Parabens in aerobic granular sludge systems: Impacts on granulation and insights into removal mechanisms

This work assessed the impact of methylparaben, ethylparaben, propylparaben, and butylparaben (200 mu g L-1 each) on the granulation process as well as on the organic matter and nutrient removal of an aerobic granular sludge (AGS) system (6-h cycle). Additionally, some insights into the main paraben removal mechanisms were provided. In the presence of parabens, aerobic granules with good settleability, but with fragile and irregular structure, were grown. No significant effect of parabens on organic matter (>90%) and nitrogen (similar to 70%) removal was evidenced. On the other hand, phosphorus removal was slightly impaired, although high removal efficiencies (similar to 70%) were reached. High paraben removal efficiencies were achieved (>85%) in the AGS system, with methylparaben being the most recalcitrant compound. Concerning the removal mechanisms, biotransformation was the main mechanism in the removal of all parabens (85.5% for methylparaben and 100% for the others), whereas, apparently, adsorption played a role only in the removal of methylparaben. In addition, this compound was also suggested as a probable intermediate of the degradation of the larger alkyl-chain parabens. Lastly, regarding the microbial community, with the exception of Mycobacterium, the reactors shared the same genera, which may explain their comparable operational performances. Additionally, some genera that developed more in the presence of parabens may be related to their degradation. Therefore, although antimicrobial agents such as parabens compromised the granule structure, AGS system maintained a good operational performance and showed to be very efficient in paraben removal. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

This study found that the structure of aerobic granules was affected in the presence of parabens, but did not significantly impact the removal efficiency of organic matter and nitrogen. The removal of parabens was mainly through biotransformation, with adsorption playing a role only in the removal of methylparaben.