Diffuse water pollution during recent extreme wet-weather in the UK: Environmental damage costs and insight into the future?

Periods of extreme wet-weather elevate agricultural diffuse water pollutant loads and climate projections for the UK suggest wetter winters. Within this context, we monitored nitrate and suspended sediment loss using a field and landscape scale platform in SW England during the recent extreme wet-weather of 2019-2020. We compared the recent extreme wet-weather period to both the climatic baseline (1981-2010) and projected near- (2041-2060) and far- (2071-2090) future climates, using the 95th percentiles of conventional rainfall indices generated for climate scenarios downscaled by the LARS-WG weather generator from the 19 global climate models in the CMIP5 ensemble for the RCP8.5 emission scenario. Finally, we explored relationships between pollutant loss and the rainfall indices. Grassland field-scale monthly average nitrate losses increased from 0.39-1.07 kg ha-1 (2016-2019) to 0.70-1.35 kg ha-1 (2019-2020), whereas losses from grassland ploughed up for cereals, increased from 0.63-0.83 kg ha-1 to 2.34-4.09 kg ha-1. Nitrate losses at landscape scale increased during the 2019-2020 extreme wet-weather period to 2.04-4.54 kg ha-1. Field-scale grassland monthly average sediment losses increased from 92-116 kg ha-1 (2016-2019) to 281-333 kg ha-1 (2019-2020), whereas corresponding losses from grassland converted to cereal production increased from 63-80 kg ha-1 to 2124-2146 kg ha-1. Landscape scale monthly sediment losses increased from 8-37 kg ha-1 in 2018 to between 15 and 173 kg ha-1 during the 2019-2020 wet-weather period. 2019-2020 was most representative of the forecast 95th percentiles of >1 mm rainfall for near- and far-future climates and this rainfall index was related to monitored sediment, but not nitrate, loss. The elevated suspended sediment loads generated by the extreme wet-weather of 2019-2020 therefore potentially provide some insight into the responses to the projected >1 mm rainfall extremes under future climates at the study location.

Enhanced primary treatment during wet weather flow using ferrate as a coagulant, coagulant aid and disinfectant.

This study evaluated the dual-function of ferrate as a coagulant and disinfectant for chemically-enhanced primary treatment during wet weather flow (WWF). For the first time, ferrate was thoroughly examined as a coagulant aid with aluminum sulfate (alum) to minimize the organic and inorganic contents along with microbial level during WWF. Ferrate as a coagulant was evaluated based on a two-level factorial design. At an optimized condition, a ferrate dose of 0.5 mg/L Fe with a cationic polymer (1.25 mg/L) removed 83% of turbidity, 87% of total suspended solids (TSS), 70% of chemical oxygen demand (COD), and 23% of ortho-phosphate (OP). Linear models were developed and used to adequately predict the removals. Ferrate as a coagulant aid added with alum showed better removal of TSS while no improvement was observed in the removals of turbidity and COD. The disinfection capacity of ferrate was evaluated at different dosing points when it was used as a coagulant, coagulant aid and as post dosed as a disinfectant. In particular, ferrate dose of 8 mg/L Fe removed only 2 logs of E. coli when it was used as a coagulant compared to more than 3-log removal of E. coli when ferrate was used as a coagulant aid and as a disinfectant. At optimal ferrate dose of 10 mg/L Fe as a coagulant aid with 6 mg/L Al achieved the target levels of turbidity (<8 NTU), TSS (<25 mg/L), and ferrate-induced iron particles (<0.6 mg/L) along with 5-log removal of E. coli within 31 min. This study suggested that using ferrate as a coagulant aid/disinfectant might be considered an effective approach for treating the wastewater during WWF.

Quantifying the Relative Contributions of Environmental Sources to the Microbial Community in an Urban Stream under Dry and Wet Weather Conditions.

Investigating sources of microbial contamination in urban streams, especially when there are no contributions from combined sewer overflows or sewage effluent discharges, can be challenging. The objectives of this study were to identify the sources of microbes in an urban stream and quantify their relative contributions to the microbial community in the stream under dry and wet weather conditions. A microbial source tracking method relying on the 16S rRNA gene was used to investigate the microbial communities in water samples of an urban stream (i.e., from 11 dry and 6 wet weather events), as well as in streambed sediment, soils, street sweepings, sanitary sewage, an upstream lake, and feces of animals and birds collected between 2013 and 2015. The results showed that the Escherichia coli levels in the stream were significantly higher in wet weather flow than in dry weather flow. The upstream lake contributed approximately 93% of the microbes in dry weather flows. Water discharged from storm drain outfalls was the biggest source of microbes in wet weather flows, with a median contribution of approximately 90% in the rising limb and peak flow and about 75% in the declining limb of storms. Furthermore, about 70 to 75% of the microbes in the storm drain outfall water came from materials washed off from the street surfaces in the watershed. Fecal samples did not appear to contribute substantially to the microbes in environmental samples. The results highlight the significance of street surfaces in contributing microbial loads to urban streams under wet weather conditions.IMPORTANCE Identifying the sources of microbial contamination is important for developing best management practices to protect the water quality of urban streams for recreational uses. This study collected a large number of water samples from an urban stream under both dry and wet weather conditions and provided quantitative information on the relative contributions of various environmental compartments to the overall microbial contamination in the stream under the two weather conditions. The watershed in this study represents urban watersheds where no dominant fecal sources are consistently present. The findings highlight the importance of reducing the direct contribution of microbes from street surfaces in the watershed to urban streams under wet weather conditions. The methods and findings from this study are expected to be useful to stormwater managers and regulatory agencies.

Urban stormwater quality: A review of methods for continuous field monitoring.

Urban stormwater is contaminated by a wide range of substances whose concentrations vary greatly between locations, as well as between and during rain events. This literature review evaluates advantages and limitations of current methods for using continuous water quality monitoring for stormwater characterization and control. High-temporal-resolution measurements have been used to improve the understanding of stormwater quality dynamics and pollutant pathways, facilitate the performance evaluation of stormwater control measures and improve operation of the urban drainage system with real-time control. However, most sensors used to study stormwater were developed for either centralized water treatment or natural water contexts and adaptation is necessary. At present, the primary application of interest in stormwater - characterization of pollutant concentrations - can only be achieved through the use of indirect measurements with site-specific relationships of pollutants to basic physical-chemical parameters. In addition, various problems arise in the field context, associated with intermittent or variable flow rates, the accumulation of debris and sediment, adverse conditions for electrical equipment and human factors. Obtaining reliable continuous stormwater quality data requires the adoption of best practices, including the calibration and regular maintenance of sensors, verification of data and accounting for the considerable uncertainties in data; however, the literature review showed that improvement is needed among the scientific community in implementing and documenting these practices.

Microplastic accumulation in sewer sediments and its potential entering the environment via combined sewer overflows: a study case in Paris.

During wet weather events, combined sewer overflows (CSOs) transfer large amount of particulate matter and associated pollutants into surrounding water bodies, thereby deteriorating the recipients' ecological health. Resuspension of sewer sediments during these events contributes significantly to pollution level of these discharges. However, how much this in-sewer process contributes to CSOs' quality regarding microplastic (MP) pollution is little known. Therefore, an investigation on sewer deposits inside the Parisian combined sewer network was carried out. The study found high MP concentrations stored in this matrix, ranging from 5 × 103 to 178 × 103 particle/kg dry weight. Polymer composition is similar to what found in raw wastewater, containing a high proportion of polyethylene and polypropylene. Thus, the results indicated the persistence of MPs in sewer network during transport during dry weather periods to treatment facilities. Once resuspension of sewer deposits happens, MPs can be released into water flow and get discharged along with CSOs. This highlights another potential pathway of MPs into freshwater environment.

Blue-green roofs as nature-based solutions for urban areas: hydrological performance and climatic index analyses.

The water-regulating capacity of nature-based solutions (NBSs) plays a crucial role in providing a full range of ecosystem services and enhancing the resilience of urban systems. This work focuses on the hydrological performance of a particular NBS, the so-called blue-green roof (BGR). The BGR is designed to collect infiltrated rainfall in a water storage layer beneath the soil to support vegetation maintenance, enhance evapotranspiration and cooling, and minimize runoff and drainage system load. The study aims to evaluate the hydrological performance of the BGR at global and event scale and, for the first time, to model climatic factors (easy to measure using common sensors) that affect its stormwater retention capacity. The data collected over 2 years and 2 months at a 5-min resolution from a pilot study in Central Italy were analysed. Additionally, a new climatic index called AWWP-x (Antecedent Wet Weather Period index) was introduced and calculated. Results show that the BGR has an overall relevant retention rate (67.1%), although the value depends on the rainfall of the observed period. Approximately 50% of the rainfall events did not produce any runoff, and during the dry season, all events were totally absorbed by the BGR. Four climatic variables were identified as significant factors for predicting BGR retention performance (R2 = 0.50). The results suggest that AWWP-130 (number of days to reach 130 mm cumulative precipitation) could be a possible proxy for the BGR stormwater retention rate. In general, this study demonstrates the potential for evaluating, planning, and designing NBSs by considering the annual and interannual climatic variability of the investigated specific location.

Under-loaded operation of an anaerobic-anoxic-aerobic system in dry and wet weather dynamics to prevent overflow pollution: Impacts on process performance and microbial community.

Effects of low hydraulic loading rate (HLR) in dry weather and high HLR in wet weather on pollutant removal, microbial community, and sludge properties of a full-scale wastewater treatment plant (WWTP) were extensively studied to explore the risk of under-loaded operation for overflow pollution control. Long-term low HLR operation had an insignificant effect on the pollutant removal performance of the full-scale WWTP, and the system could withstand high-load shocks in wet weather. Low HLR resulted in higher oxygen and nitrate uptake rate due to the storage mechanism under the alternating feast/famine condition, and lower nitrifying rate. Low HLR operation enlarged particle size, deteriorated floc aggregation and sludge settleability, and reduced sludge viscosity due to the overgrowth of filamentous bacteria and inhibition of floc-forming bacteria. The remarkable increase in Thuricola and the contract morphology of Vorticella in microfauna observation confirmed the risk of flocs disintegration in low HLR operation.

Real-time variabilities in microplastic abundance and characteristics of urban surface runoff and sewer overflow in wet weather as impacted by land use and storm factors.

Urban surface runoff (USR) and drainage system overflows during wet weather (WWF) play a key role in shaping water pollution. Particularly, the impact of large amounts of microplastic pollution on urban water bodies is unclear. We conducted an in-field investigation in six central urban drainage systems along Suzhou Creek in the Shanghai megacity of China and identified the impacts of storm factors and land use on the real-time dynamic changes in microplastic abundance and characteristics in USR and WWF. Microplastic abundances ranged from 228.3 ± 105.4-4969.51 ± 348.8, 309.3 ± 144.3-5195.8 ± 425.5, and 130.0 ± 30.0-8500.0 ± 1241.0 particles/L in the traffic and residential catchment USR, and the WWF, respectively. Under similar storm factor conditions, we observed correlations between environmental factors and microplastic abundance, especially the polymer type, verifying the significant role of land use. The microplastic abundance were 90.2 particles/L higher in the traffic catchment USR than in the residential catchment USR. Notably, we found unique microplastic polymers comprising ethylene vinyl acetate copolymer and thermoplastic elastomers in the residential and traffic catchment USR, respectively. However, land use had a minimum impact on the size and shape of microplastics: small-sized and film microplastics dominated in both USR types. We found statistical evidence of the widespread correlations between microplastic abundance and storm factors (accumulated storm depth and WWF flow) in both USR and WWF. The first flush phenomenon of microplastic dynamics was found in both USR and WWF. Microplastic characteristics also changed dynamically with storm time. With heavy storm factors, polypropylene and small-sized (<1 mm) microplastics in USR events increased and then decreased. This was also true for WWF events in granular and polyethylene terephthalate microplastics. Our results can facilitate the targeted mitigation of emerging pollutants to enhance stormwater management strategies and prevent future contamination.

Development and performance of a machine learning-based tool that predicts influent flow to a WRF 72 h in advance and integrates with existing wet weather nutrient management protocols.

Influent flow to the 75 mgd Neuse River Resource Recovery Facility (NRRRF) was modeled using machine learning. The trained model can predict hourly flow 72 h in advance. This model was deployed in July 2020, and has been in operation over two and a half years. The model's mean absolute error in training was 2.6 mgd, and mean absolute error has ranged from 10 to 13 mgd in deployment for any point during the wet weather event when predicting 12 h in advance. As a result of this tool, plant staff have optimized the use of their 32 MG wet weather equalization basin, using it approximately 10 times and never exceeding its volume. PRACTITIONER POINTS: A machine learning model was developed to predict influent flow to a WRF 72 h in advance. Selecting the appropriate model, variables, and properly characterizing the system are important considerations in machine learning modeling. This model was developed using free open source software/code (Python) and deployed securely using an automated Cloud-based data pipeline. This tool has been in operation for over 30 months and continues to make accurate predictions. Machine learning combined with subject matter expertise can greatly benefit the water industry.

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.

Biological phosphorus removal and its microbial community in a modified full-scale activated sludge system under dry and wet weather dynamics.

Enhanced biological phosphorus removal (EBPR) performance and microbial community dynamics during dry and wet-weather conditions of a full-scale treatment plant was evaluated by converting a section of activated sludge basins using low-cost operational modifications into an anoxic/anaerobic zone to promote EBPR. Two trains of the activated sludge system at the Des Moines, Iowa Metropolitan Wastewater Reclamation Facility were used for the study with one train modified for EBPR, and the other remained as nitrification-only for comparison. In addition to measuring the modification effectiveness for phosphorus removal, performance was compared during dry and wet weather conditions over the course of two summer seasons to improve understanding of wet and dry weather dynamics for EBPR. DNA sequencing and qPCR tests were conducted to develop an understanding of microbial population changes between control and modified basins and wet and dry weather conditions. Basin hydraulic retention times varied from 2.6 to 12.7 hours with an average of 8.9 hours. EBPR activity was successfully established in the modified basins with average phosphorus content of the return activated sludge 0.032 ± 0.002 compared to 0.016 ± 0.001 mg TP/mg TSS (95% confidence) in the control basins. Phosphorus removal was significantly decreased by prolonged wet weather conditions, particularly in year two of the study, however the modified basin maximum removal of 96% and average of 43.7 ± 5.3% remained significantly higher than the maximum of 46% and average 12.6 ± 2.4% removal in the control basins. DNA sequencing showed a significant increase in relative abundance of phyla Chloroflexi, Nitrospirae, and Verrucomicrobia in the modified basins, but no correlation to EBPR performance. qPCR indicated significant increase in relative quantity of Accumulibacter, but not for Actinetobacter-like phosphorus accumulating organisms (PAOs), which includes the PAO Tetrasphaera. Significant abundance of some Accumulibacter clades found within the modified basins was contrary to previous literature which focused on small-scale and batch studies. A higher than expected dominance of clade I and increased relative quantities of clades IIB and IIC during extended wet weather was observed which may have contributed to rapid recovery of phosphorus removal when dry weather resumed. The abundance of PAOs did not significantly correlate with changes in phosphorous removal performance, contrary to reports from previous small-scale and batch studies.

Restricting dairy cow access time to pasture in autumn: The effects on milk production, grazing behaviour and DM intake of late lactation dairy cows.

Extending the grazing season in pasture based systems of dairy production can increase farm profitability; poor weather and soil conditions can reduce the number of grazing days. The study objectives were to (i) examine the effect of restricted access to pasture in the autumn on the milk production, grazing behaviour and DM intake (DMI) of late lactation spring-calving dairy cows and (ii) establish the effect of alternating restricted and continuous access to pasture on dairy cow production, DMI and grazing behaviour. Cows were randomly assigned to one of four grazing treatments: (i) 22 h (full-time) access to pasture (22H; control); (ii) Two 5-h periods of access to pasture (2×5H); (iii) Two 3-h periods of access to pasture (2×3H); and (iv) alternating between full-time and 3-h access to pasture with no more than three continuous days on any one regime, e.g. Monday - full-time access, Tuesday - 2x3H access, Wednesday - 2x3H access; Thursday - full-time access, etc. (2×3HV). Restricted access to pasture was offered after a.m. and p.m. milking. Swards of similar quality and pregrazing herbage mass were offered. Treatment had no effect on milk yield (13.2 kg/day), milk fat (48.2 g/kg), protein (39.0 g/kg) or lactose content (42.6 g/kg) and milk solid yield (1.15 kg/day). Similarly, there was no effect of treatment on final BW (483 kg) or final BCS (2.66). There was no significant difference in DMI (15.1 kg DM/cow/day) between treatments. There was an effect on daily grazing time, 22H cows (565 min/cow/day) grazed for longest time, however, when the 2x3HV treatment had full-time access to pasture, they had a similar grazing time (543 min/cow/day) to the 22H cows and were similar to the 2x3H treatment on days with restricted access to pasture (357 min/cow/day). The 22H and 2x5H animals had similar grass DMI/min (29.2 g/min), the 2x3HV were higher (33.9 g/min) but were similar to the comparable treatment when offered 2x3H access time (41.6 g/min) and when offered 22H access time (27.7 g/min). The results from this study show how when offered a grass only diet of autumn pasture grazing behaviour can be modified by restricting pasture access time without reducing dairy cow production in late lactation at low production levels. There was also no effect of alternating access time between 22H and 2x3H on milk production and DMI in the 2x3HV treatment. Restricted access time to pasture in autumn may be a strategy which farmers can use to extend the grazing season.

Quantitative source apportionment of dissolved organic matters in wet weather overflows of storm drainage systems based on degradation potential index and end member mixing model.

Dissolved organic matter (DOM) in wet weather overflows (WWFs) of storm drainage systems mainly originates from anthropogenic sources, such as paved runoff, illegally discharged domestic sewage and the retained sediment. This study provides a promising method to quantitatively apportion the WWF DOM of storm drainage systems using degradation potential index (DPI) and end member mixing (EMM) model. DPI is derived from excitation-emission matrix parallel factor analysis (EEM-PARAFAC), which can endow the end members and itself of WWF DOM with numerical features, and thus help quantify the source contributions of WWF DOM in EMM model. Findings show that (1) DPI was a reliable tool in the quantitative source apportionment of WWF DOM, owing to its features of small variance within source and large variances between sources; (2) DPI combined with EMM model could help identify the factors that induce significant impacts on the source contributions of WWF DOM, such as the storm pumping discharge and antecedent dry days in our case study; (3) the identified factors could guide the development of effective strategies for WWF DOM control, e.g. sediment management in our case.

Performance and operational strategy of simultaneous nitrification, denitrification, and phosphorus removal system under the condition of low organic loading rate in wet weather.

A pilot-scale aerobic granular sequencing batch reactor (SBR) with domestic wastewater was operated to evaluate the effects of the low organic loading rate (OLR) due to wet weather flow conditions on simultaneous nitrification, denitrification, and phosphorus removal (SNDPR). As the OLR decreased from 0.85 to 0.43 kg COD m-3 d-1, the total nitrogen (TN) and total phosphorus (TP) removal efficiencies decreased from 84.0% and 94.1% to 51.3% and 73.8%, respectively, the sludge volume index (SVI) increased from 42.3 to 85.5 mL g-1, and the average granular size decreased from 1022 to 742 µm; however, no sludge disintegration and biomass loss were observed. The poor nutrient removal efficiencies and settling ability were due to the shrinking anoxic zone and substrate scarcity inside the granules, wherein the activity decay of ammonia-oxidizing bacteria and overgrowth of filamentous bacteria played an important role. Alternating the aeration intensity was effective in enhancing nitrogen removal and sludge settling by improving the anoxic activity in granules and inhibiting the proliferation of filamentous bacteria. Returning 20% of sludge from the end of one anaerobic stage to the beginning of the next anaerobic stage (midway sludge return) was beneficial for phosphorus removal as it improved phosphorus storage by phosphorus-accumulating bacteria. A smaller granular size with stronger stability and better nutrient removal performance was the new steady state of the SNDPR system under wet-weather flow conditions.

Impact of urbanisation (trends) on runoff behaviour of Pampulha watersheds (Brazil).

The paper presents an analysis of runoff behaviour of four urban catchments between the municipalities of Belo Horizonte and Contagem in Brazil, linked to their land use. Two years of online measurement of flow data, combined with spatial analysis, was linked through runoff modelisation with EPA SWMM. The coefficients of Nash obtained varying between 0.75 and 0.87 demonstrated an adequate modelling approach. A 1-year rain series was applied to evaluate the runoff behaviour of actual land cover and that of 2002. The peak flows normalised to watershed surfaces revealed as the most urbanised (85%) watershed Ressaca with 178 L/ha/s, three times more runoff intensive than the least urbanised (41%) Mergulhão with 67 L/ha/s. Statistical analysis of land cover data and modelling results on watershed and sub-watershed level showed main correlations between hydrological parameters such as peak flow, average event flow and restitution time, but also between land cover and runoff coefficient. This approach gave a linear relation between runoff and green surface, with a runoff coefficient of 0.86 for fully urbanised zone and 0.43 for full "green" cover. Prospective simulation with actual urbanisation rates varying from 4 to 34 ha/year suggested an increase between 6 and 18% of the flows and a possible end of urbanisation within the next two to three decades. These findings should contribute to a better understanding of hydrological impact of Belo Horizonte urbanisation and to the restauration of its Lake Pampulha.

Treatment of bypass wastewater using potassium ferrate(VI): assessing the role of mixing.

In-plant wastewater treatment strategies to deal with bypass wastewater in excess of plant capacity are critical in securing sustainable wastewater management. To address this issue, potassium ferrate(VI), which is a dual disinfectant and coagulant, is assessed in this study as the sole chemical applied to enhance the primary treatment of bypass wastewater. The effect of rapid mixing speed is investigated for the first time along with potassium ferrate(VI) dosage by means of central composite design and response surface methodology. Escherichia coli (E. Coli), Faecal Coliform (FC), Total Suspended Solids (TSS), and Orthophosphates ( P O 4 3 - ) were considered as the process responses. All responses other than P O 4 3 - showed good agreement between the observed and modelled values. While there was no point of maximum or minimum response for both E. Coli and FC, whose removals were found to increase with the increase of both the mixing intensity and potassium ferrate(VI) dosages, TSS removal exhibited optimal responses. The effluent quality achieved by potassium ferrate(VI), as an independent treatment, can be sufficient for certain types of unrestricted and restricted irrigation reuse purposes suggested by World Health Organisation (WHO) reuse guidelines.

Microalgal whole-cell biomarkers as sensitive tools for fast toxicity and pollution monitoring of urban wet weather discharges.

Urban wet weather discharge (UWWD) management is an important issue. UWWD often represents a significant source of pollution in all aquatic bodies. The occurrence of this pollution is difficult to predict due to the variability of storm events and the unknown contents of urban watershed leached out by rain. Previous studies have tried to demonstrate the ecotoxic impact of UWWD. However, most of them merely highlight the limitations of classic monospecific bioassays, given the high dilution of micropollutants or the presence of nutrients masking toxic effects. Overcoming this problem is therefore of great interest. In this study, we demonstrated the utility of a battery of biomarkers (e.g. membrane permeability, chlorophyll fluorescence, esterase and alkaline phosphatase activities) on the microalgae Chlorella vulgaris to detect the toxic effects of 7 UWWD samples after short exposures (2 and 24 h). These biomarkers are linked to microalgal life traits. Complementarily, monospecific bioassays were carried on Pseudokirchneriella subcapitata, Chlorella vulgaris, Daphnia magna and Heterocypris incongruens to compare their sensitivity to the UWWD samples. No toxic effect was detected in any of the bioassays. Yet, algal biomarkers indicated a disturbance in microalgae physiology, and particularly a perturbation of chlorophyll fluorescence, which was observed in all of the samples tested. While algal membrane permeability was affected by only one UWWD, these two enzymatic activities were stimulated or inhibited depending on the sample. Finally, this study demonstrates the sensitivity of algal biomarkers and the need to develop new, fruitful approaches to characterizing UWWD toxicity.

Predicted sediment toxicity downstream of combined sewer overflows corresponds with effects measured in two sediment contact bioassays.

The present study investigated the sediment toxicity along 100 m transects downstream from three different combined sewer overflows (CSOs) using a coupled substance risk assessment and bioassay approach. As a first step, a risk assessment according to the consensus based sediment quality guideline was performed to estimate the probability for an incidence of toxicity to benthic organisms in freshwater sediments using their pollutant concentrations of metals, PAHs and PCBs. Secondly, two sediment contact assays (SCAs) using the nematode Caenorhabditis elegans and embryos of the fish Danio rerio were conducted. Sediments downstream from CSOs were strongly influenced by discharged particles in terms of pollution, due to associated contaminants as well as oxygen depletion caused by oxygen consuming matter. In general, the calculated probability for sediment toxicity corresponded with results of the SCAs. With increasing distance from the CSOs both the toxic potential of the sediments as well as their effects detected in the SCAs decreased. However, clear correlations between concentrations of metals as well as PCBs and toxic effects were found for the nematode SCA. The toxicity assay with embryos of D. rerio was strongly influenced by oxygen depletion in the sediments. Therefore, it was not possible to differentiate between responses mediated by pollution or oxygen depletion using the D. rerio embryo test. The results of the present study demonstrated a clear effect of CSOs on the toxicity of downstream located sediments. As particles were identified as vector for pollutants and as source for oxygen depletion, the retention of particles within the sewer network is of high importance to minimize both stressors. The present study shows that a retention zone located between the CSO and the receiving creek is an efficient measure to enhance sediment and water quality downstream of CSOs.

Safety effects of wet-weather pavement markings.

While there has been increasing interest in wet-weather pavement markings due to their improved visibility and potential for enhancing road safety in wet-night conditions, there is a lack of research evaluating their safety effectiveness based on actual wet-night crash data. This paper presents the safety assessment of wet-weather pavement markings in the Atlanta District of the Texas Department of Transportation, conducted by two different evaluation approaches that are known to be rigorous and statistically defensible: Empirical-Bayes before-after analysis and full Bayes before-after analysis with comparison groups. The results from both approaches suggest that there are positive safety effects of wet-weather pavement markings for relevant crashes, providing evidence-based support for safety benefits of wet-weather markings.

Impacts from urban water systems on receiving waters - How to account for severe wet-weather events in LCA?

Sewage systems are a vital part of the urban infrastructure in most cities. They provide drainage, which protects public health, prevents the flooding of property and protects the water environment around urban areas. On some occasions sewers will overflow into the water environment during heavy rain potentially causing unacceptable impacts from releases of untreated sewage into the environment. In typical Life Cycle Assessment (LCA) studies of urban wastewater systems (UWS), average dry-weather conditions are modelled while wet-weather flows from UWS, presenting a high temporal variability, are not currently accounted for. In this context, the loads from several storm events could be important contributors to the impact categories freshwater eutrophication and ecotoxicity. In this study we investigated the contributions of these wet-weather-induced discharges relative to average dry-weather conditions in the life cycle inventory for UWS. In collaboration with the Paris public sanitation service (SIAAP) and Observatory of Urban Pollutants (OPUR) program researchers, this work aimed at identifying and comparing contributing flows from the UWS in the Paris area by a selection of routine wastewater parameters and priority pollutants. This collected data is organized according to archetypal weather days during a reference year. Then, for each archetypal weather day and its associated flows to the receiving river waters (Seine), the parameters of pollutant loads (statistical distribution of concentrations and volumes) were determined. The resulting inventory flows (i.e. the potential loads from the UWS) were used as LCA input data to assess the associated impacts. This allowed investigating the relative importance of episodic wet-weather versus "continuous" dry-weather loads with a probabilistic approach to account for pollutant variability within the urban flows. The analysis at the scale of one year showed that storm events are significant contributors to the impacts of freshwater eutrophication and ecotoxicity compared to those arising from treated effluents. At the rain event scale the wet-weather contributions to these impacts are even more significant, accounting for example for up to 62% of the total impact on freshwater ecotoxicity. This also allowed investigating and discussing the ecotoxicity contribution of each class of pollutants among the broad range of inventoried substances. Finally, with such significant contributions of pollutant loads and associated impacts from wet-weather events, further research is required to better include temporally-differentiated emissions when evaluating eutrophication and ecotoxicity. This will provide a better understanding of how the performance of an UWS system affects the receiving environment for given local weather conditions.