Assessment of online bacterial particle counts for monitoring the performance of reverse osmosis membrane process in potable reuse

Pathogens and antibiotic resistance genes during the landfill leachate treatment process: Occurrence, fate, and impact on groundwater

Landfill leachate is an essential source of pathogens and antibiotic resistance genes (ARGs) in the environment. However, information on the removal behavior of pathogens and ARGs during the leachate treatment and the impact on surrounding groundwater is limited. In this study, we investigated the effects of leachate treatment on the removal of pathogens and ARGs with metagenomic sequencing, as well as the impact of landfill effluent on groundwater. It is shown that the leachate treatment could not completely remove pathogens and ARGs. Twenty-nine additional pathogens and twenty-nine ARGs were newly identified in the landfill effluent. The relative abundance of pathogens and multiple antibiotic resistance genes decreased after ultrafiltration but relative abundance increased after reverse osmosis. In addition, the relative abundances of Acinetobacter baumannii, Erwinia amylovora, Escherichia coli, Fusarium graminearum, Klebsiella pneumoniae, and Magnaporthe oryzae, as well as mdtH, VanZ, and blaOXA-53 increased significantly in the landfill effluent compared to the untreated leachate. The relative abundance of some mobile genetic elements (tniA, tniB, tnpA, istA, IS91) in leachate also increased after ultrafiltration and reverse osmosis. The size of pathogens, the size and properties of ARGs and mobile genetic elements, and the materials of ultrafiltration and reverse osmosis membranes may affect the removal effect of pathogens, ARGs and mobile genetic elements in leachate treatment process. Interestingly, the pathogens and ARGs in landfill effluent were transferred to groundwater according to SourceTracker. The ARGs, mobile genetic elements, and pathogens that are difficult to remove in the leachate treatment process, provide a reference for optimizing the leachate treatment process and improving the control of pathogens and ARGs. Furthermore, this study clarifies the effect of landfill leachate sources of pathogens and ARGs in groundwater.

The status of potable water reuse implementation

A review of the current status of direct and indirect potable water reuse (DPR/IPR) implementation has been conducted, focusing on the regulatory and practical aspects and with reference to the most recent published literature. The review encompasses (a) the principal contaminant types, their required removal and the methods by which their concentration is monitored, (b) regulatory approaches and stipulations in assessing/ratifying treatment schemes and maintaining treated water quality, and (c) existing full-scale installations. Analytical methods discussed include established in-line monitoring tools, such as turbidity measurement, to more recent polymerase chain reaction (PCR)-based assay methods for microbial detection. The key risk assessment tools of quantitative microbial risk assessment (QMRA) and water safety plans (WSPs) are considered in relation to their use in selecting/ratifying treatment schemes, and the components of the treatment schemes from 40 existing IPR/DPR installations summarised. Five specific schemes are considered in more detail. The review reveals:Whilst there are a number of ongoing projects where RO is not used because of the challenge imposed by disposal of RO concentrate, the prevalence of the sequential RO-UV combination implies the importance of quantifying the impact of process upsets on these unit operations.

Integrating Virus Monitoring Strategies for Safe Non-potable Water Reuse

Wastewater reclamation and reuse have the potential to supplement water supplies, offering resiliency in times of drought and helping meet increased water demands associated with population growth. Non-potable water reuse represents the largest potential reuse market. Yet economic constraints for new water reuse infrastructure and safety concerns due to microbial water quality, and especially viral pathogen exposure, limit widespread implementation of water reuse. Cost-effective, real-time methods to measure or indicate viral quality of recycled water would do much to instill greater confidence in the practice. This manuscript discusses advancements in monitoring and modeling of viral health risks in the context of water reuse. First, we describe the current wastewater reclamation processes and treatment technologies with an emphasis on virus removal. Second, we review technologies for the measurement of viruses, both culture- and molecular-based, along with their advantages and disadvantages. We introduce promising viral surrogates and specific pathogenic viruses that can serve as indicators of viral risk for water reuse. We suggest metagenomic analyses for viral screening and flow cytometry for quantification of virus-like particles as new approaches to complement more traditional methods. Third, we describe modeling to assess health risks through quantitative microbial risk assessments (QMRAs), the most common strategy to couple data on virus concentrations with human exposure scenarios. We then explore the potential of artificial neural networks (ANNs) to incorporate suites of data from wastewater treatment processes, water quality parameters, and viral surrogates. We recommend ANNs as a means to utilize existing water quality data, alongside new complementary measures of viral quality, to achieve cost-effective strategies to assess risks associated with infectious human viruses in recycled water. Given the review, we conclude that technologies are ready for identifying and implementing viral surrogates for health risk reduction in the next decade. Incorporating modeling with monitoring data would likely result in more robust assessment of water reuse risk.

Online evaluation of bacterial cells in sand filter effluents during full-scale treatment of drinking water

Ensuring the microbiological safety of drinking water is critical to protect public health. This study aimed to evaluate the reliability of real-time bacteriological counter coupled with an online dialysis membrane-based pre-treatment system for continuously monitoring bacterial cell counts in sand filter effluents of a full-scale drinking water treatment plant. The pre-treatment system, which included anion exchange resins (porous polymeric microbeads that trap ions for releasing other ions) for dialysate regeneration, successfully achieved the stable attenuation of background interfering substances (humic acids) during the 19-d test. The real-time bacteriological counter equipped with the pre-treatment system provided a continuous profile of bacterial cell counts in the sand filter effluent (0.2-2.5 × 10⁴ counts/mL). The online analysis identified different timing of concentration peaks between particle and bacterial cell counts after backwashing. Bacterial community analysis revealed that Proteobacteria, Planctomycetes, and Cyanobacteria were the dominating phyla. Further, total bacterial cell counts determined by fluorescence microscopy and SYBR® Green I staining, a commonly accepted parameter, was found to be an indicator of online-monitored bacterial cell counts. The results indicated the potential of monitoring the bacterial cell counts in a sand filter process for providing an early warning of filter failures, which can allow plant operators to diagnose the overall system and provide countermeasures.

Membrane distillation for achieving high water recovery for potable water reuse

Achieving high water recovery using reverse osmosis membranes is challenging during water recycling because the increased concentrations of organics and inorganics in wastewater can cause rapid membrane fouling, necessitating frequent cleaning using chemical agents. This study evaluated the potential of membrane distillation to purify reverse osmosis-concentrated wastewater and achieve 98% overall water recovery for potable water reuse. The results indicate that membrane fouling during membrane distillation treatment was low (4% reduction in permeability) until 98% water recovery. In contrast, membrane fouling during reverse osmosis treatments was high (73% reduction in permeability) before reaching 90% water recovery. Furthermore, membrane distillation showed superior performance in removing dissolved ions (99.9%) from wastewater as compared with reverse osmosis (98.9%). However, although membrane distillation removed most trace organic chemicals tested in this study, a negligible rejection (11%) was observed for N-nitrosodimethylamine, a disinfection byproduct regulated in potable water reuse. In contrast, RO treatment exhibited a high removal of N-nitrosodimethylamine (70%). Post-treatment (e.g., advanced oxidation) after reverse osmosis and membrane distillation may be needed to comply with the N-nitrosodimethylamine regulations. Overall, the membrane distillation process had the capacity to purify reverse osmosis concentrate with insignificant membrane fouling.

Water reclamation and reuse

Literature published in 2019 pertinent to water reclamation and reuse has been classified into five sections: safe reuse, treatment technologies, management, assessment, and case studies. Membranes have been widely applied in integrated processes to polish secondary effluent and achieve high-quality reclaimed water. Increased efforts have also been made to facilitate feasible and safe water reuse. PRACTITIONER POINTS: This article summarizes literature published in 2019 pertinent to water reclamation and reuse. Water reclamation and reuse can be classfied into five sections: safe reuse, treatment technology, management, assessment, and case studies. Membranes were widely used in integrated processes for the production of high-quality reclaimed water.

Dialysis as a new pre-treatment technique for online bacterial counting

Real-time bacteriological counting technology is capable of providing an online profile of bacterial removal during the wastewater treatment process, and can enhance the safety of recycled water for potable water reuse. However, autofluorescence emanating from dissolved organic compounds present in treated wastewater interferes with the analysis. In this study, a novel approach is adopted, viz., dialysis treatment for the removal of dissolved interfering substances from treated wastewater, and the efficiency of this treatment protocol is evaluated as a pre-treatment technique for real-time bacteriological counting. Dialysis using membranes having a molecular weight cut-off (MWCO) of 1000 kDa and 6-8 kDa were found to successfully reduce the intensity of autofluorescence emitted from the interfering substances; whereas the courser dialysis membrane having a MWCO of 1000 kDa was found to be more effective in removing the interfering substances. Here we demonstrate for the first time that continuous online dialysis treatment aids in the direct determination of the bacterial counts in ultrafiltration- and membrane bioreactor-treated wastewaters. The results of the study indicate that the dialysis pre-treatment technique is effective for continuously reducing the concentration of interfering substances in treated wastewater, and thus allows for direct online counting of bacteria.

Online assessment of sand filter performance for bacterial removal in a full-scale drinking water treatment plant

Microbiological risks associated with drinking water can be minimized by providing enhanced integrity monitoring of bacterial removal by water treatment processes. This study aimed to evaluate the efficacy of real-time bacteriological counters for continuously assessing the performance of a full-scale sand filter to remove bacteria. Over the course of an 8-day evaluation, online counting of bacteria was successfully performed, providing continuous bacterial counts in the sand filter influent and effluent over approximate ranges from 17 × 10⁴ to 94 × 10⁴ and from 0.2 × 10⁴ to 1.3 × 10⁴ counts/mL, respectively. Periodic variations were observed with online bacterial counts in the sand filter influent because of the changes in the performance of flocculation and sedimentation processes. Overall, online removal rates of bacteria determined during the full-scale test were 95.2-99.3% (i.e., 1.3-2.2-log), indicating that online bacterial counting can continuously demonstrate over 1.3-log removal in the sand filter. Real-time bacteriological counting technology can be a useful tool for assessing variability and detecting bacterial breakthrough. It can be integrated with other online water quality measurements to evaluate underlying trends and the performance of sand filters for bacterial removal, which can enhance the safety of drinking water.