Ultraviolet disinfection impacts the microbial community composition and function of treated wastewater effluent and the receiving urban river

Abstract

Background In the United States, an estimated 14,748 wastewater treatment plants (WWTPs) provide wastewater collection, treatment, and disposal service to more than 230 million people. The quality of treated wastewater is often assessed by the presence or absence of fecal indicator bacteria. UV disinfection of wastewater is a common final treatment step used by many wastewater treatment plants in order to reduce fecal coliform bacteria and other pathogens; however, its potential impacts on the total effluent bacterial community are seemingly varied. This is especially important given that urban WWTPs typically return treated effluent to coastal and riverine environments and thus are a major source of microorganisms, genes, and chemical compounds to these systems. Following rainfall, stormflow conditions can result in substantial increases to effluent flow into combined systems. Methods Here, we conducted a lab-scale UV disinfection on WWTP effluent using UV dosage of 100 mJ/cm2 and monitored the active microbiome in UV-treated effluent and untreated effluent over the course of 48 h post-exposure using 16S rRNA sequencing. In addition, we simulated stormflow conditions with effluent UV-treated and untreated effluent additions to river water and compared the microbial communities to those in baseflow river water. We also tracked the functional profiles of genes involved in tetracycline resistance (tetW) and nitrification (amoA) in these microcosms using RT-qPCR. Results We showed that while some organisms, such as members of the Bacteroidetes, are inhibited by UV disinfection and overall diversity of the microbial community decreases following treatment, many organisms not only survive, but remain active. These include common WWTP-derived organisms such as Comamonadaceae and Pseudomonas. When combined with river water to mimic stormflow conditions, these organisms can persist in the environment and potentially enhance microbial functions such as nitrification and antibiotic resistance.

Effect of UV irradiation on microbial structure, metabolic pathways and functional genes of nitrogen metabolism in highland wastewater

“…For the diversity index Shannon, it was found that with the increase of UV radiation time, only the UV5 group was greater than UV0, suggesting that UV irradiation had some reducing effect on microbial diversity, in line with the findings of (Kauser et al, 2019). It is noteworthy that the Shannon index was overall lower than that of 5 min at 5 to 180 min of UV irradiation.…”

“…The KEGG PATHWAY database includes various metabolic pathways and is graphically plotted using Origin 8.6 software. UV irradiation has a facilitative effect on specific bacterial relative abundances (Kauser et al, 2019).…”

Impact of UV irradiation at full scale on bacterial communities in drinking water

“…Molecular DNA-based methods analyze the microbial community without the need for cultivation and, as UV irradiation causes DNA lesions and reduces the number of amplifiable target templates in the PCR reaction 13,19 , amplicon-based methods can describe which types of bacteria and genes are affected by UV [20][21][22] . Microbial inactivation of Pseudomonas aeruginosa and Enterococcus faecium by UV was assessed by cultivation and quantitative PCR (qPCR) 19 and impact of UV on adenovirus concentrations were measured by cell culture infectivity and long-range PCR with subsequent qPCR 23 .…”

“…An initial study using 16s rRNA gene amplicon sequencing conducted by Nocker et al 21 showed how some phyla of bacteria were affected by a single dose of UV in a full-scale drinking water treatment plant. The approach of using 16S rRNA gene amplicon sequencing has been used to observe changes in the bacterial community for UV wastewater disinfection 22 and UV irradiation of marine water 28 .…”

Impact of wastewater treatment plants on microbiological contamination for evaluating the risks of wastewater reuse

“…Cl, ClO 2 , PAA) or physical treatments (e.g. UV) [14]. Chlorine dioxide (ClO 2 ) has several advantages: it is a better bactericide and virucide than sodium hypochlorite and chlorine, in relationship to its greater oxidative capacity [15].…”