Carcasses of dogs, pigs and goats drifting by

Throw a rock in the Barapullah creek and you will see bubbles rising to the surface of this brownish stream just outside dwellings in Delhi. These are bubbles of methane emitted from the rotting process. Carcasses of dogs, pigs and goats drift by in this creek that was originally designed as an open storm drain. Nowadays, this drain is used for municipal and industrial discharge and is clogged with solid waste. It overflows in heavy rainfall.

It is here, alongside this creek, that Delft researchers and their Indian colleagues set up a laboratory for water purification several years ago. Earlier this week, during the visit of the Dutch King and Queen to the laboratory, it was announced that extra investment in the project to scale up the plant will allow the researchers to increase the purification capacity from 100 to 10,000 litres per day.

170 million people in India lack access to clean drinking water

Improving water purification techniques in India is of great importance. While India houses around 16% of the global population, it possesses only 4% of the world’s freshwater supply. Around 170 million people in India lack access to clean drinking water. Rapid population growth, urbanisation and climate change are making matters worse.

At the same time, India is the fastest growing economy in the world. “It has much potential for innovation and a lot of talented people in the water sector,” said project leader Merle de Kreuk, Professor of Environmental Technology at TU Delft, in an NWO (the Dutch science funding organisation and one of the sponsors) press release which was published during the Royal visit.

The pilot facility in Delhi combines various water treatment technologies which are high-tech but low-cost and robust and could, or so the researchers hope, be applied in many places in the world.

One is an anaerobic bioreactor combined with dissolved air flotation, or DAF. DAF is a technique to separate water and organic sludge. The bacteria in the reactor digest various components of the sludge. This produces biogas, which is fed into fuel cells that produce electricity. A similar bioreactor uses ceramic filters to separate sludge and water. These filters are porous tiles produced by local people.

‘Not all water needs to be of potable quality’

It sounds simple, but there are various technical challenges. The biogas contains sulphur, for instance, which causes corrosion and makes the fuel cell less efficient.

The water at the end of the process still contains nitrogen, phosphate, heavy metals, pathogens, and traces of pharmaceuticals. “We tackle these in what we call a vital urban filter,” says De Kreuk. “It is basically an artificial wetland in which plants purify the water.” Different partners are studying how to optimise this system. Eventually, the wetland will also serve an aesthetic purpose and local people will be able to harvest the flowers it produces.

The ‘polishing step’, as De Kreuk calls it, involves removing any remaining traces of pollutants using algae, and pathogen removal. “Not all water needs to be of potable quality,” stresses De Kreuk. “Water can also be used for irrigation, for instance. We aim to couple different purposes to different grades of water quality.”