Assimilative Capacity Of Water Bodies Research Articles

Successful Water Quality Improvement Practices of a Campus’s River in Ningbo Based on Water Replenishment and Circulation Since Year 2017

Rivers play a critical role in regional water quality, but from time to time concentration of surface water pollutants can easily exceed both national and local water standards. This study debates the feasibility and effectiveness of utilizing the natural treatment potential of flowing river water by replenishing treated sewage effluent and forced circulating. The research combines field experiments and laboratory analyses to assess the impact of this approach on water quality. Theoretical simulation with one-dimension modeling recommended by China’s national standard of “Code of Practice for Computation on Allowable Permitted Assimilative Capacity of Water Bodies” (GB/T 25173-2010) indicates that the target campus river water’s cycle flowing contributes to the further removal of key pollutants from treated sewage, resulting in the improvement of campus river’s water quality downstream along its forced circulation. NH3-N and CODMn levels of the campus’s river water were notably reduced and met the planning water qualities as expected.

Interactive Allocation of Water Pollutant Initial Emission Rights in a Basin under Total Amount Control: A Leader-Follower Hierarchical Decision Model.

The initial emission rights allocation is the key measure to achieve the goal of total amount control and deepen the emission trading system. Although many studies have focused on the modeling of initial emission rights allocation, such as using game theory and multi-objective optimization methods, few studies have observed the hierarchical relationship of mutual interference and restriction between watershed management agency and local governments in each subarea during allocation. This relationship directly affects the rationality of the results of regional emission rights allocation. In this study, a leader-follower hierarchical decision model (LFHDM) for allocating initial emission rights in a basin is developed. Based on the bilevel programming approach, the model simulates the interactive decision-making process between the watershed management agency of the upper-level model (LFHDM-U) and the local government of the lower-level model (LFHDM-L) in the allocation under total amount control. A case study of China's Yellow River Basin is conducted to demonstrate the feasibility and practicality of the model. Findings reveal that, compared with the single-level model, the developed LFHDM has higher satisfaction with the allocation scheme. Under different scenarios, the overall satisfaction of the configuration schemes of COD and NH3-N in each province and autonomous region remains above 0.9. In addition, the allocation volumes of COD and NH3-N in each province of the Yellow River Basin in planning year increase with the enhancement of allowable assimilative capacity of water bodies, but the interval gap of satisfaction with allocation schemes gradually narrows. It shows that when the allowable assimilation capacity of a water body is low, the decision-making of the allocation scheme needs to be more cautious. Moreover, for the Yellow River Basin, apart from Qinghai and Sichuan, the task of reducing water pollutants in other provinces in the next few years is very arduous. The average reduction of total COD and NH3-N in the basin is about 48% and 46%, respectively.

Interval two-stage stochastic programming model under uncertainty for planning emission rights trading in the Yellow River basin of China.

As a critical way to realize the optimal allocation of water environment capacity resources in the basin, emission rights trading faces multiple uncertainties, making it extremely hard and challenging to formulate appropriate decisions and plans. Therefore, this study uses interval two-stage stochastic programming (ITSP) method to model the emission rights trading process with multiple uncertainties. It can promote the secondary optimal allocation of the emission rights between the demander and the supplier after the initial allocation. Externalities caused by environmental problems are internalized through the form of emission rights trading, thereby reducing the transaction costs and promoting the coordination and integrity of water pollution control among governments in a basin. Finally, the Yellow River basin is taken as an example for case analysis. The results show that the net revenue of emission rights system in the transaction status is better than that in the non-transaction status, and the average gap of net income reaches [171.031, 193.056] billion yuan. Under different reduction policies, the average water pollutant emission reduction in transaction status is [451.15, 628.34] thousand tons, which is generally less than [516.57, 670.05] thousand tons in non-transaction status. As policies get stricter and assimilative capacity of water bodies dwindles, reduction shrinks, leading to higher risks and economic loss from being unable to meet the discharge demand. When reduction policies are relatively loose and assimilative capacity is high, emission rights trading volume peaks. At this time, the trading volume of COD reached [29.05, 40.76] thousand tons, and that of NH3-N reached [3.74, 4.31] thousand tons. All these findings will offer insights for decision-makers on how to strike a balance between economic benefits and emission rights trading plans in the Yellow River basin.

Discussion on Zero-dimension Model and Designed Hydrological Conditions in Calculation of Water Pollution Capacity

In order to implement the strictest water resource management system and ensure the sustainable utilization of water resources, it is necessary to carry out the work of limiting pollution in water function area. The calculation of water pollution capacity is the basis of pollution limitation in water function area. Code of practice for computation on allowable permitted assimilative capacity of water bodies (GB/T25173-2010) is the main reference basis for the calculation of water pollution capacity. There are some limitations in the practical application. In this paper, the zero-dimensional model is modified based on the current code of pollutant carrying capacity. And the determination of designed hydrological conditions was discussed. This would give reference for the calculation of water pollution capacity.

Numerical Simulation of Highly Saline Wastewater Discharge into Water Objects to Improve Discharge Devices

The expansion of large-tonnage chemical production (primarily, of mineral fertilizers) calls for the development of new methods for discharging excess brines into surface water objects. This task is complicated by the fact that, due to the suppression of vertical turbulent pulsations, “heavy” brines may spread over considerable distances in the near-bottom region without any significant decrease in their concentration. Some suggestions for optimizing exhaust structures designed to discharge wastewater containing heavy impurities are proposed based on numerical modeling. The calculations based on solving the three-dimensional problem with different wastewater discharge conditions have shown the structures providing location of exhaust devices near the reservoir surface to be the most efficient ones. However, such structures are difficult to implement in a certain reservoir section. In this case, an easy-to-implement and quite efficient configuration is that including bottom arrangement of exhaust devices and selective intake of highly saline wastewater from sludge storage facilities. Irrespective of the chosen scheme for disposal of highly mineralized wastewater, their discharge must be carried out in strict coordination with the hydrological regime of water intake. This approach will provide the most efficient use of the assimilative capacity of water body and the best way to reduce the ecological impact on both the water body and the environment.

GIS-based Assessment of the Assimilative Capacity of Rivers in Dnipropetrovsk Region

The objective of this paper is to identify the level of changes in the ecological status of surface reservoirs of Dnipropetrovsk region under the impact of anthropogenic factors and to find a rationale for the limit loads on aquatic ecosystems, based on a quantitative assessment of their assimilative capacity values using GIS-technologies.To characterize and evaluate economic activity in the river basins of Dnipropetrovsk re- gion, the data of state statistical reporting by the form of 2-TP "Water resources management" of the State Agency for Water Re- sources of Ukraine were used. Parameters characterizing the assimilative capacity of water bodies were determined by taking into consideration the perennial average values of river runoff resources of the priority watercourses of Dnipropetrovsk region in the years with varying degrees of supply: with an average (50%), a low (75%) and a very low (95%) river water content. The main indicators characterizing the assimilative capacity of the water bodies of Dnipropetrovsk region are actual and necessary multiplicity of waste- water dilution, the limit to assimilative capacity of surface reservoirs, index of assimilative capacity utilization of river runoff re- sources of varying degrees of supply. A classification that characterizes the level of assimilative capacity utilization for water bodies is proposed. The level of assimilative capacity utilization of the Dnipro River in the reservoir areas, regardless of the degree of river runoff supply, is estimated as “allowable” . At 95% degree of river runoff supply, the level of assimilative capacity utilization of the Oril and Vovcha Rivers is characterized as “moderate”, the Samara River (after the confluence with the Vovcha River) as “high” and the Ingulets River with tributary the Saksagan River, and the Samara River (before confluence with the Vovcha River) as “veryhigh”. It should be noted that irrespective of the level of river runoff supply, the index of assimilative capacity utilization of the Samara River (before its confluence with the Vovcha River) exceeds the limit value by 19-115 times. For the spatial analysis of hydrological parameters and visualizion of the data in the form of thematic maps, the geoinformation system “Rivers of Dnipropetrovsk region” was developed on the basis of the ESRI ArcGIS Desktop10 software package. Using the geoprocessing tools, on the basis of hydrological indices of 7 priority watercourses for each of the 22 administrative-territorial districts of Dnipropetrovsk region, the main indicators characterizing the assimilative capacity of water resources were calculated and ranked. The use of indicatorscharacterizing the assimilative capacity of river runoff resources allows us to identify the threshold levels of anthropogenic transfor- mation of aquatic ecosystems, develop and implement environmental measures to improve the ecological status and ensure environ- mental safety of surface reservoirs.

Analysis of auto-purification response of the Apies River, Gauteng, South Africa, to treated wastewater effluent

The assimilative capacity of water bodies is an important factor in the integrated management of surface water resources. The current study examined the auto-recovery processes of the Apies River from wastewater discharged into it from a municipal wastewater treatment facility, using a series of equations, including the modified Streeter-Phelps equation. Field data obtained include dissolved oxygen (DO), temperature, stream velocity, depth, and width. Water samples were also obtained at 10 sampling stations for the determination of biochemical oxygen demand (BOD) using standard methods. It was observed that the DO and BOD level (5.59 mg/L and 8.5 mg/L respectively) of the effluent from the wastewater treatment facility indicated better water quality than the Apies River background DO level (5.42 mg/L) and BOD level (13 mg/L). Also, at 270 m downstream of the effluent discharge point, another effluent stream (Skinnerspruit) adversely impacted on the Apies River with DO and BOD levels of 6.5 mg/L and 9.0 mg/L, respectively, compared to the Apies River background values of 6.81 mg/L and 8.0 mg/L, respectively. The stream, however, recovered well from both the background and imposed pollution sources as it had a computed positive auto-recovery factor of 1.74. Furthermore, the measured DO deficit was plotted against predicted DO deficit. The plot revealed a close match between the measured and predicted DO deficit, indicating that the model could be used for predicting DO deficit along other segments of the river. To further improve on the natural auto-recovery processes of the Apies River, it was recommended that flow along the Skinnerspruit should be enhanced by clearing the observed aquatic plants growing within the channel. Also, suspected pollution activities taking place further upstream on the Apies River should be investigated and appropriately addressed.

New model to assessing nutrient assimilative capacity in plant-dominated lakes: Considering ecological effects of hydrological changes

Assessing nutrient assimilative capacity of water body is an essential component of the Total Maximum Daily Load program. Nutrient assimilative capacity of lakes is affected by hydrological changes through physical effects on the dilution capacity of water body and ecological effects on nutrient removal processes. Previous research has focused on the effects of hydrological changes on dilution capacity, but rarely considered the ecological effects on nutrient assimilative capacity. In this study, a process-based model considering both ecological effects and dilution effects of hydrological changes is proposed for assessing nitrogen and phosphorus assimilative capacities of plant-dominated lakes. Plant uptake and biological denitrification are two crucial nutrient removal processes. Water depths in a lake affect plant growing area. Lake submerged condition affects nutrient accumulation capacity of plants and the intensity of biological denitrification. The model considered dynamic variations of lake water depths and submerged condition, and the associated effects on nutrient removal by plant nutrient uptake and biological denitrification in lake systems. It is a discrete 0D model depending on a small amount of data and has satisfactory simulation accuracy. We chose the largest freshwater lake in northern China (Baiyangdian Lake) as a case. The annual total assimilative capacity in the lake was 1536t for nitrogen and 157t for phosphorus. Assimilative capacity during plant-growing season accounted for over 90% of the annual total capacity. The results determined by the new model were less than half of that from previous model, demonstrating the significance of considering ecological effects of hydrological changes. The new assessment model offers a useful tool for directing pollutant emission control and eutrophication prevention in global plant-dominated lakes.

The uncertainty effects of design flow on water quality management

In water quality management, pollution control strategies have been sought to accord with the assimilative capacity of water bodies so as to preserve water quality. The waste load allocation (WLA) is a useful approach to determine the allowable loading of pollution sources in water quality management. For any WLA, a particular water body condition is needed as a basic scenario under which the relevant parameters are fixed. The particular flow rate is known as design flow and usually set at low flow in order to be protective. The design flow is traditionally a particular deterministic value, such as Q (75), implying that it is expected that the probability of water quality violation is 25% in the long run. However, this long-term expectation might not be realized in individual years due to variability of natural flow. The flow variability will make a WLA plan overoptimistic or over-conservative in different years, suggesting that the deterministic design flow without uncertainty consideration might lead to an ineffective or inefficient decision-making. To address the problem, we explicate the relationship between flow variability, design flow and water quality with different flow distributions to facilitate the understanding of the process of a WLA. In order to manifest the uncertainty effects of design flow, the results from the annual flow duration curve (AFDC) is compared with the conventional flow duration curve (FDC). The AFDC approach is capable of obtaining the uncertainty level of the design flow by generating the confidence interval rather than a fixed value. The effect of different record lengths on design flow determination is estimated as well. Finally, a refined WLA process is proposed with a re-examination of water quality violation to improve the allocation decision under uncertainty. TaHan River Basin in northern Taiwan is used as a case study.

A Time Adaptive Grid on the QUAL2E Water Quality Model

Water quality models are used extensively for maintaining and monitoring the waste assimilative capacity of water bodies when these bodies are exposed to conta…