Water is everywhere: in the air, clouds, rivers, oceans, ice, plants - and even inside the Earth. But only a small portion is available as fresh water: 97 per cent of water is saline and in the oceans. Since we cannot drink water from Victoria Harbour, we import around 70 per cent of our fresh water from the Dongjiang River in Guangdong province.
If we can remove the salt from seawater, can we drink it? Yes! Try this simple experiment with your parents at home: 1. Put an empty cup in the centre of a pot. 2. Pour salt water into the pot, and place the pot's cover upside down (so its handle is inside the pot, pointing down). 3. Boil the water. 4. The water becomes vapour, which condenses in the air as steam and forms on the surface of the pot's cover as water droplets. 5. The water droplets run down the handle and drip into the cup. The "distilled" water is now ready for drinking. Distillation is one of the earliest forms of water treatment.
Converting seawater into drinking water can be considered one of the best alternative water resources. It is abundant and less affected by climate change compared to other water resources.
More than 12,000 desalination plants already supply fresh water in 120 countries. The desalinated water market is expected to grow significantly over the coming decades. But seawater desalination has traditionally been very expensive due to its high energy consumption (as you may guess from the experiment!). That is why the first thermal desalination facility at the Lok On Pai site - built 40 years ago - was decommissioned in 1982.
Currently, reverse osmosis (RO) membranes are commonly used for seawater desalination. The new desalination plant to use an RO membrane will be located in Tseung Kwan O. It will ensure the free flow of water in Hong Kong.
Using semi-permeable membranes, RO can remove many types of molecules and ions, but the problem is the high electricity consumption needed to produce high pressure (up to 70 bar) for RO, and its sensitivity to fouling, which results in a decrease in filtrate flux and salt rejection.
Although RO technology has been continuously improved to reduce energy consumption, it still requires substantial amounts of electricity (1.5-2.5 kWh/m3).
How can we overcome these technical limitations and make desalination less expensive and easier to use? Innovations around the world have increased investment in new water technologies. We are now seeing novel technologies that have the potential to achieve sustainability for desalination.
The next generation of desalination has these goals: increase water recovery (reduce brine/concentrate), lower energy use, and increase resource (minerals) recovery.
Question: What other water resources (naturally and/or technically) are available in Hong Kong?