AiRO – the technique
AiRO is a method of unclogging fouled membrane elements using periodical air/water cleaning. The name, AiRO, is a contraction of “Air” and “RO” (reverse osmosis). The AiRO technique offers two big advantages: water purification that consumes less energy, and membrane cleaning that uses fewer chemicals.
A membrane is a selective barrier used as a high tech filter to purify water. Often the process of water purification involves the use of high-pressure membrane filtration, in which the water is forced through the membrane under pressure. This process is known as reverse osmosis (RO). The membrane is selective, that is, it lets the water through, but can retain bacteria and viruses, diluted solids, salts and lime. Usually the membranes are packed in so-called “spiral-wound membrane elements” which maximise the membrane area per cubic meter. The membrane elements contain channels through which the feed water flows. Many (Dutch) drinking water companies purify groundwater and surface water using membranes. Seawater or wastewater can also be used as feed water in a membrane installation, although this is not frequently done in the Netherlands.
The membranes can become fouled. The channels that transport the undesirable substances gradually become clogged, because bacteria accumulate and reproduce on the membrane, thereby creating a slimy coating. The water no longer flows through the membrane elements easily, which means that more energy needs to be used to produce clean water. The solution that Cornelissen and his former colleague Peter Wessels came up with is to place the membrane channels in a vertical position and to periodically introduce air and water through them, creating heavy turbulence in the channel. This is how AiRO unclogs fouled membrane channels: the power of the turbulence removes the slimy coating, the channels are unclogged and the detached material is discharged separately.
© 2017 KWR Watercycle Research Institute