Removal of cyanobacteria and cyanotoxins from drinking water by powdered activated carbon adsorption/ultrafiltration

Campinas, Margarida Páscoa

http://hdl.handle.net/10400.1/247

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Authors

Campinas, Margarida Páscoa

Advisor(s)

Rosa, Maria João

Teixeira, Margarida Ribau

Abstract(s)

PAC/UF was investigated to remove the cyanobacterium Microcysis aeruginosa and microcystins, focusing on toxins adsorption onto PAC and the combined effect of the water organic and inorganic matrices, the cells removal and lysis by UF, and PAC contribution to membrane fouling control and microcystins removal by PAC/UF. The fine-grade mesoporous PAC presented high capacity and fast kinetics for microcystins adsorption from ultrapure-water. In model and natural waters, NOM size governed microcystins-NOM competition, and inorganics contribution was crucial. Main competitor was NOM of closer size, hindering microcystins adsorption through a pore-blocking mechanism. Ionic strength induced the competition of larger compounds and diminished the competition of similar-sized compounds. Kinetic models confirmed the competing mechanisms proposed based on kinetic and isotherm data. UF ensured absolute removal of M. aeruginosa single-cells, although lysis was detected, particularly with cell ageing. However, AOM-driven microcystins rejection attenuated/avoided the permeate degradation. While not affecting the reversible fouling, PAC improved the permeate quality and membrane irreversible-fouling, minimising the chemical cleaning. The worst flux impairment was associated to polysaccharide-like AOM in background inorganics, for which PAC was apparently ineffective. PAC/UF performed better than PAC+C/F/S. For the usual concentrations of dissolved microcystins in natural waters, 10-15 mgPAC/L achieved the WHO guideline-value.