Computational Fluid Dynamics (CFD) has become an essential tool for the design, development, and evaluation of systems and processes including innovative devices utilized for the control and treatment of Urban Water. CFD is now... more
Computational Fluid Dynamics (CFD) has become an essential tool for the design, development, and evaluation of systems and processes including innovative devices utilized for the control and treatment of Urban Water. CFD is now increasingly being used as a cost-effective rapid prototyping tool for the development, design and optimization of urban water management system components without recourse to several iterations of physical models and prototypes. The ability to accurately predict fluid flow fields in 3-dimensions (including pressure, streamlines and residence time distributions) coupled with the tracking and simulation of particulate and other pollutant behaviour and fate is resulting in insights that are facilitating improved understanding of device and system characteristics; leading to improvements and rapid innovations.
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The paper describes how the contact flocculation-filtration and adsorption system (CFFA) can be used in a staged approach to cost-effectively upgrade existing Water Supply Treatment Works. A case study is presented for modifications to... more
The paper describes how the contact flocculation-filtration and adsorption system (CFFA) can be used in a staged approach to cost-effectively upgrade existing Water Supply Treatment Works. A case study is presented for modifications to the existing Water Treatment Works at Tokokoe and Befikrom in Ghana. The resulting upgraded plant is designed to be capable of handling a three-fold increase in throughput within the area occupied by the existing works units. The CFFA system has been evaluated and developed from pilot through to full-scale units. Data from operational monitoring of the system modules show consistent performance at high throughputs up to three times conventional loadings, producing potable water meeting WHO and EC guideline values.
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The paper describes the results of a programme of numerical studies that were undertaken in order to assess and optimise the fluid-dynamic performance of a novel non-powered self-cleansing combined sewer overflow (CSO) screening system,... more
The paper describes the results of a programme of numerical studies that were undertaken in order to assess and optimise the fluid-dynamic performance of a novel non-powered self-cleansing combined sewer overflow (CSO) screening system, the Hydro-Jet Screen™. The Hydro-Jet Screen™, like many other CSO systems, was developed such that it could be readily installed into either a purpose built or existing rectangular chamber. By means of simulating the system using computational fluid dynamics (CFD) software, a design configuration was identified in which the occurrence of ‘stagnant’ or ‘recirculating’ regions was minimised. The objective of the study was to reduce the likelihood of occurrence of debris accumulation and retention within the chamber, both during and after a storm spill event. Observations of the operation of both model and prototype scale units have indicated good qualitative correspondence with the predictions in terms of overall flow patterns, and have confirmed the superiority of the recommended design in terms of its self-flushing capabilities.
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Often the design, permitting, construction and startup of an in-situ mechanical device in wastewater open channels is not the hardest task — demonstrating its performance against very stringent criteria after installation is a major... more
Often the design, permitting, construction and startup of an in-situ mechanical device in wastewater open channels is not the hardest task — demonstrating its performance against very stringent criteria after installation is a major challenge and may require a very creative design and delivery approach of its own. Most grit removal systems are not tested after installation and if there is a problem, operators find out only after the system breaks down or large quantities of grit are deposited in systems downstream of the grit removal process, affecting the entire wastewater treatment plant. In most instances these deficiencies cannot be rectified until the entire headworks is up for redesign. As a result of unreliable performance of prior (often conventional style) grit removal systems, some municipalities and clients are requesting that the efficacy of new, proprietary grit removal systems be proven either before they are installed or after installation. The testing usually consists of lab testing, pilot testing, field verification or a combination of these. A system that is unable to meet the treatment goals is either replaced or modified, usually at a cost to the supplier. This paper describes the test methods and sampling procedures used to evaluate two grit removal systems installed at two treatment plants in Clearwater, Florida. The work includes pilot testing for assessing the gradation of the incoming grit and in-situ device verification after the installation of the full-scale unit. The results from the testing indicate that using a multi-pronged approach to characterize grit and size treatment systems is an effective way of ensuring that the installed system is capable of meeting the design goals. The paper recommends adopting this test methodology for assessing installed grit removal systems.
Research Interests: Engineering and GRIT
The paper presents an alternative drainage philosophy and strategy which mimics nature’s way by slowing down (attenuating) the movement of urban runoff. This approach results in cost-effective, affordable and sustainable drainage schemes.... more
The paper presents an alternative drainage philosophy and strategy which mimics nature’s way by slowing down (attenuating) the movement of urban runoff. This approach results in cost-effective, affordable and sustainable drainage schemes. The alternative strategy can be described as one of prevention rather than cure by effecting controls closer to source rather than the traditional approach which results in the transfer of problems downstream, compounding the problem, resulting in its cumulation and, the need for large scale centralised control. The alternative strategy is set in context relating to the evolution of current practice and the implications of fragmented institutional responsibilities. Issues relating to socio-economic factors and appropriate development are discussed and the alternative strategy is shown to incorporate tenets of a holistic approach. The paper concludes by recommending the adoption of the alternative strategy for the provision of urban drainage infrastructure in developing countries. It suggests that this paradigm shift should help developing countries to leap frog the developmental stages in their provision of effective urban drainage infrastructure for their rapidly burgeoning urban centres.
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The Hydro Swirl-Flo® process is an application of the dynamic separation principle to physical-chemical treatment of wastewater. The paper describes how recent developments in the technology are configured in process modes to achieve EC... more
The Hydro Swirl-Flo® process is an application of the dynamic separation principle to physical-chemical treatment of wastewater. The paper describes how recent developments in the technology are configured in process modes to achieve EC Urban Wastewater Treatment Directive (UWWTD) requirements.
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An identification study of the feed-back of soluble organic matter from the benthic sludge in facultative ponds is described, based on field data reported for the New Mexico pond system in the USA. The study employed recursive estimation... more
An identification study of the feed-back of soluble organic matter from the benthic sludge in facultative ponds is described, based on field data reported for the New Mexico pond system in the USA. The study employed recursive estimation techniques to aid the identification of appropriate model structures. Model development progressed from the analysis of a simple non-reactive system to one incorporating two sub-systems, namely the planktonic region and the benthic region. It was found that the inclusion of a temperature-related feed-back term produced good model results while the temperature-corrected decay rate constant remained constant over time. The magnitude of the feed-back term would appear to be equal to the incoming load in the hottest months of the year. The implications for performance evaluation and design are discussed.
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Over the last several years, the USEPA has listed particulates as the largest source of pollutants to water bodies in the United States. This makes an understanding of the nature and composition of sediments a critical component of water... more
Over the last several years, the USEPA has listed particulates as the largest source of pollutants to water bodies in the United States. This makes an understanding of the nature and composition of sediments a critical component of water quality studies. Whereas large sediments can be quantified using standard sieves, the same cannot be said of medium to fine sediment, which constitutes the primary source of pollution in urban stormwater runoff. This paper focuses on the use of new technology in the water quality industry with emphasis on assessing the ability to quantify fine sediment from urban stormwater runoff. The technology was assessed using influent and effluent samples from a stormwater treatment system. Subsamples were transported through this fluid imaging technology and the results from the influent and effluent samples compared. The results are also compared with the suspended sediment concentrations (SSC) from the collected samples. The particle imaging system was effective at differentiating changes in gradation between the influent and effluent samples and also provided information on the geometry of the particulates in the sample. The use of this technology has proven to be valuable and could be employed as a means of quickly assessing the performance of treatment devices for fine particulate removal. It has the added advantage of providing information on the shape and transparency of a particle which for the water quality industry could be a good differentiator between inert sediments and other materials common in stormwater runoff.
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Settling velocity of wastewater grit is a major concern in the design of grit removal devices. However, settling velocity is difficult to quantify for the size of particles encountered at wastewater treatment works. The goal of this... more
Settling velocity of wastewater grit is a major concern in the design of grit removal devices. However, settling velocity is difficult to quantify for the size of particles encountered at wastewater treatment works. The goal of this project was to take existing settling velocity techniques and optimize the design to take samples of particles of known settling velocity. The developed technique was then validated and applied to wastewater grit samples to determine their settling velocities. The particles from each sample were analyzed with a high speed imaging system that collected information on the size, shape, length of the particles and other characteristics of interest. This paper outlines the process that was used to develop the settling velocity methodology. Five different setups were tested before the final design was chosen. The different concepts tested are described along with the pros and cons of each setup. In the end the final design was a long, wide column with a central sampling point close to the bottom that is used to sample material within a given particle size range. The sampling time was based on the theoretical settling rate for clean spherical silica particles within the range of interest. The setup developed was then used to characterize the settling characteristics of samples taken from three wastewater treatment plants in the United States. The results from the analysis show that wastewater grit has different settling characteristics when compared to clean silica sand.
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The vast majority of pollutants in urban water are associated with sediments and sewer solids. Sediment has been identified as the most widespread pollutant in US Rivers and streams. In addition to sediment itself being a major pollutant,... more
The vast majority of pollutants in urban water are associated with sediments and sewer solids. Sediment has been identified as the most widespread pollutant in US Rivers and streams. In addition to sediment itself being a major pollutant, many priority pollutants such as heavy metals and toxic organics (e.g. PAHs) are associated with sediments. Becker et al. , (1996) for example found pollutants to be associated with the suspended solids that have settling velocities in the range of 0.04 – 0.90 cm/sec. Research and operational experiences have shown that considerable sediment and sewer solids deposition occurs in most sewerage (collection) systems as self-cleansing velocities are hardly attained during dry-weather flow conditions. The re-mobilization of gross sewer solids, the settled sediments and their associated pollutants during wet-weather events accounts for the observed first-foul flush during storm events especially after a prolonged period of dry weather. This highly pollut...
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This paper describes the findings of a long term study of the nitrification performance of a purpose built, large-scale, pilot plant consisting of two mirrored, aerated, continuously operated upflow filters (ACoUFs) operating under... more
This paper describes the findings of a long term study of the nitrification performance of a purpose built, large-scale, pilot plant consisting of two mirrored, aerated, continuously operated upflow filters (ACoUFs) operating under realistic conditions. The effect of temperature, liquid flow rate, aeration rate and media types on the performance of each of these filters is reported. After a start-up period of 2-3 weeks each plant performed consistently and the performance, expressed as a concentration change between influent and effluent, was found to depend directly on temperature and aeration but inversely on flow rate, with little interaction between the variables. The introduction of these aerated CoUF variants can have a considerable role to play in increasing effluent quality.
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Rapid urbanisation and its consequent increase in impermeable surface areas and changes in land use has generally resulted in problems of flooding and heavy pollution of urban streams and other receiving waters. This has often been... more
Rapid urbanisation and its consequent increase in impermeable surface areas and changes in land use has generally resulted in problems of flooding and heavy pollution of urban streams and other receiving waters. This has often been coupled with ground water depletion and a threat to water resources. The first part of this paper presents an alternative drainage philosophy and strategy which mimics nature's way by slowing down (attenuating) the movement of urban runoff. This approach results in cost-effective, affordable and sustainable drainage schemes. The alternative strategy can be described as one of prevention rather than cure by effecting controls closer to source rather than the traditional approach which results in the transfer of problems downstream, resulting in its cumulation and the need for large scale, centralised control. The second part describes a research project which has been launched in order to quantify the cost and operational benefits of source control and distributed storage. Details of the methodology of the modelling and simulation processes which are being followed to achieve this target are presented.
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ABSTRACTThe paper describes the nature and characteristics of urban runoff and the effects of urbanization and industrialization on the hydrologic/hydraulic regime and on water quality. The need for control measures to alleviate and... more
ABSTRACTThe paper describes the nature and characteristics of urban runoff and the effects of urbanization and industrialization on the hydrologic/hydraulic regime and on water quality. The need for control measures to alleviate and prevent problems caused by urban runoff is highlighted, and this is related to the adverse environmental impacts of urban runoff.Measures and techniques currently available and under development for urban runoff control are described within the framework of regulators, service providers and the general public. The need for an integrated approach to urban runoff control is highlighted, and this is followed by a number of case studies demonstrating the cost‐effectiveness of an integrated approach.
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Like most major cities in Africa, Accra is undergoing a rapid pace of urbanization fueled by economic development, population growth and rural to urban migration. The city faces major challenges with the provision of adequate and... more
Like most major cities in Africa, Accra is undergoing a rapid pace of urbanization fueled by economic development, population growth and rural to urban migration. The city faces major challenges with the provision of adequate and effective urban water infrastructure. The challenges associated with perennial flooding in Accra are reviewed in the context of recommended policy, institutional and organizational changes that are deemed to provide a more sustainable and holistic approach to urban water service provision. These have the potential of increasing the interactions of multiple stakeholders including the public, system designers, urban planners, entrepreneurs, activists, etc. and fostering an even closer link between professional practice and community participation providing the scope for spurning innovation, capacity building and job creation at a local level.
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... Management Practices in the drive for more Page 3. sustainable urban drainagesystems (SUDS) has heightened the move towards alternative innovative urbandrainage systems. Particularly in the case of 'new' developments ...
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Rainwater Harvesting, a traditional practice in parts of Ghana many centuries ago, has received very little attention in recent times. The paper describes a collaborative research effort aimed at the adaptation and development of... more
Rainwater Harvesting, a traditional practice in parts of Ghana many centuries ago, has received very little attention in recent times. The paper describes a collaborative research effort aimed at the adaptation and development of affordable technologies for capturing and retaining rainwater runoff including that from roof tops; and using this as a valuable source of water to supplement the water needs of households in Northern Ghana. The project also ultimately seeks to address issues of flooding and erosion caused by the lack of adequate drainage through the effective capturing, retention and controlled release of rainwater. The Project will verify the extent to which adoption of the adapted technologies could help greatly in conserving water resources in the Sahel and other semi-arid regions in developing countries and at the same time helping to alleviate poverty by improving the quality of life of women and children in these regions. The rainwater harvesting systems will be desi...
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1 This paper describes the findings of a long term study of the nitrification performance of a purpose built, large-scale, pilot plant consisting of two mirrored, aerated, continuously operated upflow filters (ACoUFs) operating under... more
1 This paper describes the findings of a long term study of the nitrification performance of a purpose built, large-scale, pilot plant consisting of two mirrored, aerated, continuously operated upflow filters (ACoUFs) operating under realistic conditions. The effect of temperature, liquid flow rate, aeration rate and media types on the performance of each of these filters is reported. After a start-up period of 2-3 weeks each plant performed consistently and the performance, expressed as a concentration change between influent and effluent, was found to depend directly on temperature and aeration but inversely on flow rate, with little interaction between the variables. The introduction of these aerated CoUF variants can have a considerable role to play in increasing effluent quality.
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Sewer systems that convey both sanitary sewage and stormwater through a single pipe are referred to as combined sewer systems. This system diverts all flows exceeding the design capacity to the receiving watercourses in heavy rain events.... more
Sewer systems that convey both sanitary sewage and stormwater through a single pipe are referred to as combined sewer systems. This system diverts all flows exceeding the design capacity to the receiving watercourses in heavy rain events. Therefore, environmental regulations limit the use of this system and separate sewer systems are currently used in all new developments. However, the UK, most other European, and other countries usually have narrow streets occupied by a complex network of infrastructure services. About 70% of sewer systems in the UK and Europe are combined systems. Finding a space in which to place another two sets of pipes (in a separate sewer system) is therefore challenging. This research investigates a design which is capable of overcoming this challenge by a modified system for the sewer networks. The system includes a proposed new design for the manhole shape, which will allow the storm flow and the foul flow to pass through the same manhole without mixing an...
Research Interests: Urban Water and Elsevier
... There have been a number of initiatives and projects involving Sustainable Drainage Systems (SUDS) in the ... and developers are keen to implement this approach in addition to traditional urbandrainage systems. The paper reviews the... more
... There have been a number of initiatives and projects involving Sustainable Drainage Systems (SUDS) in the ... and developers are keen to implement this approach in addition to traditional urbandrainage systems. The paper reviews the current applications of SUDS in the UK by ...
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Sustainable drainage systems are increasingly seen as a better way of draining urban areas, being ‘more natural’, less resource intensive and offering water quantity and quality control with amenity benefits. Sustainable drainage systems... more
Sustainable drainage systems are increasingly seen as a better way of draining urban areas, being ‘more natural’, less resource intensive and offering water quantity and quality control with amenity benefits. Sustainable drainage systems ‘greening’ can also reduce heat island effects. However, little attention has been given to assessing the real value and sustainability of the approach and uncertainties remain over performance and robustness, as well as ownership and maintenance. Received wisdom suggests that sustainable drainage systems have potential to help cope with climate change, while offering wider sustainability benefits over traditional piped drainage. The inherent adaptability of sustainable drainage systems allows them to be implemented incrementally as climate change knowledge advances. This paper provides evidence from a range of initiatives to show how sustainable drainage systems can contribute to a portfolio approach to tackling the problems of climate change. The ...
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This chapter discusses much of the issues related to modeling of existing hydropower plants with the Akosombo Hydroelectric Dam as a case study. The re-engineering techniques to optimize turbine intake for critical water levels would also... more
This chapter discusses much of the issues related to modeling of existing hydropower plants with the Akosombo Hydroelectric Dam as a case study. The re-engineering techniques to optimize turbine intake for critical water levels would also be discussed. These optimization techniques are vital for existing hydropower plants since it is difficult to predict and model climate and weather precisely.
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The performance of any device in which a kinetic process occurs e.g. disinfection, coagulation and chemical reactions is dependent on the mixing regime for a given set of operating conditions. Subsequently by characterising the mixing... more
The performance of any device in which a kinetic process occurs e.g. disinfection, coagulation and chemical reactions is dependent on the mixing regime for a given set of operating conditions. Subsequently by characterising the mixing regime within a device and conducting batch reactor experiments to obtain specific kinetic process parameters it is possible to determine the system’s efficiency. This has been achieved for a hydrodynamic vortex separator (HDVS) operating with no baseflow component by undertaking residence time distribution (RTD) investigations. The kinetic process investigated at both batch scale and within the continuously operated HDVS to provide comparative data was the first–order decomposition (conversion) of hydrogen peroxide (H2O2) by an enzyme catalase. The HDVS is a high rate vortex process predominantly used for the separation of solids from an incoming feed. The HDVS is typically used as a combined sewer overflow (CSO) in the drainage system and at wastewat...
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... Drainage of the media between events is also important to minimize problems associated with media going anaerobic. ... Page 10. 11th International Conference on Urban Drainage, Edinburgh,Scotland, UK, 2008 ... 442 pgs. October 1999.... more
... Drainage of the media between events is also important to minimize problems associated with media going anaerobic. ... Page 10. 11th International Conference on Urban Drainage, Edinburgh,Scotland, UK, 2008 ... 442 pgs. October 1999. Clark, S., R. Pitt, and P. Brown. ...
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‘Engineered’ or ‘hard’ structure based SuDS (Sustainable (Urban) Drainage Systems) have become popular in recent years, presenting further options to the drainage engineer beyond some of the more conventional approaches. However, as with... more
‘Engineered’ or ‘hard’ structure based SuDS (Sustainable (Urban) Drainage Systems) have become popular in recent years, presenting further options to the drainage engineer beyond some of the more conventional approaches. However, as with any approach, correct design practice must be applied if systems are to be effective and maintainable. Robust management of sediments is a prerequisite for the successful operation of any drainage system. If not adequately managed, sediments will accumulate in undesirable locations, making maintenance difficult, and will pass on to receiving watercourses, presenting a pollution threat. The paper considers best practice in the design and linking together of ‘hard’ SuDS components, specifically storage systems and sediment interceptors. It is concluded, based on the outputs of recent studies, that an optimal system will incorporate a storage chamber with designed-in sediment transfer facilities, feeding onward to well -designed flow control and sediment capture facilities.
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The design of the sewer system in hilly regions has a different concept from other areas due to the high flow velocity generated in the system that characterises a sloped system. The flow velocity of sewage or stormwater in the sewer... more
The design of the sewer system in hilly regions has a different concept from other areas due to the high flow velocity generated in the system that characterises a sloped system. The flow velocity of sewage or stormwater in the sewer system is limited by design criteria, using minimum velocity to avoid settlement of suspended solids in the pipes and maximum velocity to keep the solute homogeneous (fluid and suspended solids) and avoid pipe erosion. Maintaining these limits of the velocity within hilly regions is challenging and designers usually use steep cascade manholes to dissipate the fluid flow energy. This paper presents a new manhole design to mitigate stormwater flow energy, which is more critical than sewage flow in such areas, and using the traditional normal steps manhole for the sewage chamber. The new manhole design includes two chambers, an inner chamber used as in the traditional manhole for sewage and an outer chamber used for stormwater flow. The hydraulic propertie...
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Urban drainage networks require accurate, reliable flow control systems for their effective operation and minimisation of flood risk. Different types of flow control produce different hydraulic characteristics, having implications to... more
Urban drainage networks require accurate, reliable flow control systems for their effective operation and minimisation of flood risk. Different types of flow control produce different hydraulic characteristics, having implications to system design in particular relating to upstream storage utilisation. Vortex flow controls (VFCs) present particular opportunities, producing desirable hydraulic characteristics while also having large clearances compared to other devices. This paper describes the implementation of advanced flow control characterisation procedures and techniques allowing VFCs in particular to be characterised within a period of a few hours. The results are shown to correspond with those collected using conventional methods. Work is also described relating to the development and application of a model to allow storm hydrograph response modelling of storage-flow control combinations. It is demonstrated how the use of a VFC can lead to significantly more efficient storage ...
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Les directives du Royaume-Uni sur le traitement des rejets de deversoirs d'orage et des autres rejets urbains de temps de pluie se concentrent sur l'elimination de la pollution visuelle, ce qui a dicte l'utilisation massive... more
Les directives du Royaume-Uni sur le traitement des rejets de deversoirs d'orage et des autres rejets urbains de temps de pluie se concentrent sur l'elimination de la pollution visuelle, ce qui a dicte l'utilisation massive des systemes de degrillage. La majorite des systemes de degrillage disponibles dans le marche utilisent des composants electro-mecaniques pour eviter les depots et l'encrassement. Cependant, etant donnees les conditions difficiles en reseau d'assainissement, cela est loin d'etre l'ideal. Ce travail presente le systeme Hydro-Jet Screen , un systeme de degrillage des rejets de deversoirs d'orage auto-nettoyant, qui fonctionne sans partie mecanique mobile et ne necessite pas d'alimentation electrique. Le systeme utilise uniquement un mecanisme d'entretien hydraulique inverse, et est par consequent ideal pour une utilisation dans l'environnement des reseaux d'assainissement.