December 15 2007

Waterless Urinals - How do they work?

I am fascinated by waterless urinals. The very notion that a ammonia and nitrogen filled bodily fluid can be disposed of by a device using no flushing or running water is truly amazing to me. After doing a little reading into the science behind the products I am now even more impressed at the simple genius behind the waterless urinal!

Waterless urinals all use basically the same science. Urine flows down the bowl of the urinal past a debris-catching strainer. The urine then passes through a sealing liquid, usually a specially designed oil based fluid or simply vegetable oil, and collects in the waste pipe below. The different densities of urine and oil (urine is denser than oil - oil floats!) mean that the urine sinks through the sealing liquid and the oil floats on top of the layer of urine below. Any air bubbles rise to the top and escape leaving the urine in a relatively low oxygen environment. Odor is therefore trapped below the oil layer and cannot find the nose of bathroom occupants.

Densities of the liquids involved are:

823 kg/m3 - Ammonia



920 kg/m3 - Oil



1021 kg/m3 - Water

It is important that the urine is slowed sufficiently before it hits the oil so that laminar flow displacement doesn't move the oil to the bottom of the waste pipe. If the urine is slowed sufficiently this is not a problem. After the urine is in the waste pipe it is a simple matter of displacement that sends the urine into the regular plumbing system.

There are two varieties of waterless urinal: cartridge based and non cartridge based units. Cartridge based units use a replaceable cartridge pre-filled with sealing liquid. These units are periodically replaced as the sealing liquid is slowly eroded or degraded. Non Cartridge based systems work by simply introducing the sealing liquid into the drain hole and allowing it to naturally settle into the correct position.

Waterless urinals were introduced to the world by the Waterless Company in 1992. The first urinal used what was called an EcoTrap cartridge. Others manufacturers which started producing them almost a decade later include: Falcon Waterfree Technologies, Sloan Valve Company, Duravit, Kohler and many others.

Waterless urinals are also becoming increasingly popular as the green building movement takes hold with certification programs such as LEED. Two major barriers that once stood as impediments to the adoption of waterless urinals, regulatory and facility managers, are being gradually eroded through education on the benefits, safety and easy maintenance of the urinals.