Bellingham, WA (PressExposure) November 13, 2009 -- Metro Vancouver, BC. Wastewater treatment facilities that measure BOD (Biological Oxygen Demand) are encouraged to use vacuum-type samplers in order to prevent contamination. Automatic samplers of the peristaltic-pump type are found to falsely inflate data.
BOD is a measure of the rate at which a sample of water consumes oxygen when injected with aerobic bacteria. The bacteria is allowed to grow over 5 days at 20ÂºC, at which time an accurate measurement of bacteria is found.
Water sampling equipment itself can be a source of contamination for the BOD test. Unless it is properly cleaned, nitrifying bacteria can build up in the liquid samplerâs wetted parts, thus artificially inflating the results and prescribing inaccurate treatment of the wastewater.
Peristaltic-pump samplers are particularly prone to contamination. The peristaltic method draws in liquid by squeezing a tube around a roller assembly. As the liquid comes through the tubing, any solids or particulate inside the source liquid adhere to the wall as the tubing gets constantly pinched.
In order to take accurate samples for the BOD test on a peristaltic sampler, the tubing must be replaced regularly, even as often as every week.
The vacuum-method of sampling draws liquid into a metering chamber by creating a vacuum with a strong pump. The sample is then released into a container with a pinch valve. The only thing needing cleaning on these samplers is the metering chamber. Nothing should need replacing for many years of rigorous use.
SIRCO Samplers [http://www.sircosamplers.com] are the original vacuum-pump samplers, with over forty years of manufacturing experience. The metering chamber on a SIRCO is easily removed with two wing nuts in less than twenty seconds, and cleaning is simple and straightforward.
Because of SIRCOâs advantages, the Metro Vancouver region has advised that all wastewater treatment facilities use SIRCO Samplers whenever possible for the BOD test.