Microbiome and Respirometry Analysis of the Bacterial Community in a Bench-Scale Activated Sludge Reactor Exposed to Insecticide

Abstract

Wastewater treatment plants (WWTPs) have to treat sewage 24 h/365 days a year. Uncontrolled toxic spills can affect the microbial community in activated sludge and thus the biological treatment performance. Water below the quality requirements, established in the legislation could be, therefore released to the receiving environment, contributing to the loss of biological diversity, degradation of water resources and generating public health threats.This study aims to analyse the community changes that occurred in an activated sludge as consequence of an insecticide spill in a laboratory-scale reactor. Next-generation sequencing was applied to identify genera that could serve as key indicators of a negative biological process affection.The bench-scale system consisted of a 10-litre biological reactor with intermittent aeration cycles to remove organic matter and nutrients, which was fed with primary settled sewage, follow by a secondary clarifier with manual purging and an external recirculation to the biological reactor. Both settled sewage and mixed liquor were obtained from the same WWTP.The effect of an artificial spill of insecticide containing D-tetramethrin, cyphenothrin and pyriproxyfen on the activated sludge biomass was studied through both, respirometry and microbiome analysis.The toxic effect on the activated sludge community demonstrated to be significant, completely inhibiting nitrifying activity and changing the distribution of the microbiome. Results show that relative abundance of certain groups increased after the spill, being then the new conditions favourable for the development of these groups. By contrast, others groups are shown to be extremely sensitive to the toxic effect, such that their disappearance can act as a key indicator of an insecticide spill occurrence in a WWTP. however, the abundance of nitrifying bacteria was not affected.