News Column

Experts worry if Wasa can fully remove chemicals from water

May 30, 2014

Dhaka, May 30 (UNB) With the growing dependency of Dhaka Water and Sewerage Authority (Wasa) on surface water, the risk of consuming unsafe water goes up as its conventional water treatment system cannot entirely remove harmful chemicals and surface metals.

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 Dhaka University's Soil, Water and Environment department.

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 Shitalakkhya River contains all sorts of floating materials, dissolved chemicals and un-dissolved organic compounds," Prof Alam said.

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 Civil Engineering Department of Bangladesh University of Engineering and Technology said many chemicals and substances found in river water are impossible to be treated with the technology Wasa uses in Chadnighat water treatment plant.

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 Bangladesh Council of Science and Industrial Research (BCSIR), said Wasa needs to send surface water collected from the rivers through Ion Exchanger to neutralise the chemicals entirely with a view to protecting city dwellers from health hazards.

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.

Dr Imamul Haque observed that the quality of underground water in the city is good. "But there is possibility for the underground water to be contaminated in case of leakages in supply and sewerage lines, latrine and waste disposal place in the surrounding the sources of water," he added.

Deputy Managing Director of Dhaka Wasa Kamrul Alam Chowdhury said Wasa water is 100 percent safe and free from all organic chemicals, bacteria and metals.

"Our treatment process removes all bacteria, chemicals and even limited heavy metals. The Wasa supplied water is up to WHO's standard," he added.

Kamrul Alam, however, admitted that the conventional treatment process cannot remove heavy metals, if these are abound in the water.

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 two crore litres water is now treated through the plant.

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 Padma and Megna rivers to collect water in 2018 and 2019.

Around 22 percent of the 230-240 crore litres of water supplied by Wasa daily comes from surface sources while the rest from underground sources.

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Source: United News of Bangladesh

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