Sewage mess fears

26 June 2009

With only 60 percent of the municipal area connected to the Babesa sewage treatment plant and the plant already reaching its capacity, Thimphu may soon have to battle massive sewage that has nowhere to go.

With a daily capacity of 1750 cubic metres and sprawling 13 acres, Thimphu sewage system design was carried out in the early 1990’s by a Danish consultancy firm under a Liaison Office of Demark (LOD) financed project. The project took five years and was completed by early 1996.

In 2000, just four years after commissioning the project, another group of LOD-funded consultants from Kampsax pointed out that the capacity limit of the treatment plant was already approaching.

And as of May this year, exactly after nine years, the total sewage inflow in a day is 1650 cubic metres.

“Within the design capacity, only 20 percent of the space is left, which is allotted to Motithang area,” said a chief engineer at Thimphu City Corporation (TCC), Mahesh Pradhan, adding that the plant couldn’t take the whole of Thimphu’s waste.

According to the in-charge of the sewerage plant, Pema Khandu, apart from the waste, rain water also takes up space since the ponds are open.

The reach According to Operation and Maintenance of the Waste Water Treatment Plants of March 1996, the design would serve 12,500 people until 2005. 2005 onwards, 25,000 people would be served.

But in 2007, when the city’s population increased to 80,000, the estimated population served was 18,000 only.

And today, when the whole of Thimphu is taken into account, including the extended boundaries, the sewage plant is connected to only 20 percent of the population.

According to the draft master plan for Waste Water Handling in Thimphu, September, 2000, the extension of the sewer network to connect more of Thimphu’s areas and households has not progressed at the rate earlier foreseen by the consultants.

The location of the sewage plant also attributes to the limited reach.

“The location is something that should have been thought of,” said a BO source. The sewage plant doesn’t even serve Babesa, which is at a lower elevation than the plant. The flow of sewage depends on gravitational force.

The northern parts of Thimphu like Dechencholing, which come under the extended boundaries, are too far to be connected to the sewage plant. According to the head of the sewer section of TCC, Thukten, the cost would be extremely high.

A yearly budget worth Nu 1.5 million is allotted to lay sewer lines. But this is a problem, said an officer from TCC. “One kilometre of sewer line costs Nu 1.5 million,” he said.

The Kampsax consultants noted in the draft master plan for waste water handling that the frequency for emptying septic tanks within the municipal boundary is very low and unsatisfactory.

The cost The BO source said that the government had other options for sewage plant. He said that, in a city where land is scarce, vertical wells could have easily taken care of the current capacity issue.

“The horizontal ponds working purely on natural process are good but they eat up a lot of space, whereas the vertical wells that go deeper don’t,” he said. “Of course electricity will be required for the vertical wells which Bhutan can afford.”

According to Kampsax consultants, the extension of the plant will require more land and a huge investment – about Nu 100 million. “This is happening because of the wrong choice made that time,” said the source.

An area of 10.5 acres next to the expressway has been suggested for the extension of the sewage plant, which will bring the plant right alongside the road.

The future

A five-year project is underway to rescue the almost full plant. A mini version of the Babesa sewage treatment plant funded by the World Bank, worth Nu 10 million, will be built for north Thimphu. An ADB funded project worth Nu 15 million, inclusive of water connection, is planned for south Thimphu.

How the plant works

There are seven ponds including 3 anaerobic ponds (3 metres deep), 2 facultative ponds (2 metres deep) and 2 maturation ponds (1.5 metres deep). Domestic sewage is accumulated in anaerobic pond which is open.

Organic matters are removed and the methane gas escapes. The retention time is 3 days.

Then in the facultative pond, through vaporisation, bacteria utilise oxygen produced by algae while algae use carbon dioxide produced by bacteria in the presence of sunlight. The retention time is 39 days.

Finally, in the maturation pond, those bacteria that survive without oxygen, ammonia, phosphorus, nitrogen and nutrients are removed. It is then discharged into the water source nearby.

By Kuenzang C Choden

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