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

Tese dout., Ciências e Tecnologias do Ambiente, Universidade do Algarve, 2009PAC/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.Fundação para a Ciência e a Tecnologi

Previsão da capacidade de remoção de cianobactérias e cianotoxinas na ETA de Alcantarilha

Os blooms de cianobactérias em reservatórios de água destinada à produção de água para consumo humano originam muitos problemas, sendo o mais preocupante o facto de uma proporção significativa de cianobactérias produzirem uma ou mais toxinas. Num programa de prevenção da saúde pública, relativamente ao consumo de água com cianotoxinas, é essencial avaliar a eficiência de remoção destes compostos nas Estações de Tratamento de Água (ETA). Neste âmbito, o presente trabalho tem como objectivo efectuar uma previsão, com base em informação bibliográfica, da eficiência de remoção de cianobactérias e cianotoxinas pelo processo de tratamento instalado na ETA de Alcantarilha (Águas do Algarve, S.A.), face a um eventual bloom na água de origem. Prevê-se que a ETA de Alcantarilha (tratamento convencional com pré-ozonização) possibilite a remoção de cianobactérias e cianotoxinas intracelulares se forem utilizadas as doses de reagentes e residuais de ozono e cloro apropriados e com a utilização de carvão activado em pó (PAC) em doses relativamente elevadas. A principal incerteza prende-se com o desempenho da ETA na remoção de toxinas solúveis, uma vez que este está dependente da qualidade da água na origem e das condições de funcionamento da ozonização, da adsorção com PAC e da cloragem

Adsorption/Coagulation/Ceramic Microfiltration for Treating Challenging Waters for Drinking Water Production

Pressurized powdered activated carbon/coagulation/ceramic microfiltration (PAC/Alum/MF) was investigated at pilot scale for treating low turbidity and low natural organic matter (NOM) surface waters spiked with organic microcontaminants. A total of 11 trials with clarified or non-clarified waters spiked with pesticides, pharmaceutical compounds, or microcystins were conducted to assess the removal of microcontaminants, NOM (as 254 nm absorbance, A254, and dissolved organic carbon, DOC), trihalomethane formation potential (THMFP), aerobic endospores as protozoan (oo)cysts indicators, bacteriophages as viruses indicators, and regular drinking water quality parameters. PAC/(Alum)/MF achieved 75% to complete removal of total microcontaminants with 4–18 mg/L of a mesoporous PAC and 2 h contact time, with a reliable particle separation (turbidity < 0.03 NTU) and low aluminium residuals. Microcontaminants showed different amenabilities to PAC adsorption, depending on their charge, hydrophobicity (Log Kow), polar surface area and aromatic rings count. Compounds less amenable to adsorption showed higher vulnerability to NOM competition (higher A254 waters), greatly benefiting from DOC-normalized PAC dose increase. PAC/Alum/MF also attained 29–47% NOM median removal, decreasing THMFP by 26%. PAC complemented NOM removal by coagulation (+15–19%), though with no substantial improvement towards THMFP and membrane fouling. Furthermore, PAC/Alum/MF was a full barrier against aerobic endospores, and PAC dosing was crucial for ≥1.1-log reduction in bacteriophages