Classification of Water Pollutants
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Water pollutants can classify into the following categories
Organic Water Pollutants
The organic pollutant means “demanding oxygen pollutants.”
The organic pollutants are present in domestic sewage, plant nutrient, oil waste from food processing industries, tanneries, dairy, pesticides waste, etc.
The agencies playing an essential role in specifying the norms for various effluents to be discharged into the water bodies as well as for drinking water are:
- Indian Standards Institution (ISI)
- World Health Organization (WHO)
- The United States Public Health Services (USPHS)
- Indian Council of Medical Research (ICMR)
- Many wastes drinks of water especially sewage contains many pathogenic microorganisms which usually carried if faces and urine of infected persons.
- Waterborne diseases like cholera, dysentery, typhoid, bacillary dysentery are caused due to pathogens present in water.
Nitrogen and Phosphorus Compounds (Nutrients)
- Additional of compounds containing nitrogen and phosphorus helps in growth of algae and other plants. These compounds are nutrient for growth.
- When these concentrations are high, it causes rapid growth causing the algal bloom. Also the growth of weeds increases.
- It covers up the water surface and prevents entry of sunlight into water bodies.
- Aquatic plants along with algae thus die; the bacteria present in the water now decompose all these dead plants.
- The decayed organic matter adds unwanted colour, odour, and taste to water.
- It also reduced DO of water and led to the death of fish and other aquatic animals.
Pollutants such as heavy metals, pesticides, cyanides and many other organic and inorganic compounds are harmful to aquatic organisms.
Some of the substances like pesticides, methylmercury, etc. move into the bodies of organisms from a medium in which these organisms live.
These substances tend to accumulate in the body of the organism. This process is called Bioaccumulation.
The concentration of these toxic substances builds up at successive levels of the food chain. This process is called Biomagnifications.
Following the example of biomagnifications of DDT in an aquatic chain.
Components = DDT Concentration (ppm)
Birds = 10.00
Needlefish = 1.0
Minnows = 0.1
Zooplankton = 0.01
Water = 0.000001
Mercury dumped in water is converted to methylmercury by bacterial action. A disease called Minimata disease occurs due to consumption of methylmercury-contaminated fish.
A concentration of nitrate more than45 mg/L causes occurs blue baby diseases in infants.
Excess fluoride causes fluorosis. It affects the bones and teeth of the person.
Suspended Matter – Water Pollutants
Makes water aesthetically displeasing.
Biodegradable suspended matter causes DO depletion.
It reduced light penetration thereby reducing photosynthesis and a corresponding loss in food production.
Provides adsorption sites for harmful chemicals or biological organisms which can Effect flora and fauna of stream.
Water used for dissipation of waste heat in power plant and industries. This heated water subsequently discharged into water bodies. Increased temperature of the liquid has the following effects:
- Increase in biological activities.
- Cause death of some heat-sensitive organisms.
- DO concentration decrease this together with increased biological activities at high temperature may result in the anaerobic condition. And, it was occurring in bad odor.
- So, the growth of algae will increase.
- Toxicity of chemical pollutants increases with increases in temperature.
The word Eutrophication originated from Greek words eu=well and trophes= food. Thus the meaning is “well fed” or “nutrient-rich.”
Thus we can define eutrophication as the excessive nutrient load in a water body or enrichment of water body by nutrients like phosphorus and nitrogen.
Presence of nutrients is must for the growth of organisms, but if these nutrients are present in excessive amount then they act as pollutants because they allow
- The excessive growth of aquatic plants like algae.
- Depending upon the presence of nutrients, the water bodies (aquatic system) may classify as under:
Water bodies with the unfortunate concentration of nutrients and very low productivity of aquatic plants.
Water bodies with the moderate concentration of nutrients and average productivity of aquatic plants.
Water bodies with the high concentration of nutrients and very high productivity of aquatic plants.
What causes eutrophication?
Newly formed water bodies such as lakes, ponds, and reservoirs, whether natural or human-made has low nutrient content and low plant productivity.
Gradually, with the passage of time, these water bodies become rich in nutrients through the deposit of domestic waste, the agricultural residue (rich in nitrogen and phosphorus), and industrial waste, etc. which ultimately increase aquatic growth.
In this way, the oligotrophic water bodies turn gradually into the Mesotrophic water body.
Natural eutrophication is a prolonged process, often taking more than 100 years. But artificial eutrophication is very fast as it depends on the input of organic waste matter.
The aerobic decomposition of organic waste in the presence of oxygen by bacteria leads to eutrophication.
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The nutrient-rich water body supports the growth of algae, and the entire water pollution body becomes green.
As more plants grow due to the additional supply of nutrients, more plants also die.
Bacteria decompose these dead plants and organic waste using dissolved oxygen. As a result, the BOD of water increases.
Fish and other aquatic animals start dying due to the depletion of oxygen. Such a water body said to eutrophied.
With an increase in BOD, water starts emitting an offensive smell and aesthetic and recreational importance of the water body decreases.
Generally, it observed that the concentration of nitrogen is higher than 0.3 mg/L and phosphorus more than 0.15 mg/L cause eutrophication.
Effects of Eutrophication
- The higher growth rate of algae in the water body.
- Algae bloom restrict the penetration of sunlight in water body hence rate of photosynthesis process decreases.
- Decrease in dissolved oxygen (DO) and increase biological oxygen demand (BOD).
- Bad taste, the bad odour produced and also increases in turbidity of water.
- Moreover, The decaying organic matter causes depletion of DO, destroying fish and other aquatic species.
- Aesthetic and recreational importance of the water body decreases, i.e., fishing, swimming, boating, etc.
Control of eutrophication
Eutrophication can control by:
- Moreover, The control at sources is the best practice to prevent eutrophication. Therefore, wastewater enriches with nutrient should treat for removal of nitrogen, phosphorus, and carbon before disposal.
- Recycling of nutrient should adopt.
- Algae bloom should remove from the Water Pollutants body.
- Reducing the use of phosphate in detergents.
- Reducing the use of nitrate-containing fertilizers. The growth of algae can be control by using precipitants like alum, ferrous sulfate, and sodium aluminates but it is the very costlier affair and may be harmful to other aquatic life.
- The phosphorus can remove by precipitation and nitrogen can remove by nitrification. The denitrification, reverse osmoses, ion exchange and electrodialysis are the advanced treatment for the removal of dissolved nutrients.
- It can also reduce by applying the methods to reduce soil erosion.
- Moreover, The copper sulfate and sodium arsenite are also used to kill algae growth, but these are not favorable practice.