Estudo da remoção de parabenos em sistema de lodo granular aeróbio

Abstract

Parabens are esters of p-hydroxybenzoic acid widely used as preservatives in personal care products, drugs, food and beverages, the former being one of the main sources of these micropollutants in wastewater treatment plants. As these compounds have been associated with human health problems, as they act as endocrine disruptors, their removal from wastewater can be done, mainly by compact technologies with high capacity to remove organic matter and nutrients and that are cost-effective. Thus, in this study, the operational performance of an aerobic granular sludge system (LGA) was evaluated in the treatment of synthetic wastewater containing parabens (200 μg L-1 each) methylparaben (MeP), ethylparaben (EtP), propylparaben ( PrP) and butylparaben (BuP). In addition to the impact of these compounds on the aerobic granulation process and on the stability of the granules, the removal of organic matter, nutrients (N and P) and the parabens themselves, for which possible removal mechanisms were also identified, was evaluated. Finally, the influence of parabens on the microbial activity of removing organic matter and nutrients (N and P) was evaluated by respirometry. For this, two sequential batch reactors of variable volume (useful volume of 7.2 L), R1 (control) and R2 (with parabens), supplemented with acetate, were operated with cycles of 6 h and 50% volumetric change over of three stages, in which the sedimentation time was gradually reduced from 20 to 10 and then to 5 min. At the end of the experiment, in the presence of parabens, aerobic granules were developed with good sedimentability, but with a fragile and uneven structure due to the lower SPE production, which also affected the system's solids concentration. Regarding the removal of organic matter, N and P, there was no significant effect of parabens on the tested concentrations. As for these micropollutants, high removal efficiencies were achieved (> 85%), with MeP being probably the most recalcitrant. Although parabens were partially removed in the anaerobic phase, the aerobic phase was the main responsible for the removal of these compounds, most likely by cometabolism. While adsorption obviously did not contribute to the removal of EtP, PrP and BuP, it was the main mechanism for removing MeP (~ 57%), which was suggested as a probable intermediary for the degradation of the other parabens. Respirometric tests showed that parabens, at the concentrations tested, did not alter the activity of heterotrophic organisms. As for nitrifying organisms, these compounds negatively affected only the growth of ammonia oxidizing bacteria, however this did not compromise the nitrification efficiency of the system. Finally, in Regarding the removal of N and P, while the denitrification rate, via nitrite or nitrate, was higher in R2, the absorption rate of P, notably of phosphorus-accumulating organisms, was higher in R1. Even so, there was no significant difference between the N and P removal performance of the two reactors. Therefore, the AGSsystem is considered as a very efficient and robust treatment technology.