Safe handling of contaminated dredged materials
Hundreds of years ago, the banks of the Buriganga were a prime location when the Mughals made Dhaka their capital in 1610. The house-turned-museum of the Nawab (ruler) overlooks the river, which is the country's main waterway for trading and ferry travel. It was once the main source of drinking water for Dhaka's residents, and an hour downstream from the capital city the river is still crystal clear. But as it flows through the capital, waste from sewers and factories -- especially tanneries -- pour into it.
Now, up to 40,000 tones of tannery waste flows into the river daily along with sewage from Dhaka, a city of more than 10 million. Human waste is responsible for 60 percent of pollution in the river, followed by industrial waste at 30 percent. The rest is solid waste. Illegal structures have sprung up along its banks, narrowing the river and adding to the dirt, while ferries spill oil into its waters.
A recent survey found that a polythene stratum, measuring about 10 feet in thickness, was embedded under a certain stretch of the Buriganga. The river remains terribly polluted from domestic and industrial wastes and the polythene makes it worse, especially given the shallowness of the river. The huge quantities of garbage dumped into this arterial watercourse have turned it into an environmental nightmare.
Trashed poly bags seem to pose a far greater danger to human health than ordinary garbage. While the latter is absorbed into the environment, polythene, being non-biodegradable, is permanent garbage. Brisk business goes on with recycled poly bags along the riverbank, and during washing and drying activities a good proportion of them ends up in the river.
Against this backdrop, the recent initiative by Bangladesh Inland Water Transport Authority (BIWTA) to remove the garbage, including polythene, from the bed of the river is therefore a welcome one. It may be considered as the first step towards cleaning the river, if it is a well planned one. However, it is to be remembered that the safe disposal of the sludge removed from the bed remains a big challenge in this kind of initiative.
BIWTA, therefore, needs to identify appropriate places for dumping the sludge after necessary cleaning operation, including the recovery of poly bags for recycling. It is gathered from reports in the newspapers that Amin Bazar has been chosen as the dumping site. This has not been a right decision as Amin Bazar dumping site falls the in flood flow zone. If the dredged materials are dumped in this site all leachates, including the contaminants from the tanneries, will find their way to the surrounding environment. It would have been better if BIWTA had chosen Matuail dumping site of DCC, as it is claimed to be a sanitary landfill site. It would be also pertinent to involve the Department of Environment in this operation for giving expert opinion on the safe disposal of the sludge and for monitoring purposes.
As it is understood that the Buriganga riverbed sludge is heavily contaminated with industry effluents, including chromium from tanneries, the operation deserves extra care and caution. Recovery of poly bags for recycling and leachate collection and treatment must be stressed as a basic requirement for this operation. Needless to say, the sludge should be spread in layers and compacted. All these required are to make sure that contaminated dredged materials are kept isolated from the environment, until it is safe.
Mohammad Reazuddin is a former Director of the Department of Environment.
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