Water Quality Analysis

Manometric Method for BOD Estimation

• Advantages of the manometric method include simplicity, no dilution, no seeding, and no blank sample, with direct BOD value reading.
• The method involves keeping water samples in sealed containers fitted with a pressure sensor and NaOH to absorb CO2.
• BOD estimation requires two measurements: initial dissolved oxygen (when the water sample arrives at the lab) and final dissolved oxygen (after 5 days of incubation).

BOD, COD, and DO

• Biochemical oxygen demand (BOD) is the amount of O2 consumed by microbes to break down organic matter in a water sample during 5 days.
• Chemical oxygen demand (COD) is the oxygen amount that can be used by reactions in a measured solution, with a unit of mg/L.
• COD analysis is less specific than BOD, as it measures all chemically oxidized substances, while BOD measures biologically oxidized organic matter (biodegradable).
• Dissolved oxygen (DO) is the atmospheric oxygen that dissolves in water and is used by fish and aquatic animals to breathe.
• Healthy water should have DO concentrations above 6.5-8 mg/L.

Factors Affecting DO Levels

• Running water has high DO levels.
• DO levels increase in cold and decrease in high-temperature conditions.
• Presence of many dead plants in water decreases DO levels due to decomposer (bacteria) use of DO.
• Water depth affects DO levels.

Chemical Examination of Water

• Indicators that should be measured include:
  • Biochemical oxygen demand (BOD)
  • Chemical oxygen demand (COD)
  • Dissolved oxygen (DO)
  • Total hardness (TH)
  • pH
  • Toxicity
  • Nitrate

BOD Analysis and Water Quality

• BOD analysis indicates both water pollution and water treatment efficacy.
• BOD levels are categorized as follows:
  • Very good water quality (low organic matter): BOD = 1-2 mg/l
  • Fair water quality (moderate clean water): BOD = 3-5 mg/l
  • Poor water quality (high organic matter): BOD = 6-9 mg/l
  • Very poor water quality (very polluted water): BOD = 10- more than 10 mg/l
  • Extremely toxic water (sewage water): BOD = 100- more than 100 mg/l