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.     

Frequency analysis of river water quality using integrated urban wastewater models

In recent years integrated models have been developed to simulate the entire urban wastewater system, including urban drainage systems, wastewater treatment plants, and receiving waterbodies. This paper uses such an integrated urban wastewater model to analyze the frequency of receiving water quality in an urban wastewater system with the aim of assessing the overall system performance during rainfall events. The receiving water quality is represented by two indicators: event mean dissolved oxygen (DO) concentration and event mean ammonium concentration. The compliance probability of the water quality indicators satisfying a specific threshold is used to represent the system performance, and is derived using the rainfall events from a series of 10 years' rainfall data. A strong correlation between the depth of each rainfall event and the associated volume of combined sewer overflow (CSO) discharges is revealed for the case study catchment, while there is a low correlation between the intensity/duration of the rainfall event and the volume of the CSO discharges. The frequency analysis results obtained suggest that the event mean DO and ammonium concentrations have very different characteristics in terms of compliance probabilities at two discharging points for CSO and wastewater treatment plant effluent, respectively. In general, the simulation results provide an understanding of the performance of the integrated urban wastewater system and can provide useful information to support water quality management.     

Integrated operation of sewer system and WWTP by simulation-based control of the WWTP inflow.

In recent years numerical modelling became a standard procedure to optimise urban wastewater systems design and operation by integration. For dynamic control of the wastewater teatment plant (WWTP) inflow, a model-based predictive concept is introduced aiming at improving the receiving water quality. An on-line simulator running parallel to the real WWTP operation reflects the actual state of operation and provides this model information to a prognosis tool which determines the best option for the WWTP inflow. The investigations showed that it is possible to reduce the NH4-N peak concentrations in the receiving water by dynamic WWTP inflow control based on predictive scenario analysis.     

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.     

Simulation of a subsurface vertical flow constructed wetland for CSO treatment.

Constructed wetlands (CWs) have proved to be a highly effective measure to reduce the ecological impact of combined sewer overflows (CSOs) on receiving waters. Due to the stochastic nature of the loading regime and the multitude of environmental influences, assessment of the performance of such plants requires detailed mathematical modelling. A multi-component reactive transport module (CW2D) was applied to simulate the flow, transport and degradation processes occurring in a CW for CSO treatment. CW2D was originally developed to simulate the treatment of municipal wastewater in subsurface flow CWs. Loading and operational conditions in CSO treatment differ fundamentally from the conditions occurring for wastewater treatment. Despite these differences, first results from the simulation of lab-scale experiments show, that the model is generally applicable to this type of plant. Modelling of adsorption, degradation processes, and influent fractionation, however, require further research.     

An integrated modelling concept for immission-based management of sewer system, wastewater treatment plant and river.

Today's planning standards deal with the individual urban drainage components (sewer system, wastewater treatment plant and receiving water) separately, i.e. they are often designed and operated as single components. As opposed to this, an integral handling considers the drainage components jointly. This novel approach allows a holistic and more sustainable planning of urban drainage systems. This paper presents an integrated modelling concept. The aim is to analyse fluxes through the total wastewater system and to integrate pollution-based control in the upstream direction, that is, e.g., managing the combined water retention tanks as a function of state variables in the WWTP or the receiving water. All models of the different subsystems are based on the Activated Sludge Model (ASM) concept of IWA, including River Water Quality Model No. 1 (RWOM). Simulations can be done in truly parallel mode using the simulation environment SIMBA. The integrated modelling concept is applied to the river Dhuenn and the urban wastewater system of the municipality of Odenthal (Germany). An optimised operation of the system using RTC proves to be a very effective measure.     

3D Eutrophication Modeling of Hamilton Harbour: Analysis of Remedial Options

The Water Quality Analysis Simulation Program (WASP) was employed to create a threedimensional eutrophication model for Hamilton Harbour. Calibration of the model was performed using 1991 field data. Four remedial options, namely improvements to the waste water treatment plants (WWTPs), the combined sewer overflows (CSOs), industrial discharges, and removal of WWTP, CSO, and industrial discharges were examined. The model simulated well the response of the harbor under various loading conditions. Improvements in the harbor's water quality were found to range from minor in the case of CSO improvements to significant in the case of WWTP improvements. Specifically, the chlorophyll a, total phosphorus, and ammonia nitrogen concentrations were reduced by as much as 2% in the case of CSO improvements, between 4 and 14% for the industrial loading improvements, and between 24 and 50% for the WWTP improvements case.     

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.     

Plant-wide (BSM2) evaluation of reject water treatment with a SHARON-Anammox process.

In wastewater treatment plants (WWTPs) equipped with sludge digestion and dewatering systems, the reject water originating from these facilities contributes significantly to the nitrogen load of the activated sludge tanks, to which it is typically recycled. In this paper, the impact of reject water streams on the performance of a WWTP is assessed in a simulation study, using the Benchmark Simulation Model no. 2 (BSM2), that includes the processes describing sludge treatment and in this way allows for plant-wide evaluation. Comparison of performance of a WWTP without reject water with a WWTP where reject water is recycled to the primary clarifier, i.e. the BSM2 plant, shows that the ammonium load of the influent to the primary clarifier is 28% higher in the case of reject water recycling. This results in violation of the effluent total nitrogen limit. In order to relieve the main wastewater treatment plant, reject water treatment with a combined SHARON-Anammox process seems a promising option. The simulation results indicate that significant improvements of the effluent quality of the main wastewater treatment plant can be realized. An economic evaluation of the different scenarios is performed using an Operating Cost Index (OCI).     

Potentials of real time control, stormwater infiltration and urine separation to minimize river impacts: dynamic long term simulation of sewer network, pumping stations, pressure pipes and waste water treatment plant.

River Panke (Berlin, Germany) suffers from hydraulic peak loads and pollutant loads from separate sewers and combined sewer overflows (CSOs). Pumping the wastewater through long pressure pipes causes extreme peak loads to the wastewater treatment plant (WWTP) during stormwater events. In order to find a good solution, it is essential not to decide on one approach at the beginning, but to evaluate a number of different approaches. For this reason, an integrated simulation study is carried out, assessing the potentials of real time control (RTC), stormwater infiltration, storage and urine separation. Criteria for the assessment are derived and multi-criteria analysis is applied. Despite spatial limitations, infiltration has the highest potential and is very effective with respect to both overflows and the WWTP. Due to a high percentage of separate systems, urine separation has a similar potential and causes the strongest benefits at the WWTP. Unconventional control strategies can lead to significant improvement (comparable to infiltrating the water from approximately 10% of the sealed area).     

城市污水处理工程设计中值得探讨的几个问题

对污水处理厂设计过程中涉及到的内容和问题进行了全面系统的分析介绍。首先对污水处理厂设计基本条件及影响因素 ,如进出水水质、水量、管网系统及规划年限等进行了分析 ;然后对几种常用的污水处理工艺进行分析比较 ,指出各自特点及适用范围 ;最后对设计中可能遇到的一些热点问题进行了探讨     

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。     

Phenol wastewater remediation: advanced oxidation processes coupled to a biological treatment.

Nowadays, there are increasingly stringent regulations requiring more and more treatment of industrial effluents to generate product waters which could be easily reused or disposed of to the environment without any harmful effects. Therefore, different advanced oxidation processes were investigated as suitable precursors for the biological treatment of industrial effluents containing phenol. Wet air oxidation and Fenton process were tested batch wise, while catalytic wet air oxidation and H2O2-promoted catalytic wet air oxidation processes were studied in a trickle bed reactor, the last two using over activated carbon as catalyst. Effluent characterisation was made by means of substrate conversion (using high liquid performance chromatography), chemical oxygen demand and total organic carbon. Biodegradation parameters (i.e. maximum oxygen uptake rate and oxygen consumption) were obtained from respirometric tests using activated sludge from an urban biological wastewater treatment plant (WWTP). The main goal was to find the proper conditions in terms of biodegradability enhancement, so that these phenolic effluents could be successfully treated in an urban biological WWTP. Results show promising research ways for the development of efficient coupled processes for the treatment of wastewater containing toxic or biologically non-degradable compounds.     

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.     

Sixty-five-year old final clarifier performance rivals that of modern designs.

The Stickney plant of the Metropolitan Wastewater Reclamation District of Greater Chicago (MWRDGC), one of the largest wastewater treatment plants in the world, treats an average dry weather flow of 22 m3/s and a sustained wet weather flow of 52 m3/s that can peak to 63 m3/s. Most of the inner city of Chicago has combined sewers, and in order to reduce pollution through combined sewer overflows (CSO), the 175 km Tunnel and Reservoir Plan (TARP) tunnels, up to 9.1 m in diameter, were constructed to receive and convey CSO to a reservoir from where it will be pumped to the Stickney treatment plant. Pumping back storm flows will result in sustained wet weather flows over periods of weeks. Much of the success of the plant will depend on the ability of 96 circular final clarifiers to produce an effluent of acceptable quality. The nitrifying activated sludge plant is arranged in a plug-flow configuration, and some denitrification takes place as a result of the high oxygen demand in the first pass of the four-pass aeration basins that have a length to width ratio of 18:1. The SVI of the mixed liquor varies between 60 and 80 ml/g. The final clarifiers, which were designed by the District's design office in 1938, have functioned for more than 65 years without major changes and are still producing very high-quality effluent. This paper will discuss the design and operation of these final clarifiers and compare the design with more modern design practices.     

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.     

Dynamic optimisation of WWTP inflow to reduce total emission.

A prerequisite for an integrated control of sewer and wastewater treatment plant (WWTP) is a capacity driven inflow control to WWTP. This requires reliable information about the current status of WWTP operation and its behaviour on varying hydraulic, COD and nutrient loads. So far most of the proposed control strategies are based on hypothetical modelling studies. In this paper the behaviour of three large WWTPs on increased storm water loads is analysed based on online measurements of several years. In all cases the main limiting factors for an increase of load were the sedimentation processes in the secondary clarifier and the nitrification capacity. In one case study predictive control strategies have been developed observing these processes which are backboned by effluent control. Tests using an integrated model of sewer and WWTP demonstrate that inflow control on emission load varies significantly with rain intensity.     

The Actiflo method

The Actiflo method is a compact physico-chemical water treatment method. The method has for many years been used in waterworks for the treatment of surface water to produce drinking water, but is now to an increasing extent being used for treating wastewater and combined sewer overflows (CSO). The method works as weighted settling combined with lamella settling. Typical treatment efficiency: suspended solids 85%, COD 60%, Kjeldahl N 18% and total P 85%. The method also permits efficient removal of heavy metals. Krüger has a mobile pilot plant with a capacity of 80–120 m³/h in Scandinavia and a similar pilot plant in the USA. As an Actiflo plant can be started up in less than 15 minutes, it has many applications. Several applications may also be combined, e.g. treatment of overflows during rain and treatment of lake water in the recipient nearby in dry weather. As an alternative to detention basins in combined sewer systems the Actiflo method is often a competitive method.     

Manage Sewer In-Line Storage Control Using Hydraulic Model and Recurrent Neural Network

This paper described manage sewer in-line storage control for the city of Drammen, Norway. The purpose of the control is to use the free space of the pipes to reduce overflow at the wastewater treatment plant (WWTP). This study combined the powerful sides of the hydraulic model and neural networks. A detailed hydraulic model was developed to identify which part of the sewer system have more free space. Subsequently, the effectiveness of the proposed control solution was tested. Simulation results showed that intentionally control sewer with free space could significantly reduce overflow at the WWTP. At last, in order to enhance better decision making and give enough response time for the proposed control solution, Recurrent Neural Network (RNN) was employed to forecast flow. Three RNN architectures, namely Elman, NARX (nonlinear autoregressive network with exogenous inputs) and a novel architecture of neural networks, LSTM (Long Short-Term Memory), were compared. The LSTM exhibits the superior capability for time series prediction.