drinking water treatment plants, the coagulation process is an effective way to remove harmful algae 6. MCs may cause serious health problems in humans through the consumption of contaminated water for drinking and recreation 4, 5. aeruginosa, which can produce a suite of hepatotoxins known as microcystins (MCs) 3. Among the harmful algae, the most notorious one is M. These blooms always result in some serious issue, such as deterioration of water quality, off-flavor problems, and illness in animals and humans 1, 2. Over the past years, the presence of harmful algal blooms (HABs) in water has represented a big challenge to drinking water plants. In addition, cells with PAFC incurred relatively moderate cellular oxidative damage and could remain intact for longer time. Owing to 200 mg/L quartz sand could damage the cell’s membrane during coagulation proces, algal cells in the system lysed two days earlier than with 50 mg/L sand during flocs storage. That’s because quartz sand can enhance the coagulation so as to improve capping the EOM and MCs in flocs during coagulation process. After coagulation, the extracellular organic matter (EOM) and microcystins (MCs) in system with quartz sand was remarkably reduced. Flocs from 50 mg/L sand addition were larger than that with other sand doses, which was on account of the appropriate enhancement of collision efficiency at this dose. However, the removal efficiency with PAFC was increased not only by the enhanced floc density, but also by the enlarged floc size. The increase of removal efficiency with AlCl 3 and FeCl 3 was only due to the enhancement of floc density by the quartz sand. Results showed that quartz sand could markedly increase the algae removal efficiency and decrease the coagulant doses. In this study, low-cost and non-polluting quartz sand was respectively mixed with AlCl 3, FeCl 3 and PAFC to synergistically remove Microcystis aeruginosa.
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