Development of a prototype, desktop vapour compression distillation device to remove poisonous metals from contaminated drinking water supplies, for application in the developing world.
Background and Context to Problem
Toxic metal poisoning is a continuing global health risk. It is highly prevalent in the developing world, particularly in countries such as Bangladesh, India and regions of China. High levels of metals such as arsenic, lead, mercury and cadmium in water supplies cause a large number of deaths and disabilities each year. The Institute for Health Metrics and Evaluation (IHME) estimated that in 2017, lead exposure accounted for 1.06 million deaths and 24.4 million years of healthy life lost worldwide (disability-adjusted life years (DALYs)) [1]. In 2020, it was estimated that 94 million to 220 million people are potentially exposed to high arsenic concentrations in groundwater [2]. It is also recognized that at least 140 million people across 50 countries have been drinking water containing arsenic at levels above the WHO provisional guideline value of 10 μg/L [3]. In 2012, about 39 million people in Bangladesh were still exposed to arsenic concentrations above the national standard of 50 μg/L [4]. Half of the WHO’s ‘Ten Chemicals of Major Public Health Concerns’ are similar toxic heavy metals. This contamination and resultant poisoning are caused by agricultural fertilizers, mining byproducts and industrial waste seeping into the surface and groundwater. This leads to contamination of water supplies and wells. Although it is practically impossible to prevent such contamination at all scales, the water can be treated.
Current efforts to tackle the problem
Current measures to combat metal contamination in water supplies include reverse osmosis membranes, charcoal filters, and ion exchange resins. Yet these methods are inefficient, require regular maintenance/changing and are often wasteful. As an example, a reverse-osmosis membrane delivering 19 litres of treated water per day may discharge between 75 and 340 litres of wastewater daily [5]. Such devices are not implementable in areas where access to water is already scarce. Furthermore, in aerobic conditions, metal oxides can form and clog these membranes. Large particulates also cause fouling of the membrane leading to a replacement being required. Ion exchange resins are ineffective outside the PH range 6-9, meaning pre-treatment of the water is likely necessary.
Solution Background
Distillation is one of the few effective methods for treating water contaminated by heavy metals. Distillation uses the difference in boiling points to separate clean water from contaminants and is widely researched and documented to be highly effective at separating water from inorganic substances. Included in the distillation process, and unlike membranes, is the heat-induced deactivation of bacteria, viruses, and protozoan cysts. One study from the University of Nebraska suggests that distillation can result in water with up to 99.5% of impurities removed [5]. Distillation is not usually an option in the developing world due to its high energy requirements. However, large-scale desalination facilities and breweries use a process called vapour compression distillation to recover lost heat energy while distilling huge volumes of water. This system has a coefficient of performance (COP) equivalent to a 200-stage multi-effect distiller. This is the same as reusing the energy 200 times or using 1/200th of the energy needed to distil one gallon of water [6]. A solution for this problem must be sufficiently small and low weight. It must also not use large amounts of energy.
Project Aim
The goal of this project is to scale down the vapour compression distillation technology used in desalination plants and breweries. The aim is to develop a desktop prototype, small enough to be portable by 1-2 people, that can produce enough daily drinking water for up to 15 people, or 2 to 4 families in the developing world. The specific target is 30 litres of clean water per day. This project will evaluate the output flowrate of distillate and the (input) energy consumption to develop an estimate of overall efficiency. The device will be designed to reduce energy requirements.
Methodology and Project Plan
The project can take place remotely and if then-current restrictions allow, preferably in the Fluids & Heat Transfer Lab in the Department of Mechanical, Manufacturing and Biomedical Engineering. the specific methodology is outlined below
- Design the device. This will be done regardless of funding.
- Procure items. If funded, I will purchase off-the-shelf components to reduce time constraints. The components necessary for the device are available for purchase in Ireland. The cost can be estimated at approximately €500. (est. 2 days)
- Construct the device. (est. 3 days)
- Calibrate and commission the device (est. 1 week).
- Evaluate the output flowrate of clean water, energy usage and estimate the thermal efficiency of the device over varying time periods (est. 4 weeks).
- Note inefficiencies and potential improvements for the prototype (est. 4 weeks concurrent).
This project requires no ethics approvals as I will not be dealing with any user data.
Supervisor’s Role
Prof. O’Shaughnessy is the Ussher Assistant Professor for Energy and International Sustainable Development. He is passionate about using engineering to help solve problems facing the people most at-risk in the developing world and has much relevant research experience in developing countries. He has seen and experienced first-hand the impact that contaminated water can have in these communities and has also witnessed the hugely positive impact that simple technologies can achieve. He will actively supervise the proposed project and can offer the full resources of his lab should COVID-related restrictions allow.
Larger Optimistic Outcome of Research
The overarching goal of this project is to create a simple technology that can be used to help people without regular access to clean water. Clean water has a powerful impact on people’s livelihoods. According to Water.org [7]. “Every $1 invested in water and sanitation provides a $4 economic return from lower health costs, more productivity and fewer premature deaths “.
Interdisciplinary Focus and Collaboration
This project has an interdisciplinary and humanitarian focus. It is a mechanical (thermal) engineering project. While I will primarily work within Trinity’s Mechanical Engineering department and with Professor O Shaughnessy, I will also receive support and advice from my mentors from Dogpatch labs, where I previously worked with a water treatment start-up company. I will also receive advice from some of the water treatment NGOs I connected with throughout my time in Dogpatch.
References
[1] WA: Institute for Health Metrics and Evaluation (IHME), Compare, G. B. D., Seattle: University of Washington, 2017.
[2] Podgorski J., Berg M., Global threat of arsenic in groundwater. Science, 368(6493), 845-850. (2020) https://science.sciencemag.org/content/368/6493/845
[3] Ravenscroft P, Brammer H, Richards K. , Arsenic Pollution: A Global Synthesis, Vol. 94, Sussex: Wiley-Blackwell, 2011.
[4] BBS/UNICEF, Multiple Indicator Cluster Survey 2012-13: Final Report. Dhaka: Bangladesh Bureau of Statistics/UNICEF, 2015.
[5]-Dvorak B., Skipton S, Drinking Water Treatment: Distillation, Lincoln: University of Nebraska , 2013.
[6] – Sears S.B. , Vapor Compression Distillation – Adding High Tech Understanding to Nature’s Process, Tucson: Water Conditioning and Purification Magazine, 2006.
[7] Water.org, An Economic Crisis, Available : https://water.org , [Accessed: February 4, 2021]