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Questions and Answers
What is the unit of Biochemical Oxygen Demand (BOD)?
What is the unit of Biochemical Oxygen Demand (BOD)?
What does an increasing BOD indicate?
What does an increasing BOD indicate?
What is the BOD range for very good water quality?
What is the BOD range for very good water quality?
What is the purpose of BOD analysis?
What is the purpose of BOD analysis?
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Why is the dilution method of BOD estimation considered disadvantageous?
Why is the dilution method of BOD estimation considered disadvantageous?
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What is the BOD range for extremely toxic water?
What is the BOD range for extremely toxic water?
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What is the purpose of NaOH in the manometric method of measuring BOD?
What is the purpose of NaOH in the manometric method of measuring BOD?
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How often do you need to measure dissolved oxygen to estimate BOD?
How often do you need to measure dissolved oxygen to estimate BOD?
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What is the unit of COD?
What is the unit of COD?
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Why does the presence of dead plants in water decrease DO levels?
Why does the presence of dead plants in water decrease DO levels?
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What is the recommended total water hardness for drinking water?
What is the recommended total water hardness for drinking water?
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What is the pH range for drinking water?
What is the pH range for drinking water?
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Study Notes
Chemical Examination of Water
- Biochemical oxygen demand (BOD) measures the amount of dissolved oxygen in milligrams used by aerobic bacteria growing on organic matter in a water sample at 20°C over 5 days.
- BOD units are mg/L at 20°C over 5 days.
- Increasing BOD indicates increasing organic matter and water pollution, and increasing microbial content, including pathogens.
- BOD analysis indicates water pollution and treatment efficacy.
BOD Estimation and Water Quality
- Very good water quality: BOD = 1-2mg/L (low organic matter)
- Fair water quality: BOD = 3-5mg/L (moderate organic matter)
- Poor water quality: BOD = 6-9mg/L (high organic matter and microbial content)
- Very poor water quality: BOD = 10- more than 10mg/L (very polluted water)
- Extremely toxic water: BOD = 100 more than 100mg/L (sewage water)
BOD Estimation Methods
- Dilution method: requires dilution, seeding, and a blank sample
- Manometric method: simple, no dilution, no seeding, and no blank sample, with direct BOD value reading
Chemical Oxygen Demand (COD)
- COD measures the oxygen amount used by reactions in a measured solution
- COD unit is mg/L
- COD examination is less specific than BOD, measuring all chemically oxidized substances
Dissolved Oxygen (DO)
- DO is the atmospheric oxygen that dissolves in water and is used by fish and aquatic animals to breathe
- DO concentrations of healthy water should be above 6.5-8 mg/L
- DO levels vary depending on factors such as:
- Running water: high DO levels
- Cold temperature: increased DO levels
- Presence of dead plants: decreased DO levels due to decomposer use
- Water depth: affects DO levels
Total Hardness (TH)
- TH is the sum of the molar concentrations of calcium and magnesium in water (ppm, mg/L, or mmol/L units)
- Drinking water should have:
- Ca 2+: 40-80ppm
- Mg 2+: 20-30ppm
- Total water hardness: 2-4 mmol/L
- Iron presence in drinking water causes a brownish rust-like color
- Hard water is characterized by:
- White lime scale formation in water heaters and kettles
- Lack of foam formation when using soap
- High hardness gives a bitter taste of water
pH and Toxicity
- pH is the hydrogen ion concentration in water, with a range of 0-14
- Drinking water pH should be between 6.5-8.5
- pH estimation alone does not provide a full picture of water properties
- Toxic substances include heavy metals, pesticides, and PFAS, indicating industrial pollution
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Description
Test your knowledge on the key indicators of water quality, including biochemical oxygen demand, chemical oxygen demand, dissolved oxygen, and more. Understand the importance of these parameters in water analysis.
