Floating immobilized TiO2 catalyst for the solar photocatalytic treatment of micro-pollutants within the secondary effluent of wastewater treatment plants.

Floating immobilized spherical titanium dioxide catalysts were used to degrade micro-pollutants by solar photocatalysis. The degradation of the micro-pollutants was performed in the secondary effluent of a wastewater treatment plant. During the experimental period, the continuous measurement of the solar ultraviolet (UV) radiation intensity was performed. The micro-pollutants were degraded to an average of 55% after 9 h of irradiation. A substance-specific degradation affinity was found, whereby degradation rates varied by a factor of up to 3.5. The substance-specific adsorption behavior was identified as a major limitation of the reaction performance. With an increasing influence of adsorption limitation, the degradation kinetics changed from the pseudo-first order to pseudo-zero order. A correlation between degradation rate and solar irradiance could only be found for substances with high degradation/adsorption affinity. For diclofenac, a 95% degradation rate could be achieved at a radiation dose of approximately 190 mWh/m². The investigated technology represents a promising possibility for a minimally invasive extension of wastewater treatment plants. Possibilities of implication were estimated and discussed within this work, whereby possibilities arise for large-scale as well as decentral treatment plants.

Degradation of chlorinated volatile organic compounds from contaminated ground water using a carrier-bound TiO2/UV/O3-system.

In the present work, a suitable experimental setup was developed to successfully apply advanced oxidation processes (AOP) to real groundwater matrices. This setup combines an O3-bubble column reactor with a carrier-bound TiO2/UV-system. The degradation of various chlorinated ethene and methane derivatives commonly found of chlorinated volatile organic compound polluted regional groundwater samples was investigated. Because of known issues within water remediation using AOP such as toxification by transformation products, this study aimed at complete mineralization of the contained organic micropollutants. Moreover, the influences of variable process parameters such as flow rate, ozone concentration, and radiation dose on process performance were statistically evaluated and discussed. Parameter optimization using a Box-Behnken experimental design resulted in very promising degradation rates. It was thus possible to achieve a degradation rate of at least 98% for cis-dichloroethene, trichloroethene and tetrachloroethene and 85% for trichloromethane without formation of transformation products. The results of this work open up the possibility of developing innovative technologies based on AOP, which can be universally applied even to challenging matrices such as groundwater.