"Centralised wastewater treatment does not work"
The Centre For Scientific Research Trust (csr), Auroville, Pondicherry has pioneered the decentralised wastewater treatment system in India. Tency Baetens of this organisation speaks to R K Srinivasan
What is the wastewater treatment system promoted by your organisation?
csr promotes natural wastewater treatment. We are currently promoting the decentralised wastewater treatment system (dewats). I t comprises a settler, anaerobic baffled tanks, filter beds of gravel and sand, and a polishing tank (an open pond). But one need not have all these features. For instance, the settler and the baffled tank reactor are enough if the need is just for treating wastewater and infiltrating it back into the groundwater. The other features offer the possibility of using recycled water for irrigation. The open pond or the polishing tank recreates a living environment for the wastewater to clean itself, naturally.
How is this system designed?
The system operates without mechanical means and sewage flows by gravity through the different components of dewats.Up to 1,000 cubic metres of domestic and non-toxic industrial sewage can be treated by this system.
Where did DEWATS originate?
The septic tank is the most widely used in decentr ised wastewater treatment. It was invented by French engineers around the turn of the last century. But this system reduces pollution load by only 30 per cent. The baffled septic tank (or the baffled tank reactor) is far more efficient; it reduces pollution load by up to 90 per cent. Open ponds have been used for treating wastewater since ancient times. Root zone treatment based on use of gravel and sand filters originated in Germany about three decades back.
How does DEWATS score over conventional treatment technologies?
The normal tendency for households is to let sewage flow out of houses or compounds and let the government take care. And indeed from the sixties onwards, the government pursued the issue by constructing centralised plants, most of which were based on Western models. But when costs escalated in the1990s, the will to operate huge centralised plants dissipated. So, most such plants do not function today and investment on them has been wasted. Centralised wastewater treatment does not work. And with most of our coastal cities dumping their wastewater in to the sea, dewats has become the need of the hour.
How useful is this system for India?
dewats can operate in individual households, at the neighborhood level and even in small and big factories not connected to sewage lines. It can also be utilised in hotels, restaurants and in university campuses.
Can the system treat industrial and municipal wastewater also?
dewats can certainly treat municipal waste. But it has limitations in treating large waste outflows from industries. Moreover, we do not claim to treat heavy toxic waste.
What is the cost of implementing DEWATS? Implementing all its components requires about Rs 40,000 per cum of waste. But I reiterate that one need not have all the features of this wastewater treatment system.
What type of maintenance does this system require?
Since dewats requires the barest minimum mechanical devices, running costs are very low. But low maintenance does not mean no-maintenance. Regular checking is necessary; desludging of the tanks is also a must.
What can the recycled water be used for?
It is used for irrigation or for growing plants. This water is absolutely safe for human use.
What is the current status of the concept in India?
The Central Pollution Control Board has taken the initiative to publish guidelines for root zone treatment systems. This should pave the way for utilising this technology on a wider scale.
How long has Auroville worked in this area?
We started research and development work on small-scale treatment systems 20 year ago. Auroville has a unique in-house system that allows it to experiment on treatment systems and fine-tune them. The community here acts as a huge testing field for all kind of ideas on appropriate technologies. If the results are satisfactory, we share them with people and institutions all over the country.
Today, implementation of dewats is in full swing at the national level. There are 50 treatment plants in Auroville alone. Sulabh International, Delhi, was one of the first to build baffled tank reactors. In Kutch, several systems are being built by the non-governmental organisation Hunnar Shaala. In Bhuj, a very ambitious scheme to provide irrigation water through recycled city sewage for green corridors in the city is being developed. Up to 1,000 cubic metres of domestic and non-toxic industrial sewage can be treated by this system.
Where did DEWATS originate?
The septic tank is the most widely used in decentr ised wastewater treatment. It was invented by French engineers around the turn of the last century. But this system reduces pollution load by only 30 per cent. The baffled septic tank (or the baffled tank reactor) is far more efficient; it reduces pollution load by up to 90 per cent. Open ponds have been used for treating wastewater since ancient times. Root zone treatment based on use of gravel and sand filters originated in Germany about three decades back.
How does DEWATS score over conventional treatment technologies?
The normal tendency for households is to let sewage flow out of houses or compounds and let the government take care. And indeed from the sixties onwards, the government pursued the issue by constructing centralised plants, most of which were based on Western models. But when costs escalated in the1990s, the will to operate huge centralised plants dissipated. So, most such plants do not function today and investment on them has been wasted. Centralised wastewater treatment does not work. And with most of our coastal cities dumping their wastewater in to the sea, dewats has become the need of the hour.
How useful is this system for India?
dewats can operate in individual households, at the neighborhood level and even in small and big factories not connected to sewage lines. It can also be utilised in hotels, restaurants and in university campuses.
Can the system treat industrial and municipal wastewater also?
dewats can certainly treat municipal waste. But it has limitations in treating large waste outflows from industries. Moreover, we do not claim to treat heavy toxic waste.
What is the cost of implementing DEWATS? Implementing all its components requires about Rs 40,000 per cum of waste. But I reiterate that one need not have all the features of this wastewater treatment system.
What type of maintenance does this system require?
Since dewats requires the barest minimum mechanical devices, running costs are very low. But low maintenance does not mean no-maintenance. Regular checking is necessary; desludging of the tanks is also a must.
What can the recycled water be used for?
It is used for irrigation or for growing plants. This water is absolutely safe for human use.
What is the current status of the concept in India?
The Central Pollution Control Board has taken the initiative to publish guidelines for root zone treatment systems. This should pave the way for utilising this technology on a wider scale.
How long has Auroville worked in this area?
We started research and development work on small-scale treatment systems 20 year ago. Auroville has a unique in-house system that allows it to experiment on treatment systems and fine-tune them. The community here acts as a huge testing field for all kind of ideas on appropriate technologies. If the results are satisfactory, we share them with people and institutions all over the country.
Today, implementation of dewats is in full swing at the national level. There are 50 treatment plants in Auroville alone. Sulabh International, Delhi, was one of the first to build baffled tank reactors. In Kutch, several systems are being built by the non-governmental organisation Hunnar Shaala. In Bhuj, a very ambitious scheme to provide irrigation water through recycled city sewage for green corridors in the city is being developed.c