Runoff Pollution Control Research Articles

Characterizing nitrogen deposited on urban road surfaces: Implication for stormwater runoff pollution control

Nitrogen (N) is one of the most important pollutants on urban road surfaces. Understanding the N deposition forms, load characteristics, and influential factors can help to provide management and control strategies for road stormwater runoff pollution. This study focuses on a highly urbanized area in Guangzhou, China, and presents the characteristics of both dissolved and particulate N deposition forms as well as their correlations with land-use types and traffic factors. In addition, an artificial neural network (ANN) based classification model is utilized to estimate N pollution hotspot area and total nitrogen (TN) flux from road to receiving water bodies. The results showed that N on urban road surfaces mainly existed in the form of particulate organic nitrogen. Land use types dominated by residential area (RA) and urban village (UV) have higher TN build-up loads. Geodetector analysis indicated that land use has a greater impact on nitrogen build-up loads than traffic factors. Through classification and estimation using the ANN model, RA, and UV were classified as hotspot areas, and the TN flux from roads in the study area was calculated to be 3.35 × 105 g. Furthermore, it was estimated that the annual TN flux from roads in Guangzhou accounts for 19 % of the city's total urban domestic discharge. These findings are expected to contribute to the pollution control of stormwater runoff from urban road surfaces and provide valuable guidance for enhancing the ecological health of urban water environments.

Selection of low impact development technical measures in the distribution area of expansive soil: a case study of Hefei, China

Expansive soils are widely distributed around the world. They have significant characteristics of both hygroscopic expansion and water-loss shrinkage, which have caused serious damage to road paving, construction of low-rise houses, and construction of slopes along the banks of rivers. Similarly, the implementation of low impact development measures can cause considerable difficulties in the distribution area of expansive soil. The entire urban area of Hefei is situated on expansive soil. Although Hefei city has developed a sponge city plan, it has not been carried out on a large scale for implementation of low impact development technical measures. Experimental studies have shown that exposed expansive soils produce fissures that run up and down during wet and dry cycles. These fissures are extremely unfavorable to the infiltration of surface runoff formed by short-term heavy rainfall. This is also one of the reasons for short-term rainfall in Hefei city, resulting in serious flooding in low-lying areas with a poor drainage system. At the same time, initial rainfall is ineffective in cleaning up surface source pollution. Therefore, we can enhance the characteristics of expansive soil, keep the expansive soil unexposed, and maintain a certain level of humidity. These approaches can play a better role in the control of rainfall runoff and surface source pollution. The characteristics of expansive soils can be enhanced by mixing them with weathered sand, a physical improvement, to meet the technical requirements for infiltration, interception, and purification. It is recommended to carefully select low impact development measures in the distribution area of expansive soil to avoid the occurrence of wasteful investment and poor results.

Optimum urban runoff pollution control based on dynamic load calculation and effective control units identification – a case study in a highly urbanized basin in China

In the context of urban environmental challenges, urban runoff pollution, originating as a fundamental source of water pollution, remains a significant issue due to its widespread occurrence and sporadic release, which complicates precise monitoring and effective mitigation efforts. This study is dedicated to investigating prominent urban runoff pollution challenges in a highly urbanized basin located within the Guangdong-Hong Kong-Macao Greater Bay Area. Through a combination of field monitoring, statistical analyses, and modeling techniques, we present a comprehensive framework tailored to optimize control strategies for urban runoff pollution. The findings reveal variations in Event Mean Concentrations (EMCs) of ammonia nitrogen, ranging from 0.28 to 7.65 mg L-1, with distinct disparities observed across different rain events and land use categories. We delineated 431 drainage districts and organized them into 12 clusters based on similar discharge characteristics, which facilitates the establishment of a prioritized pollution control hierarchy. Subsequently, both the spatial and temporal load distributions were analyzed using EMC calculations, allowing us to determine a prioritized pollution control scheme that ranks units from level 1 to level 12. A 1-d mathematical model of target urbanized basin linking distributively discharged runoff pollution and dynamic river quality improvement has been established, and the dynamic simulation results ultimately demonstrate the importance sequence of managing runoff pollution discharges from 63 identified drainage districts, which accounts for 46.8% of the total urban runoff pollution load. This investigation provides a powerful research tool for urban runoff pollution control within extensive urban areas, offering valuable insights for the practical implementation of pollution control initiatives.

Design Issue Analysis and Operation Effect Evaluation of Large-Scale Storage Tank

In order to address the issue of combined sewer overflows (CSOs), W city has constructed a large-scale storage tank with a volume of 220,000 m3. The storage tank is planned for CSO control in the near term and stormwater runoff pollution control in the long term. However, the actual operation of the storage tank is unsatisfactory. This paper elucidates the design scheme and operation mode of the tank and analyzes the challenges encountered during its design and operation. A storm water management model (SWMM) model was constructed to simulate the effect of the storage tank working in a combined sewer system (CSS), a separate sewer system (SSS) and a decentralized storage situation. This study determined that during the 2022 rainy season, the actual reduction in pollutants by the storage tank was only about 60% of the designed value. As a result, the inadequate treatment capacity of the downstream wastewater treatment plant (WWTP) resulted in the water being retained in the tank for a long time, leading to unsatisfactory operation outcomes. If the storage tank works in SSS and the problem of water retention can be solved, it could reduce the total runoff volume by 30% and the total amount of pollutants by 40% during the same rainy season. At the same time, under the premise of constant total storage volume, if decentralized storage tanks were used to control runoff pollution, the reduction effect can be increased by up to 11.6% compared with that of the centralized storage.

Characterization of road-deposited sediment wash-off and accurate splitting of initial runoff pollution in heterogeneous urban spaces

Particulate materials arising from road-deposited sediments (RDS) are an essential target for the control and management of surface runoff pollution. However, the heterogeneity of urban spaces hinders the identification and quantification of particulate pollution, which is challenging when formulating precise control measures. To elucidate the factors that drive particulate pollution in heterogeneous urban spaces, the accumulation of RDS on dry days and the total suspended solids during six natural rainfall events were investigated across three urban–rural spatial units (central urban, central suburban, and remote suburban). The underlying surface type (asphalt or cement roads) and particle size composition jointly determined the spatial heterogeneity in the static accumulation and dynamic output loads of RDS during rainfall. These two factors explained 59.6% and 18.9% of the spatial heterogeneity, respectively, according to principal component analysis. A novel CPSI exponential wash-off equation that incorporates particle size composition and underlying surface type was applied. It precisely described the spatial heterogeneity of RDS wash-off loads, the estimated values exhibiting event mean concentration errors of 10.8–18.2%. When coupled with the M(V) curve, this CPSI exponential wash-off equation more precisely split the initial volume of runoff: a lower total volume (17.6–38.0%) was shown to carry a higher proportion of the load (70.0–93.7%) compared to the traditional coupled exponential wash-off equation (volume: 31.6–49.0%, load: 37–90%). This study provides a new approach to characterizing RDS wash-off processes and splitting initial runoff in heterogeneous spaces.

Roof runoff pollution control with operating time based on a field-scale assembled bioretention facility: Performance and microbial community dynamics

Bioretention facilities are essential, low-impact development measures to treat roof runoff pollution. To explore the effects of roof runoff pollution control and internal influencing mechanisms of field-scale bioretention facilities, a newly assembled bioretention facility (ABF) comprising volcanic rock and coconut coir was constructed. The results of the 21-month experiment showed that the peak concentrations of total suspended solids (TSS), ammonia nitrogen (NH4+–N), and chemical oxygen demand (COD) of roof runoff were 332.50 mg∙L−1, 3.46 mg∙L−1, and 122.33 mg∙L−1, respectively, indicating that the roof runoff was seriously polluted and needed urgent treatment. The removal rates of TSS, NH4+–N, and COD within the facility were 86.50 ± 7.31 %, 79.40 ± 19.28 %, and 51.84 ± 26.24 %, respectively. However, continuous and high-intensity rainfall decreased pollutant removal performance by weakening the adsorption effect of the media. Continuous pollutant input decreased the abundance of Arthrobacter and Hyphomicrobium within the media, and functional bacteria, such as KD4–96, Roseiflexaceae, Vicinamibacteraceae, and Gaiellales, played dominant roles in NH4+–N and COD removal to ensure the long-term stability of the facility. This study provides theoretical guidance and a practical basis for enhancing the application of ABF in mitigating roof runoff pollution.

Tributaries protect the water quality of central lake in an artificial spiderweb-structured water system, from the perspective of runoff pollution control

Urban lakes are often disconnected to the surrounding rivers, and they are affected by rainfall runoff pollution. This study focused on an artificial lake-river system in Shanghai featuring a spiderweb-structure, it is expected to detect whether the tributaries in such a system made a protective and buffering effect on the lake under the impact of rainfall runoff. A hydrodynamic model was established using MIKE 21, one of the most widely used software which can conduct two-dimensional modeling of water quality changes in surface water, to simulate the changes of total nitrogen (TN) and total phosphorus (TP), the key indicators causing lake eutrophication, under different rainfall events. The results showed that, under various conditions, storm events almost have no first or final effect on the central lake, TN and TP in the lake were improved by 5%–18% and 1%–12% among monitoring stations. However, Obvious negative effects were displayed in the water quality of radial – circular tributaries, and the first effects in circular tributaries were more serious than those on the radial because their difference in hydrological condition. With the increase of rainfall intensity, the peak value of the pollutant concentration in circular rivers increased 63%–185% as compared with the initial. As to final effects, some circular rivers were significantly impacted, and the pollutant concentration increased by approximately 40% in the seventh day as rainfall started. It was deduced that tributaries played as protective buffer against pollutants in this spiderweb water system, in that pollutants would be degraded in such dense spiderweb-structured river systems before entering the central lake, and rainfall runoff would also accelerate the flow in rivers and lakes. Therefore, the paper hold that, the central lake could not be separated from the radial – circular tributaries, and the officially planned pumps and sluices in the river estuaries would not be recommended. This study would provide technical support for the planning, construction and ecological protection of artificial urban lake-river system in similar areas.

Stormwater runoff pollution control performance of permeable concrete pavement and constructed wetland combined system: toward on-site reuse.

Urban waterlogging and the deterioration of receiving water quality caused by stormwater runoff have become increasingly significant problems. Based on the concept of combining grey and green infrastructure, a combined permeable concrete pavement (PCP) and constructed wetland (CW) system has been developed to treat stormwater runoff and enable on-site reuse. The results showed that the removal rate of suspended solids (SS) by PCP ranged from 96.61 to 99.20%; however, the chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) concentrations in the effluent did not meet the standards required for rainwater reuse. For the combined PCP-CW system, the removal rates of COD, TN and TP by the CW were 48.45-75.12%, 47.26-53.05%, and 59.04-75.28%, respectively, under different hydraulic loading (HL) rates; thus, the effluent TN concentrations did not consistently meet the reuse standards. Further optimization of aeration in different parts of the CW revealed that aeration in the middle and front sections of the wetland had the most significant effect on pollutant removal, under which the TN concentrations in the effluent met the standard required for reuse. The effluent from the combined PCP-CW system was able to fully meet the stormwater reuse standards under these optimized conditions, and the reuse of urban stormwater runoff can therefore be realized.

Optimized strategies of green and grey infrastructures for integrated control objectives of runoff, waterlogging and WWDP in old storm drainages

Frequent waterlogging occurs in old high-density urban areas where the sewage is inappropriately connected to storm drainages, resulting in serious wet weather discharge pollution (WWDP). To address urban waterlogging and runoff, the optimization of green infrastructures (GIs) and grey infrastructures (GRs) has been proposed to improve rainwater management efficiency. However, most strategies neglect WWDP and fail to achieve integrated control of runoff, waterlogging, and discharge pollution. In the present study, a new optimization method was introduced to identify optimal solutions for renovating outdated storm drainage systems, considering the management of discharge pollution in wet weather. A case study in Shanghai, China was conducted to demonstrate the application of the method. The cost-benefit index (CBI) of optimized GIs (0.06) was lower than that of optimized GRs (2.78) under 22.2 mm rainfall (no runoff and WWDP), but the costs of the former were only half those of the latter. In a 5-year return period storm (no waterlogging), optimized GIs had a significantly higher CBI (2.85 times) compared to optimized GRs, costing only 44 % of the latter. When WWDP reached the control objective (COD≤70 mg/L), the optimized GIs needed to be further optimized with GRs. The CBI of optimized GI-GRs was higher than GRs by 2.50, and the cost was 58% of the latter. In areas with frequent low-intensity rainfall, optimized GIs and GRs should be selected based on local cost or benefit requirements for drainage reconstruction. In high-intensity storm-prone areas, the optimized GI-GR combination should be selected for drainage reconstruction. The proposed method can compensate for the shortcomings of existing optimization methods in controlling WWDP for the reconstruction of old storm drainages.

Numerical study on regime shifts in an urban subtropical shallow lake: Xinglong Lake, China

Aquatic ecosystem degradation is a considerable challenge of global interest. Although substantial efforts have been accomplished to restore phytoplankton-dominated shallow lakes to a clear state with high coverage of submerged macrophytes, the phenomenon, driving mechanism, and threshold range of such nonlinear regime shifts remain unclear. Here, we constructed an aquatic ecological model based on PCLake, simulated and predicted the aquatic ecological changes before and after treatments of Xinglong Lake, a subtropical artificial shallow lake that had been completed ecological restoration in Chengdu, China. The model included the future prediction of TN, TP, Chl-a, and aquatic vegetation biomass, as well as the threshold of regime shifts using bifurcation analysis. We also quantified the impact of some common management measures (point and non-point source pollution control, water level regulation) on the stability of the lake's aquatic ecosystem. The results showed that the thresholds of Xinglong Lake from a clear state to a turbid state were 1.405 mg/m2/day and vice versa 0.68 mg/m2/day, indicating its initial turbidity and transitional state after treatment. After treatment, phosphorus loads still exceeded the threshold for a clear-water state, while the non-point source pollution of Xinglong Lake accounted for more than 80%. To prevent the aquatic ecosystem from collapsing in the future, it is necessary to combine upstream water quality improvement, runoff and air pollution control to reduce total pollution by 60%. Reasonable water level regulation, such as adjusting the water level downwards by 0.5 m in spring, is beneficial in maintaining the health and stability of aquatic ecosystems. The present study can be used to evaluate the effectiveness of the management measures of Xinglong Lake as well as to provide scientific support for the management of shallow lakes.

Assessing the characteristics of different-sized particles in the first flush of roof runoff.

The first flush occurs during urban runoff events. In this study, we aimed to assess the characteristics of different-sized particles in the first flush of roof runoff, and runoff was collected from an asphalt roof (AR), metal roof (MR), and cement roof (CR) for analysis. There were no clear patterns in the particle size distributions in the runoff from the three roofs and were affected by several factors. The strength of the first flushes differed significantly for particles in different size categories in AR, MR, and CR runoff and were very different from suspended solids (SS). The comparison showed that it would be possible to meet the SS control design expectation required by the Chinese national standard for runoff pollution control (VFF = 3 mm) for particles <45 μm but not for particles >45 μm. The methods presented provide an alternative for assessing the ability to control the transport of different-sized particles in runoff.

Optimizing first flush diverter for urban stormwater pollution load reduction by most efficiently utilizing first flush phenomena

In order to find the optimal design of first flush diverter, this study shifts the focus of first flush research from the existence of first flush phenomenon to utilization effect of the phenomenon. The proposed method consists of four parts: (1) key design parameters, which describing key structure of first flush diverter rather than first flush phenomenon; (2) continuous simulation, which replicating the uncertainty by using the full scope of runoff events that might occur over the years analyzed; (3) design optimization, through an overlapped contour graph of key design parameters and key performance indicators that are relevant to but different from conventional indicators describing first flush phenomena; (4) event frequency spectra, which presenting the diverter's behavior at daily temporal resolution. As an illustration, the proposed method was used to determine design parameters of first flush diverters for roof runoff pollution control in the northeast of Shanghai. The results show that annual runoff pollution reduction ratio (PLR) was insensitive to buildup model. This greatly reduced the difficulty of buildup modeling. The contour graph was useful in finding the optimal design, i.e., the optimal combination of design parameters that could meet PLR design goal with most concentrated first flush on average (quantified by MFF). For instances, the diverter could achieve PLR = 40% with MFF >1.95, and PLR = 70% with MFF = 1.7 at most. Pollutant load frequency spectra were generated for the first time. They showed that a better design reduced pollutant load more stably while diverting less volume of first flush within almost each runoff day.

New conceptualization and quantification method of first-flush in urban catchments: A modelling study

A major challenge for runoff pollution control lies in the quantification and identification of the first-flush. At present, there is a lack of reasonable theoretical methods to guide engineering practices. To remedy this deficiency, a novel method of cumulative pollutant mass vs. cumulative runoff volume (M(V)) curve simulation is proposed in this study. Subsequently, the first-flush phenomenon was redefined based on the M(V) curve simulation and demonstrate that the first-flush exists until the derivative of the simulated M(V) curve is equal to 1 (Ft′ = 1). Consequently, a mathematical model for first-flush quantification was developed. The Root-Mean-Square-Deviation (RMSD) and Pearson's Correlation Coefficient (PCC), as objective functions, were used to evaluate the performance of the model and the Elementary-Effect (EE) method was used to analyze the sensitivity of the parameters. The results indicated the satisfactory accuracy of the M(V) curve simulation and first-flush quantitative mathematical model. The NSE values exceeding 0.8 and 0.938, respectively, were obtained by analyzing 19 rainfall-runoff data for Xi'an, Shaanxi Province, China. The wash-off coefficient “r” was demonstrably the most sensitive factor influencing the model performance. Therefore, interactions between “r” and the other model parameters should be focused on to highlight the overall sensitivities. Overall, this study posits a novel paradigm shift from the traditional dimensionless definition criterion to redefine and quantify first-flush, which has significant implications for urban water environment management.

Removal, migration, and distribution of naphthalene in bioretention facilities: the influences of particulate matter.

Particulate matter (PM), as an important carrier of carrying and transporting runoff pollutants, can significantly affect the behavior and removal efficiency of pollutants in bioretention facilities. In order to control the pollution caused by naphthalene in bioretention facilities, the removal efficiency and migration characteristics of naphthalene were systematically investigated under the influences of PM. The results showed that the removal efficiency of naphthalene was 74 ~ 97% in bioretention facilities under the influences of PM. With the higher concentration, the lower rainfall return period, and the longer antecedent drying period, the removal efficiency of naphthalene in each medium layer were higher. Furthermore, the PM could increase the naphthalene adsorption capacity onto medium in the first 10cm depth, which showed more than 80% removal efficiency and lower mobility of naphthalene. The removal efficiency of naphthalene was significantly higher (90 ~ 97%), when the particle size and concentration of PM were 0 ~ 45μm and 500mg/L, respectively. This study investigated the important role of PM for naphthalene removal in bioretention facilities, and provided effective guidelines for runoff pollution control, design of stormwater facilities, and assessment risk of naphthalene.

Evaluation of the comprehensive efficiency of the interception pipeline in the urban rainwater pipe network for the initial rainwater collection and storage

Urban runoff pollution has become one of the important limiting factors hindering the continuous improvement of water environment. In the process of drainage system reconstruction, the evaluation of interception pipeline for the collection and storage efficiency of initial rainwater is an important work. Therefore, this study uses the analytic hierarchy process to establish an evaluation system and method containing 4 first-level indicators and 10 second-level indicators to evaluate the comprehensive efficiency of the interception pipeline for initial rainwater collection and storage. Taking the interception pipeline in a drainage system in Shanghai as a case study, the established evaluation method was adopted to evaluate it, and the comprehensive indexes under the rainfall return periods of 0.5 year, 1 year, 3 years and 5 years were calculated. The results indicated that the evaluation method could be well applied to the effectiveness evaluation of intercepting pipelines in drainage systems, and could provide technical support for the planning and design of urban runoff pollution control projects in the future.

Study on Multi-Objective Optimization of Sponge Facilities Combination at Urban Block Level: A Residential Complex Case Study in Nanjing, China

Urban block-scale sponge system design needs address how to specify the optimal approach to combine the number of areas and types of sponge facilities for diverse land conditions and sponge system design objectives, while ensuring sponge performance and economic efficiency. With the gradual application of multi-objective optimization algorithms in the design of sponge cities, multi-objective combinatorial problem solving for sponge facilities based on optimization algorithms is more accurate and efficient than traditional design methods based on the designer’s experience. This study utilizes a residential complex in Nanjing as a practical example, selects six types of typical sponge facilities to construct a multi-objective optimization combination model for sponge facilities, and employs the SPEA-2 algorithm to determine the optimal combination of sponge facility types and quantities. Finally, 186,754 combinations of sponge facilities were calculated. For the three sponge objectives of optimal performance and economy for stormwater infiltration and storage, optimal performance and economy for runoff pollution control, and optimal average overall performance for stormwater infiltration, runoff pollution control, and economy, a number of combinations of sponge types and numbers were obtained.

Influence of urban runoff pollutant first flush strength on bioretention pollutant removal performance.

Bioretention is commonly used for runoff pollution control. The first flush strength of pollutants can affect bioretention performance. To examine the influence of the first flush strength on bioretention performance, bioretention columns filled with garden soil as the main media were established. Activated carbon and water treatment residuals (WTR) were added and compared for their ability to enhance phosphorus removal. Waste edible fungus culture medium (WEFCM) as a carbon source was also explored. When WEFCM was used as a carbon source instead of wood chips, total nitrogen (TN) removal increased from 60.83 ± 21.22 to 62.21 ± 16.43%, but chemical oxygen demand (COD) leaching was observed. WTR was better able than activated carbon to enhance phosphorus removal (87.97 ± 8.87 vs. 81.66 ± 9.27%) without impacting TN removal. NH4+-N removal increased with increasing first flush strength, but there was no trend for suspended solids (SS), COD, TN, or total phosphorus. First leaching phenomenon in bioretention outflow was proposed in this study. A low first leaching was observed in the outflow when the inflow had a uniform pollutant mass (i.e., no first flush) because of media leaching. A weak first leaching outflow was observed for SS and COD when they were present at strong first flush inflow.

The Role of Spatial Patterns of Low Impact Development in Urban Runoff Pollution Control Within Parcel Based Catchments

Landscape patterns significantly affect urban runoff pollution, and a reasonable arrangement of pervious patches in urban catchments is critical to control urban non-point-source pollution. Low impact development (LID) can be recognized as a pervious surface type, and many previous studies have analyzed the LID performance at a system scale. However, the influence of the LID spatial distribution on runoff pollutant transport at a catchment scale remains unclear. This study analyzed the influence of pervious/impervious patterns on runoff pollution within two urban catchments constructed with LID. It was found that the runoff pollution was influenced by the area ratio, circumference, shape, and pervious patch connectivity of pervious surfaces (i.e., LID). Catchments with high perviousness ratios are more efficient in reducing the runoff volume and suspended solids, and LID should focus on removing runoff pollutants at catchments with high imperviousness ratios. Six typical landscape metrics that represented the fragmentation, complexity and vergence of pervious surfaces were selected to investigate the influence of pervious/impervious patterns on runoff pollution. The results show that larger fragmentation, smaller complexity and smaller vergence of pervious patches result in larger runoff volumes and more pollutants. Therefore, it is recommended that large pervious areas should be retained and close to one another to enhance the retention capacity of LID, and the outline of pervious patches should be long and irregular to reduce pollution confluence. The results of this study are helpful in arranging LID structures for efficient runoff regulation and pollution control at an urban catchment scale.

Combination of Ecological Ditch and Bioretention Pond to Control Rural Runoff Pollution

Ecological ditches and bioretention ponds have received widespread attention and application due to their runoff pollution control capabilities and ecological benefits. However, a single ecological ditch or bioretention pond often has problems, such as unstable nitrogen and phosphorus removal and substrate clogging in rural runoff pollution control. Thus, we connected the two facilities in a series to construct a combined system, using the ecological ditch to pretreat, therefore reducing the pollution load of the bioretention pond and mitigating substrate clogging. At the same time, the submerged area was set and an external natural carrier carbon source was added in the bioretention pond to improve the nitrogen removal. The effects of the carrier carbon source, rainfall intensity, and alternating wet and dry conditions on the control of rural runoff pollution by the combined system were explored. The results showed that adding straw and sawdust as carrier carbon sources could increase the TN removal of the bioretention pond by 19.9% and 20.4%, respectively. When the simulated rainfall intensity increased from light rain to heavy rain, the removal efficiencies of COD, NH4+-N, TN, and TP in the combined system with external carbon source decreased by 17.0%, 16.8%, 20.4%, and 17.2% on average, respectively. The contribution of the ecological ditch to the removal of the four pollutants decreased by 16.3%, 13.0%, 24.2%, and 22.1% on average. Alternating dry and wet operation can improve the pollutant removal. Compared with continuous inflow, the average TN removal of the sawdust group increased by 12.3% after three weeks of drought. The results of microbial community analysis showed that the α-diversity of the bioretention pond in the sawdust group and the straw group was higher than that in control group. The abundance of Thiobacillus was significantly higher in the submerged area of bioretention ponds with carbon sources than that in the control group. These research results are expected to provide technical support for the practical application of the combined system.

The Response of Runoff Pollution Control to Initial Runoff Volume Capture in Sponge City Construction Using SWMM

Source facilities can manage stormwater runoff pollutants while also limiting runoff volume in China’s sponge city construction. However, there is no apparent link between source volume control and runoff pollution reduction. This research uses SWMM to develop a model based on the basic data of a city’s catchment zone in northern China in order to statistically examine the response relationship between the initial runoff volume capture of sponge city construction and the reduction effect of stormwater runoff pollution. Based on the dimensionless constant of the runoff pollution control curve, we suggested a novel approach for evaluating runoff pollution control effectiveness. This method was used to examine the response relationship between runoff volume control and runoff pollution control in three typical initial runoff volume capture facilities in the study area, namely bioretention, permeable pavement, rain barrels, and terminal storage tanks, under various design rainfall conditions. The dimensionless constant (Dc) has good practical application value and can quantitatively quantify the control effect of various facilities on stormwater runoff pollution. The Dc value of the source facilities is higher than that of the terminal control facilities, indicating that the source facilities have a higher ability to reduce rainwater runoff pollution than the terminal facilities, particularly the infiltration facilities. The research ideas and evaluation methods proposed in this paper provide an alternative approach for selecting and optimizing facilities during the planning and designing stages of sponge city construction, which can also be used in the monitoring and evaluation stage after completion to carry out a more effective evaluation of sponge facilities’ effects.