Retention and Inactivation of Quality Indicator Bacteria Using a Photocatalytic Membrane Reactor


The development of effective disinfection treatment processes is crucial to help the water industry cope with the inevitable challenges resulting from the increase in human population and climate change. Climate change leads to heavy rainfall, flooding and hot weather events that are associated with waterborne diseases. Developing effective treatment technologies will improve our resilience to cope with these events and our capacity to safeguard public health. A submerged hybrid reactor was used to test the efficiency of membrane filtration, direct photolysis (using ultravioletC low-pressure mercury lamps, as well as ultraviolet-C and ultraviolet-A light-emitting diodes panels) and the combination of both treatment processes (membrane filtration and photolysis) to retain and inactivate water quality indicator bacteria. The developed photocatalytic membranes effectively retained the target microorganisms that were then successfully inactivated by photolysis
and advanced oxidation processes. The new hybrid reactor could be a promising approach to treat drinking water, recreational water and wastewater produced by different industries in small-scale systems. Furthermore, the results obtained with membranes coated with titanium dioxide and copper combined with ultraviolet-A light sources show that the process may be a promising approach to guarantee water disinfection using natural sunlight.

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KEYWORDS: Surface water; Water Quality Indicators; Disinfection; Photolysis; Photocatalytic Membrane Reactor.

3.2.1. Modification of the Membranes

… The membranes were modified using Titanium (IV) isopropoxide (TTiP) (SigmaAldrich, 97%) as TiO2 precursor, Copper (II) nitrate hemi(pentahydrate) (ACS reagent purity >99.99%) as Cu-dopant and acetic acid (analysis grade, Carlo Erba), as catalyst. The modification procedure was based on Kumar et al. [45] and Fisher et al. [46]. In brief, 70 mL of titanium isopropoxide (TTiP) and 120 mL of acetic acid were magnetically stirred during 30 min and further mixed slowly with 360 mL of deionized water [45]. The solution was mixed during 1 h. In parallel, a solution including 0.408 g of copper-nitrate reagent in 300 mL of deionized water was prepared [46], and after its complete homogenization was added to the TTiP solution described above, resulting in 0.75% molar ratio of Cu compared to Si.


Similarly, Fisher et al. [46], reported a rapid inactivation of bacteria using a molar ratio of 1%, under solar light. After two weeks the solution seemed stable, obtaining a blue-white homogeneous turbidity. At this point, membranes were sealed with silicon (sealant) in the holes for avoiding the filtration of the sol-gel solution and modified twice in both outer sides using a ND-DC dip coater (Nadetech Innovations, Spain), with the following conditions: immersion and withdrawal speed of 150 mm/s; immersion time of 5 s.