New insight into the combined effects of ibuprofen and Cu (II) on activated sludge system: System performance, community structure, microbial interaction network

This study aimed to investigate the combined effects of ibuprofen (IBU) and Cu (II) on the treatment performance, microbial activity, community composition, and microbial interaction network in activated sludge system. The results showed that the treatment performance was gradually inhibited by increasing IBU/Cu (II). The medium-to-high IBU/Cu (II) concentration caused the deterioration of specific oxygen uptake rate (SOUR), bacterial nitrification, and denitrification activities. Compared to the control, the increase of IBU/Cu (II) significantly decreased the microbial diversity, corresponding to some function genera, such as Nitrosomonas, Nitrospira, Candidatus_Competibacter, and Hyphomicrobium remarkably decreased. The topological characteristics of the microbial network were changed, e.g., low IBU/Cu (II) concentration promoted the network scale but inhibited the connection strength and transfer efficiency among network members. However, high IBU/Cu (II) concentration resulted in the minimum network size, strongest connection strength, and fastest transfer efficiency. As increased IBU/Cu (II), the decrease of keystone taxa including connectors and module hubs imposed restrictions on the communication between modules and the number and size of modules. The dynamic succession of microbial interaction networks induced by combined IBU/Cu (II) such as decreased network scale and keystone taxa was probably responsible for the deterioration of nutrient removal and microbial activities. This study provided an important dimension to our understanding of the effects of pharmaceutical compounds and heavy metals beyond those of simple diversity and composition.