Best portable dissolved oxygen meter use an electrochemical, polarographic, amperometric, galvanic, or optical sensor to measure the amount of oxygen gas dissolved in a water sample. DO is an important water quality parameter that affects marine life, the taste of drinking water and the corrosivity of a water sample. Common applications include groundwater recovery, wastewater treatment, aquariums and fish farms.
Dissolved oxygen (DO) is oxygen dissolved in water. Oxygen dissolves by diffusion from the surrounding air; aeration of the water that has fallen on waterfalls and rapids; and as a waste product of photosynthesis. An simplified formula is given below:
Photosynthesis (in the presence of light and chlorophyll):
Fish and aquatic animals cannot split oxygen from water (H2O) or other oxygen-containing compounds. Only green plants and some bacteria can do this through photosynthesis and similar processes. Virtually all the oxygen we breathe is produced by green plants. A total of three-quarters of the earth’s oxygen supply is produced by phytoplankton in the oceans.
If the water is too warm, there may not be enough oxygen in the water. When there are too many bacteria or aquatic animals in the area, they can overpopulate by using DO in large amounts.
Oxygen levels can also be lowered by over-fertilizing aquatic plants by runoff from farmlands containing phosphates and nitrates (fertilizer ingredients). Under these conditions, the number and size of aquatic plants grows. Then, if the weather becomes cloudy for a few days, the breathable plants will use up most of the available DO. When these plants die, they become food for the bacteria, which in turn reproduce and consume large amounts of oxygen. And that depletes all the oxygen.
How much oxygen an aquatic organism needs depends on its type, its physical condition, the water temperature, the pollutants present and much more. As a result, it is impossible to accurately predict minimum oxygen levels for specific fish and aquatic animals. For example, at 5 ° C (50 ° C), trout consume about 50 to 60 milligrams (mg) of oxygen per hour; At 25 ° C, they may need five or six times that amount. Fish are cold-blooded animals. They use more oxygen at higher temperatures because their metabolic rates increase.
Numerous scientific studies suggest that 4 to 5 ppm DO is the minimum amount that will support a large, diverse fish population. The oxygen content in good fishing waters generally averages 9.0 ppm.
The influence of the environment
The total concentration of dissolved gas in the water should not exceed 110 percent. Concentrations above this level may be harmful to aquatic organisms. Fish in waters containing excessive amounts of dissolved gases may suffer from “gas bubble disease”; however, this is a very rare phenomenon. The bubbles or blockage block blood flow through the blood vessels, causing death. External vesicles (emphysema) may also occur and can be seen on the fins, skin and other tissues. Aquatic invertebrates are also affected by gas bubble disease, but at levels higher than lethal to fish.
Adequate dissolved oxygen is essential for good water quality. Oxygen is an essential element in all forms of life. Natural stream purification processes require adequate oxygen levels to maintain aerobic life forms. When the dissolved oxygen level in water drops below 5.0 mg / l, aquatic organisms are exposed to stress. The lower the concentration, the greater the stress. Oxygen levels that remain below 1-2 mg / L for several hours can result in the death of large fish.
From a biological point of view, however, oxygen content is a much more important measure of water quality than feacal coliform. Dissolved oxygen is essential for the survival of all aquatic organisms (not just fish, but also invertebrates such as crabs, clams, zooplankton, etc.). In addition, oxygen affects a variety of other water indicators, not only biochemical but also aesthetic ones such as smell, clarity and taste. As a result, oxygen is perhaps the best-known indicator of water quality.
How Dissolved Oxygen Affects Water Supply
A high DO level in public water supplies is good because it improves the taste of drinking water. However, high DO levels accelerate the corrosion of water pipes. For this reason, the industry uses water with the lowest possible amount of dissolved oxygen. The water used in very low pressure boilers contains no more than 2.0 ppm DO, but most boiler operators try to maintain oxygen levels at 0.007 ppm or less.
Best portable dissolved oxygen meter
Equipped with a state-of-the-art optical DO sensor: measures the dissolved oxygen level reliably and easily
Minimal maintenance required. There is no need to replenish the solution or frequent membrane changes.
Easy automation. Calibration for saturated and anaerobic air
IP67 waterproof and dustproof design, perfect for use in harsh environments
Comes with a complete gauge kit including DO meter, 10ft optical probe, calibration cap, and a sturdy carrying case.
A helpful guide to the Best portable dissolved oxygen meter
Performing a dissolved oxygen test can be easy. And that’s a good thing, considering how much needed these tests are in a variety of circumstances. Water quality problems can lead to corrosion, biological catastrophes in the ecosystem, poor water treatment management, and much worse. Briefly, the dissolved oxygen sensor measures the quality of the water in relation to the proportion of dissolved oxygen in the sample.
When dealing with real-world applications, you may need to sample and monitor dissolved oxygen levels on the move. In addition to laboratory conditions, consumer-grade dissolved oxygen sensors are broadly divided into three types: optical dissolved oxygen sensors, polarographic sensors, and galvanic sensors.
And, as you might expect, each type of instrument has its own unique set of strengths and weaknesses. These are usually characteristics that derive from the operating principles underlying different types of work, but these differences also sometimes come from design decisions.
Dissolved Oxygen Sensor Selection
You can start thinking by asking yourself a few basic questions about the tool. How portable is it and how far do you need it? Is it easy to navigate its interface and access all the functions, or do you need to open the manual every time you want to read?
When it comes to a portable instrument, you’ll want to think carefully about the physical construction of the device itself. Does it have some sort of waterproof protection that would make it suitable for field testing, or is it something that will break from a single fall? Understanding what you are investing in can mean the difference between accurate testing and costly mistakes.
Galvanic vs polarographic vs optical sensors
The different types of dissolved oxygen sensor technologies include optical, polarographic, and galvanic. These differences can affect the oxygen meter you choose.
There are many different types of dissolved oxygen sensors that are commercially available in portable, compact, hand-held instruments. These instruments enable quick and accurate field detection of dissolved oxygen in aqueous solutions. The different types of dissolved oxygen sensor technologies include optical, polarographic, and galvanic.
There are advantages associated with each type of sensor. For example, an optical sensor does not require agitation or water movement for accurate measurements, while an electrochemical sensor requires some degree of water movement or agitation.
Galvanic and polarographic sensors operate by monitoring electrochemical signals. When dissolved oxygen passes over the sensor, this oxygen undergoes a chemical reaction. The resulting reaction then produces chemical signals which are picked up by a dissolved oxygen sensor. Sounds simple enough, but like so much in life the devil is in the details.
For example, polarographic sensors require a constant voltage flow to polarize the instrument. That’s why they need 5-15 minutes of warming up every time you want to use it. But galvanic sensors are self-polarizing, so they can be used right after you finish calibrating them.
Galvanic sensors also respond about 2-5 times faster than an optical sensor. But hydrogen sulfide can interfere with a galvanic sensor by permeating its membrane. Which brings us to optical sensors, capable of handling wastewater environments that contain hydrogen sulfide.
Optical dissolved oxygen sensors work on the basis of a luminescent dye. Dissolved oxygen interferes with the dye from being predictably luminescent when hitting a sample with blue light. After emitting blue light, the instrument uses a photodiode to compare the luminescence of a sample with the calibration.
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