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Display of the concentration: The instrument requires the appropriate data of the calibration curve and uses them to calculate the concentration in mg/L (ppm is identical in this case), allowing for the temperature dependency of the individual parameters
Display of the percentage of oxygen saturation: The instrument measures the sensor current and calculates the partial pressure of oxygen according to the calibration. The current air pressure is measured for the calculation of the saturation partial pressure. The display corresponds to the quotient, converted into a percentage.
Applications
A. Foods and Beverages
Many foodstuffs are packed in a Modified Atmosphere Packaging where a low or controlled oxygen level is necessary. Dissolved oxygen levels in some drinks, such as beer, should be kept in specific range. Practice of adding oxygen under pressure to bottled water to make oxygenated water has become more common. These dissolved oxygen measurements required dissolved oxygen probes that can be cleaned at elevated temperatures without being removed from the application.
B. Environmental monitoring
EID's dissolved oxygen data loggers can be left to record dissolved oxygen fluctuations in lakes, rivers etc. Deep sea oxygen probes are used in oceans and deep lakes. EId's dissolved oxygen electrodes with fast response are used to map the dissolved oxygen content of lakes and fishing waters. EId's dissolved oxygen probes are not only raised and lowered in the water, but also towed through the water at different depths to give a total picture of the state of the area concerned.
C. Fish Farming - Aquaculture
Fish farmers needed multi-channel dissolved oxygen meters. Additionally, they need dissolved oxygen monitoring and dissolved oxygen control equipment. EID's dissolved oxygen monitoring and logger are encompass alert units with both high dissolved oxygen alarm and low dissolved oxygen alarm. Equipment introduced by EID in 1977 for controlling dissolved oxygen they are been used all over the world.
D. Water treatment (Re-circulating)
The water is cleaned and filtered through mechanical and biological filters. Ozone can be added to "burn off" pollutants, either by direct ozone injection or by UV ozone activation. This process can be controlled using a redox or ORP measurement. The pH of the water is measured and controlled using a pH meter and pH controller. The dissolved oxygen content is measured and pure oxygen is injected. This oxygen injection can also be used to strip off carbon dioxide. Often only a small proportion of the water is oxygenated at high pressure. The resulting super-saturated water is mixed with the main flow to give healthy dissolved oxygen levels in the growth tanks. EID's In-line dissolved oxygen electrodes, Twist and lock mount dissolved oxygen electrodes or flow cell dissolved oxygen electrodes can be used in such high pressure oxygenation systems.
E. Hatchery and growth tanks
Water level as well as dissolved oxygen should be measured in each tank - the water supply to one tank could be cut off. Oxygen level alarms are set on the dissolved oxygen measurements. Aeration or oxygen injection to each tank is not often practiced in smaller indoor tanks, oxygen is added to the inlet or re-circulated water. Aeration or oxygen injection is, however, seen in larger tanks, requiring a separate dissolved oxygen meter with dissolved oxygen controller system for each tank. This is easily done with EID's MultiProbe TechnologyTM dissolved oxygen metering, logging and control equipment.
F. Sea cages
Since it is difficult to control the dissolved oxygen content of the sea. Dissolved oxygen measurement is very important because feed uptake and dissolved oxygen levels are interconnected. Intensive feeding after fish have experienced low dissolved oxygen levels can not only be a waste of food, but can actually harm the fish. The measurement of dissolved oxygen levels enables feed to be dosed optimally and, if relayed to the shore can warn that the cage should be moved if extremely low dissolved oxygen levels should occur.
G. Transport tanks
Dissolved oxygen measurement should also be performed during transport to the processing plant. A healthy fish gives a better finished product when contain the right level of oxygen. Another situation requiring dissolved oxygen measurement is the transport of juvenile fish to tanks or cages for growing.
H. Oxygen generator control
Pure oxygen meters and oxygen controllers equipment are also used in aquaculture. The purchase of liquid oxygen in bulk is often the most economic solution, but there are many cases where oxygen generators are installed locally. Two of the many advantages of using pure oxygen are that 1) it is possible to super-saturate the water with oxygen and 2) you save pump energy since pumping air means pumping 79% nitrogen and "only" 20.9% oxygen.
I. Waste Water Treatment
It is no longer enough just to filter the water and dump the detritus in the sea. The larger part of the waste is mainly organic, and this must be broken down in sludge tanks and the effluent water controlled and treated as necessary.
Sludge tank dissolved oxygen measurement and control is kept at approximately 2 mg/l.
Flow measurement, suspended solids measurement, sludge blanket detection, conductivity measurement, nitrate measurement and phosphate measurement utilizing EID's Industrial electrodes are also all used to enable the efficient and effective cleaning of waste water.
J. Safety Monitoring
Both oxygen detection in flammable gas and oxygen monitoring in ambient air are examples of this. Blanket gas is often used where flammable substances occur. Blanket gas is gas that cannot burn or sustain fire, i.e. it does not contain oxygen. Volumetric oxygen measurement is carried out both on the blanket gas and the surrounding air, the latter for worker safety. Special versions of the EID's dissolved oxygen electrodes are approved for use in potentially dangerous atmospheres, i.e. in classified areas.
K. Measuring biochemical oxygen demand
The BOD test requires a commitment of five (5) days from initial sample collection to the end of the analysis. During this time, samples are initially seeded with microorganisms and supplied with a carbon nutrient source of glucose-glutamic acid. The sample is then introduced to an environment suitable for bacterial growth at reproducible temperatures, nutrient sources and light within a 20C incubator such that oxygen will be consumed. Quality controls, standards and dilutions are also run for accuracy and precision. Determination of the dissolved oxygen within the samples can be determined through titration. The difference in initial DO readings (prior to incubation) and final DO readings (after a five (5) day incubation period) predicts the BOD of the sample. A suitable detection limit as per environmental quality control is 1 mg/l.
BOD calculations
Steps to calculate Biochemical Oxygen Demand (BOD). They and are based on the addition of a nutrient source (carbon - glucose - glutamic acid) and no nutrient source.
1. The BOD of the blanks (no nutrient source) = DOFinal - DOInitial
2. The BOD of the nutrient added samples = (DOFinal - DOInitial) time dilution factor per 300ml
* 300 ml is based on the volume contained in BOD bottles
The BOD of the sample and standards are calculated by subtracting the final DO from the initial DO and multiplying this factor by the dilution factor. The final value is determined by subtracting out the BOD for the blank from the BOD that has been nutrient enriched.
References
Erlich Industrial Development. D. O. theory. http://www.eidusa.com/Theory_DO.htm
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