Post-treatment
- Certain chemical products generated in the course of a photocatalytic treatment en route to complete mineralization can be more toxic than the original organic pollutants.
- Consequently, the overall toxicity as monitored by some tests can be higher than the initial toxicity during some periods of the treatment. This situation is a problem common to every oxidation method, including those commonly in use today.
- Such issues necessitate appropriate tests according to the intended destination of the treated effluent. As a precaution, an adsorption stage on activated carbon can be incorporated after the photocatalytic treatment, just as might be applied after any other oxidation treatment.
- On the other hand, photocatalysis, used as a pretreatment, can eliminate pollutants that are biorecalcitrant; for instance, photocatalysis can effectively dechlorinate various compounds.
- The main problem is to determine the optimum duration of the photocatalytic treatment in order to reach the best overall efficiency of the combined treatments. Solving this problem requires kinetic studies.
- Photocatalysis can be associated not only with a biological treatment, but also with other processes whose properties differ in some aspects from photocatalytic treatment. For instance, an initial ultrasonic treatment can allow one to destroy the CF3 group, which withstands most oxidation reactions.
- Ultrasound can also be more appropriate to start the destruction of hydrophobic compounds with long hydrocarbon chains, which interact poorly with TiO2 in water.