Summaries of Yearly Scientific Reports

The objective of the first phase of implementation of the project "Elimination of antidepressant drugs from wastewater by extraction in microemulsion coupled with photodegradation" (ANTIDEPELIM) was the design and characterization of microemulsified systems to serve as a matrix for extraction and/or photodegradation of tricyclic antidepressant residues from wastewater.

For this purpose, several types of ternary and pseudo-ternary microemulsified systems consisting of homologous esters, non-ionic surfactant and aqueous phase with or without the addition of co-surfactant have been prepared. For these systems, phase diagrams were experimentally determined and drawn on the basis of which the most advantageous systems from a practical point of view were chosen for the intended purpose. The influence of other experimental variables affecting microemulsion formation conditions, such as salinity or pH of the aqueous phase, has also been studied.

Finally, some of the more promising microemulsions were characterized from a physicochemical point of view, studying the variability with composition of important characteristics such as density, refractive index, viscosity, electrical conductivity, hydrodynamic diameter, and polydispersity index of micelles.

Part of the obtained results were disseminated in the form of three presentations at international conferences organized within the country and abroad.

The objectives of the second phase of implementation of the project "Elimination of antidepressant drugs from wastewater by extraction in microemulsion coupled with photodegradation" (ANTIDEPELIM) were extraction and concentration of tricyclic antidepressants (TCA) from simulated wastewater in the most promising microemulsion systems according to studies from the previous stage and preliminary studies of TCA photodegradation.

For this purpose, seven ternary microemulsified systems consisting of homologous esters with lower volatility, non-ionic surfactant Brij 30 and water were tested. For each, a number of parameters were experimentally determined to evaluate their effectiveness as extractors for TCA, namely extraction yield, distribution coefficient and ratio between volume of reclaimed water and volume of microemulsion generated. The best values of these parameters were obtained for propyl acetate (PRAC) microemulsion. The influence of other experimental variables affecting TCA extraction in microemulsion has also been studied, such as the TCA contaminant charge level of the aqueous phase, its ionic strength, and its pH.

TCA quantification in these experiments was possible using a gas chromatographic method also developed at this stage. Two spectrophotometric methods of quantification have also been developed, based on TCA own UV absorption and VIS absorption of TCA association complexes with two color reagents of the p-benzoquinone family.

At the same time, preliminary photodegradation studies were carried out, which revealed susceptibility to photodegradation of aqueous TCA contaminants when irradiated, especially with UV-C or UV-B radiation.

Part of the obtained results were disseminated in the form of three ISI articles in Q1 rated journals and six presentations at prestigious international conferences in the country and abroad. 

The main objective of the third phase of implementation of the project "Elimination of antidepressant drugs from wastewater by extraction in microemulsion coupled with photodegradation" (ANTIDEPELIM) was to combine the extraction of TCA from simulated wastewater into microemulsions developed in the previous phase with UV-induced photodegradation of TCA encapsulated in the microemulsion micelles.

First, the optimum conditions for photodegradation were chosen for each TCA, typically UV-C irradiation being the best option as it provided the fastest route to photomineralization (CO2, H2O, and N2 as final reaction products). UV-B irradiation also yielded fairly fast photomineralization of doxepin and chlomipramine hydrochlorides.

The kinetics of photodegradation reactions of the five TCA were studied. All showed pseudo-first order kinetics with rate constants ranging from about 0.001 to 0.8 min-1.

Finally, attempts were made to recover and reuse the microemulsions after photomineralizations for new extraction-photodegradation rounds. While the microemulsions as a whole could not be reused due to phase segregation and partial losses (especially of the ester oil component), the nonionic surfactant could be recovered in large portion and was reused successfully to prepare new batches of microemulsions for combined extraction and photomineralization of TCA contaminants.