Selection of optimal river water quality improvement programs using QUAL2K: a case study of Taihu Lake Basin, China

Mapping and assessment of river water quality under varying hydro-climatic and pollution scenarios by integrating QUAL2K, GEFC, and GIS

Water quality modelling has proved to be effective method for managing river water quality. But the most effective and comprehensive approach involving integration of river water quality simulation and pollution visualization with the objective of pollution reduction and maintenance of environmental flow strategies has gained less attention. Thus, the objective of this study was to employ an integrated approach for mapping and analysing river water quality under various hydro-climatic and pollution scenarios. Specifically, this approach involved the integration of a river water quality simulation model, QUAL2K, Global Environmental Flow Calculator (GEFC), and Geographical Information System (GIS) to develop water quality index (WQI) based map charts of water quality. The calibrated QUAL2K model was utilized to simulate WQI parameters including water temperature, pH, electrical conductivity, dissolved oxygen (DO), biological oxygen demand (BOD), nitrates (NO3), ammonia (NH4), and alkalinity. To analyse the WQI, the Weighted Arithmetic-Water Quality Index (WA-WQI) method was employed for various individual and combined pollution scenarios, environmental flow (Eflow), and climate change scenarios. The developed integrated approach was applied to the Bhadravati segment of Bhadra River, India. The findings revealed that the prevailing WQI status of the study stretch ranged from poor to unsuitable for drinking purposes. This deterioration can be attributed to the impact of both industrial and municipal effluents. By maintaining the effective Environmental Management Class (EMC) flow rates (class C flowrate of EMC (40.32 m3/s)) in conjunction with appropriate Pollution Reduction (PR) level (10% PR) at headwater and incoming drains, the stream self-purification capacity was enhanced resulting in the Bhadravati River stretch water quality transitioning to favourable water quality condition.

Integrated Assessment of Water Environmental Health Risk through Drinking Water Ingestion in Lhasa River Basin: Quantitative Analysis and Environmental Significance

An integrated assessment of water environmental health risk through drinking water ingestion in Lhasa River has been implemented. The health risks caused by different pollutants in different age groups (children, juvenile and adult groups) are in the order of 10^-8 ~ 10^-7, 10^-7 ~ 10^-5 and 10^-13 ~ 10^-8 a^-1, respectively. The total health risks for all age groups are lower than the International Commission on Radiation Protection recommended value and the U.S. Environmental Protection Agency recommended value at all points except LS4, LS12 and LS13. The total health risk levels in different age groups at most points are class III or II, which means that there are low or negligible negative effect in these points and age groups. It is more important to monitor the arsenic concentration. The water environment quality protecting in Lhasa River Basin must be consistent with the clear water and blue sky protecting in Tibet Autonomous Region and the national ecological security barrier construction on the Tibetan Plateau.

Impacts of Climate Change and Non-Point-Source Pollution on Water Quality and Algal Blooms in the Shoalhaven River Estuary, NSW, Australia

This study quantifies some of the potential impacts of climate change and nutrient pollution to identify the most important factors on water quality changes and algal blooms in the study region. Three variables, air temperature and streamflow, representing climate change, and nutrient runoff, were varied in eight hypothetical scenarios to determine their impact on water quality and algal blooms by the calibrated and validated water quality model QUAL2K. Water quality was assessed by the concentrations of dissolved oxygen, total nitrogen, and phosphorus. Algal blooms were identified by phytoplankton concentration. An increase in air temperature of up to 2 °C resulted in an average increase of 3% in water temperature and 4.79% in phytoplankton concentration, and an average decrease of 0.48% in dissolved-oxygen concentration. Projected decreases in streamflow not only made the above phenomenon more significant but also significantly increased the concentration of total nitrogen, total phosphorus, and phytoplankton with the same pollution inputs. Under climate change, the biggest cause of concern for estuarine water quality is reduced streamflow due to decreases in rainfall. Water quality improvement is possible by regulating the concentration of non-point-source pollution discharge. By reducing nutrient runoff, the total nitrogen and phosphorus concentrations were also reduced, resulting in a significant increase in the dissolved oxygen concentration. This study highlights the most significant factors for managing water quality in estuaries subject to climate change.

Water Environmental Capacity Calculation Based on Control of Contamination Zone for Water Environment Functional Zones in Jiangsu Section of Yangtze River, China

In recent years, due to unsustainable production methods and the demands of daily life, the water quality of the Yangtze River has deteriorated. In response to Yangtze River protection policy, and to protect and restore the ecological environment of the river, a two-dimensional model of the Jiangsu section was established to study the water environmental capacity (WEC) of 90 water environment functional zones. The WEC of the river in each city was calculated based on the results of the water environment functional zones. The results indicated that the total WECs of the study area for chemical oxygen demand (COD), ammonia nitrogen (NH3-N), and total phosphorus (TP) were 251,198 t/year, 24,751 t/year, and 3251 t/year, respectively. Among the eight cities studied, Nanjing accounted for the largest proportion (25%) of pollutants discharged into the Yangtze River; Suzhou (11%) and Zhenjiang (12%) followed, and Wuxi contributed the least (0.4%). The results may help the government to control the discharge of pollutants by enterprises and sewage treatment plants, which would improve the water environment and effectively maintain the water ecological function. This research on the WEC of the Yangtze River may serve as a basis for pollution control and water quality management, and exemplifies WEC calculations of the world’s largest rivers.

A simulation-based method to develop strategies for nitrogen pollution control in a creek watershed with sparse data

Well-defined targets for nitrogen (N) release into the local environment are essential for water management in creeks, but difficulties often arise from working with data that are too sparse to achieve reliable evaluations. Here, a simulation-optimization approach based on the QUAL2K model was developed to put forward strategies for nitrogen pollution control in a creek with sparse data in Shixi Creek, southeast China. The model showed good agreement with field observations from 22 sampling sites sampled over the period from March 2017 to February 2019, with normalized objective function (NOF) less than 0.360. Based on this model, the water pollutant sources in the creek were distinguished and analyzed. Rural sewage discharge in Shixi Creek was the major factor threatening water quality in the stream. Seasonal variations may influence the transformation of riverine N. To make more than 80% of the area in Shixi Creek meet the water quality standard of grade III, an optimized approach is to reduce more than 55% of the N pollution from point source pollution and 10% from nonpoint source pollution. This study proposed an approach that can effectively evaluate strategies for water management in a creek watershed with sparse data.

A bi-level multiobjective optimization model for waste load allocation in rivers

It is often difficult to apply existing waste load allocation (WLA) models to management institutions at all levels of the river basin because the existing WLA models do not consider the principles of fairness and efficiency at each management level of the basin. The implementation of environmental protection tax law has also greatly impacted WLA. This paper proposes the bi-level multiobjective allocation model under an environmental protection tax law to solve the WLA problem for different management levels. The upper allocation targets the minimal environmental Gini coefficient and the minimal unit pollutant emission cost. The impact of the environmental protection tax is also considered. The targets of the lower-level allocation are the maximal industrial output value and the minimal unevenness of reduction rates. The proposed model was applied to the case of the Wei River basin, and the results demonstrated that the bi-level multiobjective allocation model could solve the problem of WLA under an environmental protection tax law. Each level of the bi-level multiobjective allocation model considers the principles of fairness and efficiency to distribute the load in the basin, thereby offering a better reference for decision-makers at both levels.

Applicability of water quality models around the world-a review

Water quality models are important tools used in the management of water resources. The models are usually developed for specific regions, with particular climates and physical characteristics. Thus, applying these models in regions other than those they were designed for can generate large simulation errors. With consideration to these discrepancies, the goal of this study is to identify the models employed in different countries and assist researchers in the selection of the most appropriate models for management purposes. Published studies from the last 21 years (1997-2017) that discuss the application of water quality models were selected from three engineering databases: SpringerLink, Web of Science, and Scopus. Seven models for water quality simulations have been widely applied around the world: AQUATOX, CE-QUAL-W2, EFDC, QUALs, SWAT, SPARROW, and WASP. The countries most frequently applying water quality models are the USA, followed by China, and South Korea. SWAT was the most used model, followed by the QUAL group and CE-QUAL-W2. This study provides the opportunity for researchers, who wish to study countries with fewer cases of applied water quality models, to easily identify the work from that region. Furthermore, this work collated central themes of interest and the most simulated parameters for the seven countries that most frequently employed the water quality models.

Application of Export Coefficient Model and QUAL2K for Water Environmental Management in a Rural Watershed

Water quality deterioration caused by excessive nutrient discharge from various point and non-point sources are a global challenge. Understanding the pollution sources and their respective contribution is the prerequisite for environmental planning, management and restoration. In this study, the influence of complex pollution sources on the water quality of the Dengsha River watershed in Dalian, China, was investigated. The export coefficient method was coupled with the QUAL2K water quality model to estimate the loads of ammonia nitrogen (NH4-N) and total phosphorus (TP) from different sources, and to explore their respective contributions. Results indicated that animal feedlot and crop production were major sources for NH4-N load, and crop production, soil erosion and animal feedlot are the largest three sources of TP load with an annual total contribution of 98.4%. The pollutant load exhibited an intra-annual variation mainly due to the seasonality of rainfall and anthropogenic agricultural activities. The overall waste assimilation capacity (WAC) is overloaded and suggestions for water pollution control and treatment regarding each pollution source were proposed. This study addressed a new application of QUAL2K model coupled with the export coefficient model for watershed managers towards a sustainable water environmental management, and can therefore be a reference example for other small and medium-sized rural watersheds.

A fuzzy multi-stakeholder socio-optimal model for water and waste load allocation

This study proposes a fuzzy multi-stakeholder socio-optimal methodology for joint water and waste load allocation (WWLA) in river systems while addressing upstream flow uncertainty and different social choice rules (SCRs). QUAL2Kw, as the numerical river water quality model, is executed for various scenarios of water and waste loads to construct a comprehensive dataset of plausible settings, which is in turn used to train a meta-model in the form of multivariate linear regressions. The river upstream flow as the main uncertain parameter is assessed by fuzzy transformation method (FTM). Then, for different confidence levels of fuzzy uncertain input, the meta-model is linked with the non-dominated sorting genetic algorithm (NSGA-II) multi-objective optimization model to generate trade-off curves among the stakeholders' utility functions. Subsequently, five SCRs are utilized at each confidence level to determine the fuzzy interval solutions for each objective. Next, the possibility degree method is applied to rank the fuzzy interval solutions in each α-cut level. Finally, considering the priorities of all stakeholders, the fallback bargaining method is used to specify the most appropriate SCR in each confidence level. Application of the proposed methodology in Kor River, Iran, shows its efficacy to realize the socio-optimal WWLA scenario(s) among different stakeholders.

Experiments and numerical simulation on the degradation processes of carbamazepine and triclosan in surface water: A case study for the Shahe Stream, South China

We examined the occurrence and fate of pharmaceuticals and personal care products in surface water by combining laboratory experiments with numerical simulations. The degradation processes of two typical PPCPs (triclosan and carbamazepine) collected from the Shahe Stream were studied. Hydrolysis, biodegradation, and photolysis were the three major routes of triclosan (TCS) and carbamazepine (CBZ) degradation. A central composite design method was used to investigate the effects of related natural parameters (including pH, dissolved oxygen, salinity, temperature, light intensity, and humic acid) on the TCS and CBZ degradation processes in the laboratory. Our results showed that the main degradation pathway of CBZ and TCS was direct photolysis during the daytime and that the maximal biodegradation rates of CBZ and TCS occurred at 22 °C when the optimum temperature function was used. Based on our experimental results, the observed degradation of CBZ and TCS followed pseudo-first-order kinetics, and the degradation kinetic equations under the influence of multiple natural parameters were established with estimated average degradation rate constants of 1.2452E-7 s^-1 and 3.1260E-5 s^-1 for CBZ and TCS, respectively. The degradation rate constants were incorporated into a one-dimensional, simply integrated hydrodynamic and water quality model. The proposed numerical model was applied to depict the transportation and transformation of CBZ and TCS in surface water and was validated by observational data from the Shahe Stream. The results showed that our model reproduced the observed patterns of CBZ and TCS concentrations reasonably, with slight overestimations compared to the observed data; the relative errors between the simulated and the observed concentrations were 5.85%-6.82% for CBZ and -156.85%--7.18% for TCS. According to our simulation, the spatial distribution of TCS in surface water was determined by biochemical degradation processes that were most affected by temperature under natural conditions; in contrast, the distribution of CBZ was largely controlled by diffusion.

Determination of biochemical oxygen demand and dissolved oxygen for semi-arid river environment: application of soft computing models

Surface and ground water resources are highly sensitive aquatic systems to contaminants due to their accessibility to multiple-point and non-point sources of pollutions. Determination of water quality variables using mathematical models instead of laboratory experiments can have venerable significance in term of the environmental prospective. In this research, application of a new developed hybrid response surface method (HRSM) which is a modified model of the existing response surface model (RSM) is proposed for the first time to predict biochemical oxygen demand (BOD) and dissolved oxygen (DO) in Euphrates River, Iraq. The model was constructed using various physical and chemical variables including water temperature (T), turbidity, power of hydrogen (pH), electrical conductivity (EC), alkalinity, calcium (Ca), chemical oxygen demand (COD), sulfate (SO₄), total dissolved solids (TDS), and total suspended solids (TSS) as input attributes. The monthly water quality sampling data for the period 2004-2013 was considered for structuring the input-output pattern required for the development of the models. An advance analysis was conducted to comprehend the correlation between the predictors and predictand. The prediction performances of HRSM were compared with that of support vector regression (SVR) model which is one of the most predominate applied machine learning approaches of the state-of-the-art for water quality prediction. The results indicated a very optimistic modeling accuracy of the proposed HRSM model to predict BOD and DO. Furthermore, the results showed a robust alternative mathematical model for determining water quality particularly in a data scarce region like Iraq.

Assessment of Water Quality Profile Using Numerical Modeling Approach in Major Climate Classes of Asia

A river water quality spatial profile has a diverse pattern of variation over different climatic regions. To comprehend this phenomenon, our study evaluated the spatial scale variation of the Water Quality Index (WQI). The study was carried out over four main climatic classes in Asia based on the Koppen-Geiger climate classification system: tropical, temperate, cold, and arid. The one-dimensional surface water quality model, QUAL2Kw was selected and compared for water quality simulations. Calibration and validation were separately performed for the model predictions over different climate classes. The accuracy of the water quality model was assessed using different statistical analyses. The spatial profile of WQI was calculated using model predictions based on dissolved oxygen (DO), biological oxygen demand (BOD), nitrate (NO₃), and pH. The results showed that there is a smaller longitudinal variation of WQI in the cold climatic regions than other regions, which does not change the status of WQI. Streams from arid, temperate, and tropical climatic regions show a decreasing trend of DO with respect to the longitudinal profiles of main river flows. Since this study found that each climate zone has the different impact on DO dynamics such as reaeration rate, reoxygenation, and oxygen solubility. The outcomes obtained in this study are expected to provide the impetus for developing a strategy for the viable improvement of the water environment.

Pilot-scale evaluation of semi-passive treatment technologies for the treatment of septage under temperate climate conditions

Population growth in rural Canada has resulted in an increase in municipal septage generation, which could overload existing treatment facilities that rely on biological treatment approaches. To address concerns associated with potential shock loading of these systems, three semi-passive wastewater treatment technologies were compared at the pilot-scale to identify a suitable approach to augment the capacity of an existing wastewater stabilization pond facility in rural Ontario. Two of these technologies, the BioDome and BioCord systems, were commercially available systems that make use of biofilm technology to improve treatment performance and enhance the robustness to temperature and hydraulic loading fluctuations. The third approach involved the use of the natural filtration capacity of zebra mussels to improve effluent quality. The three technologies were assessed against a control for reductions in regulated wastewater parameters with an emphasis on nutrient (ammonia/ammonium, orthophosphate) reductions, air cycling, energy consumption, and performance following exposure to anoxic conditions. The BioCord system was the only technology that was found to significantly outperform the control, exhibiting reductions of 69%, 47%, 77% and 81% for NH₃/NH₄⁺, TN, COD and TSS, respectively. The BioCord system also had the lowest maintenance and energy requirements, likely due to its design, which provided the biofilm with optimal oxygen and substrate contact. Consequently, the BioCord system could develop a more stable, heterogeneous microbial population and maintain high levels of activity in its biofilm, even during periods of extended anaerobic conditions. This also suggested that the BioCord system would require less aeration, and hence a lower energy expenditure, than the other systems. Furthermore, the BioCord system showed the fastest rates of recovery, reaching significant levels of parameter reductions within one week of system re-initiation.

An integrated fuzzy-based advanced eutrophication simulation model to develop the best management scenarios for a river basin

Assessment of water quality status of a river with respect to its discharge has become prerequisite to sustainable river basin management. The present paper develops an integrated model for simulating and evaluating strategies for water quality management in a river basin management by controlling point source pollutant loadings and operations of multi-purpose projects. Water Quality Analysis and Simulation Program (WASP version 8.0) has been used for modeling the transport of pollutant loadings and their impact on water quality in the river. The study presents a novel approach of integrating fuzzy set theory with an "advanced eutrophication" model to simulate the transmission and distribution of several interrelated water quality variables and their bio-physiochemical processes in an effective manner in the Ganges river basin, India. After calibration, simulated values are compared with the observed values to validate the model's robustness. Fuzzy technique of order preference by similarity to ideal solution (F-TOPSIS) has been used to incorporate the uncertainty associated with the water quality simulation results. The model also simulates five different scenarios for pollution reduction, to determine the maximum pollutant loadings during monsoon and dry periods. The final results clearly indicate how modeled reduction in the rate of wastewater discharge has reduced impacts of pollutants in the downstream. Scenarios suggesting a river discharge rate of 1500 m³/s during the lean period, in addition to 25 and 50% reduction in the load rate, are found to be the most effective option to restore quality of river Ganges. Thus, the model serves as an important hydrologic tool to the policy makers by suggesting appropriate remediation action plans.

Development and testing of a fast conceptual river water quality model

Modern, model based river quality management strongly relies on river water quality models to simulate the temporal and spatial evolution of pollutant concentrations in the water body. Such models are typically constructed by extending detailed hydrodynamic models with a component describing the advection-diffusion and water quality transformation processes in a detailed, physically based way. This approach is too computational time demanding, especially when simulating long time periods that are needed for statistical analysis of the results or when model sensitivity analysis, calibration and validation require a large number of model runs. To overcome this problem, a structure identification method to set up a conceptual river water quality model has been developed. Instead of calculating the water quality concentrations at each water level and discharge node, the river branch is divided into conceptual reservoirs based on user information such as location of interest and boundary inputs. These reservoirs are modelled as Plug Flow Reactor (PFR) and Continuously Stirred Tank Reactor (CSTR) to describe advection and diffusion processes. The same water quality transformation processes as in the detailed models are considered but with adjusted residence times based on the hydrodynamic simulation results and calibrated to the detailed water quality simulation results. The developed approach allows for a much faster calculation time (factor 10⁵) without significant loss of accuracy, making it feasible to perform time demanding scenario runs.

Calculation of permissible load capacity and establishment of total amount control in the Wujin River Catchment--a tributary of Taihu Lake, China

The deterioration of water quality in Taihu Lake, China, has caused widespread concern in recent years. The primary pollution sources of Taihu Lake are its inflow rivers. Effective environmental water management strategies need to be implemented in these rivers to improve the water quality of Taihu Lake and to promote sustainable development in the region. In this study, the QUAL2K model is used in conjunction with the trial and error approach to assess permissible load capacities for the Wujin River (a major tributary of Taihu Lake) in terms of COD, NH3-N, TN, and TP. Results show that permissible annual loads for these pollutants are 5216.31, 491.71, 948.53, and 104.38 t, respectively. This suggests that COD, NH3-N, TN, and TP loads in the Wujin River catchment need to be reduced by 13.35, 27.26, 47.75, and 37.08 %, respectively, to satisfy national water quality objectives. Total amount control measures are proposed to control and reduce pollution loads of the Wujin River catchment. The method applied in this study should provide a sound basis for water environmental management decision-making.

Application of QUAL2K model to assess ecological purification technology for a polluted river

Industrialization and urbanization have caused water pollution and ecosystem degradation, especially in urban canals and rivers in China; accordingly, effective water quality improvement programs are needed. In this study, the Tianlai River in Jiangsu, China was taken as a research site, and a combination of ecological purification technologies consisting of biological rope, phytoremediation, and activated carbon were applied in a laboratory-scale study to examine degradation coefficients under dynamic water conditions. Coefficients were then input into the QUAL2K model to simulate various hypothetical scenarios and determine the minimum density of ecological purification combination and hydraulic retention time (HRT) to meet Grade V or IV of the China standard for surface water. The minimum densities for Grade V and IV were 1.6 times and 2 times the experimental density, while the minimum HRTs for Grade V and IV were 2.4 day and 3 day. The results of this study should provide a practical and efficient design method for ecological purification programs.

Simulation and evaluation of pollution load reduction scenarios for water environmental management: a case study of inflow river of Taihu Lake, China

In the beginning of the 21st century, the deterioration of water quality in Taihu Lake, China, has caused widespread concern. The primary source of pollution in Taihu Lake is river inflows. Effective pollution load reduction scenarios need to be implemented in these rivers in order to improve the water quality of Taihu Lake. It is important to select appropriate pollution load reduction scenarios for achieving particular goals. The aim of this study was to facilitate the selection of appropriate scenarios. The QUAL2K model for river water quality was used to simulate the effects of a range of pollution load reduction scenarios in the Wujin River, which is one of the major inflow rivers of Taihu Lake. The model was calibrated for the year 2010 and validated for the year 2011. Various pollution load reduction scenarios were assessed using an analytic hierarchy process, and increasing rates of evaluation indicators were predicted using the Delphi method. The results showed that control of pollution from the source is the optimal method for pollution prevention and control, and the method of “Treatment after Pollution” has bad environmental, social and ecological effects. The method applied in this study can assist for environmental managers to select suitable pollution load reduction scenarios for achieving various objectives.

Sources and mass fluxes of the main contaminants in a heavily polluted and modified river of the North China Plain

Many rivers in China and other newly industrialized countries have suffered from severe degradation of water quality in the context of rapid economic growth. An accounting method was developed to investigate the source and mass fluxes of the main contaminants in the Ziya River, a severely polluted and heavily modified river in a semiarid area of the North China Plain, where chemical oxygen demand (COD) and ammonia nitrogen (NH4-N) were the most important indicators of pollution. The results showed that the urban sewage with high concentration of COD and NH4-N dominated the streams, contributing to 80.7 % of the streamflow, 92.2 % of COD, and 94.5 % of NH4-N. The concentrations of COD and NH4-N in streams varied from 24.0-195.0 to 5.8-43.8 mg/L, respectively. Mass fluxes of COD and NH4-N of all pathways were quantified. Much of the polluted water was diverted to irrigation, and some eventually flowed into the Bohai Sea. Installation of adequate wastewater treatment facilities and making strict discharge standards can help improve the water quality. Our findings imply that a simple accounting method provides an extremely well-documented example for load estimation and can be useful for intervention strategies in heavily polluted and modified rivers in newly industrialized countries.

Simulation of water environmental capacity and pollution load reduction using QUAL2K for water environmental management

In recent years, water quality degradation associated with rapid socio-economic development in the Taihu Lake Basin, China, has attracted increasing attention from both the public and the Chinese government. The primary sources of pollution in Taihu Lake are its inflow rivers and their tributaries. Effective water environmental management strategies need to be implemented in these rivers to improve the water quality of Taihu Lake, and to ensure sustainable development in the region. The aim of this study was to provide a basis for water environmental management decision-making. In this study, the QUAL2K model for river and stream water quality was applied to predict the water quality and environmental capacity of the Hongqi River, which is a polluted tributary in the Taihu Lake Basin. The model parameters were calibrated by trial and error until the simulated results agreed well with the observed data. The calibrated QUAL2K model was used to calculate the water environmental capacity of the Hongqi River, and the water environmental capacities of COD_Cr NH₃-N, TN, and TP were 17.51 t, 1.52 t, 2.74 t and 0.37 t, respectively. The results showed that the NH₃-N, TN, and TP pollution loads of the studied river need to be reduced by 50.96%, 44.11%, and 22.92%, respectively to satisfy the water quality objectives. Thus, additional water pollution control measures are needed to control and reduce the pollution loads in the Hongqi River watershed. The method applied in this study should provide a basis for water environmental management decision-making.