Impacts of solids retention time and antibiotic loading in activated sludge systems on secondary effluent water quality and microbial community structure

Abstract

Solids retention time (SRT) is one of the most important factors in designing and operating activated sludge systems for biological wastewater treatment. Longer SRTs have been shown to alter the structure and function of microbial communities, thereby leading to improved treatment efficacy with respect to bulk and trace organics, nutrient removal, and membrane fouling. Research has also shown that longer SRTs and/or higher influent antibiotic concentrations may lead to increased prevalence of antibiotic resistance. However, it is unclear whether elevated, yet subclinical, concentrations of antibiotics also impact the overall microbial community. The purpose of this study was to characterize changes in microbial community structure in a laboratory-scale activated sludge system as a function of SRT (2-20 days) and influent concentrations (1×-100× ambient) of ampicillin, sulfamethoxazole, tetracycline, trimethoprim, and vancomycin. Changes in microbial community structure were evaluated based on 16S rRNA gene sequencing, and microbial community function was evaluated based on changes in effluent water quality, including attenuation of bulk and trace organics. The results confirmed that longer SRTs-but not antibiotic loadings-had a significant impact on microbial community structure and effluent water quality. Therefore, moderate spikes in influent antibiotic concentrations are not expected to adversely impact biological wastewater treatment. • Practitioner points• Longer SRTs lead to changes in microbial community structure, including alpha and beta diversity and relative abundance of various taxa. • Enhanced TOrC attenuation at longer SRTs may be linked to biomass abundance rather than changes in microbial community structure. • Moderate spikes in influent antibiotic concentrations do not impact activated sludge performance or microbial community structure. • The phyla Proteobacteria and Bacteroidetes comprise a majority of the microbial community in primary effluent and mixed liquor.

Viral Surrogates in Potable Reuse Applications: Evaluation of a Membrane Bioreactor and Full Advanced Treatment

“…Bacteroides (and more generally the phylum Bacteroidetes) dominate the western human gut microbiota (Ley et al 2006), hence their relative prominence in sewage should not be surprising. For comparison, Gerrity and Neyestani (2019) reported a lower, yet still significant, relative abundance of 7% for Bacteroides in a similar primary effluent; this value is roughly consistent with other surveys of human-derived bacteria in sewage (Fisher et al 2015;Newton et al 2015). The difference in relative abundance between these studies might be attributable to the slight difference in wastewater matrix or differences between semiquantitative methods (i.e., qPCR versus 16S rRNA gene sequencing).…”