According to experts, it is almost impossible for Wasa to fully neutralise all the chemicals pouring into the surrounding rivers of the capital from factories and industries with its traditional treatment process.
In the treatment process, they said, Wasa uses alum, liquid chlorine and cold lime to purify surface water, but these are not enough to bring the chemicals down to a permissible level.
The long-term use of chlorine may also cause diseases and complications such as colon cancer, peptic ulcer and liver and kidney damage.
"Dhaka Wasa's dependency on surface water has risen from 9 percent to 22 percent in the last five years. But, its purification process has not yet achieved the required standard, as chlorine can only destroy bacteria, not chemicals," said Prof Didar-Ul-Alam of
Among the six rivers surrounding the capital, the Buriganga is highly polluted. The five other rivers are Shitalakhya, Turag, Balu, Sonai and Debdholai.
"Even the surface water in the
Many waterborne organisms cannot also be removed if the water is not treated with right amounts of chemicals. The organic compounds, most of which are harmful to humans, cannot be removed with the conventional treatment method, he said.
Long-term use of chlorine accelerates aging, increases cancer risks and hampers cholesterol metabolism, Prof Alam said suggesting the use of peroxide instead of chlorine as many developed countries and mineral water companies do that.
Wasa's treatment method cannot reduce all the chemicals of industrial effluents such as ethanol, DDT (dichlorodiphenyltrichloroethane), diazinone, azodye, toluene and turpentine to the international standard level, he said.
Prof Alam said Wasa's use of liquid chlorine, cold lime and alum increase to an alarming level during the dry season chlorine 100kg, alum 12 tonne and cold lime 4 tonne an hour. But during the wet season, the use of chlorine is only 32kg, alum 4.3 tonne and cold lime 1 tonne.
According to the international standard, the use of chlorine is 0.3-0.5mg per litre water. However, 5-10mg chlorine should be used to purify water if the density of effluent is high, he added.
Prof Dr ABM Badruzzaman of
He said the excess use of chlorine, which is used to kill bacteria, may regenerate harmful compounds after reacting with other organic matters. These regenerated compounds such as THM (trihalomethane) cause severe health hazards.
Dr Badruzzaman said the sources of surface water should be protected as the river water is highly contaminated and it is almost impossible to neutralise it fully.
Dr SM Imamul Haque, former chairman of
He, however, said the use of Ion exchanger is costly.
Chlorine can make water free from bacteria not chemicals. Chemical test is needed before and after purification process to know how organic pollution is removed, he added.
Deputy Managing Director of Dhaka
"Our treatment process removes all bacteria, chemicals and even limited heavy metals. The Wasa supplied water is up to WHO's standard," he added.
During the dry session, Chadnighat water treatment plant is kept inoperative due to the high pollution of water, he said adding that only one to
He said the river sources should be protected and public awareness is needed to be raised to protect rivers from getting polluted. "Industries should use effluent treatment plants (ETPs) in addition to ensuring that waste disposal spots are not selected nearby the rivers."
He hoped that Wasa will be able to go to the
Around 22 percent of the
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