Insight into the risk of replenishing urban landscape ponds with reclaimed wastewater

A multidirectional pairwise coupling approach with spectral features unmixing to quantify total phosphorus, total nitrogen, and chlorophyll-a in urban rivers

Comprehensive and effective water quality monitoring is vital to water environment management and prevention of water quality from degradation. Unmanned aerial vehicle (UAV) remote sensing techniques have gradually matured and prevailed in monitoring water quality of urban rivers, posing great opportunity for more effective and flexible quantitative estimation of water quality parameter (WQP) than satellite remote sensing techniques. However, current UAV remote sensing methods often entail large quantities of cost-prohibitive in-situ collected training samples with corresponding chemical analysis in different monitoring watersheds, laying time and fiscal pressure on local environmental protection department. They suffer relatively low calculation accuracy and stability and their applicability in various watersheds is constrained. This study developed a unified two-stage method, multidirectional pairwise coupling (MDPC) with information sharing and delivery of different modeling stages to efficiently predict concentrations of WQPs including total phosphorus (TP), total nitrogen (TN), and chlorophyll-a (Chl-a) from hyperspectral data. MDPC incorporates exterior and interior feature interaction and gravity model variant to improve prediction accuracy and stability with consideration of mutual effect in the proximity. The structure design and workflow of MDPC ensure high robustness and application prospect due to achievement of good performance with less training samples, improving applicability and feasibility. The experiments show that MDPC has achieved good performance on retrieval of WQPs concentrations including TP, TN, and Chl-a, the results mean absolute percent error (MAPE) and coefficient of determination (R2) ranging from 6.34 % to 11.94 % and from 0.74 to 0.93. This study provides a systematic and scientific reference to formulate a feasible and efficient water environment management scheme.

Enhancing water quality and ecosystems of reclaimed water-replenished river: A case study of Dongsha River, Beijing, China

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.

Do all algae grow faster in environments replenished by reclaimed water? Examples of two effluents produced in Beijing

Reclaimed water with nitrogen, phosphorus, and other contaminants may trigger algal blooms during its ecological utilization in replenishing rivers or lakes. However, the effect of reclaimed water on algal growth rates is not well understood. In this study, the growth potentials of algae in terms of Cyanophyta, Chlorophyta, and Bacillariophyta, as well as mixed algae in both regular culture medium and reclaimed water produced from treatment plants in Beijing with similar N and P concentrations, were compared to evaluate whether reclaimed water could facilitate algal growth. In addition, reclaimed water was also sterilized to verify the impact of bacteria's presence on algal growth. The results indicated that most algae grew faster in reclaimed water, among which the growth rate of Microcystis aeruginosa even increased by 5.5 fold. The growth of mixed algae in reclaimed water was not enhanced due to the strong adaptive ability of the community structure. Residual bacteria in the reclaimed water were found to be important contributors to algal growth. This work provided theoretical support for the safe and efficient utilization of reclaimed water.

Identifying the drivers of chlorophyll-a dynamics in a landscape lake recharged by reclaimed water using interpretable machine learning

The water quality of lakes recharged by reclaimed water is affected by both the fluctuation of reclaimed water quality and the biochemical processes in the lakes, and therefore the main controlling factors of algal blooms are difficult to identify. Taking a typical landscape lake recharged by reclaimed water as an example and using the spatiotemporal distribution characteristics and correlation analysis of water quality indexes, we propose an interpretable machine learning framework based on random forest to predict chlorophyll-a (Chl-a). The model considered nutrient difference indexes between reclaimed water and lake water, and further used feature importance ranking and partial dependence plot to identify nutrient drivers. Results show that the NO3--N input from reclaimed water is the dominant nutrient driver for algal bloom especially at high temperatures, and the negative correlation between NO3--N and Chl-a in the lake water is the consequence of algal bloom rather than the cause. Our study provides new insights into the identification of eutrophication factors for lakes recharged by reclaimed water.

Algal or bacterial community: Who can be an effective indicator of the impact of reclaimed water recharge in an urban river

Reclaimed water has been widely utilized for water resource replenishment, yet little is known regarding its impacts on various microorganisms in the receiving water. To address this knowledge gap, we systematically investigated the responses of bacteria and algae to the recharge of reclaimed water by using the high-throughput sequencing technology in the urban Chaobai River. After the inputs of reclaimed water, lower contents of NO2--N, NH4+-N, and TP were observed in the downstream section compared to that of upstream without reclaimed water, indicating that reclaimed water could improve the water quality of the receiving water. Correspondingly, both bacterial and algal communities showed the decreased network complexity in the downstream section, but many common freshwater bacteria and typical bloom-forming algae were dominant in the downstream, potentially suggesting that algae were more sensitive to the local environmental conditions. More importantly, although nitrogen and phosphorus served as the paramount factors in shaping both bacterial and algal communities, environmental selection contributed more to algal rather than bacterial community, and simultaneously algal variations could further affect bacterial dynamics in the urban river. Overall, these findings revealed distinct characteristics of bacteria and algae in responding to the reclaimed water recharge, highlighting the superiority of algae in indicating environmental changes, especially in monitoring and regulating the replenishment of reclaimed water in urban rivers.

Investigation of phytoplankton community structure and formation mechanism: a case study of Lake Longhu in Jinjiang

In order to explore the species composition, spatial distribution and relationship between the phytoplankton community and environmental factors in Lake Longhu, the phytoplankton community structures and environmental factors were investigated in July 2020. Clustering analysis (CA) and analysis of similarities (ANOSIM) were used to identify differences in phytoplankton community composition. Generalized additive model (GAM) and variance partitioning analysis (VPA) were further analyzed the contribution of spatial distribution and environmental factors in phytoplankton community composition. The critical environmental factors influencing phytoplankton community were identified using redundancy analysis (RDA). The results showed that a total of 68 species of phytoplankton were found in 7 phyla in Lake Longhu. Phytoplankton density ranged from 4.43 × 105 to 2.89 × 106 ind./L, with the average density of 2.56 × 106 ind./L; the biomass ranged from 0.58-71.28 mg/L, with the average biomass of 29.38 mg/L. Chlorophyta, Bacillariophyta and Cyanophyta contributed more to the total density, while Chlorophyta and Cryptophyta contributed more to the total biomass. The CA and ANOSIM analysis indicated that there were obvious differences in the spatial distribution of phytoplankton communities. The GAM and VPA analysis demonstrated that the phytoplankton community had obvious distance attenuation effect, and environmental factors had spatial autocorrelation phenomenon, which significantly affected the phytoplankton community construction. There were significant distance attenuation effects and spatial autocorrelation of environmental factors that together drove the composition and distribution of phytoplankton community structure. In addition, pH, water temperature, nitrate nitrogen, nitrite nitrogen and chemical oxygen demand were the main environmental factors affecting the composition of phytoplankton species in Lake Longhu.

Biomanipulation as a strategy for minimizing ecological risks in river supplied with reclaimed water

Reclaimed water is an effective method for addressing water pollution and shortages. However, its use may contribute to the collapse of receiving water (algal blooms and eutrophication) owing to its unique characteristics. A three-year biomanipulation project was conducted in Beijing to investigate the structural changes, stability, and potential risks to aquatic ecosystems associated with the reuse of reclaimed water in rivers. During the biomanipulation, the proportion of Cyanophyta in the community structure of phytoplankton density in river supplied with reclaimed water decreased, and the community composition shifted from Cyanophyta and Chlorophyta to Chlorophyta and Bacillariophyta. The biomanipulation project increased the number of zoobenthos and fish species and significantly increased fish density. Despite the significant difference in aquatic organisms community structure, diversity index and community stability of aquatic organisms remained stable during the biomanipulation. Our study provides a strategy for minimizing the hazards of reclaimed water through biomanipulation by reconstructing the community structure of reclaimed water, thereby making it safe for large-scale reuse in rivers.

Assessing the effectiveness of intervention policies for reclaimed water reuse in China considering multi-scenario simulations

The reclaimed water is an effective tool for water environmental management. And in China, government intervention is regarded as a powerful instrument to realize its large-scale utilization due to the public welfare and social characteristics. Therefore, the tripartite evolutionary game and multi-agent simulation system were combined to explore how intervention policies, such as price subsidies and regulation of water information disclosure, can influence the behaviors of stakeholders involved in the reclaimed water market, so as to alleviate water environment crisis. The results showed that: (1) The incentive of price subsidy shows noticeable regional differences due to different initial reclaimed water utilization rates, and the policy effect on regions with medium level utilization (25%-40%) > regions with high utilization (higher than 40%) > regions with low utilization (lower than 25%); (2) enhancing water information supervision can positively regulate the stimulation of subsidy policy in regions with low wastewater reuse; (3) the intensity of price subsidies has an inverted U-shaped relationship with the market stability in regions with high wastewater reuse; (4) diverse regulatory models on water information disclosure show various chain effects on improving wastewater reuse.

Leveraging green infrastructure for efficient treatment of reclaimed water

Global water scarcity necessitates creative, yet practical, solutions to meet ever-growing demand. Green infrastructure is increasingly used in this context to provide water in environmentally friendly and sustainable ways. In this study, we focused on reclaimed wastewater from a joint gray and green infrastructure system employed by the Loxahatchee River District in Florida. The water system consists of a series of treatment stages for which we assessed 12 years of monitoring data. We measured water quality after secondary (gray) treatment, then in onsite lakes, offsite lakes, landscape irrigation (via sprinklers), and ultimately in downstream canals. Our findings show gray infrastructure designed for secondary treatment, integrated with green infrastructure, achieved nutrient concentrations nearly equivalent to advanced wastewater treatment systems. For example, we observed a dramatic decline in mean nitrogen concentration from 19.42 mg L^-1 after secondary treatment to 5.26 mg L^-1 after spending an average of 30 days in the onsite lakes. Nitrogen concentration continued to decline as reclaimed water moved from onsite lakes to offsite lakes (3.87 mg L^-1) and irrigation sprinklers (3.27 mg L^-1). Phosphorus concentrations exhibited a similar pattern. These decreasing nutrient concentrations led to relatively low nutrient loading rates and occurred while consuming substantially less energy and producing fewer greenhouse gas emissions than traditional gray infrastructure-at lower cost and higher efficiency. There was no evidence of eutrophication in canals downstream of the residential landscape whose sole source of irrigation water was reclaimed water. This study provides a long-term example of how circularity in water use can be used to work toward sustainable development goals.

Distribution, source, risk and phytoremediation of polycyclic aromatic hydrocarbons (PAHs) in typical urban landscape waters recharged by reclaimed water

A park that had used reclaimed water as the sole water supply for fourteen years, was selected to analyze the distribution, sources and risks of 16 priority polycyclic aromatic hydrocarbons (PAHs) in waters and sediments. The effects of phytoremediation were investigated in waterbodies classified as phytoremediation, transitional and non-phytoremediation areas. Diagnostic ratio (DR) and principal component analysis (PCA) were used to analyze the sources of PAHs, while risk quotient (RQ) was used as risk assessment tool. Results showed that ∑PAH concentrations in sediments ranged from 29.4 to 1245.6 ng‧g^-1, with average of 354.3 ng‧g^-1, corresponding to a moderate pollution level. The concentration of PAHs in water ranged from 10.6 to 326.3 ng‧L^-1, with average of 147.2 ng‧L^-1, corresponding to a low pollution level. The ∑PAHs in sediments showed a downward trend from northwest to southeast along with the water flow direction, with average values of 459.5, 362.9 and 246.1 ng‧L^-1 in the upstream, midstream and downstream, respectively. In contrast, PAH concentrations in water were consistent with recreational activities in the urban park area. There were 95% of water samples and 72% of sediment samples obtaining the Ant/(Ant + Phe) > 0.1 and Flu/(Flu + Pyr) > 0.5, indicating that coal combustion was the major source of PAHs in both the water and sediment. The RQ_∑PAH(NCs) values in water and sediment were all between 1 and 800, while RQ_∑PAH(MPCs) reached equal to 0, suggesting that ∑PAHs presented a low ecological risk. Acenaphthene accounted for 28.4% of RQ_(NCs), and became the most risk PAH in water column. Aquatic plants effectively removed high-ring PAHs from water and middle-ring PAHs from sediments, reducing the overall risks posed by PAHs.

Simulation Study on the Optimisation of Replenishment of Landscape Water with Reclaimed Water Based on Transparency

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.

Ecotoxicological effects of DBPs on freshwater phytoplankton communities in co-culture systems

Intensive disinfection of wastewater during the COVID-19 pandemic might elevate the generation of toxic disinfection byproducts (DBPs), which has triggered global concerns about their ecological risks to natural aquatic ecosystems. In this study, the toxicity of 17 DBPs typically present in wastewater effluents on three representative microalgae, including Scenedesmus sp. (Chlorophyta), Microcystis aeruginosa (Cyanophyta), and Cyclotella sp. (Bacillariophyta) was investigated. The sensitivities of the three microalgae to DBPs varied greatly from species to species, indicating that DBPs may change the structure of phytoplankton communities. Later, co-cultures of these phytoplankton groups as a proxy of ecological freshwater scenario were conducted to explore the impacts of DBPs on phytoplankton community succession. M. aeruginosa became surprisingly dominant in co-cultures, representing over 50% after dosing with monochloroacetic acid (MCAA, 0.1-10 mg/L). The highest proportion of M. aeruginosa was 70.3% when exposed to 2 mg/L MCAA. Although Scenedesmus sp. dominated in monochloroacetonitrile (MCAN) exposure, M. aeruginosa accounted for no less than 30% even at 40 mg/L MCAN. In this study, DBPs disrupted the original inter-algal relationship in favor of M. aeruginosa, suggesting that DBPs may contribute to the outbreak of cyanobacterial blooms in aquatic ecosystems.

Effects of hydrogen peroxide on Scenedesmus obliquus: Cell growth, antioxidant enzyme activity and intracellular protein fingerprinting

Hydrogen peroxide (H₂O₂) is an environmental-friendly algicide and it is widely used to control algal blooms in aquatic ecosystems. However, the response of algal cell metabolic characteristics and intracellular protein profile under H₂O₂ stress is still not well understood. In the present study, the green alga Scenedesmus obliquus was exposed to different concentrations of H₂O₂ (0, 2, 6, 8 and 10 mg L^-1) to evaluate the changes in algal morphological, physiological, and proteomic features to H₂O₂ exposure. The results showed that 8 mg L^-1 of H₂O₂ could effectively inhibit the cell growth and photosynthetic activity of S. obliquus including chlorophyll-a content and chlorophyll fluorescence parameters. The increased activities of superoxide dismutase (SOD) and catalase (CAT) observed in this study indicate that cells exposure to H₂O₂ caused oxidative stress. The metabolic activity of S. obliquus was significantly decreased by H₂O₂ treatment. In terms of proteomic analysis, 251 differentially expressed proteins (DEPs) were successfully identified. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed significant protein enrichment in the metabolic pathways, photosynthesis, ascorbic acid, and alginate metabolism and phenylpropane biosynthesis of S. obliquus. The analysis of protein-protein interaction system shows that the pathways of photosynthesis and metabolic pathways of S. obliquus were essential to resist oxidative stress. Taking together, these results shed new lights on exploring the cell physiological metabolism and intracellular protein mechanisms of H₂O₂ inhibition on algal blooms.

Replenishment of urban landscape ponds with reclaimed water: Spatiotemporal variations of water quality and mechanism of algal inhibition with alum sludge

Algal blooms caused by high concentrations of nutrients (especially phosphorus) limit the use of recycled water (RW) for replenishing landscape ponds in the context of global water scarcity. Previous studies have demonstrated that alum sludge is a low cost phosphorus sorption medium, which could potentially be applied in constructed wetlands and sewage treatment plants. However, whether alum sludge can be used for algae inhibition in reclaimed water urban landscape ponds (RWULPs) should be explored. In this study, phosphorus removal and algae inhibition by alum sludge were investigated in a RWULP in China. The results highlight that there is a serious risk of algal blooms in RWULPs. The algal density was found to be 1.58 × 10⁵ cell·mL^-1, which is 6.84 times higher than that of the surface water ponds. The algal blooms presented a Cyanophyta-Chlorophyta-Bacillariophyta-type, and the dominant algae species were Microcystis flos-aquae (Wittr.) Kirchner, Chlorella vulgaris, and Scenedesmus quadricauda. Moreover, the removal rate of phosphorus by alum sludge was as high as 98% and eventually leads to phosphorus stress, which has an important effect on algae growth and algae inhibition rate of 80%. In addition, the proportion of phosphorus and nitrogen in the adsorbed alum sludge increased by 3.12% and 0.32%, respectively, and Al³⁺ was reduced by only 2.18%. Alum sludge is a potential inhibitor of algae in RWULPs that does not negatively impact the environment. These results are of great importance in algal bloom control of RWULPs and may help alleviate the problem of urban water resource scarcity.

Comparative study on the bacterial diversity and antibiotic resistance genes of urban landscape waters replenished by reclaimed water and surface water in Xi'an, China

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 bla_ampC 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.

Gemini surfactant-modified montmorillonite with tetrachloroferrate (FeCl4-) as a counterion simultaneously sequesters nitrate and phosphate from aqueous solution

Alkyl quaternary ammonium-modified clay minerals, which are common environmentally friendly materials, have been widely studied and applied for the removal of pollutants. However, there are few reports on functionalizing the counterions to expand the application. In this study, the cationic gemini surfactant butane-1,4-bis(dodecyl dimethyl ammonium bromide) (gBDDA) and tetrachloroferrate (FeCl₄^-) are designed to modify montmorillonite (Mt), and the obtained FeCl₄^-/Gemini-Mt composite (FeOMt) is used for the removal of nitrate and/or phosphate from aqueous solution. The successful intercalation of gBDDA and favorable loading of FeCl₄^- into FeOMt are suggested by the characterization results of X-ray diffraction and Raman spectroscopy. Nitrate and/or phosphate are rapidly sequestered, and the respective maximum uptakes of 8.77 (N) and 28.1 (P) mg/g in the binary system are obtained. The phosphate uptake is stably maintained against many coexisting ions, but the nitrate uptake decreases with the increase in ionic strength. FeOMt is reusable and shows comparable uptake for nitrate and phosphate with respect to gBDDA-modified Mt and polymerized ferric chloride. Considering the multi-functionality and facile synthesis, FeOMt shows promising potential in the purification of wastewater contaminated simultaneously by poorly hydrated anions (e.g., ClO₄^-, TcO₄^-, etc.) and iron-selective anions (e.g., H₂AsO₄^-, etc.).

Synergetic suppression effects upon the combination of UV-C irradiation and berberine on Microcystis aeruginosa and Scenedesmus obliquus in reclaimed water: Effectiveness and mechanisms

The risk of harmful algal blooms (HABs) in the water recharged with reclaimed water is a bottleneck for water reuse. The suppression effects and mechanisms of the combination of UV-C and berberine on Microcystis aeruginosa and Scenedesmus obliquus in reclaimed water were investigated. Mono UV-C irradiation at 75 mJ cm^-2 could suppress the growth of M. aeruginosa for 7 d and that at 90 mJ cm^-2 could suppress the growth of S. obliquus for 5 d. UV-C irradiation combined with 0.2-2 mg L^-1 berberine lengthened the inhibition period of M. aeruginosa to 10- > 22 d and that of S. obliquus to 7- > 22 d and induced more rapid lethal effects on the harmful microalgal cells, in significant synergetic patterns. The combination of UV-C and berberine suppressed total, intracellular and extracellular microcystin-LR (MC-LR) more effectively and decreased the MC-LR quota significantly, which further reduced the risks of microcystin production and release. Furthermore, synergetic mechanisms of the combined treatments were systematically investigated from the aspects of photosynthetic system (photosynthetic activity and pigments), metabolic activity (ATP and membrane potential), oxidation stress (reactive oxygen species (ROS) and glutathione (GSH)), and apoptosis-like cell death (phosphatidylserine (PS) ectropion, caspase-3 activity and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positive rate). The combination treatment provided a joint attack of UV-C and berberine on photosynthetic transport chain of photosynthetic system II (PS II), and a synergetic pathway to achieve more severe disruptions in energy metabolism as well as aggravated oxidative stress. The accumulated ROS enhanced increases in programmed cell death (PCD) indicators of both microalgal species, which contributed to the enhancement effects on growth suppression. The results showed that the combination treatment achieved lower dose requirements of both UV-C irradiation and berberine for inducing the same inhibition effects on microalgal cells, which was promising to be applied in the HABs control of reclaimed water.

Occurrence and risk assessment of heavy metals in an urban river supplied by reclaimed wastewater

Heavy metals in reclaimed water are a global problem that leads to ecological risks for the replenishment water body. This study investigated concentrations and ecological risks posed by heavy metals in SH River, Beijing, which is supplied by reclaimed water. Results showed that Cr was not detected in the sample, Cd and Pb exceeded threshold values according to regulations by 1.19% and 25.00%, respectively. The characterization of temporal and spatial of heavy metals was studied. The potential ecological risks posed by heavy metals in SH River were found to be low and safe. The risk decreased in the order Pb > Cu > Zn > Ni > Cd > As by comprehensive index assessment; this changed to Pb > Cd > As > Ni > Cu > Zn according to potential ecological risk assessment. Pb posed the greatest ecological risks and was identified as most contaminated metal. According to discussion of sampling sites and water quality, it was proposed that reclaimed water and exogenous discharges were the main sources of the heavy metals identified. This should be considered when developing catchment management strategies for heavy metals elimination and protection of the aquatic environment. If a higher level of ecological risk management is required, Pb, Cd, and Cu should be considered first and should be removed in situ through ecological remediation methods. PRACTITIONER POINTS: Reclaimed water and exogenous discharges were the main sources of the heavy metals identified. The potential ecological risks posed by heavy metals in SH River were found to be low and safe. The risk decreased in the order Pb > Cu > Zn > Ni > Cd > As by comprehensive index assessment. Potential ecological risk assessment showed Pb > Cd > As > Ni > Cu > Zn. Pb posed the greatest ecological risks and was identified as most contaminated metal.

Analysis of the potential of reclaimed water utilization in typical inland cities in northwest China via system dynamics

Located in the hinterland of the Eurasian continent, the inland areas of northwestern China have an arid climate and are confronted with continuing challenges in water resources quantity and quality. Reclaimed water plays an important role in maintaining the sustainable use of urban water resources, especially in arid regions. In this paper, a system dynamics urban reclaimed water model (SDURWM) considering the status of arid regions in northwestern China was constructed. The supply and demand balance index (RWB) and the utilization efficiency index (RWUE) of reclaimed water were proposed as evaluation indicators. The potential of reclaimed water utilization (2016-2025) in three typical cities with similar natural environments and population sizes but with large economic differences were estimated by the SD model. Then the relevant values of reclaimed water quota, supply and resident awareness were adjusted within the range of 10%-20%. The predicted results from intervention demonstrate that the RWB of three cities will be closer or maintain to the ideal value, and that the RWUE will increase by about 0.1, compared with the non-intervention results. This indicates that a minor change of the targeted policies can invigorate the capacity of reclaimed water use in droughty cities. This paper provides some effective solutions for the government's planning of developing the potential of reclaimed water.

Bacterial viability and diversity in a landscape lake replenished with reclaimed water: a case study in Xi'an, China

To understand the characteristics of bacterial viability and diversity in landscape waters replenished with reclaimed water, the typical landscape lake using reclaimed water was investigated in this study. Samples were collected from a reclaimed water inlet (P1), a reclaimed water distribution outlet (P2), and a landscape lake replenished by reclaimed water (P3). By means of measuring adenosine triphosphate (ATP), flow cytometry (FCM), and 16S rRNA gene high-throughput sequencing, the bacterial viability and diversity in reclaimed water distribution system and landscape lake were illustrated. The bacterial ATP contents at P1, P2, and P3 were 3.55 ± 1.79 ng/L, 3.31 ± 1.43 ng/L, and 18.97 ± 6.39 μg/L, and the intact bacterial cell concentrations were 5.91 ± 0.52 × 10⁴ cells/mL, 7.95 ± 2.58 × 10⁴ cells/mL, and 5.65 ± 2.10 × 10⁶ cells/mL, respectively. These results indicated a significant increase of bacterial viability in the landscape lake. The Shannon diversity index of 6.535, 7.05, and 6.886 at P1, P2, and P3, respectively, demonstrated no notable change of bacterial diversity from reclaimed water distribution system to landscape lake. However, the relative abundance of Pseudomonas sp. at P3 was significantly higher than that at P1. These findings indicated that viable but non-culturable (VBNC) bacteria could be revived in the landscape lake. The bacterial viability during reclaimed water reuse should deserve special attention.

The growth suppression effects of UV-C irradiation on Microcystis aeruginosa and Chlorella vulgaris under solo-culture and co-culture conditions in reclaimed water

Harmful algal blooms (HABs) are serious problems in landscape waters sourced from reclaimed water. In this study, the suppression effects of UV-C irradiation on microalgal growth were researched to find a possible preventive approach. Microcystis aeruginosa and Chlorella vulgaris were exposed to UV-C irradiation and then cultured in real reclaimed water for 7-18 d. UV-C irradiation at 50-200 mJ cm^-2 could inhibit the growth of M. aeruginosa, C. vulgaris, and both microalgae in co-culture for 3-14, 1-3, and 1-5 d respectively. In addition, UV-C irradiation could cause damage to the cell integrity. At 100-200 mJ cm^-2 UV-C, the proportion of microalgal membrane damage (P_md) in M. aeruginosa cells increased rapidly to 56%-76% from day 3, whereas that in C. vulgaris cells increased to 23%-62% within 3 d. The photochemical efficiency (represented by Y value) of the irradiated groups was negatively affected immediately after UV-C irradiation and recovered gradually during the incubation. The Y value of M. aeruginosa cells began to recover from days 3 to 14, whereas that of C. vulgaris recovered much more quickly, from days 0.1 to 1. Overall, the irradiation-induced suppressive effects on algal growth correlated positively with the UV-C doses. Because M. aeruginosa was more sensitive to UV-C irradiation, UV-C irradiation not only controlled the total biomass of the mixed algae but also selectively reestablished the dominance of the nontoxic C. vulgaris.

Current status and characteristics of urban landscape lakes in China

Urban landscape lakes (ULLs) are important environmental elements in most cities. In order to understand the current situation of ULLs in China and formulate proper strategies to improve their landscape quality to meet public desire for water-front enjoyment, a study was conducted of 189 ULLs widely distributed in 26 provinces of China, based on existing data and field surveys. These ULLs were firstly categorized according to their topographic features, climatic zones, and water replenishment sources. Lake water quality was evaluated considering both single factors and a comprehensive pollution index (CPI). Results show that if the Chinese Surface Water Quality Standard was used as the sole criteria, about 60% of the ULLs investigated could not meet the lowest requirement. Excessive total nitrogen (TN) concentration was the most limiting factor especially when reclaimed water was the replenishment source. The differences in topographic and climatic conditions to a certain extent affected the availability of replenishment water sources but no significant correlation was identified with the single water quality factors or CPI. However, when public satisfaction was introduced in the evaluation of the ULLs' landscape effect, it was found that the water transparency in terms of Secchi Depth (SD) correlated well with people's appreciation of water landscape.

Membrane-sensitive bacterial DNA extractions and absolute quantitation of recovery efficiencies

Absolute quantification of waterborne pathogens is mandatory for microbiological risk assessment (MRA). Determination of the DNA recovery efficiency is an essential step before the quantitative molecular measurements, which has been largely ignored. In this study, we compared the DNA recovery efficiency and quality of five extraction methods, including two modified phenol-chloroform-based extractions with mechanical shearing and three commercial kits for the extraction of DNA from indigenous mixed-bacteria culture of river water. All of the methods gave relatively satisfying results from the pelleted sample through centrifugation. However, the commercial kits provided surprisingly low DNA yields for membrane-filtered samples because of DNA trapping and/or absorption on the membrane. Integrating with enzymatic lysis, bath sonication, phenol extraction, and alcohol precipitation achieved highest DNA yields and an acceptable DNA integrity for quantitative PCR. A plasmid containing the human GADPH gene fragment was demonstrated to be a suitable spiking control for determining the absolute DNA recovery efficiency. The unexpectedly low efficiencies of commercial kit extractions imply the significant underestimation of pathogenic bacteria in previous studies, which should gain enough concern in the area of pathogen monitoring in the future.

Speciation, Distribution and Risk Assessment of Metals in Sediments from a Water Body Replenished by Effluent from a Wastewater Treatment Plant

To assess the status and risk of metal pollution in landscape water body replenished by wastewater treatment plant effluent, the distribution of metals in sediments from three regions [regulation pond (RP), wetland lake (WL), and main lake (ML)] of Harbor Lake, Tianjin, China, was characterized. Higher levels of all metals (except Cr and Pb) were observed in RP sediments. As, Cr, Cu, Ni, Pb, and Zn were mainly bound to organic matter and sulfide (F3) and residual fractions (F4), while the exchangeable and carbonate fraction (F1) and Fe/Mn oxide fraction (F2) were the dominant forms for Cd. Additionally, finding showed that the overall risk of sediments in aquatic systems was affected by both metal toxicity and metal fractionation. Thus, according to a modified risk assessment code (RAC), the potential adverse effect of metals in sediments was medium (although As, Cd, Ni, and Zn had high mobility risks based on the RAC), decreasing in the order RP > WL > ML.

Release characteristics of nitrogen and phosphorus from sediments formed under different supplemental water sources in Xi'an moat, China

The endogenous release of nutrients from sediments contributes to the eutrophication of landscape water to a certain degree, which depends on the characteristics of sediments. The study explored the characteristics of nitrogen (N) and phosphorus (P) released from two different sediments, which were deposited from reclaimed water (SRW) or surface water (SSW) respectively in Xi'an moat. This paper aimed to compare the effects of nutrient release from SRW and SSW on the water quality. Results showed that the maximum increase rates reached 1.21 mg TN/(L·day) and 0.11 mg TP/(L·day), respectively, in the overlying water of SRW, which were 1.6 and 2.8 times those of SSW. The released amounts of SRW were 0.192 mg TN/g and 0.038 mg TP/g, which were 4.1 and 12.7 times those of SSW. Meanwhile, the densities of benthic algae in SRW and SSW were 5.605 × 10⁹ and 2.846 × 10⁸ cells/L, respectively. Moreover, the species number and individual sizes of benthic algae in SRW were also larger than those in SSW, which played an important role in the nitrogen circulation. Unexpectedly, oxidation reduction potential (ORP) level of SRW was lower than that of SSW, although SRW has a higher dissolved oxygen level. Therefore, the N and P concentrations in the overlying water of SRW were considerably higher than those of SSW, which was mainly attributed to the higher nutrient contents and lower ORP in SRW.

Effect of a strengthened ecological floating bed on the purification of urban landscape water supplied with reclaimed water

A floating bed (FB) system vegetated with calamus, iris, lythrum, and Hydrocotyle vulgaris, and a strengthened FB (SFB) system with zeolite and sponge iron as fillers were simultaneously applied to purify urban landscape water in different zones. The urban landscape water, an artificial lake of approximately 326m², was supplied with reclaimed water during a six-month experiment. Results indicated that the concentrations of nitrogen (N) and phosphorus (P) in the SFB zone (SFBZ) were significantly lower than those in the control zone (CZ) and the FB zone (FBZ) after six months of operation. The average removal efficiencies (AREs) in the SFBZ, FBZ and CZ were 89.98%, 77.39% and 56.37%, respectively, for ammonia nitrogen (NH₄⁺-N); 92.49%, 79.55% and 47.85%, respectively, for phosphate (PO₄^3--P). Meanwhile, the average concentration of Chlorophyll a and the algae density in SFBZ during the experiment were 12.54μg/L and 1.31×10⁴cells/mL, which were lower, obviously, than those in the FBZ and CZ. Moreover, the contribution rates analysis of nutrient removal exhibited that the plant absorption in the removal of N and P occupied 27.85% and 26.36%, whereas the filler adsorption occupied 7.93% and 11.93%, respectively, in the SFB. Thus, the water quality of the artificial lake was improved greatly by the SFB which hybridized fillers and FB together. Finally, it was found that the AREs of NH₄⁺-N and PO₄^3--P in the SFBZ could reach 73.93% and 84.56%, approximately 1.39 and 1.41 times that of the FBZ during the winter. Therefore, the application of an SFB can keep a stable water quality in urban landscape water and avoid the lower removal rate of an FB at low-temperature. In summary, the SFB could effectively improve the water quality of urban landscape water supplied with reclaimed water even in winter.