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Questions and Answers
What is the main difference between COD and BOD values?
What is the main difference between COD and BOD values?
TOC is used to express the pollution load in terms of carbon content.
TOC is used to express the pollution load in terms of carbon content.
True
What is the temperature range for drying a wastewater sample to determine Total Solids?
What is the temperature range for drying a wastewater sample to determine Total Solids?
103 - 105 deg
COD values are higher than BOD values because COD includes both degradable and non-degradable ______________________.
COD values are higher than BOD values because COD includes both degradable and non-degradable ______________________.
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Match the following wastewater parameters with their descriptions:
Match the following wastewater parameters with their descriptions:
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What is the significance of a higher BOD to COD ratio?
What is the significance of a higher BOD to COD ratio?
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Theoretical calculation of TOC can be done if the chemical formula of the given compound is known.
Theoretical calculation of TOC can be done if the chemical formula of the given compound is known.
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What is the instrument used to measure TOC directly?
What is the instrument used to measure TOC directly?
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Total Solids (TS) is the residue remaining after wastewater sample has been ______________________ and dried at a specific temperature.
Total Solids (TS) is the residue remaining after wastewater sample has been ______________________ and dried at a specific temperature.
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What is the purpose of measuring Total Solids (TS)?
What is the purpose of measuring Total Solids (TS)?
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Study Notes
Dissolved Oxygen
- Aquatic life is put under stress when dissolved oxygen levels in water drop below 5 mg/l
- Classification of water quality based on dissolved oxygen levels:
- Good: 8-9 mg/l
- Slightly polluted: 6.7-8 mg/l
- Moderately polluted: 4.5-6.7 mg/l
- Heavily polluted: 4-4.5 mg/l
- Gravely polluted: Below 4 mg/l
Physio-chemical Characteristics
- Aggregate organics:
- Total Organic Carbon (TOC)
- Chemical Oxygen Demand (COD)
- Biochemical Oxygen Demand (BOD)
- Chemical:
- Organics: proteins, carbohydrates, lipids, surfactants, phenols, pesticides, etc.
- Inorganics: pH, chlorides, alkalinity, nitrogen, phosphorus, heavy metals, etc.
- Gases: hydrogen sulphide, methane, etc.
- Physical:
- Solids
- Temperature
- Colour
- Odour
- Turbidity
- Oil and grease
- Conductivity
Theoretical Oxygen Demand (ThOD)
- ThOD is the total amount of oxygen required to completely oxidize a known compound to CO2 and H2O
- Calculated using stoichiometric principles
- Example: C6H12O6 + 6O2 = 6CO2 + 6H2O, ThOD = 1.067 g O2/g of C6H12O6 = 1067 mg/l
Chemical Oxygen Demand (COD)
- Measures pollution potential of organic matter
- Defined as the amount of a specified oxidant that reacts with the sample under controlled conditions
- Uses potassium dichromate (K2Cr2O7) as an oxygen source
- Expressed in equivalent amount of oxygen
- Procedure:
- Measure the amount of potassium dichromate reduced by the sample during 2 hours at 150°C
- Titrate the sample with Ferrous Ammonium Sulphate (FAS) using ferroin indicator
- Calculate COD using the formula: COD(mg/l as O2) = (B - S) x M x 8000
Biochemical Oxygen Demand (BOD)
- Measures the amount of oxygen required by microorganisms to stabilize decomposable organic matter
- Important factors: temperature, time, light
- BOD measurements: BOD5 and BOD3
- BOD5: BOD test carried out in an BOD incubator at 20°C for 5 days
- Exponential decay curve: oxidation of biochemical oxygen demanding substances is an exponential decay curve
- Procedure:
- Employ a bacterial seed to catalyze the oxidation of 300 mL of full-strength or diluted wastewater
- Titrate the initial sample with N/40 Sodium Thiosulfate using starch as indicator
- Keep the sample at 20°C for 5 days
- Titrate the sample again after 5 days
- Calculate BOD using the formula: BOD = (DOi - DOf) x D
Dilution Factor
- D = Vb/Vs
- Vb = sample bottle volume, usually 300 mL
- Vs = sample volume, [mL]
Method for Measuring BOD
- BODt = UBOD (1-e-kt)
- BODt = BOD after t days (mg/l)
- UBOD = Ultimate BOD (mg/l)
- k = BOD rate constant at a particular temperature (day-1)
- t = Time in days
BOD and COD Relationship
- COD values are higher than BOD values in nearly all cases
- Because COD includes both degradable and non-biodegradable substances, whereas BOD contains only biodegradable substances
- Greater BOD to COD ratio indicates higher efficiency of organic treatment by biological methods
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Description
This quiz tests your knowledge on dissolved oxygen levels in water and its impact on aquatic life. It covers the effects of oxygen levels on aquatic life and water quality.
