Antioxidant response to ZnO nanoparticles in juvenile Takifugu obscurus: protective effects of salinity.

The extensive utilization of Zinc Oxide nanoparticles (ZnO NPs) has garnered significant attention due to their detrimental impacts on ecosystem. Unfortunately, ecotoxicity of ZnO NPs in coastal waters with fluctuating salinity has been disregarded. This study mainly discussed the toxic effects of ZnO NPs on species inhabiting the transition zones between freshwater and brackish water, who are of great ecological and economic importance among fish. To serve as the model organism, Takifugu obscurus, a juvenile euryhaline fish, was exposed to different ZnO NPs concentrations (0-200 mg/L) and salinity levels (0 and 15 ppt). The results showed that a moderate increase in salinity (15 ppt) could alleviate the toxic effect of ZnO NPs, as evidenced by improved survival rates. The integrated biomarker response index on oxidative stress also revealed that the toxicity of ZnO NPs was higher in freshwater compared to brackish water. These outcomes can be attributed to higher salinity (15 ppt) reducing the bioavailability of ZnO NPs by facilitating their aggregation and inhibiting the release of metal ions. It is noteworthy that elevated salinity was found to alleviate ZnO NPs toxicity by means of osmotic adjustment via the activation of Na+/K+-ATPase activity. This study demonstrates the salinity-dependent effect of ZnO NPs on T. obscurus, suggesting the possibility for euryhaline fish like T. obscurus to adapt their habitat towards more saline environments, under constant exposure to ZnO NPs.

An optimization framework for basin-scale water environmental carrying capacity.

The interaction between water environment and social economy at a basin scale is complex and challenging to quantify. To address this issue, this study proposes an integrated framework that builds parametric connections among water, contaminants, administrative regions, and social activities. The framework, known as the water environmental carrying capacity (WECC) optimization framework, effectively captures the intricacy of the interaction and integrates socio-economic parameter structure relationships, a water environmental model, a WECC optimization model, and a sensitivity analysis of regulatory parameters. Applied to the Anhui-Huaihe Basin in mid-eastern China, the framework considers nine administrative regions and three economic factors: industry, agriculture, and GDP per capita (pGDP). Results show that the current water environmental carrying capacity of the watershed is insufficient to meet socio-economic development requirements. After optimization, the WECC for industry, agriculture, and pGDP in the region increased by 22.40%, 26.59%, and 15.08% respectively. Overall COD and NH4-N discharge decreased by 13.6% and 14.7% respectively, effectively reducing pollution loads in rivers and enhancing sustainable development potential. At the regional scale, optimization for industry, agriculture, and pGDP exhibited different characteristics, but all aimed to improve efficiency by reducing the K value (pollution discharge/output value ratio). Regions with industrial treatment rates (αwt) below 0.8 should prioritize increasing treatment rates, while those above 0.8 should consider industrial upgrading for enhanced efficiency. For agriculture, important sensitive parameters for farming and livestock breeding are the proportion of high standard farmland (αs) and the scale breeding ratio (αb), which should be increased to above 0.15 and 0.83 respectively for all regions to achieve agricultural optimization. For pGDP optimization, the focus is on improving living environments and reducing pollution discharge, with crucial measures including collecting and treating rural domestic sewage, where the rural toilet improvement rate (αt) in each region should be increased to 0.78 or above. The results emphasize the need for both interregional allocation and intraregional planning to achieve comprehensive basin optimization and a harmonious balance between regional development and water environment.

Nano La(OH)3 modified lotus seedpod biochar: A novel solution for effective phosphorus removal from wastewater.

Effective removal of phosphorus from water is crucial for controlling eutrophication. Meanwhile, the post-disposal of wetland plants is also an urgent problem that needs to be solved. In this study, seedpods of the common wetland plant lotus were used as a new raw material to prepare biochar, which were further modified by loading nano La(OH)3 particles (LBC-La). The adsorption performance of the modified biochar for phosphate was evaluated through batch adsorption and column adsorption experiments. Adsorption performance of lotus seedpod biochar was significantly improved by La(OH)3 modification, with adsorption equilibrium time shortened from 24 to 4 h and a theoretical maximum adsorption capacity increased from 19.43 to 52.23 mg/g. Moreover, LBC-La maintained a removal rate above 99% for phosphate solutions with concentrations below 20 mg/L. The LBC-La exhibited strong anti-interference ability in pH (3-9) and coexisting ion experiments, with the removal ratio remaining above 99%. The characterization analysis indicated that the main mechanism is the formation of monodentate or bidentate lanthanum phosphate complexes through inner sphere complexation. Electrostatic adsorption and ligand exchange are also the mechanisms of LBC-La adsorption of phosphate. In the dynamic adsorption experiment of simulated wastewater treatment plant effluent, the breakthrough point of the adsorption column was 1620 min, reaching exhaustion point at 6480 min, with a theoretical phosphorus saturation adsorption capacity of 6050 mg/kg. The process was well described by the Thomas and Yoon-Nelson models, which indicated that this is a surface adsorption process, without the internal participation of the adsorbent.

Spatial variation in the community structure and response of benthic macroinvertebrates to multiple environmental factors in mountain rivers.

Exploring the response between benthic community changes and environmental variables has significance for restoring the health of river ecosystems. However, little is known of the impact on communities of interactions between multiple environmental factors, and frequent changes in the flow of mountain rivers are different from those in the flow of plain river networks, which also impact differently the benthic community. Thus, there is a need for research on the response of benthic communities to environmental changes in mountain rivers under flow regulation. In this study, we collected samples from the Jiangshan River in the dry season (November 2021) and the wet season (July 2022) to investigate the aquatic ecology and benthic macroinvertebrate communities in the watershed. Multi-dimension analyses were used to analyze the spatial variation in the community structure and response of benthic macroinvertebrates to multiple environmental factors. In addition, the explanatory power of the interaction between multiple factors on the spatial variation of communities, and the distribution characteristics of benthic community and their causes were investigated. The results showed that herbivores are the most abundant forms in the benthic community of mountain rivers. The structure of benthic community in Jiangshan River was significantly affected by water quality and substrate, whereas the overall community structure was affected by river flow conditions. Furthermore, nitrite nitrogen and ammonium nitrogen were the key environmental factors impacting the spatial heterogeneity of communities during the dry and wet season, respectively. Meanwhile, the interaction between these environmental factors showed a synergistic effect, enhancing the influence of these environmental factors on community structure. Thus, controlling urban and agricultural pollution and releasing ecological flow would be effective strategies to improve benthic biodiversity. Our study showed that using the interaction of environmental factors was a suitable way to evaluate the association between environmental variables and variation in benthic macroinvertebrate community structure in river ecosystems.

Climate Change Shrinks and Fragments Salmon Habitats in a Snow-Dependent Region.

Climate change threatens biodiversity through global alteration of habitats, but efficient conservation responses are often hindered by imprecise downscaling of impacts. Besides thermal effects, warming also drives important ancillary environmental changes, such as when river hydrology evolves in response to climate forcing. Earlier snowmelt runoff and summer flow declines are broadly manifested in snow-dependent regions and relevant to socioeconomically important cold-water fishes. Here, we mechanistically quantify how climate-induced summer flow declines during historical and future periods cause complex local changes in Chinook salmon (Oncorhynchus tshawytscha) habitats for juveniles and spawning adults. Changes consisted of large reductions in useable habitat area and connectivity between the main channel and adjacent off-channel habitats. These reductions decrease the capacity of freshwater habitats to support historical salmon abundances and could pose risks to population persistence in some areas.

Phycocyanin-rich Synechococcus dominates the blooms in a tropical estuary lake.

Cyanobacterial blooms challenge the safe water supply in estuary reservoirs. Yet, data are limited for the variation of phytoplankton dynamics during an algal bloom event at refined scales, which is essential for interpreting the formation and cessation of blooms. The present study investigated the biweekly abundances and dynamics of pico- and nano-phytoplankton in a tropical estuary lake following a prolonged bloom event. Flow cytometry analysis resolved eight phenotypically distinct groups of phytoplankton assigned to nano-eukaryotes (nano-EU), pico/nano-eukaryotes (PicoNano-EU), cryptophyte-like cells (CRPTO), Microcystis-like cells (MIC), pico-eukaryotes (Pico-EU) and three groups of Synechococcus-like cells. Total phytoplankton abundance ranged widely from 2.4 × 104 to 2.8 × 106 cells cm-3. The phytoplankton community was dominated by Synechococcus-like cells with high phycocyanin content (SYN-PC). Temporal dynamics of the phytoplankton community was phytoplankton- and site-specific. Peak values were observed for SYN-PC, SYN-PE2 (Synechococcus-like cells with low levels of phycoerythrin) and Pico-EU, while the temporal dynamics of other groups were less pronounced. Redundancy analysis (RDA) showed the importance of turbidity as an abiotic factor in the formation of the current SYN-PC induced blooms, and Spearman correlation analysis suggested a competitive relationship between SYN-PC and Pico-EU.

Antibiotics along an alpine river and in the receiving lake with a catchment dominated by grazing husbandry.

The livestock breeding industries face overuse of antibiotics, which has been intensively studied in recent years. However, the occurrence and fate of antibiotics as well as their potential threats to the aquatic environments in alpine and arid regions remain unclear. This study investigated the relationship of the occurrence and concentrations of antibiotics between the Kaidu River and Bosten Lake in a typical alpine basin in China. Hot spots with antibiotic pollution source were explored. The antibiotic concentrations in river water and suspended sediment (SPS) were 2.20-99.4 ng/L and 1.03-176 ng/g. The dominant antibiotics were tetracyclines, sulphacetamide, and ofloxacin in river water and sulfonamides, clarithromycin, roxithromycin, and ofloxacin in SPS. The apparent differences in pollution sources and landscapes in different reaches led to the obvious spatial patterns of antibiotics in the Kaidu River. Higher partition coefficient of antibiotic between SPS and water phases for sulfonamides than tetracyclines was because that tetracyclines strongly responded to clay contents while sulfonamides significantly responded to organic carbon contents in SPS. There were significant differences in detected antibiotic categories between the river and the lake. Fluoroquinolones (especially ciprofloxacin and enrofloxacin) were detected in the lake while sulphacetamide was only detected in the river. Therefore, the surrounding husbandry and aquaculture around the Bosten Lake was an important antibiotic pollution source in addition to inputs from the Kaidu River. This research suggested that alpine lakes could be an important sink of antibiotics in alpine dry regions, and thus impose greater threats to the aquatic ecosystem.

The Effectiveness of Waist-Shaped and Straight-Shaped Interdental Brushes in Cleaning Implant Overdenture Attachments: A Self-Controlled Clinical Trial.

Elderly patients often find it challenging to remove plaque accumulated on the attachments of implant overdentures (IODs) using conventional cleaning instruments. Further, excessive plaque accumulation can lead to peri-implant diseases and occasionally to respiratory diseases. Therefore, here, we aimed to compare the effectiveness of waist-shaped interdental brushes (WIBs) with that of straight-shaped interdental brushes (SIBs) in plaque removal from the locator attachments of IODs. Twenty participants with 2 locator attachments retaining mandibular IODs participated in this study. After the baseline cleaning, the participants refrained from oral hygiene maintenance for 3 days. A dentist cleaned 1 of the attachments using the WIB and the other attachment using the SIB. The pre- and post-cleaning modified plaque index (mPLI) scores were recorded. After another 3 days free from oral hygiene maintenance, the trained participants repeated the same cleaning procedure using the WIB and SIB. Pre- and post-cleaning mPLI scores were recorded. Regardless of the type of brush used, the post-cleaning mPLI scores were lower than the pre-cleaning scores. After the cleaning procedure, the overall mean mPLI score was lower in the WIB group than in the SIB group. The post-cleaning mPLI scores at the line angles and on the axial surfaces of the attachments were also lower in the WIB group than in the SIB group. There was no difference in the cleaning effectiveness between the dentist and participants when they used the same type of interdental brush. The WIB was significantly more efficient in plaque removal than the SIB, especially at the line-angle sites.

Characterization and source identification of tetracycline antibiotics in the drinking water sources of the lower Yangtze River.

The occurrence and spatio-temporal patterns of five tetracyclines (TCs) and six of their degradation products were investigated in twenty-eight drinking water sources along the lower Yangtze River (LYR) over dry, normal and flood seasons. Tetracycline (TC), oxytetracycline (OTC) and doxytetracycline (DXC) were the dominant antibiotics detected with the highest occurrence. The maximum concentrations of TC, OTC and DXC were found in dry season as 11.16, 18.98, and 56.09 ng/L, respectively, because of the low dilution, low degradation, and high consumption in this season. Cluster analysis indicated distinct variations in the TCs' compositional profiles in both space and time. OTC and its metabolites contributed 18.5-59.6% of the TC load in dry season, possibly due to the seasonally increased release of pharmaceutical OTCs from sewage effluents, but they were seldom detected in other seasons. Pollution load index analysis showed that tributaries carrying large amounts of veterinary TCs derived from breeding wastewater and untreated rural sewage contributed larger proportions of the TC load for most drinking water sources than sewage outlets. The contribution ratio of the TC load from tributaries (74.5%) was approximately three times higher than that from sewage discharges (25.5%). The study demonstrated that the control of load from tributaries is the key to mitigating TC pollution of the drinking water sources in the LYR. An effective source tracking method for evaluating the contribution of antibiotic load from multiple diffuse pollution origins and identifying the high-risk contamination sources was established for antibiotic management and control.

Hypoxia Remediation and Methane Emission Manipulation Using Surface Oxygen Nanobubbles.

Algal blooms in eutrophic waters often induce anoxia/hypoxia and enhance methane (CH4) emissions to the atmosphere, which may contribute to global warming. At present, there are very few strategies available to combat this problem. In this study, surface oxygen nanobubbles were tested as a novel approach for anoxia/hypoxia remediation and CH4 emission control. Incubation column experiments were conducted using sediment and water samples taken from Lake Taihu, China. The results indicated that algae-induced anoxia/hypoxia could be reduced or reversed after oxygen nanobubbles were loaded onto zeolite micropores and delivered to anoxic sediment. Cumulated CH4 emissions were also reduced by a factor of 3.2 compared to the control. This was mainly attributed to the manipulation of microbial processes using the surface oxygen nanobubbles, which potentially served as oxygen suppliers. The created oxygen-enriched environment simultaneously decreased methanogen but increased methanotroph abundances, making a greater fraction of organic carbon recycled as carbon dioxide (CO2) instead of CH4. The CH4/CO2 emission ratio decreased to 3.4 × 10-3 in the presence of oxygen nanobubbles, compared to 11 × 10-3 in the control, and therefore the global warming potential was reduced. This study proposes a possible strategy for anoxia/hypoxia remediation and CH4 emission control in algal bloom waters, which may benefit global warming mitigation.

Effects of nutrient temporal variations on toxic genotype and microcystin concentration in two eutrophic lakes.

Harmful cyanobacterial blooms are a growing threat to freshwater ecosystems worldwide due to the production of microcystin (MC), which can have detrimental effects on water quality and human health. The relations between MC-producing Microcystis, MC production, and environmental variables especially nutrient conditions in eutrophic lakes, Lake Taihu and Lake Yanghe, were investigated during the bloom season of 2015. Results showed that toxigenic cells contributed to 8.94-75.68% and 7.87-58.69% of the total Microcystis in Lake Taihu and Lake Yanghe, respectively. The dynamics of toxigenic cells and MC production were positively associated with NH3-N concentration in Lake Taihu, while positively associated with the concentrations of TP, TDP and PO4-P in Lake Yanghe, indicating that the dominant nutrient factor affecting the toxic blooms was nitrogen in Lake Taihu, whereas it was phosphorus in Lake Yanghe. The significant relationship between TLR eq (total MC after transformation of MC-RR and MC-YR into MC-LR) and Chlorophyll-a (Chl-a) concentration implied that Chl-a could be an alternative measure to predict MC risk in the two lakes, and the safe threshold value of Chl-a was proposed as 25.38 and 31.06 µg/L in Lake Taihu and Lake Yanghe, respectively.

Improve the performance of full-scale continuous treatment of municipal wastewater by combining a numerical model and online sensors.

Mathematical models based on instant environmental inputs are increasingly applied to optimize the operation of wastewater treatment plants (WWTPs) for improving treatment efficiency. This study established a numerical model consisting of the activated sludge module ASM3 and EAWAG bio-P module, and calibrated the model using data from a full-scale experiment conducted in a WWTP in Nanjing, China. The calibrated model was combined with online sensors for water temperature, chemical oxygen demand, NH+ 4-N and PO3- 4-P to optimize and dynamically adjust the operation of the WWTP. The results showed that, compared to the original default operation mode, the effluent water quality was significantly improved after optimization even without supplementation of external carbon or alkalinity, and the required aeration rate in spring, summer, autumn, and winter was reduced by 15, 41, 33 and 11%, respectively. The study indicated that there was the potential for application of closed-loop automatic control to regulate operating parameters to improve wastewater treatment processes through the integration of data on influent characteristics and environmental conditions from sensors, and results from simulation models.

Sieved Transport and Redistribution of Bioavailable Phosphorus from Watershed with Complex River Networks to Lake.

An innovative approach was developed to reveal phosphorus (P) transport and redistribution in large and complex river networks in the Lake Taihu basin by establishing the relations between sediment P spatial distribution and P sorption behavior on particles with different grain size, sorted by hydrodynamics. The sediment P fractionation composition changed greatly across the basin, where 69% consisted of acid-soluble fractions (HCl-P) in upstream rivers while 70% was in fractions associated with reducible metal hydroxides (BD-P) and amorphous hydroxides (NaOH25-P) in downstream rivers. Fine particles enriched in BD-P and NaOH25-P fractions tended to sorb liberated P during the resuspension process, and fine particles were more easily delivered downstream toward the lake, forming a sieved transport of P in the river networks. This will lead to a great potential for sediment P release when environmental anoxia develops in the sediments or high pH occurs in the sediment surface during intensive algal blooms in the shallow lake. Reduction of external P from point sources from urbanized areas is an important requirement at the basin scale; however, long-term efforts are needed to restore aquatic macrophytes in the lake, which would decrease P recycling rates at the water-sediment interface.

Tracking Nitrogen Sources, Transformation, and Transport at a Basin Scale with Complex Plain River Networks.

This research developed an innovative approach to reveal nitrogen sources, transformation, and transport in large and complex river networks in the Taihu Lake basin using measurement of dual stable isotopes of nitrate. The spatial patterns of δ15N corresponded to the urbanization level, and the nitrogen cycle was associated with the hydrological regime at the basin level. During the high flow season of summer, nonpoint sources from fertilizer/soils and atmospheric deposition constituted the highest proportion of the total nitrogen load. The point sources from sewage/manure, with high ammonium concentrations and high δ15N and δ18O contents in the form of nitrate, accounted for the largest inputs among all sources during the low flow season of winter. Hot spot areas with heavy point source pollution were identified, and the pollutant transport routes were revealed. Nitrification occurred widely during the warm seasons, with decreased δ18O values; whereas great potential for denitrification existed during the low flow seasons of autumn and spring. The study showed that point source reduction could have effects over the short-term; however, long-term efforts to substantially control agriculture nonpoint sources are essential to eutrophication alleviation for the receiving lake, which clarifies the relationship between point and nonpoint source control.

Carbon Emission from Cascade Reservoirs: Spatial Heterogeneity and Mechanisms.

Carbon emission from reservoirs is considered to tarnish the green credentials of hydropower and has been extensively studied in single reservoirs. However, it remains unclear how carbon emission differs in cascade reservoirs and the mechanism behind the differences. In this study, carbon dioxide (CO2) and methane (CH4) emissions from cascade hydropower reservoirs were measured in the Lancang River, the Chinese section of the Mekong River. Our results demonstrate that carbon emissions from the river were increased by dam construction but exhibited spatial heterogeneity among cascade reservoirs. The first, most upstream, reservoir acted as the hotspot of CH4 and CO2 emissions, which were 13.1 and 1.7 times higher than those in downstream reservoirs, respectively. Similarly, the CH4/CO2 ratio of 0.023 in the first reservoir was higher than the others and made a greater contribution to the global warming effects of the cascade reservoirs. The sediment organic carbon in downstream reservoirs was negatively correlated with reservoir age (r2 = 0.993) and decreased at a rate of 0.389 mg g-1 yr-1, suggesting a potential decrease of carbon emission in the future. This study adds to our understanding of carbon emissions from cascade reservoirs and helps to screen effective strategies for future mitigation of the global warming effects from cascade hydropower systems.

Will wearing dentures affect edentulous patients' breathing during sleep?

PURPOSES: The purpose of this study is to investigate the effect of wearing dentures on obstructive sleep apnea and hypopnea among completely edentulous patients. METHODS AND MATERIALS: A self-controlled study was conducted among 30 edentulous patients. Polysomnograms were recorded in the sleep laboratory on two consecutive nights. Participants slept with their dentures in one night and without dentures in the other. The apnea and hypopnea index (AHI), lowest oxygen saturation (L-SpO2), and morning blood pressure (MBP) were collected for statistical analysis. RESULTS: Among the edentulous participants, 24 showed a higher AHI when sleeping with dentures. The average AHI for all 30 participants was significantly higher when they slept with dentures than without dentures (16.3 ± 14.7 vs 13.4 ± 14.0/h, P < 0.05). Participants in the non-obstructive sleep apnea-hypopnea syndrome (non-OSAHS) subgroup (AHI <5 when sleeping without dentures) had a significant increase in AHI when sleeping with dentures, and nearly half of them (5 out of 11) reached the diagnostic standard for OSAHS (AHI >5). A higher morning diastolic blood pressure was recorded when participants slept with dentures (P < 0.05), while no significant difference was found in the L-SpO2 score and morning systolic blood pressure. CONCLUSIONS: Wearing dentures can lead to significant increase of AHI and diastolic MBP among edentulous people. Hence, we suggest that Chinese edentulous people should remove their dentures before sleep. TRIAL REGISTRATION: ChiCTR-IOR-16008404.

Optimizing external carbon source addition in domestics wastewater treatment based on online sensoring data and a numerical model.

The removal of total nitrogen in wastewater treatment plants (WWTPs) is often unsatisfactory for a variety of reasons. One possible measure to improve nitrogen removal is the addition of external carbon. However, the amount of carbon addition is directly related to WWTP operation costs, highlighting the importance of accurately determining the amount of external carbon required. The objective of this study was to obtain a low nitrate concentration in the anoxic zone of WWTPs efficiently and economically by optimizing the external carbon source dosage. Experiments were conducted using a pilot-scale pre-denitrification reactor at a Nanjing WWTP in China. External carbon source addition based on online monitoring of influent wastewater quality and a developed nitrification-denitrification numerical model was investigated. Results showed that carbon addition was reduced by 47.7% and aeration costs were reduced by 8.0% compared with those using a fixed-dose addition mode in the pilot reactor. The obtained technology was applied to the full-scale Jiangxinzhou WWTP in Nanjing with promising results.

Numerical modelling of a three-phase internal air-lift circulating photocatalytic reactor.

The photocatalytic degradation process has been recognized as a low-cost, environmentally friendly and sustainable technology for water and wastewater treatment. As a key carrier of the photocatalytic process, the semiconductor TiO2 has been used in many studies. Analysis and modelling of hydrodynamics in the three-phase flow system can provide useful information for process design, operation and optimization of the three-phase flow photocatalytic reactor, which requires research on the mixing and flow characteristics of the interphase regions in the reactor. In this study, we modelled the hydrodynamics in an internal air-lift circulating photocatalytic reactor using an Eulerian multi-fluid approach. Localized information on phase holdup, fluid flow patterns and mixing characteristics was obtained. The simulation results revealed that the distribution of solid particle concentration depends on the flow field in the internal air-lift circulating photocatalytic reactor. The distance between the draft tube and wall of the reactor and changes in the superficial gas velocity (Ug) were found to be influential factors in reactor performance. The computational model developed could support optimizing reactor design to improve the hydrodynamics and provide guidance for scale-up.

Modelling the presence and identifying the determinant factors of dominant macroinvertebrate taxa in a karst river.

Modelling the macroinvertebrate community is important for evaluating the status of aquatic ecosystem health. Alternative to physical-based approaches, this study proposed two data-driven methods, support vector machine (SVM) and artificial neural network (ANN), to model the presence of macroinvertebrate species in rivers based on abiotic features. A famous karst river, Lijiang River, in Southwest China was selected as the study case. A total of 300 records containing data on 11 physicochemical parameters were collected from the upstream, midstream and downstream reaches of the river over a 2-year period (2009-2010) and were used for model construction and verification. Ten dominant macroinvertebrate taxa in the study area were modelled. In addition, the performance of the two methods was compared, and the relative importance of the independent variables was identified. The obtained results mapped abiotic factors to the species presence and could be used in combination with a two-dimensional hydro-environmental model to assess the impacts of flow regulation on macroinvertebrate dynamics. Furthermore, the SVM model performed slightly better than the ANN model in the studied case.

Simultaneous denitrification and denitrifying phosphorus removal in a full-scale anoxic-oxic process without internal recycle treating low strength wastewater.

Performance of a full-scale anoxic-oxic activated sludge treatment plant (4.0×10(5) m(3)/day for the first-stage project) was followed during a year. The plant performed well for the removal of carbon, nitrogen and phosphorus in the process of treating domestic wastewater within a temperature range of 10.8°C to 30.5°C. Mass balance calculations indicated that COD utilization mainly occurred in the anoxic phase, accounting for 88.2% of total COD removal. Ammonia nitrogen removal occurred 13.71% in the anoxic zones and 78.77% in the aerobic zones. The contribution of anoxic zones to total nitrogen (TN) removal was 57.41%. Results indicated that nitrogen elimination in the oxic tanks was mainly contributed by simultaneous nitrification and denitrification (SND). The reduction of phosphorus mainly took place in the oxic zones, 61.46% of the total removal. Denitrifying phosphorus removal was achieved biologically by 11.29%. Practical experience proved that adaptability to gradually changing temperature of the microbial populations was important to maintain the plant overall stability. Sudden changes in temperature did not cause paralysis of the system just lower removal efficiency, which could be explained by functional redundancy of microorganisms that may compensate the adverse effects of temperature changes to a certain degree. Anoxic-oxic process without internal recycling has great potential to treat low strength wastewater (i.e., TN<35 mg/L) as well as reducing operation costs.