Presentation on theme: "Chemical Oxygen Demand Presentation By Douglas Rittmann, Ph.D., P.E."— Presentation transcript:
1Chemical Oxygen Demand Presentation By Douglas Rittmann, Ph.D., P.E. Water/Wastewater ConsultantToCE 4153OnApril 18, 2006
2General Considerations * COD test allows measurement of a waste in terms of total quantityrequired for oxidation to carbon dioxide and water* The COD tests oxidizes organic compounds by the action of strongoxidizing agents under acid conditions* The amino nitrogen will be converted to ammonia nitrogen and organicnitrogen will be converted to nitrates.* Organic is converted to carbon dioxide and water regardless of thebiological assimilability of the substances. Ex: glucose & lignin areboth oxidized completely, hence, COD is higher than BOD.
3Advantages and Disadvantages * One of the limitations of COD is its inability to differentiate betweenbiologically oxidizable and biologically inert organic matter.* It does not provide any evidence of the rate at which the biologicallyactive material would be stabilized under conditions in nature.* Major advantage is the short time required for evaluation in 3 hours versus5 days for the BOD test.* COD data can be interpreted in terms of BOD values after sufficientexperience has been accumulated to establish reliable correlation factors.
4History of COD Test* Chemical oxidizing agents have long been used to measure the oxygendemand of sewage and polluted waters.* Potassium permanganate were used for many years, and the results werereferred to as oxygen consumed from Potassium Permanganate.* Oxidation by potassium permanganate was highly variable due to strengthof oxidant and with respect too various types of compounds.* Oxygen consumed values were always less than the 5-day BOD becauseof the inability of permanganate to carry the oxidation to particular endpoint* Potassium dichromate is the most practical oxidizing agent with a silver ioncatalyst in an acid state and refluxed at high temperatures to completelyoxidize organics to carbon dioxide and water.
5Chemical Oxygen Demand by Dichromate COD results are reported in mg/L of oxygen.A 0.25 N dichromate solution is equivalent to 2 mg of oxygen.An excess of oxidizing agent must be present to ensure that all organicmatter is completely oxidized.Ferrous ammonium sulfate titrant is an excellent reducing agentto measure the excess dichromate after oxidation.6Fe++ + Cr2O7 + 14H Fe3+ + 2Cr3+ + 7H2OBlanks are required because extraneous organic matter isimpossible to exclude.Indicator – Ferroin is an excellent indicator for dichromate reduced by ferrous
6CalculationsCOD (mg/L) = 8000 (blank titr.- sample titration) (norm. Fe(NH4)2(SO4)2)/ml sampleAlternate Procedures: COD test is precise and accurate for samples withA COD of 50 mg/L or greater. It is important in any modification that theVolume of sample plus dichromate solution be maintained at 1:1 ratio.If it is smaller, the oxidizing power of the solution will decrease, whileIf it is larger, the blank consumption of dichromate becomes excessive
7Inorganic Interferences Chlorides can cause high results but eliminated by the addition ofmercuric sulfate prior to the addition of other reagents.Nitrites and nitrates interference can be eliminated by sulfamic acid.Ferrous and sulfides can interfere but are low in concentration.
9Virtually eliminates hazardous metals waste disposal Manganese III Method for CODVirtually eliminates hazardous metals waste disposalConcerned about mercury, chromium or silver in waste streams? With the newManganese III COD (chemical oxygen demand) Method, disposal of these heavy metals wastes is virtually eliminated. The patented Manganese III COD Reagent1 eliminates using characteristic heavy metal oxidizers, catalysts and chloride removal agents used in traditional COD testing.Hach researchers have applied many innovations used in the original USEPAapproved2 micro COD system to develop a new method for monitoring wastewater treatment processes. The Manganese III COD Method can be used for: • Municipal and industrial wastewater• Municipal and industrial process waters • Environmental monitoring • Food and beverage industry • Pulp and paper industry • Manufacturing plants
10Manganese III Method for COD Simplifies COD analysisIn less than 90 minutes, up to 25 COD tests can be completed. Like Hach’s reliable USEPA-approved Dichromate COD Method, the new Manganese III COD Method relies on a closed reflux micro method, which is both easier and less labor intensive than the open reflux macro method. Plus, analysts at all skill levels can get accurate results with this new method.The Manganese III COD System uses prepared reagents, a simplified procedure, and reliable Hach equipment, including the COD Reactor and a colorimeter or spectrophotometer. The new method alsoincludes a Vacuum Pretreatment Device (VPD) and patent-pending Chloride Removal Cartridges, which eliminate the use of mercury-containing reagents for sample chloride removal. After preparingthe samples, simply digest them in the COD Reactor for one hour.
11Manganese III Method for COD The Manganese III COD Reagent contains Manganese 3+, an oxidizer, and concentrated sulfuric acid. The reagent does not contain metal catalysts or mercuric sulfate. The Manganese III COD Reagent offersseveral advantages when compared to open reflux COD testing:• Provides a distinct color change for easy analysis• Simplifies process control testing• Minimizes handling and exposure to corrosive chemicals• Virtually eliminates a hazardous metals waste stream and disposal costs
12Application of COD Data * Used extensively in analysis of industrial samples* Used to determine losses in sewer systems* Due to short time for analysis, errors can be corrected the same day* BOD test with COD Test can determine toxic conditions more effectively* COD test used widely for better operation of wastewater facility because ofits speed in analysis.