16.2 WATER POLLUTION AND ITS CONTROL

16.2 WATER POLLUTION AND ITS CONTROL 

• Human beings have been abusing the water-bodies around the world by disposing into them all kinds of waste. 
• We tend to believe that water can wash away everything not taking cognizance of the fact that the water bodies are our lifeline as well as that of all other living organisms. 
• Can you list what all we tend to try and wash away through our rivers and drains? 
• Due to such activities of human kind, the ponds, lakes, stream,rivers, estuaries and oceans are becoming polluted in several parts of the world. 
• Realising the importance of maintaining the cleanliness of the water bodies, the Government of India has passed the Water (Prevention and Control of Pollution) Act, 1974 to safeguard our water resources.

16.2.1 Domestic Sewage and Industrial Effluents:

• As we work with water in our homes in the cities and towns, we wash everything into drains. 
• Have you ever wondered where the sewage that comes out of our houses go? 
• What happens in villages? 
• Is the sewage treated before being transported to the nearest river and mixed with it? 
• A mere 0.1 per cent impurities make domestic sewage unfit for human use (Figure 16.2). 

• You have read about sewage treatment plants in Chapter 10. 
• Solids are relatively easy to remove, what is most difficult to remove are dissolved salts such as nitrates, phosphates, and other nutrients, and toxic metal ions and organic compounds. 

Biochemical Oxygen Demand (BOD):

• Domestic sewage primarily contains biodegradable organic matter, which readily decomposes – thanks to bacteria and other micro-organisms, which can multiply using these organic substances as substrates and hence utilise some of the components of sewage. 
• It is possible to estimate the amount of biodegradable organic matter in sewage water by measuring Biochemical Oxygen Demand (BOD). 
• Can you explain how? 
• In the chapter on microorganisms you have read about the relation between BOD, microorganisms and the amount of biodegradable matter. Figure 16.3 shows some of the changes that one may notice following discharge of sewage into a river. 

• Micro-organisms involved in bio-degradation of organic matter in the receiving water body consume a lot of oxygen, and as a result there is a sharp decline in dissolved oxygen downstream from the point of sewage discharge. 
• This causes mortality of fish and other aquatic creatures.

Algal bloom

• Presence of large amounts of nutrients in waters also causes excessive growth of planktonic (free-floating) algae, called an algal bloom (Figure 16.4) which imparts a distinct colour to the water bodies. 

• Algal blooms cause deterioration of the water quality and fish mortality. Some bloom-forming algae are extremely toxic to human beings and animals. 
• You may have seen the beautiful mauve-colored flowers found on very appealingly-shaped floating plants in water bodies. 
• These plants which were introduced into India for their lovely flowers have caused havoc by their excessive growth by causing blocks in our waterways. 
• They grow faster than our ability to remove them. 
• These are plants of water hyacinth (Eichhornia crassipes), the world’s most problematic aquatic weed, also called ‘Terror of Bengal’. 
• They grow abundantly in eutrophic water bodies, and lead to an imbalance in the ecosystem dynamics of the water body. 
• Sewage from our homes as well as from hospitals are likely to contain many undesirable pathogenic microorganisms, and its disposal into a water without proper treatment may cause outbreak of serious diseases, such as, dysentery, typhoid, jaundice, cholera, etc. 

Biomagnification:

• Unlike domestic sewage, waste water from industries like petroleum, paper manufacturing, metal extraction and processing, chemical manufacturing, etc., often contain toxic substances, notably, heavy metals (defined as elements with density > 5 g/cm3 such as mercury, cadmium, copper, lead, etc.) and a variety of organic compounds. 
• A few toxic substances, often present in industrial waste waters, can undergo biological magnification (Biomagnification) in the aquatic food chain. 
• Biomagnification refers to increase in concentration of the toxicant at successive trophic levels. 
• This happens because a toxic substance accumulated by an organism cannot be metabolised or excreted, and is thus passed on to the next higher trophic level. 
• This phenomenon is wellknown for mercury and DDT. Figure 16.5 shows biomagnification of DDT in an aquatic food chain. 

• In this manner, the concentration of DDT is increased at successive trophic levels; say if it starts at 0.003 ppb (ppb = parts per billion) in water, it can ultimately reach 25 ppm (ppm = parts per million) in fish-eating birds, through biomagnification. 
• High concentrations of DDT disturb calcium metabolism in birds, which causes thinning of eggshell and their premature breaking, eventually causing decline in bird populations. 

Metal	Disorder	Symptoms
Hg	Minimata disease	Numbness in lips, Blurred vision, Mental retardation
Pb	Plumbism	Brain damage and madness
Cd	Itai-Itai disease or ouch-ouch disease	Skeletal deformities
Ar	Black foot disease	Diarrhoea, peripheral neuritis & Hyperkeratosis
F	Fluorosis	Moltting of teeth, knocking knees & weak bone
Nitrates	Blue baby syndrome	Methaemoglobin (Hypoxia & inhibits HbO2 formation)
Cu		Hypertension and Uraemia

Eutrophication:

• Eutrophication is the natural aging of a lake by nutrient enrichment of its water. 
• In a young lake the water is cold and clear, supporting little life. 
• With time, streams draining into the lake introduce nutrients such as nitrogen and phosphorus, which encourage the growth of aquatic organisms. 
• As the lake’s fertility increases, plant and animal life burgeons, and organic remains begin to be deposited on the lake bottom. 
• Over the centuries, as silt and organic debris pile up, the lake grows shallower and warmer, with warm-water organisms supplanting those that thrive in a cold environment. 
• Marsh plants take root in the shallows and begin to fill in the original lake basin. 
• Eventually, the lake gives way to large masses of floating plants (bog), finally converting into land. 
• Depending on climate, size of the lake and other factors, the natural aging of a lake may span thousands of years. 

Cultural or Accelerated Eutrophication:

• However, pollutants from man’s activities like effluents from the industries and homes can radically accelerate the aging process. This phenomenon has been called Cultural or Accelerated Eutrophication. 
• During the past century, lakes in many parts of the earth have been severely eutrophied by sewage and agricultural and industrial wastes. 
• The prime contaminants are nitrates and phosphates, which act as plant nutrients. 
• They overstimulate the growth of algae, causing unsightly scum and unpleasant odors, and robbing the water of dissolved oxygen vital to other aquatic life. 
• At the same time, other pollutants flowing into a lake may poison whole populations of fish, whose decomposing remains further deplete the water’s dissolved oxygen content. 
• In such fashion, a lake can literally choke to death. 

Heated (thermal) waste waters:

• Heated (thermal) waste waters flowing out of electricity-generating units, e.g., thermal power plants, constitute another important category of pollutants. 
• Thermal wastewater eliminates or reduces the number of organisms sensitive to high temperature, and may enhance the growth of plants and fish in extremely cold areas but, only after causing damage to the indigenous flora and fauna.

16.2.2 A Case Study of Integrated Waste Water Treatment 

• Wastewater including sewage can be treated in an integrated manner, by utilising a mix of artificial and natural processes. 
• An example of such an initiative is the town of Arcata, situated along the northern coast of California. 
• Collaborating with biologists from the Humboldt State University, the townspeople created an integrated waste water treatment process within a natural system. 

The cleaning occurs in two stages – 

• (a) the conventional sedimentation, filtering and chlorine treatments are given. After this stage, lots of dangerous pollutants like dissolved heavy metals still remain. To combat this, an innovative approach was taken and 
• (b) the biologists developed a series of six connected marshes over 60 hectares of marshland. Appropriate plants, algae, fungi and bacteria were seeded into this area, which neutralise, absorb and assimilate the pollutants. 
• Hence, as the water flows through the marshes, it gets purified naturally. 
• The marshes also constitute a sanctuary, with a high level of biodiversity in the form of fishes, animals and birds that now reside there. 
• A citizens group called Friends of the Arcata Marsh (FOAM) are responsible for the upkeep and safeguarding of this wonderful project.

                     

‘EcoSan’ toilets: 

• All this time, we have assumed that removal of wastes requires water, i.e., the creation of sewage. 
• Ecological sanitation is a sustainable system for handling human excreta, using dry composting toilets. 
• This is a practical, hygienic, efficient and cost-effective solution to human waste disposal. 
• The key point to note here is that with this composting method, human excreta can be recycled into a resource (as natural fertiliser), which reduces the need for chemical fertilisers. There are working ‘EcoSan’ toilets in many areas of Kerala and Sri Lanka.
Think-
• What if water is not necessary to dispose off human waste, like excreta? 
• Can you imagine the amount of water that one can save if one didn’t have to flush the toilet? 
• Well, this is already a reality. (‘EcoSan’ toilets)