Domestic sewage and Industrial Effluents:
Answers
Even a small quantity of about 0.1% impurities in water, can make it unfit for human consumption. Solids are relatively easy to separate but dissolved salts such as nitrates, phosphates, other nutrients and toxic metal ions as well as organic compounds, are difficult to remove.
Domestic sewage is one of the most common source of water pollution. It contains biodegradable organic matter. It readily gets decomposed by bacteria and other microorganisms. They use organic matter as substrate and utilise some amount of sewage. It is possible to estimate biodegradable organic matter in sewage water by measuring Biochemical Oxygen Demand (BOD). It is the amount of dissolved oxygen required by microorganisms for decomposing the organic matter present in water. It is expressed in milligram of oxygen per litre (mg/L) of water. High BOD indicates intense level of microbial pollution.
Microorganisms involved in biodegradation of organic matter in water body consume lot of dissolved oxygen. This results in sharp decline in oxygen level of water which leads to mortality of fish and other aquatic creatures.
Presence of large amount of nutrients in water causes excessive growth of planktonicfree-floating algae specially, blue green algae.
This is called algal bloom which gives colour to the water bodies. Algal bloom often releases toxins in water. So, fish die due to toxicity. Quality of water deteriorates and becomes toxic for human beings and other animals. Another threat to aquatic ecosystem, is water hyacinth (Eichhornia crassipes). It is an aquatic plant, native of amazon basin, highly problematic invasive species. It was first introduced in India for its lovely purple coloured flowers. But, now it is a nuisance as it grows excessively and covers entire water body. This plant grows faster than our ability to remove it. It is commonly called ‘Terror of Bengal’.
Answer:
They includes sewage and industrial effluent. Sewage is waste water generated from residential areas like community whereas industrial effluent is waste water generated from various industries. Domestic sewage and industrial effluent differ in their composition and nature of pollutant.