Sediment and biofilm affect disinfectant decay rates during long-term operation of simulated reclaimed water distribution systems

Abstract

Unique water chemistry and operational conditions of reclaimed water distribution systems facilitated accumulation of sediment which resulted in depletion of disinfectants and microbial regrowth.

Interplay of Biologically Active Carbon Filtration and Chlorine-Based Disinfection in Mitigating the Dissemination of Antibiotic Resistance Genes in Water Reuse Distribution Systems

“…11,50−53 This controlled head-to-head study provides new insights into drivers of ARG occurrence patterns that occur in RWDSs, shaping water quality at the point of use. A prior study of the simulated RWDSs, conducted before the sacrificial sampling examined herein, demonstrated that unfiltered and unchlorinated systems were especially vulnerable to biofilm and sediment accumulation, disinfectant decay, and microbial regrowth, 17,30 factors that create potential for ARGs to proliferate. Here, we applied shotgun metagenomic sequencing toward revealing interactive effects of BAC filtration and disinfectant on occurrence patterns of ARGs in water, biofilm, and sediment with increasing water age.…”

“…The detailed RWDS setup has been previously published. 17 PVC was selected as the pipe material because it is commonly used in full-scale distribution systems 31 and is less reactive than metal pipes, thus removing confounding factors such as corrosion. Four sampling locations, corresponding to the calculated water ages of 0-day (P0), 1-day (P1), 2.5-d (P2), and 5-d (P5), were incorporated into the RWDSs.…”

“…Comprehensive water chemistry profiling, including disinfectant residuals, dissolved oxygen, total and assimilable organic carbon, total cell count, nitrite, nitrate, and ammonia analyses, was conducted at Reservoir, P0, P1, P2, and P5 and have been published previously. 17 Bulk water samples for microbial analysis were collected from raw unfiltered and filtered source water, the reservoirs, the lowest (P0) and the highest (P5) water ages of the RWDS. Seven hundred and fifty milliliters of bulk water was collected in sterile bottles and sodium thiosulfate was added immediately to quench the remaining disinfectant residuals.…”

“…The volume and characteristics of the sediment from each pipe condition were reported previously. 17 1 ml of sediment samples was collected in triplicate from each pipe condition for DNA extraction and downstream molecular analyses.…”

“…Further, RWDSs are often used only seasonally and tend to experience prolonged water age and stagnation, 15 both of which are known to create conditions more amenable to pathogen survival and growth in biofilms. 16 Compared to potable water distribution systems, RWDSs are more vulnerable to the accumulation of biofilms and sediments, 17 which might provide conducive environments for horizontal gene transfer (HGT) of ARGs. A wide range of treatments have been applied for producing water for nonpotable reuse, including conventional sand filtration, ultra-/nanofiltration, UV, ozone, and chemical disinfection, including chlorination and chloramination.…”