Characteristics of wastewater
A number of chemical and physical characteristics are used to describe wastewater. The most common are:
Biochemical Oxygen Demand (BOD) is a measure of the amount of unstable organic matter in the water. It measures how much oxygen is required by the available micro organisms to break down the readily available organic matter into simpler forms, such as carbon dioxide, ammonia and water.
Total Nitrogen (TN) and Total Phosphorus (TP) are the sum of all forms of nitrogen and phosphorus in the water, respectively. Both nitrogen and phosphorus are nutrients essential for plant growth. A shortage of either one, or both, may limit the rate of plant growth in a water body. If the supply of the limiting nutrient is increased (and other circumstances such as appropriate amount of sunlight and appropriate temperature are favourable) blooms of algae or waterweeds may occur.
Faecal Microbes (which includes viruses, bacteria and protozoans) are found in wastewater and may cause disease. Faecal coliforms and faecal streptococci are bacteria that are found in the digestive tracts of humans and animals, including birds. Their presence in a waterbody indicates faecal contamination.
The average characteristics of raw wastewater are:
- Biochemical oxygen demand 250-300 mg/L
- Total nitrogen 50-60 mg/L
- Total phosphorus 10-15 mg/L
- Faecal coliforms 10,000,000 cfu/100 mL
mg/L = milligrams per litre
cfu/100 mL = colony forming units per 100 millilitre
(Source - Bulletin No3 Wastewater Treatment - Water Corporation)
