The ecological recharge of urban landscapes with reclaimed water plays a crucial role in alleviating urban water shortage. In Yinchuan, we examined the effects of recharging urban rivers with either Yellow River or reclaimed water on the abundance and diversity of microbial communities. This study aimed to support the effective utilization of reclaimed water. We monitored six sites: three in the reclaimed water recharge area (Lucaowa inlet (ZLJ), Lucaowa channel (ZLH), and Lucaowa outlet (ZLC)) and three in the Yellow River water recharge area (Ningcheng lock (FNCZ), Qingfengjie (FQFJ), and Laifosi (FLFS)). Various indicators (pH, turbidity, temperature (T), dissolved oxygen (DO), electrical conductivity (EC), chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN), ammonia nitrogen (NH3-N), and nitrate nitrogen (NO3-N)) were used to assess the water quality. The microbial community abundance and diversity were evaluated using 16S rRNA high-throughput sequencing. The results indicated that throughout the monitoring period, the reclaimed water recharge area exhibited increased water transparency and greater microbial community abundance and diversity than the Yellow River water recharge area. However, the reclaimed water recharge area also showed significantly higher levels of nitrogen, phosphorus, organic matter, and electrical conductivity, along with an increase in Firmicutes. Seasonal changes significantly influenced water quality factors, significantly affecting Cyanobacteria and Campylobacter populations, as demonstrated by RDA analysis, which showed a close relationship between microbial communities and environmental factors. Further comparative analysis revealed that erythrocytic bacteria were predominant in the reclaimed water recharge area, whereas Actinobacteria, Planktonia, and Aspergillus spp. were more significant in the Yellow River water recharge area. Predictive analysis of microbial functions suggested that carbon and nitrogen cycle-related functions were more abundant in the reclaimed water recharge area, indicating that reclaimed water recharge could improve the self-purification capacity of the water body.

The use of reclaimed water for urban river replenishment has raised concerns regarding its impact on water quality and aquatic ecosystems. This study aims to reveal the improvements seen in an urban river undergoing a practical water eco-remediation after being replenished with reclaimed water. A one-year monitoring of water quality, phytoplankton, and zooplankton was carried out in Dongsha River undergoing eco-remediation in Beijing, China. The results showed that compared to the unrestored river, the concentrations of COD, NH4+-N, TP, and TN decreased by 28.22 ± 7.88 %, 40.24 ± 11.77 %, 44.17 ± 17.29 %, and 28.66 ± 10.39 % in the restoration project area, respectively. The concentration of Chlorophyll-a in the restoration area was maintained below 40 μg/L. During summer, when algal growth is vigorous, the density of Cyanophyta in the unrestored river decreased from 46.84 × 104cells/L to 16.32 × 104cells/L in the restored area, while that of Chlorophyta decreased from 41.61 × 104cells/L to 11.87 × 104cells/L, a reduction of 65.16 % and 71.47 %, respectively. The dominant phytoplankton species were replaced with Bacillariophyta, such as Synedra sp. and Nitzschia sp., indicating that the restoration of aquatic plants reduces the risk of Cyanophyta blooms. Zooplankton species also changed in the restoration area, especially during summer. The density of pollution-tolerant Rotifer and Protozoa decreased by 31.06 % and 27.22 %, while the density of clean water indicating Cladocera increased by 101.19 %. We further calculated the diversity and evenness index of phytoplankton and zooplankton within and outside the restoration area. The results showed that the Shannon-Weaver index for phytoplankton and zooplankton in the restoration area was 2.1 and 1.91, which was higher than those in the river (1.84 and 1.82). This further confirmed that aquatic plant restoration has positive effects. This study can provide a practical reference and theoretical basis for the implementation of water ecological restoration projects in other reclaimed water rivers in China.

Water-scarce cities have fewer surface water (SW) resources available for ecological use, causing landscape water to deteriorate due to water shortage and fail to perform their intended landscape functions. As a result, many cities use reclaimed water (RW) to replenish them. However, this could cause concern among the people, as RW usually has higher nutrient concentrations, which may stimulate algae growth and deteriorate the aesthetic senses of the receiving water bodies. In order to assess the feasibility of using RW for this purpose, this study used Xingqing Lake in Northwest China as insight into the effect of RW replenishment on the visual landscape quality of urban landscape water. Water transparency (measured by SD) is used as an intuitive indicator to reflect the comprehensive influence of suspended solids and algae growth on the water\'s aesthetic quality. Scenario analyses were carried out after calibrating and validating one-year data in MIKE 3 software with both SD and algae growth calculations, and the results showed that the low concentration of suspended matter in RW could compensate for the decrease in SD due to algal blooms caused by high concentrations of nitrogen and phosphorus, and the effect on SD is especially pronounced under conditions that are not conducive to algal growth, such as good flow conditions and low temperature. In addition, to meet a SD ≥ 70 mm, the total water inflow required can be significantly reduced with the optimal application of RW. It is also indicated that partial or complete utilization of RW to replace SW for replenishing the landscape water could be feasible from the viewpoint of landscape quality, at least for the landscape water investigated in this study. This can provide a method for the improvement to urban water management practices by using RW for replenishment in water-scarce cities.

Reduced availability of agricultural water has spurred increased interest in using recycled irrigation water for U.S. food crop production. However, there are significant knowledge gaps concerning the microbiological quality of these water sources. To address these gaps, we used 16S rRNA gene and metagenomic sequencing to characterize taxonomic and functional variations (e.g., antimicrobial resistance) in bacterial communities across diverse recycled and surface water irrigation sources. We collected 1 L water samples (n = 410) between 2016 and 2018 from the Mid-Atlantic (12 sites) and Southwest (10 sites) U.S. Samples were filtered, and DNA was extracted. The V3-V4 regions of the 16S rRNA gene were then PCR amplified and sequenced. Metagenomic sequencing was also performed to characterize antibiotic, metal, and biocide resistance genes. Bacterial alpha and beta diversities were significantly different (p < 0.001) across water types and seasons. Pathogenic bacteria, such as Salmonella enterica, Staphylococcus aureus, and Aeromonas hydrophilia were observed across sample types. The most common antibiotic resistance genes identified coded against macrolides/lincosamides/streptogramins, aminoglycosides, rifampin and elfamycins, and their read counts fluctuated across seasons. We also observed multi-metal and multi-biocide resistance across all water types. To our knowledge, this is the most comprehensive longitudinal study to date of U.S. recycled water and surface water used for irrigation. Our findings improve understanding of the potential differences in the risk of exposure to bacterial pathogens and antibiotic resistance genes originating from diverse irrigation water sources across seasons and U.S. regions.

Reclaimed water and stormwater are two important alternative water sources to mitigate water resource shortage. They can be reused by discharging into drinking water sources. Due to different sources, characteristics of dissolved organic matter (DOM, a precursor of disinfection by-products, DBPs) present in reclaimed water and stormwater would be different. This study selected reclaimed water to compare with stormwater (including both stormwater runoff and rainwater) by investigating their DOM characteristics, including concentrations, aromaticity, molecular weight, hydrophobicity/hydrophilicity, composition and DBPs formation potential. The results showed that reclaimed water had higher dissolved organic carbon (DOC) concentrations (6.02-10.8 mg/L) than stormwater (3.62-5.48 mg/L) while SUVA254 values of stormwater runoff (1.92-2.53 L/(mg-C·m)) were higher than reclaimed water (1.11-1.24 L/(mg-C·m)). Additionally, reclaimed water is more hydrophobic while stormwater runoff and rainwater are more hydrophilic. Although all water types included the highest fraction of DOM with molecular weight <1 kDa (43.0 %-77.5 %), reclaimed water primarily contained soluble microbial products (SMPs)-like and humic acid-like substances while stormwater runoff primarily contained humic acid-like DOM. In terms of DBPs, reclaimed water showed relatively higher formation potential than stormwater runoff while rainwater had the lowest DBPs formation potential. These results can contribute to effective water resource management. Particularly, when reclaimed water or/and stormwater are discharged into drinking water sources, these outcomes can help on efficient drinking water treatment.

Planktonic microorganisms play an important role in urban aquatic ecosystems; however, environmental changes significantly affect their role in the degradation and transformation of pollutants. The highly artificial North Canal River was chosen as the research area in this study. Seasonal changes in planktonic microbial community structure were studied using 16S rRNA high-throughput sequencing. The seasonal change mechanism of planktonic microbial diversity in urban rivers supplied with reclaimed water and its response relationship with environmental parameters were examined. The results showed that there were significant seasonal changes in the diversity and structure of the planktonic microbial community. The alpha diversity in summer was significantly higher than that in spring, owing to the enhancement of water diffusion capacity caused by seasonal rainfall and physical disturbance of the reclaimed water supply. The beta diversity of the planktonic microbial community in summer was weakened compared to that in spring, also owing to the enhancement of water diffusion capacity. Seasonal runoff and temperature were the main driving factors of the seasonal variation in hydrology and water quality in the highly artificial urban river. The changes in NO2--N and TP caused by seasonal runoff and temperature change were the main reason for planktonic microbial diversity changes in the river. The reductive environment of the river was caused by static and discontinuous flow in the spring. Anaerobic bacteria such as Bacteroidetes related to the degradation of dissolved organic matter and Gracilibacteria related to the denitrification process were dominant in the river. Seasonal runoff and frequent rainfall in summer, as well as the increase in the opening and closing frequency of river sluice gates, enhanced the reoxygenation capacity of the river. This significantly alleviated nutrient pollution in the North River Cannel. Additionally, aerobic bacteria and facultative anaerobic bacteria were dominant species in the river during spring. Cyanobacteria with high temperature characteristics, Chloroflexi and other autotrophic microorganisms, as well as Acidobacteria and Gemmatimonadetes played an important role in the degradation and transformation of pollutants. The results of this study have practical significance for urban river pollution control and ecological restoration with reclaimed water as the recharge water source.

Pathogenic bacteria and antibiotic resistance genes (ARGs) in urban landscape waters may pose a potential threat to human health. However, the investigation of their occurrence in the urban landscape waters replenished by reclaimed water (RW) and surface water (SW) is still insufficient. The water samples collected from six urban landscape waters replenished by RW or SW were used to analyze bacterial diversity using high-throughput sequencing of 16S rRNA gene and to detect 18 ARGs and 2 integron-integrase genes by means of quantitative PCR array. Results indicated that Proteobacteria was the dominant phylum in all six urban landscape waters. The bacterial species richness was lower in urban landscape waters replenished by RW than that by SW. Sulfonamide resistance genes (sulI and sulIII) were the major ARGs in these urban landscape waters. No significant difference in the relative abundance of sulfonamide resistance genes, tetracycline resistance genes, and most of beta-lactam resistance genes was observed between RW-replenished and SW-replenished urban landscape waters. By contrast, the relative abundance of blaampC gene and qnrA gene in RW-replenished urban landscape waters was significantly higher than that in SW-replenished urban landscape waters (p < 0.05), which suggested that use of RW may increase the amount of specific ARGs to urban landscape waters. Interestingly, among six urban landscape waters, RW-replenished urban landscape waters had a relatively rich variety of ARGs (12-15 of 18 ARGs) but a low relative abundance of ARGs (458.90-1944.67 copies/16S × 106). The RW replenishment was found to have a certain impact on the bacterial diversity and prevalence of ARGs in urban landscape waters, which provide new insight into the effect of RW replenishment on urban landscape waters.

Advanced treatment is of great significance to water reclamation and reuse, which can improve water quality, control microbial risks and guarantee the safety of water reuse. This study evaluates the microbial quantity and bacterial community dynamics during advanced wastewater treatment and reuse processes (i.e. denitrification biofilter (DNBF), ultrafiltration (UF), ozonation, ultraviolet (UV) disinfection) at a large-scale water reclamation plant. It is found that different treatment processes had significant influence on the cultivability of total bacteria and the log reduction values of fecal coliform at DNBF, UF, ozonation and UV are calculated as 0.38, 2.46, 0.38 and 1.63 respectively. Moreover, the bacterial diversity in the treatment process showed apparent spatial differences, among which the effluent from ozonation process had the lowest bacterial diversity. Sequencing analysis indicated the existence of pathogenic bacterium such as Arcobacter, Bacteroides and Pseudomonas in the secondary effluent. Notably, Pseudomonas remained the most dominant species (relative abundance 41.9% in UV effluent) in reclaimed water after advanced treatment processes, which calls for high attention to sustainable water reuse. In order to inhibit bacterial regrowth in the storage tank, chlorine disinfection is recommended to improve the continuous disinfection capability of the system.

In this long-term field study, to restore a dried river ecosystem, reclaimed water was used as a supplementary water source. The main aim of this study was to investigate the accumulation and migration potential of EDCs in groundwater during long-term utilization of reclaimed water and the changes in microbial community during the removal of EDCs. A long-term field study was conducted in order to ascertain the temporal and spatial distribution of four selected endocrine-disrupting chemicals (EDCs) in an underground aquifer in the Chaobai watershed, where reclaimed water is the primary water source. Anew, the microbial community structure at different groundwater depths, along with related environmental factors were also determined. Based on the results obtained from this long-term study, it was found that the EDCs in the surface water of the Chaobai river have entered a depth of 80 m in the groundwater aquifers, within a distance of 360 m from the river. The vertical profiles of the concentrations of bisphenol A (BPA), 4-nonylphenol (NP), estrone (E1), and estriol (E3) decreased significantly from the surface to different groundwater depths with first-order attenuation rates of 0.0416, 0.0343, 0.0498, and 0.0173 m-1. The aquifer depth, water temperature, conductivity, and coexisting anions correlated well with the distribution of EDCs in groundwater.

Due to the quality difference between reclaimed water and natural groundwater, managed aquifer recharge (MAR) with reclaimed water may pose environmental risks. A river infiltration of reclaimed water for groundwater recharge in north China has been in operation for over 10 years. To investigate the actual impact on native groundwater under long-term MAR, 10-year monitoring data of recharge water and groundwater were analyzed. Due to the effect of recharge, the hydrochemical type of groundwater rapidly changed from Ca-Mg-HCO3 into Na-HCO3 which was the type of recharge water. Cl- was used as a conservative tracer in a physical mixing model, and the mixing was concluded to be dominant in the groundwater hydrochemical change under long-term MAR. The hydraulic travel time to the 30 m depth was determined to be about 6.5 months by obtaining the best-fit linear cross correlation between the concentrations of Cl- in recharge water and those in groundwater. In application of this method, the monitoring wells should be located downstream and as close as possible to the recharge site (e.g., <50 m). Based on the travel time, behaviors of total nitrogen (TN), NO3-N, NO2-N, and NH4-N were determined by attenuation factor (Af). As the main nitrogen compound, NO3-N was well attenuated under high hydraulic load, resulting in the Af > 1, with an attenuation rate of 99.6%. The Af < 1 of NH4-N indicated the additional input of NH4-N in groundwater. Fluctuations of NH4-N in recharge water exceeded 4 mg/L changes sorption equilibrium, resulting in the sorption/desorption of NH4-N in soil-groundwater system. The concentration of NH4-N in groundwater increased in the later period of monitoring. The overall attenuation rate of NH4-N was 26.3%. These findings contributed to improving the environmental benefits of this MAR site and provided guidance for other similar projects.