Aug 2017, Volume 11 Issue 4

Cover illustration

  • Cover story (see: Nanqi Ren, Qian Wang, Qiuru Wang, Hong Huang& Xiuheng Wang, 2017, 11(4):9)
    Facing the pressure of excessive water consumption, high pollution load and rainstorm waterlogging, linear and centralized urban water system, system 2.0, as well as traditional governance measures gradually exposed characters of water-sensitivity, vulnerability and unsustainability, subsequently re [Detail] ...

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    Haifeng Jia, Shaw L. Yu, Huapeng Qin
    Isam Alyaseri, Jianpeng Zhou, Susan M. Morgan, Andrew Bartlett

    Impacts of rain gardens on stormwater were evaluated through field monitoring.

    Statistical analysis is vital to evaluate field collected data.

    Due to rain gardens, pollutant levels increased initially, but decreasedover time.

    E. colilevel decreasedfrom the beginning after rain gardens were installed.

    Rain gardens could result in 76% stormwaterreduction in affected combined sewers.

    Green infrastructures such as rain gardens can benefit onsite reduction of stormwater runoff, leading to reduced combined sewer overflows. A pilot project was conducted to evaluate the impact of rain gardens on the water quality and volume reduction of storm runoff from urban streets in a combined sewer area. The study took place in a six-block area on South Grand Boulevard in St. Louis, Missouri. The impact was assessed through a comparison between the pre-construction (2011/2012) and the post-construction (2014) phases. Shortly after the rain gardens were installed, the levels of total suspended solids, chloride, total nitrogen, total phosphorous, zinc, and copper increased. The level of mercury was lower than the detection level in both phases. E. coliwas the only parameter that showed statistically significant decrease following the installation of rain gardens. The likely reason for initial increase in monitored water quality parameters is that the post-construction sampling began after the rain gardens were constructed but before planting, resulted from soil erosion and wash-out from the mulch. However, the levels of most of water quality parameters decreased in the following time period during the post-construction phase. The study found 76% volume reduction of stormwater runoff following the installation of rain gardens at one of studied sites. Statistical analysis is essential on collected data because of the encountered high variability of measured flows resulted from low flow conditions in studied sewers.

    Haifeng Jia, Zheng Wang, Xiaoyue Zhen, Mike Clar, Shaw L. Yu

    Barriers and challenges of Sponge City construction were presented.

    Several key technical points on Sponge City implementation were discussed.

    Recommendations on Sponge City implementation strategy are proposed.

    Since 2014, China has been implementing the Sponge City Construction initiative, which represents an enormous and unprecedented effort by any government in the world for achieving urban sustainability. According to preliminary estimates, the total investment on the Sponge City Plan is roughly 100 to 150 million Yuan (RMB) ($15 to $22.5 million) average per square kilometer or 10 Trillion Yuan (RMB) ($1.5 Trillion) for the 657 cities nationwide. The Sponge City Plan (SCP) calls for the use of natural processes such as soil and vegetation as part of the urban runoff control strategy, which is similar to that of low impact development (LID) and green infrastructure (GI) practices being promoted in many parts of the world. The SCP includes as its goals not only effective urban flood control, but also rainwater harvest, water quality improvement and ecological restoration. So far, the SCP implementation has encountered some barriers and challenges due to many factors. The present paper presents a review of those barriers and challenges, offers discussions and recommendations on several technical aspects such as control goals and objectives; planning/design and construction of LID/GI practices; performance evaluation. Several key recommendations are proposed on Sponge City implementation strategy, Site-specific regulatory framework and technical guidance, Product innovation and certification, LID/GI Project financing, LID/GI professional training and certification, public outreach and education. It is expected that the successful implementation of the SCP not only will bring about a sustainable, eco-friendly urbanization process in China, but also contribute enormously to the LID/GI research and development with the vast amount of relevant data and experiences generated from the Sponge City construction projects.

    Shiting Ren, Mengchen Li, Jianyu Sun, Yanhong Bian, Kuichang Zuo, Xiaoyuan Zhang, Peng Liang, Xia Huang

    An electrochemical reactor with connected anode and cathode was designed.

    Phosphate and ammonia were concentrated 4~5 times continuously and selectively.

    Concentration differences between chambers were utilized to control the separation.

    Long-term operation with struvite formation was proved to be repeatable.

    To separate and concentrate NH4+ and PO43 from the synthetic wastewater to the concentrated solution through a novel electrochemical reactor with circulated anode and cathode using the difference of the concentration between electrode chamber and middle chamber.

    In recent years, the research on electrochemical processes have been focused on phosphate and ammonium removal and recovery. Among the wide range of possibilities with regards to electrochemical processes, capacitive deionization (CDI) saves the most energy while at the same time does not have continuity and selectivity. In this study, a new electrochemical reactor with electrolyte cyclic flowing in the electrode chambers was constructed to separate and concentrate phosphate and ammonium continuously and selectively from wastewater, based on the principle of CDI. At the concentration ratio of NaCl solution between the electrode chambers and the middle chamber (r) of 25 to 1, phosphate and ammonium in concentration level of domestic wastewater can be removed and recovered continuously and selectively as struvite. Long-term operation also indicated the ability to continuously repeat the reaction and verified sustained stability. Further, the selective recovery at the certain r could also be available to similar technologies for recovering other kinds of substances.

    Hannah Kratky, Zhan Li, Yijun Chen, Chengjin Wang, Xiangfei Li, Tong Yu

    Bioretention in cold climate pushes the boundary of current applications.

    Coarser media is required in cold climates to maintain hydraulic performance.

    More research is needed on water quality performance of cold climate bioretention.

    Bioretention is a popular best management practice of low impact development that effectively restores urban hydrologic characteristics to those of predevelopment and improves water quality prior to conveyance to surface waters. This is achieved by utilizing an engineered system containing a surface layer of mulch, a thick soil media often amended with a variety of materials to improve water quality, a variety of vegetation, and underdrains, depending on the surrounding soil characteristics. Bioretention systems have been studied quite extensively for warm climate applications, but data strongly supporting their long-term efficacy and application in cold climates is sparse. Although it is apparent that bioretention is an effective stormwater management system, its design in cold climate needs further research. Existing cold climate research has shown that coarser media is required to prevent concrete frost from forming. For spring, summer and fall seasons, if sufficient permeability exists to drain the system prior to freezing, peak flow and volume reduction can be maintained. Additionally, contaminants that are removed via filtration are also not impacted by cold climates. In contrary, dissolved contaminants, nutrients, and organics are significantly more variable in their ability to be removed or degraded via bioretention in colder temperatures. Winter road maintenance salts have been shown to negatively impact the removal of some contaminants and positively impact others, while their effects on properly selected vegetation or bacteria health are also not very well understood. Research in these water quality aspects has been inconsistent and therefore requires further study.

    Robert G. Traver, Ali Ebrahimian

    Research shows GSI Practices outperform static volume crediting.

    Recommend including exfiltration and evapotranspiration for dynamic design.

    Expand design to include climate, insitu soil and vegetation to take advantage of GSI Properties.

    This paper compares ongoing research results on hydrologic performance to common design and crediting criteria, and recommends a change in direction from a static to a dynamic perspective to fully credit the performance of green infrastructure. Examples used in this article are primarily stormwater control measures built for research on the campus of Villanova University [1,2]. Evidence is presented demonstrating that the common practice of crediting water volume based on soil and surface storage underestimates the performance potential, and suggests that the profession move to a more dynamic approach that incorporates exfiltration and evapotransporation. The framework for a dynamic approach is discussed, with a view to broaden our design focus by including climate, configuration and the soil surroundings. The substance of this work was presented as a keynote speech at the 2016 international Low Impact Development Conference in Beijing China [3].

    Shuhan Zhang, Yingying Meng, Jiao Pan, Jiangang Chen

    The average reused rainwater was 5256 m3 annually in the school.

    The runoff removal rate was 80.37% annually in the school.

    Runoff pollutant concentration was positively related with the rainfall interval.

    The NSP reduction effectiveness of the LID system was very obvious.

    Building a rainwater system based on the idea of low-impact development (LID) is an important aspect of the current “sponge city” construction in China. The “sponge city” concept emphasizes that the runoff can permeate the soil or be stored temporarily, and rainwater could be used again when it is needed. Beijing is one of the earliest cities to study rainwater harvesting and LID techniques in China. Through long-term monitoring of rainfall, runoff flow, and water quality of a campus demonstration project in Beijing, the runoff quantity and pollutant concentration variations have been analyzed. Furthermore, the runoff reduction effects of single LID measure, such as green roof, filtration chamber, and permeable pavement, have been investigated. Additionally, the overall reduction effectiveness of the LID system on the average annual rainfall runoff and pollution load has been discussed. Preliminary studies suggest that runoff pollutant concentration is positively correlated with the rainfall interval time, and the longer rainfall interval time leads to higher runoff pollutant concentrations. The very good outflow quality of the rainwater harvesting system could satisfy the reclaimed water quality standard for scenic entertainment use. The non-point-source pollution reduction effects of the LID system are obvious because the pollutants could be removed by filtration on the one hand and the pollution load could be reduced because of the significantly reduced outflow on the other hand.

    Xin Dong, Senchen Huang, Siyu Zeng

    A stepwise design approach for real time control strategy was proposed.

    Three typical strategies (static, constant and equal-filling strategy) were studied.

    The fourth urban drainage system in Kunming was used for case study.

    Equal-filling strategy was found to be able to reduce CSO effectively.

    Real time control (RTC) of urban drainage systems (UDSs) is an important measure to reduce combined sewer overflow (CSO) and urban flooding, helping achieve the aims of ‘Sponge City’. Application of RTC requires three main steps: strategy design, simulation-based evaluation and field test. But many of published RTC studies are system-specific, lacking discussions on how to design a strategy step by step. In addition, the existing studies are prone to use hydrologic model to evaluated strategies, but a more precise and dynamic insight into strategy performance is needed. To fill these knowledge gaps, based on a case UDS in Kunming city, a study on RTC strategy design and simulation-based evaluation is performed. Two off-line volume-based RTC strategy design principles, Maximize WWTP inflow and Make full use of space, are emphasized. Following these principles, a detailed design procedure is shown for the case UDS resulting in three RTC strategies: static, constant and equal filling. The proposed strategies are evaluated based on a hydrodynamic model- Storm Water Management Model (SWMM) - under four typical rainfall events characterized by different return periods (1-year or 0.5 year) and different spatial distributions (uniform or uneven). The equal filling strategy outperforms other two strategies and it can achieve 10% more CSO reduction and 5% more flooding reduction relative to the no-tank case.

    Chen Qian, Wei Chen, Wei-Hua Li, Han-Qing Yu

    The defects of PARAFAC were demonstrated when handling real wastewater.

    PFFCA method was applied into real wastewater analysis for the first time.

    Robustness and interpretability of PFFCA method were validated.

    Rapid monitoring of water quality is crucial to the operation of municipal wastewater treatment plants (WWTPs). Fluorescence excitation-emission matrix (EEM) in combination with parallel factor analysis (PARAFAC) has been used as a powerful tool for the characterization of dissolved organic matter (DOM) in WWTPs. However, a recent work has revealed the drawback of PARAFAC analysis, i.e., overestimating the component number. A novel method, parallel factor framework-clustering analysis (PFFCA), has been developed in our earlier work to resolve this drawback of PARAFAC. In the present work, both PARAFAC and PFFCA were used to analyze the EEMs of water samples from a full-scale WWTP from a practical application point of view. The component number and goodness-of-fit from these two methods were compared and the relationship between the relative score change of component and the actual concentration was investigated to evaluate the estimation error introduced by both methods. PFFCA score and actual concentration exhibited a higher correlation coefficient (R2 = 0.870) compared with PARAFAC (R2<0.771), indicating that PFFCA provided a more accurate relative change estimation than PARAFAC. The results suggest that use of PARAFAC may cause confusion in selecting the component number, while EEM-PFFCA is a more reliable alternative approach for monitoring water quality in WWTPs.

    Jinsong Tao, Zijian Li, Xinlai Peng, Gaoxiang Ying

    GSI systems perform very well for low intensity and short duration events.

    GSI systems have the worst performance for high intensity events.

    GSI systems are capable for CSO control in long-term control strategy.

    GSI systems are not suitable for the urban flooding control.

    Stimulated by the recent USEPA’s green stormwater infrastructure (GSI) guidance and policies, GSI systems have been widely implemented in the municipal area to control the combined sewer overflows (CSOs), also known as low impact development (LID) approaches. To quantitatively evaluate the performance of GSI systems on CSO and urban flooding control, USEPA-Stormwater Management Model (SWMM) model was adopted in this study to simulate the behaviors of GSI systems in a well-developed urban drainage area, PSW45, under different circumstances. The impact of different percentages of stormwater runoff transported from impervious surfaces to the GSI systems on CSO and urban flooding control has also been investigated. Results show that with current buildup, GSI systems in PSW45 have the best performance for low intensity and short duration events on both volume and peak flow reductions, and have the worst performance for high intensity and long duration events. Since the low intensity and short duration events are dominant from a long-term perspective, utilizing GSI systems is considered as an effective measure of CSO control to meet the long-term control strategy for PSW45 watershed. However, GSI systems are not suitable for the flooding control purpose in PSW45 due to the high occurrence possibility of urban flooding during or after high intensity events where GSI systems have relatively poor performance no matter for a short or long duration event.

    Ruifen Liu, Elizabeth Fassman-Beck

    A bioretention with internal water storage zone enhances hydrologic performance.

    A medium with marine sand is better at delaying drainage than one with pumice sand.

    In column studies, air entrapment affects filling of an internal water storage zone.

    Medium-specific characteristics are recommended for SWMM v5.1.11 model estimations.

    Hydrologic performance of bioretention systems is significantly influenced by the media composition and underdrain configuration. This research measured hydrologic performance of column-scale bioretention systems during a synthetic design storm of 25.9 mm, assuming a system area:catchment area ratio of 5%. The laboratory experiments involved two different engineered media and two different drainage configurations. Results show that the two engineered media with different sand aggregates were able to retain about 36% of the inflow volume with free drainage configuration. However, the medium with marine sand is better at delaying the occurrence of drainage than the one with pumice sand, denoting the better detention ability of the former. For both engineered media, an underdrain configuration with internal water storage (IWS) zone lowered drainage volume and peak drainage rate as well as delayed the occurrence of drainage and peak drainage rate, as compared to a free drainage configuration. The USEPA SWMM v5.1.11 model was applied for the free drainage configuration case, and there is a reasonable fit between observed and modeled drainage-rates when media-specific characteristics are available. For the IWS drainage configuration case, air entrapment was observed to occur in the engineered medium with marine sand. Filling of an IWS zone is most likely to be influenced by many factors, such as the structure of the bioretention system, medium physical and hydraulic properties, and inflow characteristics. More research is needed on the analysis and modeling of hydrologic process in bioretention with IWS drainage configuration.

    Nanqi Ren, Qian Wang, Qiuru Wang, Hong Huang, Xiuheng Wang

    Cities in China confront full-scale and serious water crises due to urbanization.

    System 2.0 with fragmented gray engineering measures showed inadaptability.

    A novel water-cycling system is developed to systematically solve water crises.

    Multi-purpose system 3.0 with integrated strategy shows powerful vitality.

    Urban water system 3.0 (Blue, gray, brown and yellow arrows represent water flow, wastewater flow, resource and energy respectively)

    Facing the pressure of excessive water consumption, high pollution load and rainstorm waterlogging, linear and centralized urban water system, system 2.0, as well as traditional governance measures gradually exposed characters of water-sensitivity, vulnerability and unsustainability, subsequently resulting in a full-blown crisis of water shortage, water pollution and waterlogging. To systematically relieve such crisis, we established healthy urban water-cycling system 3.0, in which decentralized sewerage systems, spongy infrastructures and ecological rivers play critical roles. Through unconventional water resource recycling, whole process control of pollutions and ecological restoration, system 3.0 with integrated management measures, is expected to fit for multiple purposes which involve environmental, ecological, economic and social benefits. With advantages of flexibility, resilience and sustainability, water system 3.0 will show an increasingly powerful vitality in the near future.

    Jiao Zhang, Zhen Wei, Haifeng Jia, Xia Huang

    Pollutants were of low concentration in a river originated with reclaimed water.

    Turbidity was affected by algal contents, TOC and flow rate.

    The specific growth rate of algae was affected by temperature and flow rate.

    The diversity of algal community was strongly negatively correlated with TN.

    The water quality in a typical urban river segment originated with reclaimed water in Beijing was monitored for two years to investigate the evolution of water quality along the river, and statistical analysis was applied to determine factors influencing water quality of such river recharged by reclaimed water. It was found that no significant change in pollutant concentrations (including COD, NH4+-N, TN and TP) was observed during this time, and their average values were close to those of the original reclaimed water. However, turbidity and algal contents fluctuated temporally in the direction of river flow. Statistical analysis showed that turbidity was strongly positively correlated with algal contents for flow rate<0.1 m·s1, whereas it was strongly positively correlated with both algal contents and TOC for flow rate>0.1 m·s1. It was observed that diatom was the absolute predominant phyla with Melosira as the major species. In terms of algal bloom control, the specific growth rate of algae was strongly correlated to temperature, and was influenced by flow rate as well. Compared with two other rivers originated with reclaimed water and one originated with natural water, the Shannon–Wiener index in the objective river was the lowest, with values between 0.7 and 1.6, indicating a high risk for algal bloom. Statistics showed that Shannon–Wiener index was strongly negatively correlated to nutrient salts and cations.

    John C. Radcliffe, Declan Page, Bruce Naumann, Peter Dillon

    Low Impact Development was able to be adopted over a 50 year period by the City of Salisbury as it expanded from 4160 to 137,000 people

    The management of stormwater and groundwater was integrated through use of wetlands and managed aquifer recharge.

    Federal, state and local government contributed with developers and local industry to establish the integrated system as a commercial business supplying recycled water for non-potable amenity and industrial use.

    It has been shown with little additional water treatment, water originally treated through wetlands and aquifer storage could be safely withdrawn for a range of uses including as a potable water source.

    Australia has developed extensive policies and guidelines for the management of its water. The City of Salisbury, located within metropolitan Adelaide, South Australia, developed rapidly through urbanisation from the 1970s. Water sensitive urban design principles were adopted to maximise the use of the increased run-off generated by urbanisation and ameliorate flood risk. Managed aquifer recharge was introduced for storing remediated low-salinity stormwater by aquifer storage and recovery (ASR) in a brackish aquifer for subsequent irrigation. This paper outlines how a municipal government has progressively adopted principles of Water Sensitive Urban Design during its development within a framework of evolving national water policies. Salisbury’s success with stormwater harvesting led to the formation of a pioneering water business that includes linking projects from nine sites to provide a non-potable supply of 5 × 106 m3·year−1. These installations hosted a number of applied research projects addressing well configuration, water quality, reliability and economics and facilitated the evaluation of its system as a potential potable water source. The evaluation showed that while untreated stormwater contained contaminants, subsurface storage and end-use controls were sufficient to make recovered water safe for public open space irrigation, and with chlorination, acceptable for third pipe supplies. Drinking water quality could be achieved by adding microfiltration, disinfection with UV and chlorination. The costs that would need to be expended to achieve drinking water safety standards were found to be considerably less than the cost of establishing dual pipe distribution systems. The full cost of supply was determined to be AUD$1.57 m−3 for non-potable water for public open space irrigation, much cheaper than mains water, AUD$3.45 m−3at that time. Producing and storing potable water was found to cost AUD$1.96 to $2.24 m−3.

    Jianwei Liu, Kaixiong Yang, Lin Li, Jingying Zhang

    The integrated-bioreactor consists of a suspended zone and an immobilized zone.

    H2S and NH3 from WWTP were effectively eliminated by the integrated-bioreactor.

    Different microbial populations dominated in the individual zones.

    Most of the H2S was bio-oxidized into elemental sulfur and sulfate in IZ.

    Large amount of NH3 was converted into nitrate and nitrite in SZ.

    A full-scale integrated-bioreactor consisting of a suspended zone and an immobilized zone was employed to treat the ordours emitted from a wastewater treatment plant. The inlet concentrations of H2S and NH3 were 1.6–38.6 mg·m3 and 0.1–6.7 mg·m3, respectively, while the steady-state outlet concentrations were reduced to 0–2.8 mg·m3 for H2S and 0–0.5 mg·m3 for NH3. Both H2S and NH3 were eliminated effectively by the integrated-bioreactor. The removal efficiencies of H2S and NH3 differed between the two zones. Four species of microorganisms related to the degradation of H2S and NH3 were isolated. The characteristics and distributions of the microbes in the bioreactor depended on the inlet concentration of substrates and the micro-environmental conditions in the individual zones. Product analysis indicated that most of the H2S was oxidized into sulfate in the immobilized zone but was dissolved into the liquid phase in the suspended zone. A large amount of NH3 was converted into nitrate and nitrite by nitration in the suspended zone, whereas only a small amount of NH3 was transferred to the aqueous phase mainly by absorption or chemical neutralization in the immobilized zone. Different microbial populations dominated the individual zones, and the major biodegradation products varied accordingly.

    Xiao Zhang, Biwu Chu, Junhua Li, Chaozhi Zhang

    • SO2/NH3 affected the role of seed particles in secondary aerosol (SA) formation.

    • Effects of seed particles on SA formation depended on their acid-base properties.

    • H2SO4 accelerated SA formation under either SO2 or NH3 condition.

    Seed particles Al2O3, Al2(SO4)3 and H2SO4 were selected to investigate their effects on secondary aerosol (SA) formation in toluene/NOx photooxidation under sulfur dioxide (SO2) and ammonia (NH3). Effect of seed particles on SA formation was related to their acid-base properties and the presence of acid or alkaline gases. Under NH3-poor condition, SA formation increased with increasing SO2 concentration due to the acid-catalyzing effect of the oxidation products of SO2 (i.e. H2SO4). The enhancing effect of SO2 became unobvious under NH3-rich condition, because NH3 would eliminate the acid-catalyzing effect by neutralizing the acid products. Acidic seeds H2SO4 accelerated SA formation under either SO2 or NH3 condition. Weak acidic Al2(SO4)3 seeds didn’t affect obviously on SA formation. The inhibiting effect of amphoteric seeds Al2O3 on SA formation was related to the presence of SO2 / NH3 due to their acid-base property. Under NH3-poor condition, the inhibiting effect of Al2O3 on SA formation decreased with increasing concentration of SO2, while under NH3-rich condition, the inhibiting effect wasn’t remarkable.

    Quanming Liang, Jian Li, Hong He, Wenjun Liang, Tiejun Zhang, Xing Fan

    CeO2 improved the De-NOx activity and sulfur resistance of catalysts.

    The De-NOx activity of 3% CeO2 -VWT catalyst reached 89.9 % at 140°C.

    CeO2 promoted the oxidation of NO to NO2 and inspired the fast SCR reaction.

    Active components content and BET decreased slightly after entering SO2.

    The largest loss rate was 0.024%/°C at 380°C–390°C in poisoned catalyst.

    The CeO2-V2O5-WO3/TiO2 (CeO2-VWT) catalysts were prepared by one-step and two-step impregnation methods. The effects of different loading of CeO2 and different preparation methods on De-NOx activity of catalysts had been investigated. CeO2 helped to improve the De-NOx activity and sulfur resistance. The optimal loading of CeO2 was 3% with the De-NOx efficiency reached 89.9% at 140°C. The results showed that the De-NOx activity of 3% CeO2-VWT catalysts by one-step method was the same as two-step method basically and reached the level of industrial applications, the N2 selectivity of catalysts was more than 99.2% between 110°C and 320°C. In addition, CeO2 promoted the oxidation of NO to NO2, which adsorbed on the Lewis acid site (V5+═O) to form V5+═NO3 and inspired the fast SCR reaction. Not only the thermal stability but also the De-NOx activity of catalysts decreased with excess CeO2 competed with V2O5. Characterizations of catalysts were carried out by XRF, BET, XRD, TG and FT-IR. BET showed that the specific surface area of catalysts decreased with the loading of CeO2 increased, the active components content and specific surface area of catalysts decreased slightly after entering SO2. Ammonium sulfate species were formed in poisoned catalyst which had been investigated by XRF, BET, TG and FT-IR. The largest loss rate of weight fraction was 0.024%·°C1 at 380°C–390°C, which was in accordance with the decomposition temperature of NH4HSO4 and (NH4)2SO4.

    Xinfeng Wang, Tao Wang, Likun Xue, Wei Nie, Zheng Xu, Steven C. N. Poon, Wenxing Wang

    The loss degree of PAN signal in a TD-CIMS caused by NO is tested and quantified.

    TD-CIMS is applicable for PAN measurement in urban areas with necessary correction.

    The PAN formation efficiency in urban Hong Kong increased with NO2 concentration.

    Peroxyacetyl nitrate (PAN) is an important indicator of photochemical smog and has adverse effects on human health and vegetation growth. A rapid and highly selective technique of thermal dissociation–chemical ionization mass spectrometry (TD-CIMS) was recently developed to measure the abundance of PAN in real time; however, it may be subject to artifact in the presence of nitric oxide (NO). In this study, we tested the interference of the PAN signal induced by NO, evaluated the performance of TD-CIMS in an urban environment, and investigated the concentration and formation of PAN in urban Hong Kong. NO caused a significant underestimation of the PAN signal in TD-CIMS, with the underestimation increasing sharply with NO concentration and decreasing slightly with PAN abundance. A formula was derived to link the loss of PAN signal with the concentrations of NO and PAN, which can be used for data correction in PAN measurements. The corrected PAN data from TD-CIMS were consistent with those from the commonly used gas chromatography with electron capture detection, which confirms the utility of TD-CIMS in an urban environment in which NO is abundant. In autumn of 2010, the hourly average PAN mixing ratio varied from 0.06 ppbv to 5.17 ppbv, indicating the occurrence of photochemical pollution in urban Hong Kong. The formation efficiency of PAN during pollution episodes was as high as 3.9 to 5.9 ppbv per 100 ppbv ozone. PAN levels showed a near-linear increase with NOx concentration, suggesting a control policy of NOx reduction for PAN pollution.

    Xing Fang, Junqi Li, Yongwei Gong, Xiaoning Li

    Comprehensive stormwater management needs both LID and detention basins.

    Zero-increase in peak discharge policy is still valid/used in developed countries.

    Design rainfalls for LID are smaller than ones for detention basin.

    Detention basin reduces peak discharges for several return-period rainfalls.

    Financial responsibility and sustainable development demand zero-increase policy.

    For urban land development, some or all natural land uses (primarily pervious) are converted into impervious areas which lead to increases of runoff volume and peak discharge. Most of the developed countries require a zero increase in peak discharge for any land development, and the policy has been implemented for several decades. The policy of zero increase in peak discharge can be considered as historical and early stage for the low impact development (LID) and sustainable development, which is to maintain natural hydrological conditions by storing a part or all of additional runoff due to the development on site. The paper will discuss the policy, the policy implementation for individual projects and their impact on regional hydrology. The design rainfalls for sizing LID facilities that are determined in 206 weather stations in USA are smaller than design rainfalls for sizing detention basins. The zero-increase policy links to financial responsibility and sustainability for construction of urban stormwater infrastructures and for reducing urban flooding. The policy was compared with current practices of urban development in China to shine the light for solving urban stormwater problems. The connections and differences among LID practices, the zero-increase policy, and the flood control infrastructure were discussed. We promote and advocate the zero-increase policy on peak discharge for comprehensive stormwater management in China in addition to LID.

    Te Xu, Haifeng Jia, Zheng Wang, Xuhui Mao, Changqing Xu

    A SWMM-based methodology of block-scale LID-BMPs planning was developed.

    LID-BMP chain layout optimization was combined with block-scale scenario analysis.

    A strategy was devised to couple NSGA-II to SWMM.

    Planning targets were satisfied in the case study in Tianjin.

    Scenario evaluation and selection was robust with varied weight values.

    Low impact development type of best management practices (LID-BMPs) aims to mitigate urban stormwater runoff and lessen pollutant loads in an economical and eco-friendly way and has become a global concern in modern urban stormwater management. A new methodology based on stormwater management model (SWMM) for block-scale LID-BMPs planning was developed. This method integrated LID-BMP chain layout optimization in site-scale parcels with scenario analysis in the entire block-scale urban area. Non-dominated sorting genetic algorithm (NSGA-II) was successfully coupled to SWMM through Python to complete the site-scale optimization process. Different LID scenarios of the research area were designed on the basis of the optimized LID-BMP chain layout. A multi-index evaluation that considered runoff quantity indices, pollutant loads, and construction costs simultaneously helped select the cost-effective scenario as the final planning scheme. A case study in Tianjin, China, was conducted to demonstrate the proposed methodology. Results showed that more than 75% control rate of total runoff volume, 22%–46% peak flow reduction efficiency, and more than 32% pollutant removal rate were achieved. The robustness analysis indicated that the selected final planning scheme was considerably robust with varied weight values.