On the Factors Influencing the Performance of Solar Reactors for Water Disinfection with Photosensitized Singlet Oxygen

Abstract

Two solar reactors based on compound parabolic collectors (CPCs) were optimized for water disinfection by photosensitized singlet oxygen (1O2) production in the heterogeneous phase. Sensitizing materials containing Ru(II) complexes immobilized on porous silicone were produced, photochemically characterized, and successfully tested for the inactivation of up to 10(4) CFU mL(-1) of waterborne Escherichia coli (gram-negative) or Enterococcus faecalis (gram-positive) bacteria. The main factors determining the performance of the solar reactors are the type of photosensitizing material, the sensitizer loading, the CPC collector geometry (fin- vs coaxial-type), the fluid rheology, and the balance between concurrent photothermal--photolytic and 1O2 effects on the microorganisms' inactivation. In this way, at the 40 degrees N latitude of Spain, water can be disinfected on a sunny day (0.6-0.8 MJ m(-2) L(-1) accumulated solar radiation dose in the 360-700 nm range, typically 5-6 h of sunlight) with a fin-type reactor containing 0.6 m2 of photosensitizing material saturated with tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) (ca. 2.0 g m(-2)). The optimum rheological conditions require laminar-to-transitional water flow in both prototypes. The fin-type system showed better inactivation efficiency than the coaxial reactor due to a more important photolytic contribution. The durability of the sensitizing materials was tested and the operational lifetime of the photocatalyst is at least three months without any reduction in the bacteria inactivation efficiency. Solar water disinfection with 1O2-generating films is demonstrated to be an effective technique for use in isolated regions of developing countries with high yearly average sunshine.

Generating Singlet Oxygen Bubbles: A New Mechanism for Gas–Liquid Oxidations in Water

“…Si phthalocyanine (Pc) was selected because it possessed a strong absorption in the red spectral region (extinction coefficients >10 5 M -1 cm -1 ), and the 1 O 2 quantum yield (Φ Δ ) was reported to be ∼0.2. 16,17 …”

Photosensitive chitosan for visible-light water pollutant degradation

“…One of the possibility of effective photochemical degradation using sunlight is photosensitized oxidation process [8][9][10][11][12][15][16][17][18][19]. It is a complex process in which the photosensitizer excited by absorption of light initiates oxidation reactions of organic compounds.…”

“…Interesting results were obtained in studies on drinking water purification, using phenanthroline and bipyridine ruthenium (II) complexes as photosensitizers [8]. The metal complexes were immobilized in the porous film of the silicone polymer.…”

“…The authors were also concluded that the use of solar radiation significantly reduces operating costs, making the photosensitized oxidation method competitive compared to the method using the system TiO 2 /UV [8]. Organic polymers carriers also allow for effective immobilization of photosensitizers.…”

Bacterial Inactivation by a Singlet Oxygen Bubbler: Identifying Factors Controlling the Toxicity of 1O2 Bubbles

“…Visible-light photocatalysis holds promise for the treatment of microbe-tainted water, 1–4 although factors such as water turbidity and photosensitizer breakdown can be problems. 5,6 Rather than using a photocatalyst in water, a significant advance could emerge from a unique sensitized disinfection method, which carries singlet oxygen ( 1 O 2 ) in bubbles.…”