Investigating the effect of storm events on the particle size distribution in a combined sewer simulator.

The changes in particle size of sewer sediment particles rapidly eroded from a previously deposited sediment bed are described, using a rotating annular flume as a laboratory scale sewer simulator. This is the first time that particle size distributions of eroded sewer sediments from a previously deposited sediment bed have been monitored in such a controlled experimental environment. Sediments from Loenen, The Netherlands and Dundee, UK were used to form deposits in the base of the annular flume (WL Delft Netherlands) with varying conditions for consolidation in order to investigate the effect of changing consolidation time, temperature and sediment type on the amount and size of particles eroded from a bed under conditions of increasing shear. The median size of the eroded particles did not change significantly with temperature, although the eroded suspended solids concentration was greater for the higher temperature under the same shear stresses, indicating a weaker bed deposit. An increase in consolidation time caused an increase in median size of eroded solids at higher bed shear stresses, and this was accompanied by higher suspended solids concentrations. As the shear stress increased, the solids eroded from the bed developed under a longer consolidation time (56 hours) tended towards a broad unimodal distribution, whilst the size distribution of solids eroded from beds developed under shorter consolidation times (18 or 42 hours) retained a bi- or tri-modal distribution. Using different types of sediment in the flume had a marked effect on the size of particles eroded.     

Assessing dry weather flow contribution in TSS and COD storm events loads in combined sewer systems

Continuous high resolution long term turbidity measurements along with continuous discharge measurements are now recognised as an appropriate technique for the estimation of in sewer total suspended solids (TSS) and Chemical Oxygen Demand (COD) loads during storm events. In the combined system of the Ecully urban catchment (Lyon, France), this technique is implemented since 2003, with more than 200 storm events monitored. This paper presents a method for the estimation of the dry weather (DW) contribution to measured total TSS and COD event loads with special attention devoted to uncertainties assessment. The method accounts for the dynamics of both discharge and turbidity time series at two minutes time step. The study is based on 180 DW days monitored in 2007-2008. Three distinct classes of DW days were evidenced. Variability analysis and quantification showed that no seasonal effect and no trend over the year were detectable. The law of propagation of uncertainties is applicable for uncertainties estimation. The method has then been applied to all measured storm events. This study confirms the interest of long term continuous discharge and turbidity time series in sewer systems, especially in the perspective of wet weather quality modelling.     

合流制排水系统雨季污染物溢流的截流与调蓄控制研究

截流式合流制排水系统是我国主要的排水体制之一。以昆明市主城区明通河合流制排水系统为背景,研究了雨季产污及迁移规律及削减入湖污染物的措施,并进行了工程示范。示范研究结果表明,在CODCr截留率小于80%、截流倍数n0=1~3、调蓄量2~20 mm(以不透水地面计),提高截流倍数或调蓄量均可显著提高污染物截留率。截流倍数与调蓄量可表述为截留系数的函数,截流倍数增加1等效于调蓄量增加8 mm,截留系数为CODCr截留比率的幂函数。     

Relationship between turbidity and total suspended solids concentration within a combined sewer system

This article confirms the existence of a strong linear relationship between turbidity and total suspended solids (TSS) concentration. However, the slope of this relation varies between dry and wet weather conditions, as well as between sites. The effect of this variability on estimating the instantaneous wet weather TSS concentration is assessed on the basis of the size of the calibration dataset used to establish the turbidity - TSS relationship. Results obtained indicate limited variability both between sites and during dry weather, along with a significant inter-event variability. Moreover, turbidity allows an evaluation of TSS concentrations with an acceptable level of accuracy for a reasonable rainfall event sampling campaign effort.     

Integrated real-time control for a sequencing batch reactor plant and a combined sewer system.

Integrated real-time control (RTC) concepts, which are trying to operate drainage systems and WWTPs depending on the current capacities of both systems, are becoming more and more important. While almost all publications in this field have been concentrating on continuous flow systems, this paper will present a project which has been initiated to realise an integrated RTC strategy for a Sequencing Batch Reactor (SBR) plant in simulation as well as in full-scale. The results of the simulation are that SBR plants can handle high hydraulic loads. The cost-benefit analysis shows that an integrated operation is reasonable concerning environmental and economic aspects. In order to verify the simulation results, full-scale operation has been started in January 2004. The first results seem to confirm the results of the simulation study.     

Speciation and bioavailability of particulate phosphorus in forested karst watersheds of southern Ontario during rain events

Understanding riverine phosphorus (P) dynamics, its transport, and transformation mechanisms from sources in the watersheds to receiving water bodies are essential for the development of effective strategies to decrease excess P loading and reduce eutrophication. Karst watersheds are thought to be especially vulnerable to P pollution due to their geomorphological features. In this study, we investigated the dynamics of particulate P (PP) chemical phases in two karst watersheds from a Great Lakes Area of Concern in southern Ontario (Bay of Quinte, Canada). Suspended solids were collected during different hydrological regimes representing storm events with low and high discharge, and particulate P binding forms were measured using extraction techniques. Our results show that in these karst watersheds, particulate P is dominated by chemical species that are likely to be highly bioavailable and contribute 62–75% to total PP. Concentrations of these bioavailable P binding forms in suspended solids increase two- to three-fold on dry mass basis during periods of high river flow. Electron microprobe and energy dispersive X-ray spectroscopy suggest that the primary carriers of particulate P are aggregates of Fe oxyhydroxides and Al-silicates. Our results underscore the influence of particulate P sources on the ongoing eutrophication in the Bay of Quinte Area of Concern.     

Development and verification of a general approach to describe the efficiency of vortex separators in combined sewer systems.

The water framework directive (CEC, 2000) asks for cost-effective measures for achieving good ecological conditions in receiving waters. Because of low operation costs and good pollutant removal efficiency, vortex separators (VS) are an attractive alternative to traditional stormwater tanks. The German design standard for CSO structures, ATV-A 128 (1992), demands long-term pollution load simulations. Today's simulation software, however, considers the removal processes in CSO structures either very rudimentarily or not at all. The higher pollutant removal efficiency of a structure like a VS cannot be taken into account. This might be one reason why VS are used still comparatively scarcely. A mathematical model describing the removal efficiency could increase the acceptance of VS. Several functions describing the removal efficiency have been derived from model tests or large-scale studies within the last few years. Within this paper, the data from three large-scale studies are used to verify the general applicability of one steady-state and one dynamic approach. The results show that the complex processes involved with CSO facilities and the large error related to monitoring make the validation of models a difficult task. Anyhow, especially the dynamic approach was applicable at all considered facilities.     

Treatment performance of a constructed wetland during storm and non-storm events in Korea

The efficiency of a free water surface flow constructed wetland (CW) in treating agricultural discharges from stream was investigated during storm and non-storm events between April and December, 2009. Physico-chemical and water quality constituents were monitored at five sampling locations along the flow path of the CW. The greatest reduction in pollutant concentration was observed after passing the sedimentation zone at approximately 4% fractional distance from the inflow. The inflow hydraulic loading, flow rates and pollutant concentrations were significantly higher and variable during storm events than non-storm (baseflow) condition (p <0.001) that resulted to an increase in the average pollutant removal efficiencies by 10 to 35%. The highest removal percentages were attained for phosphate (51 ± 22%), ammonium (44 ± 21%) and phosphorus (38 ± 19%) while nitrate was least effectively retained by the system with only 25 ± 17% removal during non-storm events. The efficiency of the system was most favorable when the temperature was above 15 °C (i.e., almost year-round except the winter months) and during storm events. Overall, the outflow water quality was better than the inflow water quality signifying the potential of the constructed wetland as a treatment system and capability of improving the stream water quality.