Wastewater almost as pure as drinking water 

As one of the very first cities in the world to do so, Kuching on Borneo is looking into the possibility of establishing an integrated waste water system that incorporates ecological purification.
The smell is the first thing Monica Chin Lee Yung mentions. It's gone.

"Before when you went outdoors, there was a pervading stench from the open sewers that run behind the houses. The smell was overpowering and the drains became easily blocked. But not any more," smiles this friendly housewife, whose modest home is in the Hui Sing Garden, Kuching City.

Today domestic waste water is run off in enclosed piping down to the open sewer, and instead of being dumped straight into the Sarawak River it is cleansed in an underground facility beneath a park only 50 metres away. Monica Chin Lee Yung's family is one of nine families living in a row of terraced houses who are currently testing a new ecological waste water purification system in Kuching.

Private households

The pilot project is a practical element in Kuching's plans to transform the city's environmental administration into a new environmental management system. The biggest single source of waste water pollution stems from domestic use and therefore the project is focusing on private households.

If the pilot project proves to be a viable solution, Kuching with its 500,000 inhabitants could become one of the first large cities in the world to utilise ecological waste water purification on a large scale to solve its massive pollution problems.

Waste water dumped directly into the river
The challenges are monumental. Kuching has no sewage system as such, only open drainage channels. Purification of the grey waste water from kitchens, bathrooms and domestic cleaning is virtually non-existent.

The waste water ends up being dumped into the Sarawak River which flows through the city. And the black waste water from toilets receives only perfunctory cleansing in private septic tanks, which at best removes only half the organic material and does not significantly reduce the bacteria content.

Raised bog

With bacteria in the river at alarming levels, a comprehensive solution to the problem had become imperative. However, it was soon apparent to those working on the project that a conventional sewage system involving a central purification plant, as is common in Western Europe, would not serve as a general solution.

"Much of Kuching is built on metre-thick raised bog. Drainage pipes laid in such terrain would easily break, and then you would face an even worse problem as the bacteria seeped into the drinking water. Also, a conventional sewage system is prohibitively expensive as a general solution for all urban areas, so we were forced to look for alternative solutions," says COWI Chief Technical Adviser Ib Larsen.

Published: 27.10.2004
By: Janne Toft Jensen, jaje@cowi.com


Ecological purification 
Only a small, perfectly shaped hill and the ends of some black pipes sticking up through the grass give any indication of the pioneering work that has taken place in Hui Sing Garden’s local park.

The grey waste water from the houses is first led through an oil separator. From there it is pumped up into four tanks which serve as biological filters. The tanks are located beneath the artificial hill in the park, close to the houses. Here the water is cleansed of organic matter.

It is then run into an artificial wetlands area containing crushed limestone, which cleanses it of nutrients such as phosphorous and nitrogen. The entire system is low-technology and can be maintained by local manpower.

The grey water plant has been constructed in collaboration with the Agricultural College of Norway. The wetlands area has been constructed based on Norwegian dimensions, but initial experience suggests that Kuching's warm climate will make it possible to purify water using a much smaller area than would be required in Scandinavia - further reducing costs.