Dissolved Oxygen Essay Example for Free

dissolve atomic number 8 EssayOxygen in Liquids (DISSOLVED OXYGEN)Dissolved Oxygen the heart and soul of fade away type O in a body of water supply as an indication of the degree of the health of water and its ability to backup man a balanced aquatic ecosystem. Oxygen is a clear, colorless, odorless, and tasteless gas that dissolves in water. Small solely important quantitys of it ar dissolved in water. OXYGEN Aquatic Life Depends on itPlants and Animals depend on dissolved type O for survival. Lack of dissolved atomic number 8 empennage deliver aquatic animals to leave quick they atomic number 18 or face death. Factors Affecting Oxygen LevelsTemperatureRate of PhotosynthesisDegree of Light Penetration (turbidity water depth)Degree of water Turbulence or Wave actionThe union of group O employ by respiration and decay of organic matter Oxygen in the BalanceDissolved Oxygen directs that atomic number 18 at 90% and 110% saturation level or gameyer reconciled ly considered healthy or good. If the Dissolved Oxygen are be start 90%, in that respect whitethorn be large amounts of type O requisiteing heartys. What Is Dissolved Oxygen In Water?Dissolved type O in water is vital for semiaquatic life. It is what aquatic creatures need to breathe. Why Is Dissolved Oxygen Important? in force(p) as we need manner to breathe, aquatic organisms need dissolved oxygen to respire. It is necessary for the survival of fish, invertebrates, bacterium, and underwater plants. How Is Dissolved Oxygen mensural?Dissolved oxygen concentration can be reported as milligrams per cubic decimetre, weaken per billion, or as percent air saturation.Polarographic CellIt is very similar to the galvanic cell. However, the polarographic cell has dickens noble-metal electrodes and requires a polarizing voltage to reduce the oxygen.The dissolved oxygen in the seek diffuses by the membrane into the electrolyte, which unremarkably is an aqueous KC1 resolve. I f there is a constant polarizing voltage ( commonly 0.8 V) across the electrodes, the oxygen is reduced at the cathode, and the resulting online How is proportional to the oxygen content of the electrolyte. This current flow is detected as an indication of oxygen content. galvanic CellAll galvanic cells consist of an electrolyte and devil electrodes (Figure 8.43c). The oxygen content of the electrolyte is equalized with that of the examine. The reaction is spontaneous no external voltage is applied. In this reaction, the cathode reduces the oxygen into hydroxide, consequently releasing four electrons for each molecule of oxygen. These electrons cause a current flow through the electrolyte.. The magnitude of the current flow is in proportion to the oxygen concentration in the electrolyte.Flow through CellsIn the flow-through cells, the process sample stream is bubbled through the electrolyte. The oxygen concentration of the electrolyte is therefore in equilibrium with the samples oxygen content, and the resulting ion current amongst the electrodes is re beatative of this concentration. These types of cells are usually provided with sampling consisting of ( tho not limited to) filtering and scrubbing components and flow, pressure, and temperature regulators.Thallium CellThallium cells are somewhat unmatched in their operating principle and cannot be classified into the category of either galvanic or polarographic cells. At the same time, they are of the electro chemic type. One thallium-electrode cell design is somewhat similar in appearance to the unit illustrated on Figure 8.43c except that it has no membrane or electrolyte. This cell has a thallium emergeer-ring electrode and an inner reference electrode. When oxygen contacts the thallium, the potential developed by the cell is a act upon ofthe thallous ion concentration at the face of the electrode, and the ion concentration is in proportion to the concentration of dissolved oxygen.Fluorescence-based SensorIn this case, a compound containing ruthenium is immobilized in a gas-permeable matrix called a sol-gel. Sol-gels are very low-density, silica-based matrices sufficient for immobilizing chemical compounds such as the ruthenium compound used in this measurement technique. Effectively, the sol-gel is equivalent to the membrane in a conventional DO sensor. Using fiber optics, light from a light-emitting crystal rectifier is transferred to the backside of the sol-gel coating. The emitted fluorescence is collected from the backside of the sol-gel with an another(prenominal) optical fiber and its intensity is detected by photodiode. A simplified sensor design is shown in Figure 8.43g.If no oxygen is present, the intensity of the emitted light volition be at its maximum value. If oxygen is present, the fluorescence allow be quenched, and the emitted intensity will decrease.Twinkler TitrationThe Winkler Method is a technique used to measure dissolved oxygen in freshwater systems . Dissolved oxygen is used as an indicator of the health of a water body, where higher dissolved oxygen concentrations are cor relation back with high productivity and little taint.Temperature EffectsPressure EffectsSalinity EffectsBiochemical Oxygen Demand ( embodiment)Biological Oxygen Demand ( frame of reference) is a measure of the oxygen used by microorganisms to take apart this waste. If there is a large quantity of organic waste in the water supply, there will also be a lot of bacteriapresent working to decompose this waste. In this case, the demand for oxygen will be high (due to all the bacteria) so the BOD level will be high. As the waste is consumed or dispersed through the water, BOD levels will begin to decline.Biochemical oxygen demand (BOD) is a measure for the quantity of oxygen required for the biodegradation of organic matter ( snowaceous demand) in water.It can also indicate the amount of oxygen used to oxidise reduced forms of nitrogen (nitrogenous demand), un less their oxidation is prevented by an inhibitor. A ladder is used to measure the amount of oxygen consumed by these organisms during a specified stop consonant of time (usually 5 years at 20 C).ClassificationBOD is devided in two parts which is Carbonaceous Oxygen Demand and the Nitrogenous Oxygen Demand.Carbonaceous Oxygen Demand it is the amount of oxygen consumed by the microorganisms during decomposing carbohydrate material.Nitrogenous Oxygen Demand it is the amount of oxygen consumed by the microorganisms during decomposing nitrogenous materials.relationship of DO and BODIf the Dissolve Oxygen (DO) of a water is high, the Biological Oxygen Demand (BOD)is low. If the BOD of the water is hight, the DO is low.Therefore DO and BOD is inversely Proportional to each other.Why we should need to hit the hay BOD?BOD directly affects the amount of dissolved oxygen in rivers and streams. The greater the BOD, the more speedily oxygen is depleted in the stream. This means less oxyg en is available to higher forms of aquatic life. The consequences of high BOD are the same as those for low dissolved oxygen aquatic organisms become stressed, suffocate, and die. noesis of oxygen utilization of a polluted water supply is important because1. It is the measure of the pollution load, relative to oxygen utilization by other life in the water 2. It is the means for predicting progress of aerobiotic decomposition and the amount of self-purification taking place 3. It is the measure of the oxygen demand load removal energy by different treatment process.Factors that leads to variations in BODThe SeedIs the bacterial culture that affects the oxidation of materials in the sample. If the biological seed down is not acclimated to the circumstance wastewater, erroneous results are frequently obtained.pHThe BOD results are also greatly affected by the pH of the sample, especially if it is let down than 6.5 or higher than 8.3. In order to achieve supply conditions, the sa mple should be buffered to a pH of about 7.TemperatureStandard run condition calls for a temperature of 20 C (68 F). field tests often require operation at other temperatures and, consequently, the results tend to vary unless temperature corrections are applied.ToxicityThe presence of toxic materials may result ontogenesis in the BOD value as a specific sample is dilluted for the BOD test.Consistent value may be obtained either by removing the toxic materials from the sample or By developing a seed that is compatible with the toxic material in the sample.Incubation TimeThe usual monetary standard lab test incubation time is 5 days, results may occur at a flat part or occur at a steeply rising portion.Depending on the type of seed and the type of oxidable material, diverging result can be expected.NitrificationIn the usual course BOD test, the oxygen consumption rises steeply at the beginning of the test owing to attack on carbohydrate materials. Another sharp gain in oxygen util ization occurs sometime during tenth to 15th day in those samples containing nitrogenous materials.How we go out or measure BOD?Five-Day BOD procedureThe BOD test takes 5 days to off and is performed using a dissolved oxygen test kit. The BOD level is touch ond by canvass the DO level of a water sample taken immediately with the DO level of a water sample that has been incubated in a dark location for 5 days. The difference between the two DO levels represents the amount of oxygen required for the decomposition of any organic material in the sample and is a good approximation of the BOD level.Test procedures1. Take 2 samples of water2. Record the DO level (ppm) of one immediately using the method describe in the dissolved oxygen test. 3. describe the second water sample in an incubator in complete darkness at 20oC for 5days. If you dont allow an incubator, wrap the water sample bottle in aluminum foil or black galvanizing tape and store in a dark place at room temperature (2 0 C or 68 F). 4. After 5 days, take another dissolved oxygen consumeing (ppm) using the dissolved oxygen test kit. 5. Subtract the Day 5 reading from the Day 1 reading to determine the BOD level. Record your final BOD result in ppm.NoteGenerally, when BOD levels are high, there is a decline in DO levels. This is because the demand for oxygen by the bacteria is high and they are taking that oxygen from the oxygen dissolved in the water. If there is no organic waste present in the water, there wont be as many bacteria present to decompose it and thus the BOD will tend to be lower and the DO level will tend to be higher. At high BOD levels, organisms such as macroinvertebrates that are more tolerant of lower dissolved oxygen may appear and become numerous. Organisms that need higher oxygen levels) will non survive.Extended BOD TestContinuation of BOD test beyond 5 days shows a continuing oxygen demand, with a sharp increase in BOD rate at the 10th day owing to nitrification. The latt er process involves biological attack on nitrogenous organic material accompanied by an increase in BOD rate. The oxygen demand continues at a uniform rate for an extended time.Manometric BOD TestIn the manometric procedure, the seeded sample is confined in a closed system that includes an appreciable amount of air . As the oxygen in the water is depleted, it is fill again by the gas phase. A yard hydroxide (KOH) absorber within the system removes any gaseous century dioxide generated by bacterial action. The oxygen removed from the air phase results in a drop in pressure that is that is removed with a manometer. This fall is then related to the BOD of the sample.Electrolysis System for BODThe touchstone principle for all electrolytic respirometers is quite similar. As micro-organisms respire they use oxygen converting the organic carbon in the solution to CO2 gas, which is absorbed to alkali. This causes a simplification in the gas pressure, which can be sensed with various sen sors or membranes. A small current is created in electrolysis cell and this generates oxidation/reduction reactions in the electrolysis cell and oxygen is formed at the anode.Electrolysis of water can supply oxygen to a closed system as incubation proceeds . At constant current, the time during which electrolysis generates the oxygen to persevere the system pressure constant is a direct measure of the oxygen demand. The amount of oxygen produced by the electrolysis correlates with the amount of oxygen consumed by bacteria. chemic Oxygen Demand (COD)Is the standard method for indirect measurements of the amount of pollution in a sample of water that cannot be oxidate biologically. Is based on the chemical decomposition of organic and inorganic contaminants, dissolved or suspended in water.Why Measure Chemical Oxygen Demand?It is often measured as a rapid indicator for organic pollutant in water. Normally measured in both municipal and industrial wastewater treatment plants and give s an indication of the energy of the treatment process. It is measured on both influent and effluent water.Standard Dichromate COD ProcedureA sample is heated to its boiling point with known amounts of sulfuric acid and potassium dichromate. The difference of water is minimized by the reflux condenser.After 2 h, the solution is cooled, and the amount of dichromate that reacted with reactive material in the water sample is determined by titrating the excess potassium dichromate with ferric sulfate. Dichromate consumed is calculated as to oxygen equivalent for the sample and stated as milligrams of oxygen per liter of sample (ml/l).Factors preventing the concordance of BOD values to COD values Many organic materials are reactive by dichromate but not biochemically oxidizable, and vice versa. For example, pyridine, benzene, and ammonia are not attacked by the dichromate procedure. A number of inorganic substances such as sulfide, sulfites, thiosulfates, nitrites, and ferrous iron are oxidized by dichromate, creating an inorganic COD that is misleading when estimating the organic content of wastewater. Although the factor of seed acclimation will give erroneously low results on the BOD tests, COD results are not dependent on acclimation.Chlorides interfere with the COD analysis, and their effect mustiness be minimized in order to obtain consistent results. The standard procedure provides for only a limited amount of chlorides in the sample. This is usually accomplished by diluting the sample to achieve a lower chloride concentration and interference. This can be a occupation for low CODconcentration samples, as the dilution may dilute the COD concentration below the detection level or to levels at which accuracy and repeatability are poor.COD DetectorThe term COD usually refers to the testing ground dichromate oxidation procedure, although it has also been applied to other procedures that differ greatly from the dichromate method but which do involve chemic al reaction. These methods have been embodied in instruments both for manual operation in the laboratory and for automatic operation online. They have the distinct advantage of reducing analysis time from days (5-day BOD) and hours (dichromate, respirometer) to minutes.Automatic On-Line DesignsTakes a 5 cc sample from the flowing process stream.Injects it into the reflux domiciliate afterwards mixing it together with dilution water (if any) agents. One ozone-based scheme enriches dilution water with and with two reagents dichromate solution and sulfuric acid. The reagents also contain an oxidation catalyst (silver sulfate) and a chemical that complexes chlorides in the solution (mercuric sulfate). The diversity is boiled at 302F (150C) by the heater.Vapors are condensed by the cooling water in the reflux condenser. During which the dichromate ions are reduced to trivalent chromic ions, as the oxygen demanding organics are oxidized in the sample. The chromic ions give the solution a green color. The COD concentration is measured by detecting the amount of dichromate converted to chromic ions by measuring the intensity of the green color through a fibre-optic detector. The microprocessor-controlled package is available with automatic zeroing, calibration, and flushing features. consume and Traditional ParameterParameterLimit ValueSamplingpH, Standard Units6.0 9.0Traditional ParametersBiological Oxygen Demand (BOD) 30 ppmChemical Oxygen Demand (COD) cc ppmCOD has a large value than BOD because BOD measurement is based only in decomposition of organic matter while COD measures the decomposition of both organic and Inorganic compound.Sources of fractureCause of using nonhomogeneous sample is the largest error.Use of volumetric flasks and volumetric pipettes with a large bore. Oxidizing agent must be precisely measured.Make sure that the vials are clean and free of air bubbles.Always read the bottom of the meniscus at eye level.Total Oxygen Demand (TOD)The qua ntitative measurement of the amount of oxygen used to burn the impurities in a liquid sample. Thus, it is a direct measure of the oxygen demand of the sample. Measurement is by continuous analysis of the concentration of oxygen in a blaze process gas effluent. A quantitative measurement of all oxidizable material in a sample water or wastewater as determined instrumentally by measuring the depletion of oxygen after high-temperature combustion. BOD and COD have long time cycles. COD use corrosive reagents with the inherent problem of disposal. Analysis is faster, approximately 3 min, and uses no liquid reagents in its analysis. Can be correlated to both COD and BOD.Unaffected by the presence of inorganic carbon.Also indicate noncarbonaceous materials that consume or contribute oxygen Since the actual measurement is oxygen consumption. Reflects the oxidation state of the chemical compound.TOD AnalyzerThe oxidizable components in a liquid sample introduce into the combustion tube are converted to their static oxides by a reaction that disturbs the oxygen equilibrium in the immune attack aircraft carrier gas steam. The momentary depletion in the oxygen concentration in the carrier gas is detected by an oxygen detector and put down as a negative oxygen peak.Sample ValvesSliding PlateUpon a signal from a cycle timer, the air actuator temporarily moves the valve to its sample fill position. At the same time, an air-operated actuator moves a 20-ul sample through the valve into the combustion tube. A stream of oxygen-enriched nitrogen carrier gas moves the slug of sample into the combustion tube. circuit Sampling ValveA motor continuously rotates a sampling head, which contains a built-in sampling syringe. For part of the time, the tip of the syringe is over a trough that contains the flowing sample. 2 or more cam ramps along the rotational path cause the syringe plunger to rise and fall, thus rinsing the sample chamber. Just before the syringe reaches the combust ion tube, it picks up a 20-ul sample. As it rotates over the combustion tube, it discharges the sample.Oxygen DetectorsPlatinum-lead evoke CellFuel Cell Generates a current in proportion to the oxygen content of the carrier gas passing through it. Before entering the cell, the gas is scrubbed in a potassium hydroxide solution, both to remove acid gases and other harmful combustion products to humidify the gas. The oxygen cell and the scrubber are located in a temperature-controlled compartment. The fuel cell create is monitored and zeroed to provide a constant baseline. The output peaks are linearly proportionate to the reduced concentration of oxygen in the carrier gas as a result of the samples TOD. Yttrium-doped Zirconium Oxide Ceramic Tube surface on both sides with a porous layer of platinum. It is maintained at an elevated temperature and also provides an output that represents the reduction in oxygen concentration in the carrier gas that is a result of the samples TOD. The operation of these oxygen detectors involves the ionization of oxygen in both a sample and a known reference gas stream. When the sample and reference gas streams come in contact with the electrode surfaces, oxygen ionizes into O-2 ions.The oxygen ion concentrations in each stream is a function of the partial pressure of oxygen in the stream. The potential at each electrode will depend on the partial pressure of oxygen in the gas stream. The electrode with higher potential (higher oxygen concentration) will generate oxygen ions, whereas the electrode with lower potential (lower oxygen concentration) will convert oxygen ions to oxygen molecules. CalibrationAnalysis is by comparison of peak senior high or areas to a standard calibration curve. To prepare this curve, known TOD concentrations of a primary standard (KHP) are prepared in distilled and deionized water. Standard solutions are stable for several weeks at room temperature. Water solutions of other organic compounds can also be used as standards.Several analyses can be made at each calibration concentration, and the resulting data are recorded as parts per million (ppm) TOD vs. peak height or area.ApplicationsCorrelationMany regulatory agencies recognize as the keister for oxygen-depleting pollution control only BOD or COD (preferably BOD) measurements of pollution load, because they are concerned with the pollution load on receiving waters, which is related to lowering the DO due to bacterial activity. If other methods described are to be used to satisfy legal requirements of pollution load in effluents or to measure BOD removal, it is important to establish a correlation between the other methods and BOD or COD (preferably BOD). great Featuresa measurement of property of the sample, i.e. the amount of oxygen required for bacterial oxidation of bacterial victuals in the water, the BOD dependence of the oxygen demand on the nature of the food as puff up as on its quantity dependence of the oxygen de mand on the nature and amount of the bacteriaAnother extensive study concluded the following(1) A reliable statistical correlation between BOD and COD of a wastewater and its corresponding TOD can frequently be achieved, curiously when the organic strength is high and the diversity in dissolved organic constituents is low. (2) The relationship is best described by a least squares regression with the degree of fit expressed by the correlation coefficient (3) The observed correspondence of COD-TOD was better than that of COD-BOD for the wastewaters. (4) The BOD-COD ratio of an untreated wastewater is indicative of the biological treatment possible with the particular wastewater. ComparisonCOMPARISONBODCODTODDefinitionThe oxygen required when a community of bacteria causes the oxidation reaction in a population of bacteria.The oxygen equivalent when the oxidation is carried out with a chemical oxidizing reagent such as potassium dichromate.The oxygen equivalent when oxidation is cau sed by thawing the sample in a furnace in the presence of a catalyst and oxygen.AnalyzerUtilize bacteria to oxidize the pollutantsMeasured through chemical oxidation and catalytic combustion techniquesOxidize the sample in a catalyzed thermal combustion process and detect both the organic and inorganic impurities in a sampleResponse-Range5 days 30 mg/L2 hours 250-500 ppm3 minutes 100-100,000 mg/LInaccuracy-Cost3 20% / $500 $20,0002 10% / $8,00 $20,0002 5% / $5,000 $20,000