Define COD, BOD, TLV.

Chemical Oxygen Demand (COD):

• Definition: The amount of oxygen required to chemically oxidize organic and inorganic substances in water.
• Significance: COD is a critical parameter for assessing water quality, indicating the level of pollutants that can deplete dissolved oxygen, affecting aquatic life.
• Measurement: Expressed in milligrams per liter (mg/L), COD is determined by adding a strong oxidizing agent to the water sample and measuring the oxygen consumed.
• Note: COD values are typically higher than Biochemical Oxygen Demand (BOD) values because COD measures both biodegradable and non-biodegradable substances.

Biochemical Oxygen Demand (BOD):

• Definition: The amount of dissolved oxygen required by aerobic microorganisms to decompose organic matter in water over a specific time period, usually 5 days at 20°C.
• Significance: BOD is an essential indicator of the organic pollution level in water, with higher BOD values signifying greater pollution, which can lead to oxygen depletion and harm aquatic organisms.
• Measurement: Expressed in mg/L, BOD is measured by incubating a sealed water sample and determining the decrease in dissolved oxygen over the incubation period.
• Note: BOD primarily measures biodegradable organic matter, whereas COD measures both biodegradable and non-biodegradable substances.

Threshold Limit Value (TLV):

• Definition: The maximum concentration of a chemical substance to which a healthy worker can be exposed without adverse effects during a standard workday (8 hours) and workweek (40 hours).
• Significance: TLVs are guidelines used to ensure occupational safety by limiting exposure to hazardous substances, thereby preventing health issues among workers.
• Measurement: TLVs are expressed in parts per million (ppm) for gases and vapors, and in milligrams per cubic meter (mg/m³) for particulates.
• Note: TLVs are established by organizations such as the American Conference of Governmental Industrial Hygienists (ACGIH) and are used worldwide to promote workplace safety.