Rejection performance and stability of MF/UF ceramic membranes towards TiO2 photocatalyst in PMRs

Details

Supervisors

Luis Alconero, Patricia

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en chimie et science des matériaux

Abstract

Worldwide, clean water is increasingly becoming a acutely scarce resource, notably because of toxic organic pollutants such as cytostatic drugs contained in the waterways, which represent a threat to the health and safety of aquatic life. As these pharmaceuticals cannot be removed by conventional wastewater treatments, photocatalytic membrane reactors (PMRs) have recently been proposed as a promising technology to degrade the organic contaminants. In order for this emerging technology to work properly, the membrane module must efficiently retain the photocatalytic particles by operating under suitable flow conditions which minimise membrane fouling and mechanical abrasion caused by the photocatalyst. The investigations on the influence of feed cross-flow velocity (CFV) and feed water composition on the fouling and stability of ceramic membranes in a PMR are presented in this work. Moreover, the filtration efficiency of the fouling cake layer towards small pharmaceutical active compounds (PhACs) is discussed. Alumina (UF-Al2O3/ZrO2) and titania (UF-TiO2) ultrafiltration membranes with a molecular weight cut-off of 100 kDa, and one titania microfiltration (MF-TiO2) membrane with maximum pore size of 0,2μm were investigated. Experiments were conducted at constant TMP (3 bar) and fixed TiO2 photocatalyst loading (1.5 g/dm3) and by progressively decreasing the applied CFV from 6 to 1 m/s. For all UF membranes, regardless of the membrane compactness and material, increasing the CFV above 3 m/s had no impact on the membrane permeability while working at low CFV (i.e. 1 m/s) led to a significant decrease of the permeability. At low CFV, TiO2 catalyst concentration in the bulk feed decreased by 65-75% which was attributed to membrane fouling. In case of MF membrane a major influence of the CFV on membrane fouling was observed when the flow was reduced from 6 m/s to 3 m/s. Moreover, the use of wastewater instead of laboratory grade water (LGW) as well as working under more turbulent conditions had almost no impact on the membrane performance in the whole range of CFV (6-1 m/s). Indeed, only the UF-TiO2 membrane at 3 m/s showed a small reduction of permeate flux with wastewater in comparison with LGW. Additionally, for the UF membranes, the rejection of PhACs was not influenced by fouling cake layer while its selectivity towards small organic compounds was enhanced. After 150h of PMR operation, the UF-Al2O3/ZrO2 membrane did not lose its separation properties at high cross-flow velocity (CFV = 6 m/s).