Water treatment wakes up to oxygen
Oxygen is catching up with air in the world of water treatment as costs are pushed down, opening up the way for smaller, more efficient water treatment plants.While most plants still use aeration, oxygen is making inroads into the market, with oxygen produced on-site at water treatment plants leading the way.
Using pure oxygen is much more effective and gives a more stable process, as well as using less energy, than aeration - pumping air into water only results in around 4% of the gas actually dissolving, with the rest rising up and causing turbulence and foaming. Meanwhile, almost all (90%) of the oxygen stream is dissolved.
"It's a bit like giving oxygen to a hospital patient gasping for air- it makes breathing much easier and you need lower volumes of the gas," explained Peter Barratt, business technology manager at Air Products, the first company to develop on-site oxygen production facilities for water treatment.
Because much less gas is pumped into the water, energy costs come down - while aeration dissolves around 2kg of oxygen per kWh it uses, with pure oxygen a kWh will get 2.5kWh produced and dissolved.
This may not seem a very significant difference, but aeration takes up a large chunk of energy used in water treatment, itself an energy-intensive process.
"We can now provide oxygen treatment at the price of aeration," Peter Barratt said.
Adapting a technology called Vacuum Swing Absorption (VSA) to the small volumes of oxygen needed in water treatment, Air Products have been able to make oxygen production much cheaper and drive down the running costs.
Low energy use is just one of the benefits of oxygen - it greatly reduces foaming, treats water more effectively and requires less space. The volumes of reactor needed to treat water are reduced from three to as much as ten-fold when VSA is used, according to Air Products.
Most of the market continues to use aeration, and Peter Barratt admits that oxygen is unlikely to ever replace air in water treatment. But thanks to VSA, as opposed to the costlier liquid oxygen option, it may go up from around 1% of the market it currently occupies to 5% or so.
Research and development efforts are now focused on further minimising the costs and energy use.
"What we are trying to do it to demonstrate that you really can approach the costs of aeration with an oxygen system, and get all the added benefits.
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