Assessing the impact of swales on receiving water quality

Swales are one type of sustainable drainage system (SuDS) which contribute to the management of water quality in receiving waterbodies. Using a semi-quantitative approach, an impact assessment procedure is applied to the residual water quality that is carried forward to surface waters and groundwaters following treatment within a swale. Both volumetric and pollutant distributions are considered as stormwater passes through the swale system. The pollutant pathways followed by TSS, nitrate, chloride, metals (Cd, Cu, Pb, Zn) and polyaromatic hydrocarbons (PAHs) are determined for a swale receiving highway runoff. For TSS, metals and PAHs between 20% and 29% of the total mean influent pollutant load is predicted to be directed to infiltration through the underlying soils compared to between 4% and 16% of chloride and nitrate. Although surface water impacts are deemed possible, the discharges of swales to groundwaters are assessed to represent a negligible impact for effectively maintained systems.     

Performance of grass swales for improving water quality from highway runoff

The performance of grass swales for treating highway runoff was evaluated using an experimental design that allowed for influent and effluent flow and pollutant concentration measurements to be taken at specific intervals through each storm event. Two common swale design alternatives, pre-treatment grass filter strips and vegetated check dams, were compared during 45 storm events over 4.5 years. All swale alternatives significantly removed total suspended solids and all metals evaluated: lead, copper, zinc, and cadmium. The probability of instantaneous concentrations exceeding 30 mg/L TSS was decreased from 41–56% in the untreated runoff to 1–19% via swale treatment. Nutrient treatment was variable, with generally positive removal except for seasonal events with large pulses of release from the swales. Nitrite was the only consistently removed nutrient constituent. Chloride concentrations were higher in swale discharges in nearly every measurement, suggesting accumulation during the winter and release throughout the year. Sedimentation and filtration within the grass layer are the primary mechanisms of pollutant treatment; correspondingly, particles and particulate-bound pollutants show the greatest removal via swales. Inclusion of filter strips or check dams had minimal effects on water quality.     

Comparative Study of Rainfall Infiltration into a Bare and a Grassed Unsaturated Expansive Soil Slope

It is generally thought that vegetation has a stabilization effect on a slope; however, very limited quantitative field data are available for verifying this perception. In order to improve our understanding on the vegetation effect on rainfall infiltration and hence on slope stability, a well-instrumented field study was carried out on an unsaturated expansive soil slope in China. The field program consisted of two neighboring monitoring areas (both 16 m wide by about 30 m long): namely a bare area and a naturally grassed area (real slope). Artificial rainfall events were produced in succession in the two areas with a specially-designed sprinkler system. In this paper, the relevant monitored results from the two areas are directly compared and discussed. Prior to the artificial rainfall, the measured higher initial soil suction in the grassed area than that in the bare areas was attributed to the evapo-transpiration effect of the grass. During the rainfall, the presence of the grass greatly increased the infiltrability of the upper soil layer and delayed the onset of surface runoff. The observed delayed responses (i.e., about 3 days) of surface runoff, soil suction and water content to the rainfall in the grassed area was about twice the duration of the delayed response in the bare area (i.e., about 1.5 days). The influence of the simulated rainfall on the changes of soil suction and water content in the grassed area was found to be more significant and about 1.5 m deeper than that in the bare area. The greater depth of influence observed in the grassed area may be attributable to the greater depth of open cracks due to the evapo-transpiration effect of grass.     

Evaluation of the COMIS Model by Comparing Simulation and Measurement of Airflow and Pollutant Concentration

Abstract This paper describes the measured and calculated results of airflow rates and pollutant concentration profiles in an airtight test house, the aim being to evaluate the calculation model COMIS for multizone air infiltration and pollutant transport. Firstly, the leakage areas of internal doors, exterior walls and windows were measured by the fan pressurization method. Secondly, two measurements were carried out, assuming that the test house consisted of ten zones. The concentrations and injection rate of SF₆ were measured in order to determine the airflow rates by a system identification method. The boundary conditions, such as indoor and outdoor temperatures, wind speed and direction, and wind pressures were also recorded in situ and saved simultaneously on diskettes, using a computerized data acquisition system. Thirdly, the measured boundary data and leakage characteristics were used as input in the simulation of airflow using COMIS; initial concentrations, injection rate, along with the previous data were used for simulating pollutant transport, assuming tracer gas SF6 as a pollutant. Lastly, the comparisons between measurement and simulation results of airflow rates and pollutant concentrations were carried out by linear regression analysis. The correlation coefficient between the measured and calculated air change rates was 0.72, and that for pollutant concentration was 0.94.     

全预混式灶具污染物排放的实验研究

用多孔介质制作火盖,结合3种型式的引射器,提出了全预混式灶具设计方案,对其相应的燃烧污染物排放量进行了实验研究.采用一种新的污染物测试方法,即在灶具火焰附近直接测量污染物的排放量.通过分析各方案燃烧污染物排放量的特点,提出全预混式灶具在降低NOx排放的同时,还应控制其他污染物排放量的设计原则.     

Towards the application of indoor ventilation efficiency indices to evaluate the air quality of urban areas

Ventilation efficiency (VE) indices for indoor environments are widely used to evaluate the ventilation performance and air quality of indoor domains. These indices are considered effective for outdoor air quality assessments too. In this paper, application of the ventilation efficiency indices for indoor environments to urban domains is presented and their effectiveness is confirmed. Three indices for indoor VE indices are considered here: the purging flow rate (PFR: the effective airflow rate required to purge pollutants from the domain), visitation frequency (VF: the number of times a pollutant enters the domain and passes through it) and residence time (TP: the time a pollutant takes from once entering or being generated in the domain until its leaving), which can be calculated by means of computational fluid dynamics (CFD) simulations. Two examples for evaluating the air quality of urban domains in terms of the VE indices were presented. In the first, CFD simulations were carried out using a two-building model to assess the effects of urban street width and street building heights on the VE indices of a domain located within a street. In the second example, numerical simulations were carried out to estimate the influence of the arrangement of building arrays on the VE indices of selected domains located within these arrays. The results of the study showed that the ventilation efficiency indices of indoor environments appear to be a promising tool in the assessment of the air quality of urban domains as well. One of the features of applying these indices is that it is not necessary to consider the location of the pollutant source within the study domain. In addition, the VE indices are able to describe the pollutant behavior within the domain, which is very important for obtaining a complete assessment for the wind ventilation performance within urban domains.     

Hydraulic performance of grass swales for managing highway runoff

The hydraulic performance of grass swales as a highway stormwater control measure was evaluated in a field-scale study adjacent to a Maryland highway. Two common swale design alternatives, pretreatment grass filter strips and vegetated check dams, were compared during 52 storm events over 4.5 years. Swale performance is described via three regimes, dependent on the relative size of the rainfall event. Overall, half of the events were small enough that the entire flow was stored, infiltrated, and evapotranspirated by the swales, resulting in no net swale discharge. Swales significantly reduced total volume and flow magnitudes generally during events with rainfall less than 3 cm. While the majority of improvement can be attributed to the swales, inclusion of check dams increases swale effectiveness. Pretreatment grass filter strips produced mixed effects. The swales demonstrated essentially no volumetric reduction during large storm events, functioning instead as conveyance, and smoothing fluctuations in flow.     

建筑施工过程中的环境管理

从噪声、粉尘、污水、大气污染物、固体废弃物等方面阐述了施工企业常见的环境污染因素,并提出了控制各种环境污染因素的措施,指出企业应在施工中进行合理的环境管理,解决好环境问题,从而提高企业形象,增强企业竞争能力。     

Hydrologic influence on stormwater pollution at two urban monitoring sites

The pollutant transport process operated by stormwater runoff on urban paved surfaces and the relationship between the parameters of the wash-off function and the controlling hydrologic variables are investigated in the present work. Data collected during two monitoring campaigns carried out at the plot scale within a residential area and an auto dismantler site are used to this aim. The observed runoff events are classified into different mass delivery processes and the occurrence of the first flush phenomenon is also investigated. The maximum flow discharge obtained as the average value over the time of concentration of the drainage network is proposed as the controlling factor for the total mass of pollutant that is made available for wash-off during each runoff event.     

Effects of rainfall patterns on highway runoff pollution and its control

The magnitude of pollution from highway runoff is highly dependent on rainfall patterns. To demonstrate the effects of rainfall on the characteristics of highway pollution and its control, runoff from two sections of a major highway in Taiwan was monitored, representing respectively the uncontrolled runoff and the runoff treated using a swale system. Event mean concentrations (EMCs) of suspended solids, chemical oxygen demand, total nitrogen, total phosphates, iron, copper and zinc were calculated from monitored data. Annuals loads were also obtained from long‐term simulations using the US Environmental Protection Agency Stormwater Management Model. Results indicated that, despite high traffic volumes, both EMCs and annual loads from the studied highway were low compared with those found in literatures. The lower potentials of runoff pollution were attributed to a pattern of infrequent but intense rainfalls of the study area. The specific rainfall pattern also caused the swale system to be less effective in controlling nitrogen and phosphorus because of significant erosion.     

城市交通隧道洞口污染物扩散的控制策略研究

通过大型环境风洞试验的方法,研究了绿化隔离带以及中隔墙对城市交通隧道洞口污染的扩散进行了研究.对于设置绿化隔离带工况,研究了不同风速大小/风向下绿化隔离带对废气的洞口直接排放中污染物扩散影响,获得了洞口排放污染物在不同来流风速/风向条件下的浓度衰减规律及其影响范围;对于设置中隔墙工况,试验涉及了三种不同中隔墙长度(隧道...     

Pollutant emissions from vehicles with regenerating after-treatment systems in regulatory and real-world driving cycles

Regenerating exhaust after-treatment systems are increasingly employed in passenger cars in order to comply with regulatory emission standards. These systems include pollutant storage units that occasionally have to be regenerated. The regeneration strategy applied, the resultant emission levels and their share of the emission level during normal operation mode are key issues in determining realistic overall emission factors for these cars. In order to investigate these topics, test series with four cars featuring different types of such after-treatment systems were carried out. The emission performance in legislative and real-world cycles was monitored as well as at constant speeds. The extra emissions determined during regeneration stages are presented together with the methodology applied to calculate their impact on overall emissions. It can be concluded that exhaust after-treatment systems with storage units cause substantial overall extra emissions during regeneration mode and can appreciably affect the emission factors of cars equipped with such systems, depending on the frequency of regenerations. Considering that the fleet appearance of vehicles equipped with such after-treatment systems will increase due to the evolution of statutory pollutant emission levels, extra emissions originating from regenerations of pollutant storage units consequently need to be taken into account for fleet emission inventories. Accurately quantifying these extra emissions is achieved by either conducting sufficient repetitions of emission measurements with an individual car or by considerably increasing the size of the sample of cars with comparable after-treatment systems.     

某化学实验室机械通风模拟

针对三种不同通风方案,运用CFD软件进行数值模拟,研究实验室内污染物浓度场、空气速度场、空气流线图等,分析不同送排风口位置时室内的通风效果,得出最佳通风方案,并对存在的问题提出了建议,对实际工程有一定的参考价值.     

Effects of subbase materials on phosphorous attenuation in permeable pavement system and correlation between pollution attenuation and subbase materials

In this study, laboratory models of six permeable pavement system (PPS) columns with various subbase configurations were examined for phosphorus attenuation. Experiments were carried out under varying intensities and durations of rainfall to investigate possible PPS modifications to enhance the performance of phosphorus attenuation and the likelihood of phosphorus leaching back to infiltration. The results show the inefficiencies of phosphate attenuation in the conventional PPS structure. During long-duration rainfall events, phosphates can be leached back to the infiltrate through the conventional PPS structure. The intensity of rainfall affects the attenuation of total phosphorus through the six permeable pavement columns. To achieve an enhanced phosphate attenuation, the findings of this study suggest modifying the PPS structure by incorporating thin sand layers in the subbase. Also, the correlation between pollutant attenuation and subbase materials is found. Finally, design modification of PPS is recommended to enhance the pollutant attenuation capacity of the PPS.     

污泥驯化阶段MBR与CAS工艺特性比较

在接种污泥、进水水质、反应器尺寸及水力停留时间相同的条件下，比较了膜生物反应器（MBR）和传统活性污泥工艺（CAS）在污泥驯化期的除污效果和污泥特性。结果表明，MBR对COD的去除效果优于CAS的，两工艺对氨氮的去除效果差异不大；MBR中的污泥絮体较CAS中的分散，原生动物和后生动物的种类也较少；MBR中的污泥浓度远高于CAS工艺的，其污泥的体积平均粒径小于CAS的；两反应器中的活性污泥均表现出了较好的沉降性能。     

Wastewater quality and pollutant loads in combined sewers during dry weather periods

An observatory of urban pollutants was created in Paris in order to assess, at the urban catchment scale, the quality of sanitary sewage and pollutant loads during dry weather periods in the Paris combined sewer. Investigations were carried out for six urban catchments (varying from 42 to 2580 ha) focusing on a wide range of parameters, including: suspended solids (SS), chemical and biochemical oxygen demand (COD and BOD₅), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), heavy metals (Cd, Cu, Pb, Zn), and aliphatic and polycyclic aromatic hydrocarbons (AHs and PAHs). Despite the marginal intra-site variability of some pollutants, which serves to reflect the impact of point sources, this work attests to the spatial homogeneity, at the physical scales considered, of wastewater quality and pollutant loads within the Paris combined sewer network. These results imply that similar production and transfer processes are occurring within sewers during dry weather periods and strongly suggest that data obtained on one specific catchment could be extrapolated to smaller or larger catchments that display quite similar land use and sewer characteristics.     

Characterization and distribution of petroleum hydrocarbons and heavy metals in groundwater from three Italian tank farms

The present paper highlights the utility of petroleum chemical fingerprinting in investigating known or suspected tank farm releases. A detailed characterization of groundwater was carried out in three tank farms located in north, central and south Italy. Eighteen parent polycyclic aromatic hydrocarbons (naphthalene through coronene), n-alkanes (n-C(10) through n-C(36)), isoprenoids pristane and phytane, vanadium, nickel and lead were determined. Distribution profiles and diagnostic ratios of specific fuel constituents were studied in order to identify contamination sources. Data analysis shows that in the study sites multiple pollutant sources affecting the tank farms and the surrounding industrial areas are present. Both high concentrations of contaminants coming from fuel releases and noticeable concentrations of biogenic compounds were found. A detailed data analysis suggests the origin and the level of pollution of the three sites. The results demonstrate that threshold concentration approach is not always sufficient and it is necessary to carry out studies of contaminant distribution and their diagnostic ratios in order to perform a successful forensic investigation.     

Spatial distribution and temporal variation of metals in the vicinity of a municipal solid waste incinerator after a modernization of the flue gas cleaning systems of the facility

In June 1994 and 1997, the concentrations of a number of elements were determined in soil and herbage samples collected in the vicinity of a municipal solid waste incinerator (MSWI) (Tarragona, Catalonia, Spain). In August 1997, an adaptation to the EU legislation on pollutant emissions from the stack was carried out to the incinerator. In June 1999, soil and herbage samples were collected again at the same sampling points and the levels of arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), manganese (Mn), mercury (Hg), nickel (Ni) and vanadium (V) were measured by ICP-MS or AAS with graphite furnace. The results are compared with those obtained in the 1994 and 1997 surveys. In the period 1997-1999, the only significant changes in soil levels corresponded to Cd and Pb, with decreases of 21.0% and 53.5%, respectively. In vegetation, only Mn levels showed a significant reduction, which contrasts with the notable increases found in the concentrations of As, Hg and Ni. According to the results of this survey, it seems evident that other metal emission sources in the same area of study are masking the environmental improvements carried out in the MSWI.     

Quantify impacted scope of human expired air under different head postures and varying exhalation rates

Many researches indicate human respiration flow and background ventilation are two important aspects leading to possible respiratory disease spread. However, current studies on respiration flow and the resulted exhaled pollutant dispersion are limited, because different head postures, respiration mode, breath rate, room ventilation and so on, can exert profound impacts that are not understood very clearly. To evaluate the role of head postures on transmission of human exhaled pollutants, this study uses a computational fluid dynamics (CFD) program to study the exhalation flow of a sitting adult in a calm indoor office. Four different head postures are considered: sitting upright viewing front, sitting upright but head tilted viewing upward, sitting upright but head turned viewing the lateral, and sitting but pillowing head on a table. Based on the decay percentage of a gas concentration, the impacted scope of expired air is identified. The common posture by sitting upright viewing front is selected to investigate the change of impacted scope with increasing exhalation rates. The experimental test is also carried out using a breathing thermal manikin. This study finds out that the impacted scope of expired air under different head postures is different. The horizontal impacted distance is highly dependent on the specified threshold concentration. If a person sits around at a table and makes a deep exhalation, other people shall be apart from him/her with a larger distance to be free from the exhaled pollutant exposure, once his/her thermal plume is blocked by the table.     

An integrated approach to assess air pollution threats to cultural heritage in a semi-confined environment: The case study of Michelozzo's Courtyard in Florence (Italy)

An example of an integrated approach to assess air pollution threats to cultural heritage in a semi-confined environment is presented in this work, where the monitoring campaign carried out at the Michelozzo's Courtyard (in Palazzo Vecchio, Florence, Italy) is used as a case study. A wide research project was carried out, with the main aim of obtaining the first quantitative data on air quality and microclimate conditions inside the Courtyard, and, if possible, identifying the main causes of degradation and suggesting appropriate conservation strategies. The investigation adopted a holistic approach involving thermographic measurements on the wall paintings, microclimatic analysis, gaseous pollutant monitoring, atmospheric particles characterisation and dry deposition compositional analysis. Attention was focused on the wall painting depicting the city of Hall because of its anomalous and critical conservation conditions, which are visible at a glance, due to the contrast between a wide darker zone around the central subject of the painting and external lighter areas.