Solar Photocatalytic Oxidation of Pretreated Wastewaters: Laboratory Scale Generation Of Design Data for Technical-scale Double-skin Sheet Reactors

Abstract

Batchwise heterogeneous photocatalytic oxidation of model wastewater (solutions of the azo dye "Acid Orange 7" in tap water) has been performed in a laboratory-scale stirred vessel reactor with non-submerged UV-A lamps using titanium dioxide "P25" as photocatalyst. Comparison to results of solar pilot-scale Plexiglass double-skin sheet reactor (DSSR) experiments indicates that the lab-scale method may predict area demand for technical-scale DSSR design. Characteristic UV-A fluences leading to TOC or COD reduction to e(-1) of the initial concentrations were determined in lab-scale stirred vessel experiments for treated effluents of seven different industrial branches, secondary municipal effluent and biologically treated greywater. Predicted areas for solar photocatalytic oxidation of these effluents in DSSRs yielding mineralization of 95% of organics in 100 m3 of the respective effluents for a TiO2 concentration of 2 g l(-1) and a sky and solar radiation of 3.9kWh m(-2) d(-1) within one day greatly varied from below 6,000 m2 (biologically treated lubricating oil refinery effluent) to more than 100,000 m2 (highly saline biologically treated effluent of chemical industry). Especially municipal and refinery effluents (except oil reclaiming) have been identified as promising candidates for reuse after solar photocatalytic oxidation. Mineralization efficiency was decreasing with increasing alkalinity of effluents. This was interpreted by competition of hydrogen carbonate anions with organics for binding sites on photocatalyst surface and by OH radical scavenging by hydrogen carbonate. Dependence on alkalinity was superimposed by salinity influence as some effluents with high alkalinity also exhibited high salt concentrations (especially chloride).

Toward chemical-free reclamation of biologically pretreated greywater: solar photocatalytic oxidation with powdered activated carbon

“…The pH was between 7 and 8. Alkalinity and phosphate concentrations were not determined, but other samples from the same source exhibited 320-335 mg L À1 CaCO 3 and about 3 mg L À1 PO 4 3À -P, resp., while their TOC concentrations were between 4.9 and 6.4 mg L À1 [14].…”

“…As photolysis, i.e. TOC removal by UV-A irradiation of biologically treated greywater in the absence of photocatalyst, was minute in previous experiments [14], no control experiments (UV irradiation without PAC and TiO 2 ) were performed in this study.…”

“…Unfortunately, solar photocatalytic oxidation of biologically pretreated greywater requires large areas compared to other pretreated wastewaters: In a recent publication, for a well insolated area (southern Florida) an area of 350 m 2 was estimated from laboratory investigation data for reducing TOC of 1 m 3 of this water to below 2 mg L À1 [14]. This area demand is large compared to the same process for a secondary municipal effluent which would require about 70 m 2 to achieve an equal purification target.…”

“…This area demand is large compared to the same process for a secondary municipal effluent which would require about 70 m 2 to achieve an equal purification target. The relatively low photocatalytic oxidation efficiency for biologically treated greywater was hypothesized to be caused by its alkalinity and/or content of other inorganic constituents [14].…”

Photocatalytic Removal of Microbiological Consortium and Organic Matter in Greywater

“…However, photocatalytic disinfection potential should also be taken into consideration when talking about greywater containing various types of microorganisms in significant concentrations. Referring to a literature survey on photocatalytic treatment of greywater, it was found that almost all studies emphasized removal of organic matter content rather than simultaneous removal of organic matter and bacteria [5,22]. Through the literature, only Sanchez and co-workers were the ones who checked both organic matter content and bacterial removal in greywater by TiO 2 photocatalysis and they concluded that complete removal of bacteria was achieved in hotel greywater.…”