Water Quality Quiz: Test Your Knowledge

Study Notes

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

Description

Measure the indicators of water quality, including biochemical oxygen demand, chemical oxygen demand, dissolved oxygen, and more. Learn how to analyze water samples and understand the importance of these indicators.