What is Dissolved Oxygen?
In waterbodies, dissolved oxygen (DO) is the form of oxygen that is available to sustain aquatic organisms but it does not include the oxygen associated with a molecule of water. Water bodies become oxygenated through various means. In the natural environment, the main source is atmospheric oxygen, however other pathways include agitation (waterfalls) and photosynthetic aquatic plants. Surface waters typically have over 8 ppm DO, but levels can be as low as 4 ppm in certain conditions. Concentrations lower than 2 ppm DO are called hypoxic. As many aquatic organisms rely on dissolved oxygen to survive, hypoxic conditions can stress or outright kill aquatic life. Fish consume DO through their gills and microorganisms consume oxygen as they feed on pollutants or decaying matter.
The concentration of DO is dependent on several environmental factors. Temperature, pH, season, and time of day will influence DO levels. Temperature has a very large impact, as cold water can retain more dissolved oxygen than warm water.
Wastewater treatment facilities often treat wastewater using the activated sludge process which relies on aerobic microorganisms to breakdown or oxidize excess nutrients and pollutants. Aerators inject bubbles of oxygen into waste to maintain the microorganism population. A level of at least 2 ppm DO must be maintained for this process to work.
Industrial water treatment operators monitor oxygen levels in boilers. At elevated temperatures, oxygen is highly corrosive to metals as it causes pitting. High-pressure boilers and deep well oil recovery equipment are particularly vulnerable to this attack. To prevent costly corrosion damage, liquids in contact with metal surfaces must be treated to mitigate oxygen concentration, usually by a combination of physical and chemical means. Deaeration can reduce the dissolved oxygen concentration of boiler feedwater from several ppm to a few ppb. Chemical reducing agents (referred to as oxygen scavengers), such as hydrazine, DEHA and sodium sulfite, may be used instead of or in conjunction with deaeration.
Why Test for Dissolved Oxygen?
DO concentration is a basic measurement for assessing the health of a body of water. Environmental groups, consulting firms, and government agencies regularly monitor aquatic ecosystems’ DO concentration to ensure they can support life. Frequent DO testing is an effective way to catch conditions that can cause hypoxia before they can threaten aquatic life.
Industries that rely on metal systems like high-pressure boilers measure DO concentrations to prevent costly or catastrophic equipment corrosion. DO measurements also help operators determine whether they are dosing oxygen scavenger effectively to limit chemical waste.
About Our Test Kits
Two oxygen test methods are available that offer different measurement ranges:
CHEMetrics has manufactured quality dissolved oxygen test kits since 1969. We offer visual and instrumental options that measure in ppb ranges, perfect for high-pressure boilers, and ppm ranges for environmental applications.
CHEMetrics visual test kits feature CHEMets® self-filling ampoules that contain pre-measured reagent for a single test. Simply snap the ampoule directly in a sample to draw in the correct volume of sample and then compare to the supplied color standards to find the concentration.
CHEMetrics instrumental test kits feature Vacu-vials® ampoule technology. Vacu-vials ampoules utilize the same self-filling technology as CHEMets ampoules, but the vials have a 13mm diameter, so they are compatible with most photometers or spectrophotometers.
Click on a catalog number below for more information or to purchase a test kit.
|Range||MDL||Method||Kit Catalog No.||Refill Catalog No.|
|0-20 ppb||2 ppb||Rhodazine D||K-7511||R-7511|
|0-40 ppb||2.5 ppb||Rhodazine D||K-7540||R-7540|
|0-100 ppb||5 ppb||Rhodazine D||K-7599||R-7540|
|5-180 ppb||5 ppb||Rhodazine D||K-7518||R-7518|
|0-1 ppm||0.025 ppm||Rhodazine D||K-7501||R-7501|
|1-12 ppm||1 ppm||Indigo Carmine||K-7512||R-7512|
|Range||Method||Kit Catalog No.|
|0-1.000 ppm||Rhodazine D||K-7553|
|0-15.0 ppm||Indigo Carmine||K-7513|
|0-15.0 ppm||Indigo Carmine||I-2002|
Application Overview: Monitoring Dissolved Oxygen in High-Pressure Boiler Systems