Study Of Microcysits Aeruginosa Removal By Magnetic Composite Coagulant

With the deterioration of eutrophication, the problem of algae blooms have become major concerns for drinking water providers worldwide. A lot of running water plants which use lake water as resource suffer from filter blocking and spend a large amount of cost on algae removal. As the most common step in conventional water treatment processes, coagulation has been under the researchers' attention, and it provides a promising future of algae removal especially with the development of composite coagulant.In this paper, a magnetic compostie coagulant was prepared by magnetic nanoparticles and polyferric chloride (PFC) for Microcystis aeruginosa removal. The magnetic nanoparticles, PFC and Magnetic nanopartilces/PFC (MPFC) were characterised in terms of typical properties, structure and morphological ananlysis (TEM, XRD, pHpzc, FTIR and Fe distribution). The coagulation performances of MPFC and PFC were compared under different initial pH conditions, coagulant dosages and ionic strength conditions. The effects of magnetic nanoparticles on the settling rate of flocs, the coagulation performance in the presence of natural organic matter (NOM) and the removal efficiency of microcystins (MCs) were also studied. In addition, the mechanisms of PFC and MPFC were discussed.It can be seen from the characterization that the magnetic Fe3O4 particles are nanosized particles with spinel structure. The combination with PFC has no effect on the stucture of magnetic nanoparticles, but Fe distribution in PFC has changed. Coagulation experiments on M. aeruginosa removal under different conditions reveal that MPFC gives a synergistic improvement in the removal efficiency when the dosage exceeds a certain value, as compared to PFC. The coagulation performance of MPFC shows slight pH, coagulant dosage and ionic strength dependence, which means that the scope of application of MPFC is wider. The M. aeruginosa removal efficiency reaches 100% at dosage of 2 mg/L (as Fe) with initial pH 10. The results of settling kinetics of flocs reveal that the presence of magnetic nanoparticles accelerates the settling rate. A new semi-empirical kineitc eqution is proposed to better describe the settlement characteristics of flocs. Settling kinetics of MPFC fits the equation better and the smaller the diffusion constant k and reaction index n are, the better settling efficiency is achieved. Investigations on the influence of the water background NOM on the removal of M. aeruginosa by two coagulants show higher maximal M. aeruginosa removal value, better NOM removal efficiency and lower trendency of disinfection byproducts (DBPs) formation of MPFC. What's more, MPFC achieves better MCs removal efficiency and mitigates the threats of intracellular microcystins release. The predominant M. aeruginosa removal mechanism of PFC and magnetite suspensions is charge neutralization and adsorption, respectively. The improved coagulation efficiency of MPFC owes to the co-effect of PFC and magnetic nanoparticles. The newly added magnetite acts as an adsorber, which favors the M. aeruginosa removal by adsorbing negatively charged algae cells, NOM, and MCs on the surface. The high polymer of Fe and iron hydroxide then facilitate the formation of large and settleable flocs by enmeshment.