An integrated approach for improving the wastewater discharge and treatment systems

Since treatment plants have been built all over Germany during the last decades, the water quality of receiving streams has been improved remarkably. But there are still a lot of quality problems left, which are caused e.g. by combined sewer overflows (CSO), treatment plant effluents or rainwater discharges from separate sewer systems. At present different efforts are undertaken to control sewer systems in order to improve the operation of urban drainage systems or more generally, design processes. The Emschergenossenschaft and Lippeverband (EG/LV) are carrying out research studies, which are focusing on a minimization of total emissions from sewer systems both from wastewater treatment plant (WWTP) effluents and from CSO. They consider dynamic interactions between rainfall, resultant wastewater, combined sewers, WWTP and receiving streams. Therefore, in an advanced wastewater treatment, a model-based improvement of WWTP operation becomes more and more essential, and consequently a highly qualified operational staff is needed. Some aspects of the current research studies are presented in this report. The need and the use of an integrated approach to combine existing model components in order to optimize dynamic management of combined sewer systems (CSS) with a benefit for nature are outlined.     

Occurrence and fate of organic pollutants in combined sewer systems and possible impacts on receiving waters.

Selected organic pollutants are classified based on an intensive literature survey. Two wastewater parameters (COD and ammonium) and six selected organic pollutants (polycyclic aromatic hydrocarbons (PAH), diethylhexylphthalate (DEHP), estradiol (E2), ethinylestradiol (EE2), ethylenediamine tetraacetic acid (EDTA) and nitrilo triaceticacid (NTA)) are specified. As a result, for the first time representative concentrations in dry weather flow, surface runoff and effluent of wastewater treatment plants (WWTPs) in combined sewer systems (CSS) are stated. The second part of the paper presents a first estimation of main emission out of a combined sewer system and possible receiving water impacts in terms of (1) annual discharged loads calculated by pollution load simulations in a hypothetical catchment and (2) concentrations calculated in combined sewer overflows (CSO) discharges and resulting receiving water concentrations.     

城市河流综合整治工程的治理效果预测研究

以湖南省常德市穿紫河综合整治工程为例,利用美国环保局开发的综合水质模型QUAL2E对该工程治理方案进行效果预测。根据综合整治的主要治理措施设计了穿紫河水质模拟的五大类情景,模拟了CODCr、DO、BOD5、NH3 N等4项指标,进一步分析了不同截污程度、引水方案和引水量组合工程措施对提高水质达标率的作用,为穿紫河综合整治工程提供合理化建议。     

污水处理系统的集成控制策略研究

以实现河流水质目标为前提,充分利用河流纳污能力,根据不同环境与气候条件调节污水处理厂运行状况和排水管网的污水排放量,可有效保护河流生态质量。基于城市污水处理系统集成仿真平台,提出了4种以河流水质为目标的城市污水处理系统集成控制方案,通过对排水管网和污水处理厂的协调控制,实现了河流水质的改善。仿真结果验证了集成控制策略的有效性。     

On the effect of spatial variances in historical rainfall time series to CSO performance evaluation.

Historical, high-resolution rain series are the backbone of modern combined sewer overflow (CSO) structure design. These rain series are the input to the computational estimation of the performance of the measures with respect to CSO pollution abatement. However, those historical precipitation measurements are available at only a few locations. Frequently rain series have to be used from gauging stations at a significant distance. In order to judge and to compensate for this influence an estimate between rain characteristics and combined sewer outflow (CSO) performance indicators would be useful. In this paper such correlations have been sought for a collection of 37 rain series covering large areas of Europe. It was found that the mean annual rain volume can explain most of the variances for the performance indicators Number of overflows and CSO volume. For explaining the spatial differences in the efficiency of the CSO structure another rain characteristic, i.e. the maximum event with a return period of one year, is to be used.     

Series of surveys for enteric viruses and indicator organisms in Tokyo Bay after an event of combined sewer overflow.

Combined sewer overflows (CSOs) have been recognised as one of the serious sources of pollution to the water environment during rain events, although field surveys to investigate the effect of their magnitude and duration on receiving waters have been very limited. The fates of enteric viruses (norovirus G1, G2, enteroviruses) and coliforms were determined in the wastewater treatment plant on a fine day and on a rainy day. Not all microorganisms were reduced in the primary treatment, but were reduced in the secondary treatment. Occurrences of enteric viruses and levels of coliforms were surveyed in the receiving coastal area after a CSO event, with the profiles of the enteric viruses in the coastal seawater being almost at the same positive ratio for 4 d after the CSO event.     

Influent flow control to increase the pollution load treated during rainy periods

The European Directive of May 1991 concerning urban wastewater treatment points out that sewerage systems must be designed to limit the pollution of receiving watercourses by stormwater discharges. As for the system management, the French Decree of 22 December 1995 states that flows or pollution loads exceeding the reference capacity of the treatment plant may be temporarily admitted. This is especially interesting in the case of separate wastewater sewerage, as inappropriate connections of runoff water and rainfall induced infiltration cause hydraulic overloads in such networks. An automated influent flow control has been implemented on a 8000 population equivalent plant to admit a maximum of twice the dry weather peak flow: the clarifier is then dynamically managed so that neither sludge loss nor degradation through anoxic conditions may occur. A yearly simulation of such a strategy on a smaller treatment plant shows a very significant reduction (90%) of the volume discharged during rainy periods. It can therefore be concluded that a plant with additional hydraulic capacity and good sludge quality can play a significant role in limiting the stormwater discharges from separate sewerage systems. However this operational benefit depends on the inflow composition in the sewerage system (wastewaters, rain and infiltration waters).     

Dynamics of rain-induced pollutographs of solubles in sewers.

When looking at acute receiving water impacts due to combined sewer overflows the characteristics of the background diurnal sewage flux variation may influence the peak loads from combined sewer overflows (CSO) and wastewater treatment plant (WWTP) effluent significantly. In this paper, effects on the dynamic compounds transported in the sewer, on CSO discharges and WWTP loading are evaluated by means of hydrodynamic simulations. The simulations are based on different scenarios for diurnal dry-weather flow variations induced by different infiltration rates.     

Using CANARY event detection software for water quality analysis in the Milwaukee River

Urban water sources are susceptible to various contamination events as a result of natural, accidental, and human-induced occurrences. An early warning monitoring system provides timely information on changes in urban water quality. In this study, an analysis was made with CANARY event detection software (EDS) to monitor water quality parameters in river water and to identify the onset of anomalous water quality periods. Water quality signals including pH, conductivity, and turbidity from the Milwaukee River over specified periods during the summer season of 2018–2020 were employed as inputs to event detection algorithms in CANARY. The data analysis results show that CANARY can be useful as an early warning system for monitoring contamination in urban water sources and help to identify abnormal conditions quickly. The sensibility of the model relies on optimizing the configuration parameters, which involves selecting the ideal set of parameters for the event detection algorithm and adjusting the BED parameters to increase or decrease the probability of generating an alarm. The number of events reported between the Linear Prediction Correction Filter (LPCF) and Multivariate Nearest Neighbor (MVNN) algorithms varied as a result of different residual calculation mechanisms. Climate factors that contributed to the abnormal water quality events in the river were examined. The analysis of rainfall on water quality was carried out using a statistical method by determining whether there is a significant difference (p-value) between the seasonal mean water quality data and the mean value of water parameters during the sampling duration. Regression analysis was also performed to estimate the best model that describes the relationship between each of the water quality parameters and temperature.     

集成膜技术工业废水深度处理回用试验研究

试验采用超滤+反渗透集成膜分离技术,目的是研究其集成工艺处理有色冶金工业废水的合理性和可行性。超滤试验主要测试了在不同水质情况下超滤膜的相关运行参数,主要测定指标有超滤系统的进水、产水和反冲洗水的水量,运行压力,出水浊度,SDI值等;反渗透试验主要测定指标有电导率,反渗透系统的进、出水量,运行压力等。试验研究表明:以预处理+超滤+反渗透组成的集成膜处理工艺,能够满足有色冶金工业废水处理回用的要求。     

Integrated modelling for the evaluation of infiltration effects.

The objective of the present study is the estimation of the potential benefits of sewer pipe rehabilitation for the performance of the drainage system and the wastewater treatment plant (WWTP) as well as for the receiving water quality. The relation of sewer system status and the infiltration rate is assessed based on statistical analysis of 470 km of CCTV (Closed Circuit Television) inspected sewers of the city of Dresden. The potential reduction of infiltration rates and the consequent performance improvements of the urban wastewater system are simulated as a function of rehabilitation activities in the network. The integrated model is applied to an artificial system with input from a real sewer network. In this paper, the general design of the integrated model and its data requirements are presented. For an exemplary study, the consequences of the simulations are discussed with respect to the prioritisation of rehabilitation activities in the network.     

Model based hydropower gate operation for mitigation of CSO impacts by means of river base flow increase.

In river stretches being subjected to flow regulation, usually for the purpose of energy production (e.g. Hydropower) or flood protection (river barrage), a special measure can be taken against the effect of combined sewer overflows (CSOs). The basic idea is the temporal increase of the river base flow (during storm weather) as an in-stream measure for mitigation of CSO spilling. The focus is the mitigation of the negative effect of acute pollution of substances. The measure developed can be seen as an application of the classic real time control (RTC) concept onto the river system. Upstream gate operation is to be based on real time monitoring and forecasting of precipitation. The main objective is the development of a model based predictive control system for the gate operation, by modelling of the overall wastewater system (incl. the receiving water). The main emphasis is put on the operational strategy and the appropriate short-term forecast of spilling events. The potential of the measure is tested for the application of the operational strategy and its ecological and economic feasibility. The implementation of such an in-stream measure into the hydropower's operational scheme is unique. Advantages are (a) the additional in-stream dilution of acute pollutants entering the receiving water and (b) the resulting minimization of the required CSO storage volume.     

Characterization of runoff from various urban catchments at different spatial scales in Beijing, China

In order to investigate the characterization of runoff in storm sewer from various urban catchments, three monitoring systems at different spatial scales have been installed separately. They have been held since July 2010 in urban area of Beijing (China). The monitoring data revealed that chemical oxygen demand (COD), total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), and NH(3)-N values significantly exceed the Class V surface water quality standard developed by Ministry of Environmental Protection of the People's Republic of China (MEP). A surface solids buildup and wash off model for small watershed was adopted to analyze and discuss the process of a runoff pollutant discharge. More than a half of pollutant parameters presented a good fit to the model. However, a slightly worse-fit to the wash off model appeared in less than half of the data. Due to the influence of sewer sediments, sewer system characteristics, catchment characteristics, and other reasons, first flush was seldom observed in storm sewer runoff from these three survey areas. Meanwhile, the correlation between TSS and any other pollutant was analyzed according to cumulative load of pollutants in runoff events. An event mean concentrations (EMCs) approach was adopted to quantify the pollution of runoff. EMCs of various pollutants in storm sewer runoff between different rainfall events were slightly higher than the typical values observed in similar areas at home and abroad, according to other studies reported in literature. Based on quantitative analysis, it can be concluded that urban non-point source pollution is recognized as the major causes of quality deterioration in the receiving water bodies. This is after the point source pollution has been controlled substantially in Beijing. An integrated strategy, which combines centralized and decentralized control, along with the conditions of meteorology, hydrology, urban planning, existing drainage system, etc., will be an effective and economic approach to urban runoff pollution control.     

A conceptual CSO emission model: SEWSIM

CSO emission is widely considered a significant pollution source to receiving waters in urban areas. The existing deterministic sewer models are not able to predict CSO emission effectively. In this study, a conceptual CSO emission model SEWSIM has been developed using a powerful programming package MATLAB and SIMULINK. A sewer system consisting of an impervious catchment and a sewer network is schematised as two linear dynamic reservoirs. The following physical processes are conceptually modelled: rainfall-runoff; surface solids buildup and washoff; sewer sediment erosion and deposition. The model is suitable for both event-based and continuous simulations. Some simulation results demonstrate that SEWSIM predicts pollution load of CSO emission more effectively than deterministic models.     

Assessment and Use of Indicator Bacteria to Determine Sources of Pollution to an Urban River

Elevated levels of indicator bacteria within a river system represent a significant impairment to surface water quality in many urban areas within the Great Lakes watershed. Outfalls from combined sewer systems are assumed to be the major source of bacteria to streams in many of these urban areas, including the Rouge River of southeastern Michigan. Current remediation strategies largely disregard other potential sources, including water entering the river from its headwaters region, rural runoff, and contaminated groundwater. These other potential sources of bacterial pollution to the Rouge River were assessed and compared with bacteria contributed from combined sewer outfalls (CSOs). Fecal coliform (FC) and fecal streptococci (FS) densities were determined at 28 locations in the Rouge River Watershed during the spring and summer of 1997, 1998, and 1999. The mean levels of both indicator groups vary considerably along each branch of the river and show no correlation to CSO locations. The magnitude of both FC and FS levels are, in fact, frequently greater at sites upstream of the part of the river influenced by discharges from CSOs. The highest FC levels coincided with rainfall events, but FC levels at various sites along each branch of the Rouge River violated acceptable water quality standards (200 colonies/100 mL) at nearly 50% of the sites even during dry weather. Total suspended solids were moderately correlated with FC (r = 0.79) throughout the watershed, suggesting that solids may play a role in transporting bacteria into the Rouge River. The data depict a strong influence of upstream water and rural runoff on the water quality of the Rouge River. FC to FS ratios (FC/FS) suggest the primary source of bacteria throughout the watershed is from domesticated animals and wildlife and not from sewage derived from CSOs.     

广州市中心城区典型合流制排水口污染负荷排放规律分析

随着广州市中心城区河道水环境治理力度的加大,合流制溢流污染问题越来越突出,对城市河道水体构成了日益严重的威胁。本文选取广州市中心城区典型合流制排水口进行了18场降雨的径流污染监测,总结了在典型小雨、典型中雨及典型大雨场次下排水口各水质指标随降雨历时的变化规律,同时分析了18场降雨的排水口最高浓度、平均浓度与总降雨量的关系,研究成果可为合流制污染控制工程的设计提供参考。     

城市屋面降雨冲刷污染物变化模型模拟研究

城市屋面降雨径流污染是受纳水体质量恶化的主要影响因子。以典型屋面作为汇水单元,开展天然降雨情况下雨水径流水文水质过程监测试验,水质指标包括SS、COD、TN。利用雨水径流产流负荷替代降雨强度校正了传统冲刷模型,研究有效降雨深度与径流水质之间的相关函数关系,构建了雨水径流污染物浓度变化模型,对相关参数进行求解。模型模拟的SS、COD、TN的浓度变化过程精度较高,纳什效率系数均在0.87以上。表明模型的实用性较好,可为城市雨水资源高效利用、面源污染控制技术与措施制定、海绵城市建设等提供依据。     

Model-based knowledge acquisition in environmental decision support system for wastewater integrated management

The main goal of the Water Framework Directive is to achieve good chemical and ecological status of water bodies by 2015. The implementation of integrated river basin management, including sewer systems, wastewater treatment plants and receiving water bodies, is essential to accomplishing this objective. Integrated management is complex and therefore the implementation of control systems and the development of decision support systems are needed to facilitate the work of urban wastewater system (UWS) managers. Within this context, the objective of this paper is to apply integrated modelling of an UWS to simulate and analyse the behaviour of the 'Congost' UWS in Spain, and to optimize its performance against different types of perturbations. This analysis results in optimal operating set-points for each perturbation, improves river water quality, minimizes combined sewer overflows and optimizes flow lamination from storm water tanks. This is achieved by running Monte Carlo simulations and applying global sensitivity analysis. The set-points will become part of the knowledge base composed of a set of IF-THEN rules of the environmental decision support system being developed for this case study.