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Investigation of microbial inactivation during wastewater treatment and in a pilot-scale reactor by means of solar photocatalysis

Koumaki Kassandra

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Summary

The objective of this thesis was to investigate the disinfection potential of solar photocatalysis and constructed wetlands on secondary municipal effluent.For the solar photocatalysis experiments, binary doped TiO2 with Al/Fe, In/Fe, Al/Mn and Mn/Co as well as CuOx doped BiVO4 were used. Both types of catalysts are known to be photo-activated by visible light. Different dopant concentrations were tested. Gram negative E. coli and Gram positive Enterococcus sp. were chosen as indicators of the bacterial inactivation. Experiments were conducted in a lab scale solar light simulator and in pilot scale, using a compound parabolic collector (CPC) reactor under natural light irradiation. An >99.99% inactivation was achieved for both indicators after 60min of lab treatment with all the catalysts used. Reactivation after 24 h dark incubation, was inhibited by the presence of CuOx. Pilot scale experiments exhibited a 93-99,98% inactivation after 150 min of treatment, strongly depending on the seasonal irradiance level. Different flow rates were tested but did not provide comprehensive results.Constructed wetland disinfection was tested by sampling the influent and effluent of a mesocosm, throughout an annual period of time and estimating E. coli, Enterococcus sp. and MS2 coliphage concentration. A reduction of >99% for the bacterial indicators and 100% for the viral ones was observed during all seasons.Concentration of E. coli, Enterococcus sp. and MS2 coliphage was also monitored at several stages of the conventional municipal wastewater treatment plant of the city of Chania. Right after screening process, E. coli and Enterococcus sp. found to be about 105-106 CFU/100mL, while MS2 coliphages were approximately 105 PFU/100mL. A 2-3 Log reduction was observed for all microbial indicators tested in the effluent of the secondary sedimentation tank. In the chlorination tank, bacterial concentration reached the level of 50 CFU/100mL for both species, while coliphages were not detected.The conclusion reached, is that constructed wetlands can efficiently disinfect municipal effluents throughout the year and replace chloriosis. Solar photocatalysis can be applied as a house wastewater treatment plant and satisfy seasonal demands for disinfection.

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