Carbon key-properties for microcystin adsorption in drinking water treatment: structure or surface chemistry?

Dissertação para Obtenção de Grau de Mestre em Engenharia Química e Bioquímica

The carbon key-properties (structure and surface chemistry) for microcystin-LR (MC-LR) adsorption onto activated carbon were investigated. Waters with an inorganic background matrix approaching that of the soft natural water (2.5 mM ionic strength) were used. Also, model waters with controlled ionic make-up and NOM surrogate with similar size of MC-LR (tannic acid - TA) with MC-LR extracts were tested with activated carbon NORIT 0.8 SUPRA. For this AC, two particle sizes, 125-180 μm and 63-90 μm were tested. The surface chemistry of NOR 125-180 μm was modified by thermal treatment and was also preloaded with TA. The integrated analysis of carbon’s chemical and textural characterization and of kinetic and isotherm modeling using non-linear models allowed concluding that: i) the heating method is an efficient and simple process for reducing a relatively hydrophilic activated carbon and thereby enhancing its MC-LR adsorption capacity; ii) from a combination of the modification of the carbon surface chemistry and the carbon structure, it is demonstrates that both properties play an important role in the adsorption process, although carbon surface chemistry seems to be more important than its porous structure – MC-LR adsorption correlated with meso and macroporous volume and particularly well with carbon hydrophobicity (inverse of oxygen content); iii) the smaller the particle size, the more important is external mass transfer over intraparticle diffusion; iv) similar sized NOM strongly competes with MC-LR for the same AC sites; v) direct competition governs the simultaneous MC-LR and NOM adsorption; vi) the preloading phenomena reduces significantly the performance of activated carbon adsorption.