Polluted surface water poses threat to health of one crore city dwellers

The main sources of water pollution in the capital are domestic sewage, including human excreta, bathroom and kitchen wastewater, industrial wastewater including toxic chemicals, pesticides and fertilisers used in the agricultural fields around city.

At present, colour of water of these four rivers, canals and ditches in and around the city has become almost black with bad smells making it impossible for fish to survive as the organic wastes have been absorbing the dissolved oxygen from water.

Prof Dr M Mujibur Rahman, a teacher of Civil Engineering Department of Buet, and environmentalist, said the polluted surface water may cause a disastrous situation if effective steps are not taken immediately.

Prof Mujib said treatment of human waste is a must to keep the surface water clean, and added the Wasa sewerage system can not cover the whole city. A combination of medium and low cost technologies, including properly designed septic tank system and water-sealed pit latrines, can be introduced to control surface water pollution, he added.

Wasa sewerage system covers only 20 percent of the total population in Dhaka City. Forty percent of the population use septic tanks, 20 percent use water-sealed pit-latrines and rest 20 percent use unhygienic means like open latrines.

Referring to actual condition of sewerage system in Dhaka, he said 60 percent people still use unhygienic methods while hygienic system covers only 40 percent.

As a result of the damage of the sewerage lines in different places, the Wasa sewerage treatment plant at Pagla in Narayanganj receives only one-third of its capacity in dry season, he added.

He said in the capital less than 20 percent people use properly designed septic tanks and about 10 percent use water-sealed pit latrines.

Prof Mujib said most of the city dwellers, including the residents of the posh areas, may think that their excreta does not pollute the environment as they use costly toilets.

But in reality, the excreta discharged by many of these toilets ultimately goes to the open canals or water bodies through broken sanitary sewers or storm sewerage lines without treatment and pollute the environment equally, he added.

He said in the city, 85 percent of the drinking water supply come from ground water and the rest is provided by treating surface waters. People in the city are surviving as they use drinking water after boiling to free it from contamination, he added.

At present, about 400 deep tube-wells are extracting ground water in the capital. As a result, the water level on and average is going down three metres annually. Excessive exploitation of ground water may cause environmental disaster in future, Prof Mujib pointed out.

Industries at Postogola, Fatullah, and a huge number of tanneries at Hazaribagh have been polluting the river Buriganga. Tanning waste contains sulfuric acid, chromium, ammonium sulfate, chloride and calcium oxides.

The industries are the major source of pollution of the Turag river while many others dump their wastes in the rivers Balu and Shitalakhya.

Saidabad water treatment plant and Chadnighat waterworks are installed only to refine natural surface water from rivers. These are not designed to process polluted water containing toxic substances, he added.

Four rivers surround Dhaka city, he said and added polluted surface waters of these rivers have become the hub of fatal water-borne diseases.

Prof Mujib said in Bangladesh, people are to spend about Tk 500 crore annually to fight against water-borne diseases including diarrhoea and skin diseases.

Referring to solutions of surface water pollution, he said the environmental issues are emotional and hence political decisions are necessary to implement technical solutions.

Globally, every year, polluted water is estimated to affect the health of about 1200 million people and contribute to death of about 15 million children under five, he added.