What work in the United Arab Emirates is revealing about the wet-stuff...
Jodie Harris is a sixth form student at Ribston Hall School in Gloucestershire. She was a finalist in the Academy Excellence Awards, chemistry category, with this submission...
Wellbeing was referred to as the quality of life by ecological economist, Robert Costanza ; but what are happiness, health and prosperity without life itself? Physical and emotional wellbeing both rely heavily on the chemistry of the human body, which in turn relies greatly on water. Dihydrogen monoxide - or H2O - is the essential solvent, the transport medium of the body that, among other things, gives humans the ability to regulate temperature and is crucial in the digestion and absorption of food. Indeed, it is one of the basic components of life and is why, after the discovery of ancient lakes on Mars, billions are being poured into space missions to look for life, past or previous, on the red planet and beyond. But closer to home, water shortage problems worldwide have highlighted mankind’s dependence on this important molecule.
There are large areas of the world that have high water poverty, not because of insufficient funds but because of their physical geography. Most of these countries lie on the equator where the high temperatures and limited seasonal rainfall force people to search for other reliable water sources. Without the work of chemists and researchers worldwide, life and prosperity would not be able to flourish in these areas of the planet.
This issue has been focused on in particular by the governing body in the United Arab Emirates , which has the money and resources to enable a wide range of research. Whilst it has the richest city in western Asia, the UAE has dwindling fresh groundwater supplies and depends greatly on water cleansing technology. A significant proportion of freshwater for the UAE is created through desalination of seawater. The processes of desalinisation can be divided into two main categories, those that use thermal energy and those that depend on electrical energy . The most commonly used technique is called reverse osmosis, which uses large amounts of electrical energy in order to push water against its potential gradient through a semi-permeable membrane. Unfortunately, reverse osmosis still has a number of problems, including membrane fouling and high energy requirements.
An alternative method of desalinisation is forward osmosis. This technique would utilise water’s tendency to move down a water potential gradient from seawater to a draw solution. The draw solution contains a solute, or draw chemical, which can be later removed by a chemical or physical process. The original draw chemical used was ammonium bicarbonate, which decomposes to form carbon dioxide and ammonia when heated. These products can then be reused, forming a closed loop system. Current research is trying to utilise nanotechnologies which would allow the forward osmosis technique to work at lower temperatures, possibly using just the heat from the Sun.
One way in which this might work would be to use nanoparticles covered in an amphiphilic molecule in the draw solution. At temperatures below 34°C, water-nanoparticle hydrogen bonding would dominate, lowering the water potential of the draw solution and allowing osmosis from the salty seawater solution to the draw solution. Then the draw solution could be collected and heated to above 35°C. At these higher temperatures nanoparticle-nanoparticle interactions would dominate as hydrogen bonds are disrupted, causing the nanoparticles to clump together in a globular formation. This would allow the nanoparticles to be removed easily, using either a weak magnetic field or simple nanofiltration. The nanoparticles can then be reused with the entire process consuming very little energy in comparison to current desalination techniques . However, both osmosis techniques are still very much in development with new materials being tested for the semi-permeable membrane.
Another, alternative, desalinisation process doesn’t use osmosis at all, but is instead based on the simple process of distillation. Seawater is heated up and evaporates, leaving salt crystals behind, and then the steam is condensed to give salt-free water. There are a number of different distillation techniques; multi stage flash distillation (MSF) accounts for around 85% of desalinisation worldwide . It is the simplest method, by which multiple evaporation chambers are used to collect fresh water. Vacuum distillation has also been growing in popularity, in which the pressure on the water body is reduced, causing it to evaporate at much lower temperatures.
Two general problems for all desalination methods are the uptake of seawater, and the output of a highly concentrated salt solution, both of which can damage the aquatic environment if not properly regulated . Money needs to be invested in constructing efficient distribution systems when the plants are built, and the rate of water uptake needs to be controlled. At the Kwinana Desalination Plant in Perth, Australia, water is continuously sucked up from the ocean at 0.1 ms-1, giving fish the chance to swim away from the pipes . Whilst some methods of desalination do not result in the production of concentrated brine, those that do must control the reintroduction of salt water. Either they can release the salt water in an area with fast flow or currents, thereby quickly dispersing it, or use numerous pipes with small holes along the length, allowing the brine to be released over a larger area.
There are also other options in the production of fresh water, waste water treatment and water conservation. Waste water treatment used directly for drinking water is currently only used in one country, Singapore . There are a number of steps in the process that they use, including filtration, biological treatments and settling, making it both energy and time consuming. Current research is focused on increased efficiency of these processes with reuse of some of the waste products to make energy. Industrial waste water treatment usually involves reverse osmosis to remove dissolved substances, so using it this form of treatment as a primary source of fresh water over desalination is not a sustainable option.
However, research into nanotechnology has opened up the possibility of renewable energy and clean water production from waste water as a result of the photocatalytic fuel cell (PFC) system. The process uses titania (TiO2) nanotubes with a narrow band gap semi-conductor, such as copper(I)oxide, to break down the organic compounds in waste water to form CO2 and H+ ions. The hydrogen ions are then reduced at the cathode and react with oxygen to produce water. This process can use visible light from the sun rather than the enhanced UV light previously used in similar nanotechnology systems . With developments like this, as well as more efficient forms of waste water treatment, recycling water is definitely competing with desalination as a possibility for clean water production worldwide.
On the other hand, efficient water conservation can act as a preventative measure against shortages. Whilst having some of the biggest water shortage problems in the world, Dubai uses nearly three times more water per person per day, than other cities in the developed world . Huge quantities of water are used unnecessarily on a daily basis: 22,000 gallons for each show at the Dubai Fountain , enough water to run the 2 water parks and a ski resort, and soon, a theme park covering 186 million square meters . Environmental bodies in Dubai have been looking closely at the issue, and have calculated that by following three rules, Dubai can reduce water consumption by up to 46%, or 410 billion litres of water a year. The three rules are simple: turn off taps, take a shower not a bath, and use a bucket and sponge instead of a hose to wash your car. These rules do not limit or constrain wellbeing, but could save the country a great deal of money, simultaneously significantly reducing its carbon footprint.
Whilst there are lots of very simple methods to conserve water, money can also be invested in areas such as xeriscaping, a very water efficient form of landscaping. Scientists have carried out experiments in order to find the best soils, irrigation systems and alternative turfs for different environments. This could make a massive change in places like Abu Dhabi, naturally a desert city, which is covered in grass golf courses and open areas, all using hundreds of inefficient sprinkler systems.
It is clear that research in these areas has huge potential, and I have no doubt that in the near future these technologies will be introduced around the world in order to improve the availability of water, thus improving wellbeing. The UAE in particular is at a critical stage in its development, in which demands from increasing tourism and construction is exceeding water production capabilities, thereby risking further water poverty. With the introduction of the most suitable fresh water production and conservation techniques, this country could produce millions of litres of clean water without destroying its environment and saving billions of dollars. The increased access to water would allow citizens in the country to focus on improving other areas of their lives, giving them the freedom and ability to reach their full potential, and improve quality of life for future generations.