Biochemical oxygen demand (BOD):
- The total amount of oxygen (in milligrams) consumed by microorganisms in decomposing the waste in one litre ut water at 20°C for a period of 5 days is called biochemical oxygen demand (BOD).
- its value is expressed in ppm.
- BOD is used as a measure of degree of water pollution.
- BOD is only a measurement of consumed oxygen by microorganims to decompose the organic matter. Clean water would have BOD value less than 5 ppm
Chemical ox gen demand (COD):
- Chemical oxygen demand is defined as the amount of oxygen required by the organic matter in a sample of water for its oxidation by a strong oxidising agent like K7Cr2 O7 in acidic medium for a period of 2 hours.
- Its value is expressed in mg / litre.
- COD is a measure of amount of organic compounds in a water sample.
- COD refers to the requirement of dissolved oxygen for both the oxidation of organic and inorganic constituents
- Clean water would have COD value greater than 250 mg/ litre.
2. Viable and non-viable particulate pollutants Viable pollutants:
- The viable particulates are small size living organisms such as bacteria, fungi. moulds, algae which are dispersed in air.
- They are all organic particulates.
- They contain living organisms.
- Eg. ftingi, bacteria, algae, moulds. Viable particles are the particles with at least one microorganism affecting the sterility of the product.
Non-viable pollutants:
- The non-viable particulates are small solid particles and liquid droplets suspended in air.
- They are all inorganic particulates.
- They contain non-living organisms.
- Eg. Smoke, dust, mist, fumes.
- Non-viable particles are the particles without microorganisms but act as transporting agent for viable particles.
