Water Pollution and River Cleaning: Causes and Schemes

Water pollution is any change in the physical, chemical or biological quality of water that makes it unfit for its intended use or harmful to living things. India has large rivers and heavy rainfall, yet a great part of its surface water carries untreated sewage, industrial effluent and farm chemicals. The subject therefore appears in examinations from two sides: the science of how water is fouled and measured, and the laws and missions through which India tries to clean its rivers.

Sources of water pollution

Pollution sources are grouped as point and non-point. A point source discharges at one identifiable place, such as a sewage outfall or a factory effluent pipe, and can be measured and regulated. A non-point source is diffuse, such as fertiliser and pesticide washed off fields, run-off from city streets, or silt from construction, and it is far harder to control.

• Domestic sewage: the largest single load on Indian rivers, carrying organic matter, detergents and disease-causing organisms.
• Industrial effluent: heavy metals such as mercury, cadmium, lead, chromium and arsenic, along with acids, alkalis and dyes from tanneries, distilleries, paper mills and electroplating units.
• Agricultural run-off: nitrates and phosphates from fertilisers and residues of pesticides such as DDT and endosulfan.
• Thermal pollution: hot water returned from power stations and factories, which lowers the oxygen the water can hold.
• Others: oil spills, radioactive waste, plastic and immersion or dumping of solid waste into rivers and lakes.

How water quality is measured

Eutrophication and biomagnification

Eutrophication is the enrichment of a water body with nutrients, chiefly nitrates and phosphates from fertilisers, detergents and sewage. The nutrients trigger a bloom of algae that covers the surface and shuts out light; when the algae die, decomposers consume the dissolved oxygen, and fish and other life suffocate. Where humans cause it the process is called cultural eutrophication. Water hyacinth, the floating weed known as the terror of Bengal, spreads in such nutrient-rich water and chokes the surface.

Biomagnification is the build-up of a persistent poison at each higher level of a food chain. Pesticides such as DDT enter plankton in small amounts, pass into small fish, then into large fish and finally into birds and human beings, where the concentration may be thousands of times greater than in the water itself.

Diseases caused by polluted water

Pathogens in sewage-contaminated water spread cholera, typhoid, dysentery, hepatitis A and diarrhoeal illness. Chemical contamination causes its own set of diseases, and examiners ask these as pairs. Minamata disease, first reported in Japan, is caused by mercury; Itai-Itai disease, also from Japan, is caused by cadmium. Excess nitrate in drinking water causes methaemoglobinemia, the blue baby syndrome, in infants. Excess fluoride causes fluorosis, which mottles teeth and deforms bones, and is a serious problem in parts of Rajasthan, Gujarat and Andhra Pradesh. Arsenic in groundwater causes arsenicosis and skin lesions, and is worst in the Ganga-Brahmaputra plains of West Bengal, Bihar and Assam.

Laws and institutions

The Water (Prevention and Control of Pollution) Act of 1974 is the foundation. It set up the Central Pollution Control Board and the State Pollution Control Boards, and it requires the consent of the board before any industry may discharge effluent. It was followed by the Water (Prevention and Control of Pollution) Cess Act of 1977, the Environment (Protection) Act of 1986, which gave the Centre wide powers to set standards, and the National Green Tribunal Act of 2010, under which a specialised tribunal hears environmental cases.

River cleaning programmes in India

The Ganga Action Plan was launched in 1985 as India’s first large river-cleaning effort, intercepting and treating sewage in the towns along the river; its second phase and the Yamuna Action Plan followed in 1993. In 1995 these were brought together under the National River Conservation Plan, which extended the work to other rivers. The Ganga was declared a national river in 2008 and the National Ganga River Basin Authority was set up in 2009.

The present effort is the Namami Gange Programme, launched in 2014 as an integrated conservation mission and carried out by the National Mission for Clean Ganga under the Ministry of Jal Shakti. Its work is organised around building sewage treatment capacity, cleaning the river surface of floating waste, monitoring industrial effluent, restoring river-fronts and ghats, afforestation along the banks, protecting aquatic biodiversity such as the Gangetic dolphin, developing Ganga Grams along the river and raising public awareness. A Clean Ganga Fund was created to take contributions for the purpose.

Treatment and prevention

Sewage is treated in three stages. Primary treatment is physical, using screens and settling tanks to remove solids. Secondary treatment is biological, using the activated sludge process or trickling filters in which micro-organisms consume the organic matter. Tertiary treatment removes nutrients and disinfects the water before discharge or reuse. Industries use effluent treatment plants, and clusters of small units share a common effluent treatment plant; the strictest standard, zero liquid discharge, requires that no effluent leave the premises at all. Natural systems also work: the East Kolkata Wetlands treat the city’s sewage through fish ponds and are recognised as a wetland of international importance.