Effect of intermediate compounds and products on wet oxidation and biodegradation rates of pharmaceutical compounds

Abstract

Kinetics of pure compounds in batch agitated reactors are useful data to clarify the characteristics of a given reaction, but they frequently do not provide the required information to design industrial mixed continuous processes because in this case the final and intermediate products interact with the reaction of interest, due to backmixing effects. Simultaneously, the presence and transformations of other compounds, frequent in industrial wastewater treatments, adds more complexity to these types of interactions, whose effect can be different, favorable or unfavorable, for chemical or biological reactions. In this work, batch laboratory reactor data were obtained for the wet oxidation and biodegradation of four phenolic compounds present in a pharmaceutical wastewater and then compared with those collected from industrial continuous stirred tank reactors. For wet oxidation, batch laboratory degradation rates were significantly lower than those found in industrial continuous stirred operation. This behavior was explained by a different distribution of intermediate compounds in lab and industrial treatments, caused by the degree of backmixing and the synergistic effects between phenolic compounds (matrix effects). On the other hand, the specific utilization rates during aerobic biodegradation in the continuous industrial operation were lower than those measured in the laboratory, due to the simultaneous presence of the four pollutants in the industrial process (matrix effects) increasing the inhibitory effects of these compounds and its intermediates.