Contribution of domestic effluents to hydrocarbon levels of dry weather flow in combined sewers

The importance of hydrocarbon contamination of the sewer network has been reported by many authors recently. Most of the studies are focused on the introduction of such pollutants into combined sewers by street and roof stormwater, but few evaluate the contribution of domestic inputs to hydrocarbon pollution. As a consequence, this work—carried out on the framework of the OPUR (Observatory of Urban Pollutants) research program—assesses the resolved aliphatic (AH), unresolved complex mixture (UCM) and polycyclic aromatic hydrocarbon (PAH) concentrations of domestic effluents (DE) and evaluates the role played by such effluents on the hydrocarbon levels of dry weather flow (DWF) in combined sewers. Results show hydrocarbon concentrations in the 200 – 300 μg · l^?1, 300 – 1 000 μg · l^?1 and 0.9 – 1.4 μg · l^?1 ranges for AHs, UCM and the 16 PAHs of the US-EPA, respectively. The assessment of hydrocarbon fluxes conveyed by domestic effluents on the scale of the ‘Le Marais’ experimental urban catchment (42 ha, centre of Paris) reveals the predominant contribution of domestic inputs to the DWF pollution and highlights the unsuspected role of households.     

Spatial variability of the characteristics of combined wet weather pollutant loads in Paris

An on-site observatory of urban pollutant loads in combined sewers has been created in Paris in order to investigate wet weather pollutant loads at different spatial scales. This observatory is composed of six urban catchments, covering areas from 41 to 2581ha. For a wide range of parameters including suspended solids (SS), volatile suspended solids (VSS), chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), metals (Cd, Cu, Pb, Zn), aliphatic hydrocarbons and polycyclic aromatic hydrocarbons (AHs and PAHs), this article serves to evaluate the potential scale effect on wet weather flow (WWF) quality. Although the extensive data set compiled herein has emphasized the high variability in WWF quality from one rain event to the next, no scale effect could be observed for a given rain event on pollutant concentrations, distributions between dissolved and particulate phases, pollutant contents and loads. Such results are of prime importance since they suggest (i) no spatial scale influence on WWF quality for the considered catchments and (ii) similar dominant sources and transfer processes at the various spatial scales.     

Contribution of different sources to the hydrocarbon pollution during a rain event at the scale of an experimental catchment in Paris centre

Increased impervious surface area is a consequence of urbanization, with correspondent and significant effects on the hydrologic cycle. It is intuitive that an increased proportion of impervious surface brings with it shorter lag times between onset of precipitation and subsequently higher runoff peaks and total volume of runoff in receiving waters. Yet, documentation on quantitative relationships between the extent and type of impervious area and these hydrologic factors remains dispersed across several disciplines. We present a literature review on this subject to better understand and synthesize distinctions among different types of impermeable surface and their relative impacts, and describe the manner in which these surfaces are assessed for their putative impacts on landscape hydrology.     

Bed shear stress evaluation in combined sewers

Experiments have been undertaken on two sewer trunk lines in order to identify an accurate and practical technique for estimating bed shear stresses in combined sewers. Various methods were tested to determine both local bed shear stress values (one based on the logarithmic velocity profile and the other on the Reynolds shear stress distribution) and mean bed shear stress values (using a method based on the energy slope). Velocity measurements were performed using a micropropeller and an Acoustic Doppler Velocimeter (ADV) under dry weather flow conditions. In sewers without sediments, both the wall law and Reynolds shear stress distribution methods lead to the same bed shear stress estimation. A method based on the logarithmic velocity profile obtained by micropropeller is proposed herein to evaluate local shear stress in combined sewers. Calculations based on channel slope lead to an over-estimation of bed shear stress due to the inaccuracy of bed slope data. If the energy slope S _c , as calculated from the Darcy-Weisbach or Manning formula, is used to calculate the mean shear stress in sewer sections without sediments, results are consistent with the local shear stress measurements.     

Distribution and disinfection of bacterial loadings associated with particulate matter fractions transported in urban wet weather flows

Urban runoff is a resource for reuse water. However, runoff transports indicator and pathogenic organisms which are mobilized from sources of fecal contamination. These organisms are entrained with particulate matter (PM) that can serve as a mobile substrate for these organisms. Within a framework of additional treatment for reuse of treated runoff which requires the management of PM inventories in unit operations and drainage systems there is a need to characterize organism distributions on PM and the disinfection potential thereof. This study quantifies total coliform, Escherichia coli, fecal streptococcus, and enterococcus generated from 25 runoff events. With the ubiquity and hetero-dispersivity of PM in urban runoff this study examines organism distributions for suspended, settleable and sediment PM fractions differentiated based on PM size and transport functionality. Hypochlorite is applied in batch to elaborate inactivation of PM-associated organisms for each PM fraction. Results indicate that urban runoff bacterial loadings of indicator organisms exceed U.S. wastewater reuse, recreational contact, and Australian runoff reuse criteria as comparative metrics. All monitored events exceeded the Australian runoff reuse criteria for E. coli in non-potable residential and unrestricted access systems. In PM-differentiated events, bacteriological mobilization primarily occurred in the suspended PM fraction. However, sediment PM shielded PM-associated coliforms at all hypochlorite doses, whereas suspended and settleable PM fractions provide less shielding resulting in higher inactivation by hypochlorite.     

Contributions of wastewater, runoff and sewer deposit erosion to wet weather pollutant loads in combined sewer systems

An observatory of urban pollutants was created in Paris for the purpose of assessing the dynamics of wastewater and wet weather flow (WW and WWF) pollutant loads within combined sewers. This observatory is composed of six urban catchments, covering land areas ranging in size from 42 ha to 2581 ha. For a wide array of parameters including total suspended solids (TSS), chemical and biochemical oxygen demand (COD and BOD₅), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), heavy metals (Cu and Zn) and polycyclic aromatic hydrocarbons (PAHs), this article is intended to evaluate the contributions of wastewater, runoff and in-sewer processes to WWF pollutant loads through the use of an entry–exit mass balance approach. To achieve this objective, a total of 16 rain events were sampled on these sites between May 2003 and February 2006. This study has confirmed that at the considered catchment scale (i.e. from 42 ha to 2581 ha) the production and transfer processes associated with WWF pollutant loads do not vary with basin scale. Entry–exit chemical mass balances over all catchments and for a large number of rain events indicate that wastewater constitutes the main source of organic and nitrogenous pollution, while runoff is the predominant source of Zn. For Cu, PAHs and TSS, the calculation underscores the major role played by in-sewer processes, specifically by sediment erosion, as a source of WWF pollution. A significant loss of dissolved metals was also observed during their transfer within the sewer network, likely as a consequence of the adsorption of dissolved metals on TSS and/or on sewer deposits. Moreover, the nature of eroded particles was examined and compared to the various sewer deposits. This comparison has highlighted that such particles exhibit similar organic and PAH contents to those measured in the organic layer, thus suggesting that the deposit eroded during a wet weather period is organic and of a nature comparable to the organic layer. Despite the extent of initial field investigations, no organic deposit was observed to be present on sewer lines within the catchments, which implies that this organic deposit is probably present in another form or to be found elsewhere in the main trunks.     

Additional elements regarding the muddy layer in combined sewers

For 25 years, major efforts have been undertaken to improve the basic knowledge of solid dynamics in sewers. However, various aspects still require further research. The French national project ‘SER’ was conducted from 2009 to 2012, in providing the opportunity for new experimental set-ups to enhance knowledge of solid dynamics. The present work has originated from this ‘SER’ project and benefited from the various research tasks completed. The experimental site and set-up are briefly introduced before displaying the daily dry weather pattern of the muddy layer observed at the top of the deposit. A discussion is provided on the conditions most favourable to the constitution and origin of such a layer. A mass balance is also presented, showing that the muddy layer is moving into the sewer network on a daily basis.     

Trace element carriers in combined sewer during dry and wet weather: an electron microscope investigation

The nature of trace element carriers contained in sewage and combined sewer overflow (CSO) was investigated by TEM-EDX-Electron diffraction and SEM-EDX. During dry weather, chalcophile elements were found to accumulate in sewer sediments as early diagenetic sulfide phases. The sulfurization of some metal alloys was also evidenced. Other heavy metal carriers detected in sewage include metal alloys, some iron oxihydroxide phases and neoformed phosphate minerals such as anapaite. During rain events, the detailed characterization of individual mineral species allowed to differentiate the contributions from various specific sources. Metal plating particles, barite from automobile brake, or rare earth oxides from catalytic exhaust pipes, originate from road runoff, whereas PbSn alloys and lead carbonates are attributed to zinc-works from roofs and paint from building siding. Soil contribution can be traced by the presence of clay minerals, iron oxihydroxides, zircons and rare earth phosphates. However, the most abundant heavy metal carriers in CSO samples were the sulfide particles eroded from sewer sediments. The evolution of relative abundances of trace element carriers during a single storm event, suggests that the pollution due to the "first flush" effect principally results from the sewer stock of sulfides and previously deposited metal alloys, rather than from urban surface runoff.     

A survey of heavy metals in municipal wastewater in combined sewer systems during wet and dry weather periods

During wet weather, combined sewer system overflows affect the quality of water in watercourses. For planning overflows, the lowest possible load of priority substances according to Directive 2008/105/EC is crucial and the knowledge of variability in concentrations of elements in the sewer system is necessary. The behaviour of heavy metals in a sewer system was observed in the course of dry weather flow (DWF) and wet weather flow (WWF). We found, from the comparison of concentration medians for the WWF and DWF that during wet weather periods, an increase in the concentrations of As, Cr, Cd, Pb, Mn and Fe occurs in the sewer system and the effect of nonpoint sources manifests itself. Zn, Cu and Ni concentrations decreased during wet weather periods, and Hg concentrations did not significantly change. During the WWF period, a considerable nonhomogeneity of the sewage system was demonstrated.     

Modeling the contribution of point sources and non-point sources to Thachin River water pollution

Major rivers in developing and emerging countries suffer increasingly of severe degradation of water quality. The current study uses a mathematical Material Flow Analysis (MMFA) as a complementary approach to address the degradation of river water quality due to nutrient pollution in the Thachin River Basin in Central Thailand. This paper gives an overview of the origins and flow paths of the various point- and non-point pollution sources in the Thachin River Basin (in terms of nitrogen and phosphorus) and quantifies their relative importance within the system. The key parameters influencing the main nutrient flows are determined and possible mitigation measures discussed.The results show that aquaculture (as a point source) and rice farming (as a non-point source) are the key nutrient sources in the Thachin River Basin. Other point sources such as pig farms, households and industries, which were previously cited as the most relevant pollution sources in terms of organic pollution, play less significant roles in comparison. This order of importance shifts when considering the model results for the provincial level. Crosschecks with secondary data and field studies confirm the plausibility of our simulations. Specific nutrient loads for the pollution sources are derived; these can be used for a first broad quantification of nutrient pollution in comparable river basins. Based on an identification of the sensitive model parameters, possible mitigation scenarios are determined and their potential to reduce the nutrient load evaluated.A comparison of simulated nutrient loads with measured nutrient concentrations shows that nutrient retention in the river system may be significant. Sedimentation in the slow flowing surface water network as well as nitrogen emission to the air from the warm oxygen deficient waters are certainly partly responsible, but also wetlands along the river banks could play an important role as nutrient sinks.     

Assessment of annual pollutant loads in combined sewers from continuous turbidity measurements: Sensitivity to calibration data

This article presents a methodology for assessing annual wet weather Suspended Solids (SS) and Chemical Oxygen Demand (COD) loads in combined sewers, along with the associated uncertainties from continuous turbidity measurements. The proposed method is applied to data from various urban catchments in the cities of Paris and Nantes. The focus here concerns the impact of the number of rain events sampled for calibration (i.e. through establishing linear SS/turbidity or COD/turbidity relationships) on the uncertainty of annual pollutant load assessments. Two calculation methods are investigated, both of which rely on Monte Carlo simulations: random assignment of event-specific calibration relationships to each individual rain event, and the use of an overall relationship built from the entire available data set. Since results indicate a fairly low inter-event variability for calibration relationship parameters, an accurate assessment of pollutant loads can be derived, even when fewer than 10 events are sampled for calibration purposes. For operational applications, these results suggest that turbidity could provide a more precise evaluation of pollutant loads at lower cost than typical sampling methods.     

Respiratory responses to diverse indoor combustion air pollution sources

Diverse indoor combustion sources contribute to the indoor air environment. To evaluate the effect of these sources on human respiratory health, we examined associations between respiratory conditions and household factors in the 2360 children's fathers (mean = 38.4 years old) and associations between lung function and household factors in 463 primary school children (mean = 8.3 years old) from Wuhan, China. Factor analysis developed new uncorrelated 'factor' variables. Unconditional logistic regression models or linear regression models, controlling for important covariates, estimated the respiratory health effects. Coal smoke derived from home heating ('heating coal smoke') was associated with high adult reporting of persistent cough, persistent phlegm, and wheeze. Cooking coal smoke was associated with physician-diagnosed adult asthma and decreased forced vital capacity (FVC), and forced expiratory volume at 1 s (FEV(1)) in children. The presence of any home cigarette smoker was associated with more reports of persistent cough, persistent phlegm, cough with phlegm, and bronchitis. Our study suggests that in Wuhan, there may be independent respiratory health effects of different indoor combustion sources and their exposure factors for these study populations. PRACTICAL IMPLICATIONS: We conclude that multiple indoor air pollution sources could have adverse respiratory health effects on both children and middle-aged men in the city of Wuhan, China. These results may have implications for the Wuhan local government, the Chinese government, or other related organizations in efforts on protecting public health through regulation of indoor air pollution from indoor combustion sources.     

Outdoor sources of indoor air pollution

Conservation measures that seal a building, such as storm window installation, can significantly reduce its energy requirements. These measures also protect its occupants from air pollutants having outdoor sources but amplify any harmful effects of those generated indoors. Which effect is greater?Since it is inadequate to consider pollution levels constant, we assume that they follow daily cycles and can thus be well represented by Fourier series. We conclude that the indoor concentration of any pollutant generated solely outdoors also follows a daily cycle but its maximum lags behind and is lower than the outdoor maximum to an extent depending in an inverse manner on v, the air exchange (ventilation + infiltration) rate. A simple measure of the daily variation of pollutant concentrations and indoor production rates can be derived from their Fourier series and used to test whether these quantities can be assumed constant.Although average daily indoor and outdoor pollutant concentrations of any pollutant are the same if there are no indoor sinks, lowering v will still protect a building's occupant if: (1) the outdoor peak or variation above its average is much greater than its average, and (2) the peak is short-lived.Lowering v probably raises indoor average and peak pollutant concentrations from all indoor sources by at least as much as it lowers only peaks from just one outdoor source, rush hour traffic, thus increasing indoor pollutant levels.     

Characterisation of pollutants washed off from road surfaces during wet weather

This paper presents the results of a monitoring programme carried out to study the washoff of various pollutants from impermeable road surfaces by the runoff produced under artificial and real rainfall conditions. Among the pollution parameters analysed are solids (total, suspended and total volatile), COD (chemical oxygen demand), ammonium and heavy metals (lead, copper, zinc and iron). Analysis of the results indicates a linear relationship between the mass loading rate of total solids, volatile solids and COD. The effect of runoff rate on the magnitude of pollution washed off has also been investigated. Particle size analysis, of the washoff solids shows that the predominant size fraction is < 50 μm. The average diameter of solids has been found to increase with an increase in the runoff rate.     

The interaction of local weather and air pollution problems

First we have to clarify our objectives: scientists must not work too remotely from the crude phenomena of air pollution or disproportionate effort will be applied in useless directions, and we must not seek the abolition of pollution but rather arrange our priorities so that the earliest and largest effort is placed where it will be most beneficial.

It is soon discovered that the priorities vary according to the local weather, and of course according to the location and nature of the local pollution sources. “Average weather conditions” are often meaningless in this context, and local conditions affect the results on various scales, namely architectural, urban, in valleys and mountains, height of cloud base, and according to the efficacy of the scavenging mechanisms.

Certain sources may create quite new problems in special climates and local conditions may exert an overriding effect on the planning of surveys. Modelling is considered to be of little value compared with field observations.     

Captured streams and springs in combined sewers: A review of the evidence,consequences and opportunities

Captured streams and springs may be flowing in combined sewers, increasing clean baseflow in pipes and wastewater treatment works (WwTWs), reducing pipe capacity and increasing treatment costs. The UK water industry is aware of this in principle, but there has been no explicit discussion of this in the published literature, nor have there been any known attempts to manage it. Instead, the current focus is on the similar intrusion of groundwater infiltration through pipe cracks and joints. We have conducted a thorough review of literature and international case studies to investigate stream and spring capture, finding several examples with convincing evidence that this occurs. We identify three modes of entry: capture by conversion, capture by interception, and direct spring capture. Methods to identify and quantify capture are limited, but the experience in Zurich suggests that it contributed 7–16% of the baseflow reaching WwTWs. There are negative impacts for the water industry in capital and operational expenditure, as well as environmental and social impacts of loss of urban streams. For a typical WwTW (Esholt, Bradford) with 16% of baseflow from captured streams and springs, we conservatively estimate annual costs of £2 million to £7 million. A detailed case study from Zurich is considered that has successfully separated captured baseflow into daylighted streams through the urban area, with multiple economic, environmental and social benefits. We conclude that there is a strong case for the UK water industry to consider captured streams and springs, quantify them, and assess the merits of managing them.     

Characteristics of wet and dry weather heavy metal discharges in the Yeongsan Watershed, Korea

A comprehensive water quality monitoring program was conducted in the Yeongsan (YS) River, Korea from 2005 to present to investigate wet and dry weather pollutant discharge in an attempt to establish point and non-point pollution management strategies. As part of this monitoring program, 11 heavy metal species were measured during dry and wet weather conditions in the YS River, where Gwangju City (GJ), a subcatchment of the YS River, was further monitored to clarify the responsibility of different metal species discharged into the mainstream. Monthly grab water samples showed that greater amounts of metals along the YS River were discharged during the wet summer months due largely to storm runoff. In addition, further monitoring results revealed that GJ, a highly urbanized area, was a significant contributor of the heavy metals being discharged into the YS River during both wet and dry weather. The most abundant metal species discharged from GJ were manganese, aluminum and iron with different contributions of wet and dry weather flows to the total discharge load. Wet weather flow was a significant contributor to the annual dissolved metal loads, accounting for 44-93% of the annual load depending on the metal species, with the exception of chromium and cadmium (9% and 27%, respectively). Mostly, metal loads during wet weather were shown to be proportional to the rainfall depth and antecedent dry period. A substantial fraction of metals were also associated with solids, suggesting that sedimentation might be an appropriate management practice for reducing the metal load generated in GJ. Overall, although dissolved metal concentrations in YS River were at an acceptable level for aquatic community protection, continual metal discharge throughout the year was considered to be a potential problem in the long-term due to gradual water quality degradation as well as continuous metal accumulation in the system.     

Contribution from the primary and secondary sources to the atmospheric formaldehyde in Kolkata, India

A novel and straight forward method is adopted to segregate the contribution of primary and secondary sources of formaldehyde based on the rates of its formation and removal at different times in the urban atmosphere of Kolkata. To achieve the above objective, the diurnal and seasonal mixing ratios of formaldehyde were measured during dry season at two busy roadside locations. The maximal secondary formation fluxes of formaldehyde during summer and winter were found to be 6.63 × 10⁷ and 1.23 × 10⁷ molecules cm^− 3 s^− 1, respectively. Apart from formaldehyde (C₁), several other carbonyls were quantified in this study. An overall good correlation between acetaldehyde (C₂) and propanal (C₃) indicates the contribution of vehicular emission to the carbonyl budget. The secondary formaldehyde contributions in summer and winter were about 71% and 32%, respectively. The relative mean contributions of C₁, C₂ and ozone towards generation of OH fluxes in summer were found to be 1.56 × 10⁷, 6.96 × 10⁵, and 1.29 × 10⁷ molecules cm^− 3 s^− 1, respectively, which were 3.2, 3.4 and 1.6 times higher than those in winter.     

Groundwater pollution by volatile halogenated hydrocarbons; sources of pollution and methods to estimate their relevance

An investigation was made of the prevalence of volatile halogenated hydrocrabons in groundwater used for production of drinkingwater in the Netherlands. In some cases concentrations of tri- and perchloroethylene were found at levels higher than 10/ μg/l. In 50% of the groundwatersources these substances were detected at levels than l /μg/l but higher than the detection limit of 0.01 /μg/l, even in well protected areas. Cases with levels higher than 10/μg/l and probably 1/μg/l could be argued to be due to direct (point) discharges to the ground. From data of the Dutch emission inventory system it is calculated that air pollution may be the cause of groundwater-pollution at lower levels.The emission inventory system allows sources of pollution to be classed by level of emission, industrial branche and type of installation, enabling a systematic identification of pollutants and their point sources.     

PCB dry and wet weather concentration and load comparisons in Houston-area urban channels

All 209 PCB congeners are quantified in water in both dry and wet weather urban flows in Houston, Texas, USA. Total water PCBs ranged from 0.82 to 9.4 ng/L in wet weather and 0.46 to 9.0 ng/L in dry. Wet weather loads were 8.2 times higher (by median) than dry weather with some increases of over 100-fold. The majority of the PCB load was in the dissolved fraction in dry weather while it was in the suspended fraction in wet weather. Dissolved PCB loads were correlated with rain intensity and highly developed land area, and a multiple linear regression (MLR) equation was developed to quantify these correlations. PCA generated five PCB components with nearly all positive loadings. They were interpreted as DOC-associated A1248, wet weather primarily suspended fraction A1254/A1260 likely from building sealants, truly dissolved-associated wastewater dechlorination, watershed-sourced PCB 11, and monochlorinated PCBs (likely connected to a different state or source of dechlorination). The PCB 11 component was statistically higher in wet versus dry weather when no other component showed such clear distinctions. Hierarchical cluster analysis (HCA) did not always group dry and wet weather samples from the same location together illustrating the different congener composition that often exists between dry and wet conditions. Four wet weather samples from high percentage developed land (> 90%) watersheds had nearly the same fingerprint suggesting a generic “urban” signature in runoff, which in this case was caused by residual A1254/A1260 PCB stocks and currently produced PCB 11 in consumer goods.