‘Conventional system can\\\'t remove chemicals from WASA water’

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, reports UNB.
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 0.9 per cent to 22 per cent 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 Shitalakkhya, 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 amount 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.
The treatment method of WASA 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 increases to an alarming level during the dry season -chlorine 100kg, alum 12 tonnes and cold lime 4 tonnes an hour. But during the wet season, the use of chlorine is only 32kg, alum 4.3 tonnes 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 (BUET) 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.