Solar Disinfection of Drinking Water
Title: Continuous flow solar disinfection system
Project coordinator
Dr. Laurence Gill
Email: gilll@tcd.ie
Tel: +353 1 896 1047
Research Students
Dr Orlaith McLoughlin [complete]
Dr. David Misstear [complete]
Ms. Joanne Mac Mahon
Email: MACMAHOJ@TCD.IE
Description
This project aims to use solar radiation, an abundant resource in most developing countries, to disinfect water supplies. In developing countries water related diseases account for the majority of premature deaths which, in many cases, could be alleviated by providing an adequate supply of safe water. In such situations there are often neither the finances nor the resources to construct and maintain the energy and chemically intensive water treatment processes used in more industrialised countries. The purpose of this project is to develop a water treatment process which requires little or no energy, involving water flowing through a transparent pipe at the focal point of a compound parabolic reflector, optimally angled beneath the pipe for maximum sunlight capture to disinfect water supplies.
Photolytic disinfection
The continuous flow solar disinfection system has been designed with a village/rural application in mind, although the potential applications for the system are numerous. The basic principle of the system is shown below. The germicidal effects of UV radiation are well documented and solar radiation contains part of its electromagnetic spectrum as UV radiation (wavelength 100-400nm) of which only a fraction of the UV-B and UV-A wavelength bands reach ground level through the ozone layer. This system aims to optimise the use of both incident and reflected light from a reflector onto a clear pipe which carries the requisite water flow.
Initial research involved a series of laboratory scale trials, which were carried out using a solar simulator to establish the disinfection kinetics of the system with E. coli, S. typhimurium and V. cholera in a variety of different reactors. The laboratory scale reactors were then tested under real sunlight at Platforma Solar de Almeria in southern Spain, before refining the design of a full-scale prototype for trials at tropical latitude.
Small-scale solar photocatalytic disinfection reactor
The first full-scale continuous flow solar disinfection system was installed in the village of Ndulyani in the Kitui district of Kenya to supply safe drinking water for approximately 600 people. The site selection, community liaison and installation of the pilot system were carried out by Colin Price in 2008, an MSc student in Civil Engineering, whilst working for the Irish NGO GOAL. The site chosen included the construction of a subsurface dam to store enough of the annual rainfall (which falls in a short rainy season) to supply the community for the rest of the year. The subsurface dam was selected in order to minimise evaporative losses and also provide some degree of protection from pollution. The water from the dam then flows by gravity into the solar disinfection system.
Photolytic disinfection in Africa
Photocatalytic disinfection
Recent research (IRCSET funded) has been investigating the enhancements to the process by an additional photocatalytic effect using a fixed titanium dioxide insert. This has been proved to be particularly effective at preventing re-growth of bacteria, which sometimes occurs following normal solar disinfection. Research has been carried out to devise a fixed photocatalyst for the continuous flow reactors, looking at both the type of photocatalyst and also the morhphometry of the fixed structure to optimise the process. The research has used laboratory experiments and Computational Fluid Dynamics analysis to optimise the shape of an insert. Equally, the synergistic effect of temperature and solar UV has also been shown to promote faster disinfection rates in experiments carried out at water temperatures of 45oC. Such water temperatures can easily be sustained in the reactor if the reflectors are designed to concentrate the solar energy from a slightly wider field.
Current research (IRCSET funded) aims to evaluate the disinfection kinetics of the optimised fixed photocatalytic insert with respect to the standard photolytic (solar) system. Its effectiveness at stopping the phenomenon of regrowth of pathogenic micro-organisms will also be closely studied. Another aim is to redesign the reactor in order to maintain the water temperature to at least 45oC in order to gain a synergistic thermal UV disinfection system. The expected enhancement to both the photolytic and photocatalytic reactors will then be evaluated. Such designs will be compared with respect to treatment efficiency and reactor size (and thus cost) in order to define an optimised system. Both these modifications to the standard photolytic system will be tested under both laboratory and real conditions in the field. Finally, the benefit of using a combination of photocatalytic insert and enhanced temperature will be ascertained in order to optimise the materials requirement for the reactor.
Fundamental to the research is for the system to remain as simple, inexpensive and robust as possible to ensure long-term viability in the harsh conditions of a rural environment. It is also envisaged that local manufacture of disinfection units should be promoted, adding the benefit of employment opportunities and contributing to the local economy.
Potential benefits of system
Community:
- Renewable resource - sunshine is normally an abundant resource in countries where access to clean water is often very limited.
- Water quantity - a centralised village system reduces the time and effort taken to collect water from more remote areas, work normally carried out by women and children
- Water quality - the system provides a safe source of clean water which will help to break the cycle of infection of water bourne / related disease (such as cholera, typhoid, dysentries etc)
Such illnesses and mortalities from the use of polluted water, in addition to the time and effort involved in collecting water, severely hamper the day to day activities of such communities, hindering their sustainability and development.
Operation:
- No pumping of water through system required
- Disinfection of water ensured by system (ie, no by-pass)
- Storage of treated water provided so water can be collected any time
- Minimal maintenance
Title: On-site wastewater treatment
Project coordinator(s)
Dr. Laurence Gill
Email: gilll@tcd.ie
Tel: +353 1 896 1047
Assistant Prof. Paul Johnston
Email: pjhnston@tcd.ie
Tel: +353 1 896 1372
Associate Prof. Bruce Misstear
Email: bmisstear@tcd.ie
Tel: +353 1 896 2800
Research Student(s)
Dr Cormac O`Suilleabhain [complete]
Mr. Niall O’Luanaigh
Email: noluanai@tcd.ie
Mr Titiksh Patel
Email: patelt@tcd.ie
Description
Domestic wastewater from over one third of the Irish population is treated in small-scale independent systems where connection to a sewer is deemed unfeasible. In such cases, the most prevalent treatment application is the conventional septic tank system with percolation area. A series of projects, funded by the EPA, have been investigating the performance of such on-site systems on seven different sites over the past 5 years. The linked projects have been looking at the breakdown of on-site effluent (both septic tank and secondary) as it percolates through subsoil of different characteristics; evaluating the performance of different secondary treatment processes (particularly sand filters and reed beds); characterizing the quantity and patterns of domestic wastewater production and; assessing the efficiency of various distribution devices.
Subsoil treatment processes
The research projects have been designed to test the three dimensional performance of a number of different percolation areas treating domestic wastewater was monitored. The percolation areas have been chosen according to the nature of their subsoil in terms of unsaturated percolation rate. Samples are taken across the percolation field and at a number of different depths to assess the attenuation of chemical and microbiological parameters in both septic tank and secondary treated effluent. Other instrumentation allows the dilution by effective rainfall to be calculated. The fate of certain Endocrine Disrupting Chemicals (EDCs) in on-site domestic effluent has also been studied.
The current project is investigating sites where the on-site effluent is being discharged into highly permeable sandy soils where, although permitted in current Irish EPA guidelines, a feeling exists amongst local councils and practitioners that the effluent could pose a subsequent risk to groundwater - a major source of drinking water in Ireland - if it percolates at an excessive rate. Hence, this project is particularly concentrating on the attenuation of microbiological parameters (bacteria and viruses).
Percolation trench being constructed with instrumentation
Treatment processes (constructed wetlands & sand filters)
In situations where a conventional septic tank installation is considered unsuitable, some form of secondary treatment system may have to be installed to improve the quality of the effluent before discharge to subsoil. Equally, if the subsoil is not suitable then a tertiary treatment process may have to be constructed.
Constructed wetlands (reed beds)
See "Constructed wetlands for domestic and agricultural wastewater treatment project" below.
Sand filters
Stratified sand filters have been studied as both secondary and tertiary treatment processes for on-site effluent. The effectiveness of different types of media has been analysed both in the laboratory and in real on-site conditions, including the use of recycled glass as an alternative media. Another area of research has been to design the optimum distribution manifold for the pumped discharge of effluent onto the top of the filters, thereby improving the overall treatment efficiency.
Stratified sand filter being used for on-site wastewater treatment
Distribution devices
One cause for concern in Ireland is poor distribution of the wastewater effluent between the percolation trenches, which is assumed in the design of the overall percolation area. Poor distribution results in hydraulic and biological overloading of one or more of the trenches, and even if the soil hydraulic conductivity is adequate for transmitting the liquid away from the trenches, the formation of an organic clogging layer (biomat) may restrict wastewater percolating through the subsoil. Both laboratory and field testing is currently being carried out on a range of different distribution devices to ascertain their efficiency under realistic loading rates and also their sensitivity to effluent quality and poor installation.
Opposite: Modified distribution device undergoing trials on-site
Title: Constructed wetlands for domestic and agricultural wastewater treatment
Project coordinator(s)
Dr. Laurence Gill
Email: gilll@tcd.ie
Tel: +353 1 896 1047
Assistant Prof. Paul Johnston
Email: pjhnston@tcd.ie
Tel: +353 1 896 1372
Research Student(s)
Mr. Niall O’Luanaigh
Email: noluanai@tcd.ie
Description
On-site wastewater treatment
In separate situations where a conventional septic tank installation is considered unsuitable, some form of secondary treatment system may have to be installed to improve the quality of the effluent before discharge to subsoil. Reed bed treatment systems are one such technology which has seen significant growth recently, being deemed an effective and low-cost alternative treatment system used for either secondary or tertiary treatment applications in place of the percolation area. However, local councils in Ireland to date are still reluctant to permit the use of reed beds as stand-alone secondary treatment systems given the scarcity of reliable long-term performance data relevant to Ireland and its climate, and their apparent poor winter treatment performances.
An ongoing project, funded by the EPA, is investigating the performance of three horizontal flow subsurface reed beds used as secondary or tertiary treatment processes for on-site wastewater effluent. The reed beds are being intensively studied for a period of two years during which their treatment performance for chemical and microbiological parameters is being measured across different climatic conditions.
Reed bed being used as tertiary treatment for domestic on-site effluent
Agricultural wastewater
The use of Integrated Constructed Wetlands (surface flow, soil-based constructed wetlands) for the treatment of farmyard and dairy parlour washings has been studied at a number of sites in Waterford.
Highway runoff
The use of surface flow, soil-based constructed wetlands for the treatment and hydraulic attenuation of road runoff is currently being studied at a site on the Monasterevin bypass.
See "Investigation of the hydrology and chemistry of road runoff, including treatment options" project, under hydrology.
Constructed wetland being used to treat highway runoff shortly after planting
Title
The impact of on-site wastewater treatment for small community developments on groundwater quality
Project Coordinator(s)
Dr. Laurence Gill
Email: gilll@tcd.ie
Tel: +353 1 896 1047
Assistant Prof. Paul Johnston
Email: pjhnston@tcd.ie
Tel: +353 1 896 1372
Research Student(s)
Patrick Morrissey
Email: morrisp2@tcd.ie
Tel: +353 1 896 2045
Description
Groundwater is an increasingly important resource in Ireland. Over the coming years it is estimated that water supply arising from groundwater sources will rise, with increasing pressures on current supplies and the possible introduction of water charges. Groundwater also accounts for a significant proportion of base flow for many of our streams and rivers around the country. It is therefore of great importance that we maintain the quality of our groundwater resources into the future.
Over the past number of years there has been a large increase in the number of small community developments outside of urban areas, often referred to as cluster developments. Planning policy varies across the country towards these types of developments and it is not generally known what (if any) impact these kinds of development and their density has on groundwater quality. This current research is evaluating groundwater quality at separate cluster developments in different areas of groundwater vulnerability. Continued monitoring of these study sites will take account of seasonal variances such as agricultural practices and fluctuations in the groundwater table. It is hoped that the results of this study will indicate if the density of cluster developments using de-centralised wastewater treatment systems has an impact on groundwater quality. This study will be used to develop a model which in turn could assist local authorities when planning future developments.
Title
Assessment of disposal options for treated wastewater from single houses in low permeability subsoil settings
Project Coordinator(s)
Dr. Laurence Gill
Email: gilll@tcd.ie
Tel: +353 1 896 1047
Project Manager
Dr. Donata Dubber
Email: dubberd@tcd.ie
Tel: +353 1 896 3199
Subproject Supervisor
Prof. Vincent O'Flaherty (NUIG)
Dr. Tim McCarthy (NUIM)
Associated Researcher
Assistant Prof. Paul Johnston
Email: pjhnston@tcd.ie
Tel: +353 1 896 1372
Associate Prof. Bruce Misstear
Email: bmisstear@tcd.ie
Tel: +353 1 896 2800
Postdoctoral Researcher
Mr. David Smyth (NUIM)
Research Students
Mary Keegan
Email: keeganm2@tcd.ie
Tel: +353 1 896 2781
Sean Curneen
Email: curneens@tcd.ie
Tel: +353 1 896 2781
Kathryn Kilroy (NUIG)
Project website: www.onsiteresearch.ie
Description
The domestic wastewater of over one third of the population in Ireland is treated by on-site treatment systems. In these systems the soil attenuation that takes place while the effluent percolates through the subsoil is playing an important role and protects the groundwater from pollution. The effectiveness of treatment however is highly dependent on the thickness and permeability of the subsoils. If the effluent loading on the subsoil is too high, the permeability of the subsoil very high or there is an insufficient depth of subsoil then the groundwater beneath a percolation area is at risk of pollution. Alternatively, if there is insufficient permeability in the subsoil to take the effluent load - the main focus of this research - surface ponding may occur with associated health risk and there will be a risk of effluent discharge and runoff of pollutants to surface water. The nutrient load in the effluent can contribute to eutrophication in sensitive water bodies, whilst contamination of water sources by human enteric pathogens can promote the outbreak of disease. The project aims to not only assess the pollution risk by old septic tank soakaway systems but moreover to investigate possible effluent disposal options in low permeability subsoil settings on the basis of both cost-benefit and environmental impact/sustainability principles.
Within this project the performance of existing septic tank soakaways in different subsoil settings with high, moderate and low permeability is being monitored to establish the degree of contamination to groundwater and/or surface water. Alternative methods of on-site effluent distribution, such as drip irrigation and low pressure pipe systems, will then be assessed for their suitability to improve effluent percolation and the natural attenuation of nutrients and pathogens. Willow evapotranspiration systems are seen as one potential effluent disposal option in areas of very low subsoil permeability. To investigate their performance under different Irish climatic conditions two systems have been constructed and will be monitored in the west of Ireland in order to augment the information being gained during an ongoing research project with trial systems in Co. Wexford. Using geospatial modelling different options for the treatment and disposal of wastewater effluent in areas of low subsoil permeability will be explored. This will be part of the development of a decision making prototype toolset for Local Authority planners and managers to evaluate alternative strategies and reduce the risk posed by current domestic septic tank treatment solutions.
Title
Sourcing of sustainable groundwater supplies: An investigation of a weathered crystalline rock aquifer system in central Uganda
Supervisors(s)
Associate Prof. Bruce Misstear
Email: bmisstear@tcd.ie
Tel: +353 1 896 2800
Dr. Eleanor Jennings (DkIT)
Dr. Suzanne Linnane (DkIT)
Dr. Albert Rugumayo (Makerere)
Research Student(s)
Sam Kagwisagye
Description
This PhD project is focusing on groundwater sources in a rural area of central Uganda. Wells are being surveyed for their functionality, water quality and susceptibility to pollution sources. A catchment has been selected and instrumented for the collection of hydrometric data, and a water balance for the catchment is being evaluated using a lumped parameter hydrological model. The impacts of changing climate will be assessed using the model, including the impacts of future climate scenarios on groundwater resources and potential well supplies. The project is part of the larger Water is Life research project being coordinated by Dundalk IT, which involves several Irish third-level institutions and Makerere University in Uganda. The project is funded by HEA/Irish Aid.
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