Sewer Solids Research Articles

Three-dimensional computational fluid dynamics (volume of fluid) modelling coupled with a stochastic discrete phase model for the performance analysis of an invert trap experimentally validated using field sewer solids

Invert traps are used to trap sewer solids flowing into a sewer drainage system. The performance of the invert trap in an open rectangular channel was experimentally and numerically analysed using field sewer solids collected from a sewer drain. Experiments showed that the free water surface rises over the central opening (slot) of the invert trap, which reduces the velocity near the slot and allows more sediment to be trapped in comparison with the case for the fixed-lid model (assuming closed conduit flow with a shear-free top wall) used by earlier investigators. This phenomenon cannot be modelled using a closed conduit model as no extra space is provided for the fluctuation of the water surface, whereas this space is provided in the volume of fluid (VOF) model in the form of air space in ANSYS Fluent 14.0 software. Additionally, the zero atmospheric pressure at the free water surface cannot be modelled in a fixed-lid model. In the present study, experimental trap efficiencies of the invert trap using field sewer solids were fairly validated using a three-dimensional computational fluid dynamics model (VOF model) coupled with a stochastic discrete phase model. The flow field (i.e., velocities) predicted by the VOF model were compared with experimental velocities obtained employing particle image velocimetry. The water surface profile above the invert trap predicted by the VOF model was found to be in good agreement with the experimentally measured profile. The present study thus showed that the VOF model can be used with the stochastic discrete phase model to well predict the performance of invert traps.

Sensitivity analysis on the pollutant trapping efficiencies of a novel sewerage overflow screening device

A novel ‘Comb Separator’ was developed and tested with the aim of improving sewer solids capture efficiency and reducing blockages on the screen. Experimental results were compared against the industry standard ‘Hydro-Jet™’ screen. Analysing the parameter sensitivity of a hydraulic screen is a standard practice to get better understanding of the device performance. In order to understand the uncertainties of the Comb Separator's input parameters, it is necessary to undertake sensitivity analysis; this will assist in making informed decisions regarding the use of this device. Such analysis will validate the device's performance in urban sewerage overflow scenarios. The methodology includes multiple linear regression and sampling using the standard Latin hypercube sampling technique to perform sensitivity analysis on different experimental parameters, such as flowrate, effective comb spacing, device runtime, weir opening and comb layers. The input parameters ‘weir opening’ and ‘comb layers’ have an insignificant influence on capture efficiency; hence, they were omitted from further analysis. Among the input parameters, ‘effective spacing’ was the most influential, followed by ‘inflow’ and ‘runtime’. These analyses provide better insights about the sensitivities of the parameters for practical application. This will assist device managers and operators to make informed decisions.

Solids in Sewers: Characteristics, Effects and Control of Sewer Solids and Associated Pollutants

This Report presents information on the current state of knowledge of the origins, occurrence, nature and effects of sewer solids for use by engineers, scientists, administrators and water quality planners for the planning, design and operation of sewerage systems. The report addresses both sewer maintenance requirements and environmental protection issues. Increasing environmental standards, coupled with public expectations, have led to stringent water quality standards. In response to this, it has been necessary to develop new methodologies and computer based analytical techniques to model and understand the performance of all aspects of waste water systems. Fundamental to these techniques is the understanding of the way in which sewer solids contribute to the poor performance of wastewater systems and consequential environmental damage. The information presented in this Report about the origins, nature, movement, hydraulic and polluting effects of solids in sewers has enabled strategies and rules to be developed for the management of sewerage systems to minimise the deleterious effects of these solids and associated pollutants. This title belongs to Scientific and Technical Report Series ISBN: 9781900222914 (Print) ISBN: 9781780402727 (eBook)

Development and performance testing of 'Comb Separator', a novel sewer overflow screening device

Rivers and creeks receive a lot of sewer solids due to sewer overflow. This overflow causes a serious concern for the environment, aesthetics and public health. To manage such sewer overflow, different types of screening device were developed. The initial expense, maintenance costs, poor sewer capture efficiency and blinding on the screen were discussed as the limitations of these overflow devices. Most screens had electro-mechanical systems that were expensive, complex and caused concern for possible malfunctions in unstaffed remote locations. Consequently, a novel sewerage overflow device 'Comb Separator' was conceived, developed and tested. Optimum criteria were achieved for the device using trial and error method; robustness of the experimental set-up was tested to reproduce consistent results. There was minimal blockage on the screen and higher capture efficiency than Hydro-JETTM. The 'Comb Separator' has a good application potential to improve the sewer solids capture in the urban sewerage system.

Automatic Vacuum Flushing Technology for Combined Sewer Solids

An extensive literature review on existing sewer sediment flushing technologies was conducted. The innovative vacuum flush system recently developed by the U.S. EPA was tested under laboratory conditions. The tests revealed a strong correlation between the strength of the flushing wave and the speed of the vacuum break. The original design did not succeed in providing a fast enough vacuum break despite being tested in different configurations. To improve the vacuum brake time, Rutgers developed two alternative mechanisms. These alternative designs showed promising results in the laboratory but remain to be tested under field conditions. This title belongs to WERF Research Report Series . ISBN: 9781780400471 (eBook)

Applicability of artificial neural network in hydraulic experiments using a new sewer overflow screening device

During wet weather conditions, sewer overflows to receiving water bodies raise serious environmental, aesthetic and public health problems. These issues trigger the need the most appropriate device/system for a particular installation, especially at unmanned remote locations. A new sewer overflow device consists of a rectangular tank and a sharp crested weir with a series of vertical combs is presented. A series of laboratory tests to determine trapping efficiencies for common sewer solids were conducted for different flow conditions, number of combs layers and spacing of combs. To overcome physical limitations inherent in laboratory studies such as significant cost and time. Artificial neural model was adopted as it has the capacity to accurately predict the outcome of complex, non-linear physical systems with relatively poorly understood physicochemical processes. A series of laboratory tests were conducted with 55 different sets of data. Forty-seven sets of experimental data are used with 60% for training, 20% each for testing and validation of the model. A separate validation data sets were used to judge the overall performance of the trained network. The model can successfully predict the experimental results with more than 90% accuracy with an average absolute percentage error of around 7%.

Applicability of Artificial Neural Network in Hydraulic Experiments Using a New Sewer Overflow Screening Device

During wet weather conditions, sewer overflows to receiving water bodies raise serious environmental, aesthetic and public health problems. These issues trigger the need the most appropriate device/system for a particular installation, especially at unmanned remote locations. A new sewer overflow device consists of a rectangular tank and a sharp crested weir with a series of vertical combs is presented. A series of laboratory tests to determine trapping efficiencies for common sewer solids were conducted for different flow conditions, number of combs layers and spacing of combs. To overcome physical limitations inherent in laboratory studies such as significant cost and time. Artificial neural model was adopted as it has the capacity to accurately predict the outcome of complex, non-linear physical systems with relatively poorly understood physicochemical processes. A series of laboratory tests were conducted with 55 different sets of data. Forty-seven sets of experimental data are used with 60% for training, 20% each for testing and validation of the model. A separate validation data sets were used to judge the overall performance of the trained network. The model can successfully predict the experimental results with more than 90% accuracy with an average absolute percentage error of around 7%.

Modelling sewer sediment deposition, erosion, and transport processes to predict acute influent and reduce combined sewer overflows and CO2 emissions

Understanding of solids deposition, erosion, and transport processes in sewer systems has improved considerably in the past decade. This has provided guidance for controlling sewer solids and associated acute pollutants to protect the environment and improve the operation of wastewater systems. Although measures to decrease combined sewer overflow (CSO) events have reduced the amount of discharged pollution, overflows continue to occur during rainy weather in combined sewer systems. The solution lies in the amount of water allotted to various processes in an effluent treatment system, in impact evaluation of water quality and prediction technology, and in stressing the importance of developing a control technology. Extremely contaminated inflow has been a serious research subject, especially in connection with the influence of rainy weather on nitrogen and organic matter removal efficiency in wastewater treatment plants (WWTP). An intensive investigation of an extremely polluted inflow load to WWTP during rainy weather was conducted in the city of Matsuyama, the region used for the present research on total suspended solid (TSS) concentration. Since the inflow during rainy weather can be as much as 400 times that in dry weather, almost all sewers are unsettled and overflowing when a rain event is more than moderate. Another concern is the energy consumed by wastewater treatment; this problem has become important from the viewpoint of reducing CO(2) emissions and overall costs. Therefore, while establishing a prediction technology for the inflow water quality characteristics of a sewage disposal plant is an important priority, the development of a management/control method for an effluent treatment system that minimises energy consumption and CO(2) emissions due to water disposal is also a pressing research topic with regards to the quality of treated water. The procedure to improve water quality must make use of not only water quality and biotic criteria, but also modelling systems to enable the user to link the effect of changes in urban sewage systems with specific quality, energy consumption, CO(2) emission, and ecological improvements of the receiving water.

Three-Dimensional CFD Modeling for Optimization of Invert Trap Configuration to Be Used in Sewer Solids Management

Flow field prediction and optimization of invert trap configuration have been carried out by using three-dimensional computational fluid dynamics (CFD) modeling with the help of FLUENT software using renormalization group (RNG) k-ϵ along with the discrete phase model (DPM). A hexagonal/tetrahedral shape and map-type nonuniform grid were chosen to discretize the entire computational domain, and a control volume finite difference method was used to solve the governing equations. In the present study, five different invert trap configurations (rectangular with and without lid on both sides, trapezoidal, trapezoidal with rectangular base, and rectangular with trapezoidal base with lid on both sides) have been simulated for the flow of three different inert sediment types (sand, styrocell, and plastic beads) at six flow rates (0.35, 0.70, 1.05, 1.35, 4.55, and 9.95 Lps) for each trap. The discharges selected in the present study cover the entire range of discharge expected in channels during dry weather flow and monsoon. The simulation results are capable of showing particle trajectories and the effect of flow rate and trap geometry on the flow patterns developed within the trap. Based on 3-D CFD modeling and experimental measurements, it has been concluded that the invert trap having a rectangular shape with trapezoidal base with lids on both sides is the most efficient trap configuration with highest sediment retention ratio.

Estimation of uncertainty in long term combined sewer sediment behaviour predictions, a UK case study

There are regulatory driven requirements for UK water companies to reduce the number of properties at risk of sewer flooding. One of the potential causes of sewer flooding is the presence of persistent sediment deposits in sewers. This is a common problem in many combined sewers. Although the regulation is risk based, there is a gap in current knowledge on how risk assessment is affected by the uncertainty in sewer solids behaviour prediction. This paper describes a UK case study exploring the possibility of estimating uncertainty in sewer sediment deposit level predictions, using Monte Carlo simulations combined with a response database.

Sewer solids separation by sedimentation – the problem of modeling, validation and transferability

Sedimentation of sewer solids in tanks, ponds and similar devices is the most relevant process for the treatment of stormwater and combined sewer overflows in urban collecting systems. In the past a lot of research work was done to develop deterministic models for the description of this separation process. But these modern models are not commonly accepted in Germany until today. Water Authorities are sceptical with regard to model validation and transferability. Within this paper it is checked whether this scepticism is reasonable. A framework-proposal for the validation of mathematical models with zero or one dimensional spatial resolution for particle separation processes for stormwater and combined sewer overflow treatment is presented. This proposal was applied to publications of repute on sewer solids separation by sedimentation. The result was that none of the investigated models described in literature passed the validation entirely. There is an urgent need for future research in sewer solids sedimentation and remobilization!

합류식 관거 내 고형물 퇴적량 산정기법 분석

건조기 때의 합류식 관거 내 고형물의 퇴적으로 인해 통수능이 감소하여 여름철 장마시 국지적인 침수가 발생하며 이로 인해 관거 내 퇴적을 더욱 초래할 수가 있다. 또한 관거 시스템에 퇴적된 고형물로 인해 우기시 'first-flush' 현상을 초래하기도 한다. 이와 같은 문제를 해결하기 위해서는 장기간에 걸친 관거 내 고형물 퇴적량을 관측할 필요가 있으나 많은 비용과 노력이 수반되어야 한다. 따라서 본 연구에서는 미국환경보호청에서 개발한 건조기의 합류관거 내 고형물 퇴적량 산정기법을 우리나라의 배수유역에 적용하여 분석하였다. 분석결과 적용 배수유역의 가용 자료에 따라 모형을 선택하여 실무에서 간편하게 적용할 수가 있지만 모형별 변수산정 방법별로 많은 차이를 보이고 있다. 초기에 유도된 Eqs. (1)<TEX>$\sim$</TEX>(4)가 후에 유도된 Eqs. (5)<TEX>$\sim$</TEX>(9)보다 산정치가 모두 크게 나타나고 있으며 전반적으로 중간모형이 정밀모형이나 단순모형보다 크게 나타나고 있다. 건조기 동안의 관거 내 퇴적고형물의 관측자료가 구비되어 있지 않아 실질적으로 비교하기가 곤란하지만 대상 배수유역 관거에서의 장기적인 관측이 이루어지고 이에 따라 국내실정에 맞도록 산정공식의 수정이 이루어지면 실무에서 많은 비용과 노력을 줄이고 관거 관리를 할 수 있다고 판단된다. The deposition of sewer solids during dry weather in combined sewer systems results in a loss of flow capacity that may restrict flow and cause a local flooding and enhanced solids deposition. Sewer solid accumulations in drainage systems also create the 'first-flush' phenomena during wet weather runoff periods. In order to solve these problems, measurement of these loadings for a given sewer system for extended period is needed but this task is very difficult and extremely expensive. In this study, generalized procedures for estimating sewer sediment solid during dry weather in combined sewer systems developed by the U. S. Environmental Protection Agency were applied in a drainage system in Korea. As result, the appropriate equation can be selected and applied according to the available data. However, the estimated solid sediment shows considerable difference between methods which classified by model and estimation methods of variable. The estimated values using equations (1) <TEX>$\sim$</TEX> (4) are greater than that of equations (5) <TEX>$\sim$</TEX> (9) and intermediate models show greater values than elaborate or simplest models. The comparison between simulated and measured solid deposition is difficult due to the absent of measurement data, but this estimation method can be used usefully for the management of sewer solid with reduction of cost and effort if the measurement is carried out and the equation is adjusted according to the actual drainage systems in Korea.

Sewer solids—20 years of investigation

Knowledge about sewer solids has advanced rapidly in the last few decades due to academic research triggered by an emerging renewed interest from sewer operators. It is now known that sewer solids are implicated in: loss of conveyance; potential for acute and chronic pollution of watercourses and effects inside sewers such as generation of malodorous gases and fabric corrosion. Despite this advance in knowledge, there is much that still needs to be understood, particularly the details of some of the mechanisms of flow-solids interactions, such as deposition, consolidation, erosion, biochemical interactions and processes. The history of knowledge development is outlined and areas where there is a need for further elucidation are highlighted.

Solids separation efficiency of combined sewer overflows

The removal of sewer solids at combined sewer overflow locations depends on the flow patterns inside the overflow structure on the one hand and on the sediment characteristics on the other hand. Flow conditions can be described by the residence time distribution; sewer sediments can be characterised by their settling velocity distribution. The combination of both distributions leads to a dimensionless efficiency curve, which gives the removal efficiency as a function of the Hazen number. For field conditions this efficiency curve is mainly influenced by the settling velocity distribution of the sewer sediments and, as a consequence, nearly identical efficiency curves are found for different types of prototype CSO structure. For design purposes, a methodology using return frequency analysis is proposed.

The influence of biodegradability of sewer solids for the management of CSOs

The re-suspension of sediments in combined sewers and the associated pollutants into the bulk water during wet weather flows can cause pollutants to be carried further downstream to receiving waters or discharged via Combined Sewer Overflows (CSO). A typical pollutograph shows the trend of released bulk pollutants with time but does not consider information on the biodegradability of these pollutants. A new prediction methodology based on Oxygen Utilisation Rate (respirometric method) and Erosionmeter (laboratory device replicating in-sewer erosion) experiments is proposed which is able to predict the trends in biodegradability during in-sewer sediment erosion in wet weather conditions. The proposed new prediction methodology is also based on COD fractionation techniques.

European Research into Sewer Sediments and Associated Pollutants and Processes

Research investigating all aspects of solids in sewer systems has been underway in Europe for nearly two decades. Due to the early development of European sewer systems, originally as part of the industrialization process more than 100 years ago, urbanization has caused the original sewer networks to become overloaded and unable to function efficiently. Operational problems of interest include loss of ability to convey (designed) flows and the performance of “overflows” to relieve the high flows discharging directly into rivers and other watercourses. Research has characterized the nature of the solids getting into sewer systems, how they behave in terms of transport, and some of the main aspects of their effects. It has been possible to demonstrate that much of the pollutants found in suspension during storms, and likely to be discharged from overflows, originate from the predominantly organic “near bed solids” which accumulate in systems during dry weather. New ideas for the way in which the sediments are transported and the importance of the transformation processes, are leading toward the development of a unified and integrated understanding of the way in which sewer solids behave and the associated biochemical transformation processes.

Sewer-Sediment Control: Overview of an Environmental Protection Agency Wet-Weather Flow Research Program

This paper presents a historical overview of the sewer sediment control projects conducted by the Wet-Weather Flow Research Program of the United States Environmental Protection Agency. The research presented includes studies of the causes of sewer solids deposition and development/evaluation of control methods that can prevent sewer-sediment accumulation. Discussions focus on the relationship of wastewater characteristics to flow-carrying velocity, abatement of solids deposition and solids resuspension in sewers, and sewerline flushing systems for removal of sewer sediment. Methods for abating sewer sedimentation include steeper sewer slope, pipe bottom shapes that maintain high velocity during low-flow conditions, and periodic sewer flushing. The future research program plan for sewer-sediment control is also presented.

Life cycle analysis and sewer solids

The search for sustainable ways of living has necessitated a new look at the way in which water services are provided. The new paradigm includes whole-system perspectives for each of the primary criteria groups: social, environmental and economic. Whilst Life Cycle Analysis (LCA) techniques have been used successfully for products, they are much less used to assess processes. Nonetheless there is much to learn from the use of LCA for a much wider range of applications. An application is described whereby LCA has been used to determine energy, mass flows and environmental impacts for a number of sewer-related options for handling sewer solids, using the SimaPro software. This work has been part of a wider study to provide enhanced decision support systems for water utilities.

Managing sewer solids for the reduction of foul flush effects – Forfar WTP

In times of high sewer flow, conditions can exist which enable previously deposited material to be re-entrained back into the body of the flow column. Pulses of this highly polluted flow have been recorded in many instances at the recently constructed wastewater treatment plant (WTP) in Forfar, Scotland. Investigations have been undertaken to characterise the incoming flows and to suggest remedial measures to manage the quality fluctuations. Initial visits to the works and incoming pipes indicated a high degree of sediment deposition in the two inlet pipes. Analyses were carried out and consequently, changes to the hydraulic regime were made. Measurements of sediment level, sediment quality, wall slime and bulk water quality were monitored in the period following the remedial works to observe any improvements. Dramatic alterations in each of the determinands measured were recorded. Analyses were then undertaken to determine long term sediment behaviour and to assess the future usefulness of existing upstream sediment traps. It was concluded that with proper maintenance of the traps, the new hydraulic regime is sufficient to prevent further significant build up of sediment deposits and reduce impacts on the WTP. Further investigations made by North of Scotland Water Authority highlighted trade inputs to the system which may also have contributed to the now managed foul flush problem.

The management of sediment in combined sewers

Sediments in sewers are ubiquitous because of the diverse nature of the inputs. Over the past decade or so, new understanding of the provenance, behaviour and nature of sewer solids is now allowing more effective means for solids management. Whilst current computer models are good at representing the hydraulic performance of sewer systems, their handling of sewer solids and associated processes is still embryonic. Hence any attempts to manage in-sewer solids more effectively require a diversity of approaches, both for any modelling studies and for the selection of the most appropriate option. Little information currently exists on which to draw to determine cost-effective or wholelife solutions. Nonetheless significant advances have been made in enhancing the traditional approaches to sewer solids management which have been in use for more than a century.