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Chapter 8: Oxygen Demand

Chapter 8: Oxygen Demand. It is a measure of the amount of “reduced” organic and inorganic matter in a water Relates to oxygen consumption in a river or lake as a result of a pollution discharge Measured in several ways BOD - Biochemical Oxygen Demand COD - Chemical Oxygen Demand

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Chapter 8: Oxygen Demand

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  1. Chapter 8: Oxygen Demand • It is a measure of the amount of “reduced” organic and inorganic matter in a water • Relates to oxygen consumption in a river or lake as a result of a pollution discharge • Measured in several ways • BOD - Biochemical Oxygen Demand • COD - Chemical Oxygen Demand • ThOD - Theoretical Oxygen Demand

  2. Theoretical Oxygen Demand C6H12O6 + 6O2 = 6CO2 + 6H2O Oxygen Demand 6moles*32g/mole Oxygen/1mole*180g/mole = 1.06 O2 / Glucose If glucose concentration is 360 mg/L THOD is 1.06 * 360 mg/L = 384 mg/L Oxygen

  3. BOD: A Bioassay Briefly, the BOD test employs a bacterial seed to catalyze the oxidation of 300 mL of full-strength or diluted wastewater. The strength of the un-diluted wastewater is then determined from the dilution factor and the difference between the initial D.O. and the final D.O. BOD Bottle

  4. BOD with Dilution When BOD>8mg/L • Where • BODt = biochemical oxygen demand at t days, [mg/L] • DOi = initial dissolved oxygen in the sample bottle, [mg/L] • DOf = final dissolved oxygen in the sample bottle, [mg/L] • Vb = sample bottle volume, usually 300 or 250 mL, [mL] • Vs = sample volume, [mL]

  5. BOD Bottle BOD Bottle BOD Bottle BOD Bottle BOD Bottle BOD - loss of biodegradable organic matter (oxygen demand) Lo Lo-Lt = BODt Lt L or BOD remaining Time

  6. BOD L=oxidizable carbonaceous material remaining to be oxidized

  7. BOD Modeling "L" is modelled as a simple 1st order decay: Which leads to: And combining with: We get:

  8. NBOD Nitrogeneous BOD (NBOD) 2 moles oxygen/1 mole of ammonia 4.57 grams oxygen/gram ammonia-nitrogen Inorganic NH3, NO3- NO2- Organic Proteins, Amino acids TKN = Ammonia-N + Organic Nitrogen

  9. COD: A chemical test The chemical oxygen demand (COD) of a waste is measured in terms of the amount of potassium dichromate (K2Cr2O7) reduced by the sample during 2 hr of reflux in a medium of boiling, 50% H2SO4 and in the presence of a Ag2SO4 catalyst.

  10. Solids: significance • TDS: used as a measure of inorganic salt content in drinking waters and natural waters • TSS: used to assess clarifier performance • VSS: used to estimate bacterial populations in wastewater treatment systems

  11. Solids Analysis

  12. 2. Pour Sample 1. Weigh new filter and insert 5. Measure Change in Weight 3. Start suction pump 4. Remove filter and re-weigh Suction Flask & Filter Holder Filtration for Solids Analysis 6. Divide this by the Volume filtered and you get TSS

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