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 Situation poses multiple challenges, says IIT-Madras group

A group in IIT-Madras is developing a robot to clean septic tanks. After mock trials in the lab scheduled for April and May, the robot will undergo site trials in July through August. The dire need for such an invention is starkly obvious with six persons killed on Tuesday near Chennai while cleaning a septic tank.

Deepthi Sukumar, national co-convener of the Safai Karamchari Andolan (SKA), points out, “From January 2019 alone, some 15 deaths have taken place.”

The number of septic tanks in India runs into hundreds of thousands, and though it is illegal, sending a person down to clean the chamber is not uncommon. According to the 2011 Census, about 400 million people in India use septic tanks.

“The liquid on top can be pumped out, but the bottom layer has thick sludge. It is to remove this that people are sent in,” said Ms. Sukumar.

Technical obstacles

Propelling a robot in this environment is a major challenge, explains Prabhu Rajagopal of the Centre for Non-Destructive Evaluation at IIT-Madras, who has been working on the project for about four years.

To move in the fluid, a robot needs to have a propeller but the conditions in a septic tank pose specific problems.

Dr. Rajagopal explains, “If you use a rotary propeller, like in an aircraft, the blades will get congested within this fluid.”

The group hence opted for bio-inspired fins. Three master’s projects later, they now have a standalone six-fin propeller, which was developed by Srikanth, an M.S. student.

To simulate the tank liquid, they are now trying to procure sludge from the oil and gas sector, whose properties are similar and are working with Professor Indumathi Nambi of the Environmental Engineering group at IIT-Madras in this regard.

As a first step, the group has developed a cutter that can homogenise the sludge, which can then be sucked out. Initially working with a simplistic cutter model, they now they have an umbrella-like cutter. “It is retracted, put into the septic tank, then it opens again; we rotate it and the contents of the septic tank are cut up. Then it can be sucked out using vacuum pumps,” explains Dr. Rajagopal.

Talking to the SKA members, who work with sanitary workers involved in cleaning drains and septic tanks, added a sense of responsibility to the group. “We met two women who had lost their husbands when they entered septic tanks,” Dr. Rajagopal recalls. The group is in close talks with the SKA for a partnership.

It is not that cleaning solutions do not exist, but these are expensive. Dr. Rajagopal cites a cost for the IIT robot of ₹10-30 lakh, admitting that even that is expensive.

But the engineering challenges remain. For instance, the robot has to be spark-proof, because the septic tank environment includes gases that are inflammable.

Stand alone solution

However, using the cutter alone is less expensive and can be a stop-gap solution. Eventually, a complete robot will be needed that moves inside the septic tank, and that is what the group plans to develop.

“This is excellent work. Now, under the Swachh Bharat scheme, many toilets are being built in remote areas with narrow streets where the pumps cannot enter. This invention will be very useful for these cases,” says Ms. Sukumar.

The funding for the project was met partly by IIT- Madras Socially Relevant Project on Compact Robotic Vehicle for Sewer lines and Septic tank inspection, 2017-2018, and by 2018 Carbon-Zero National Energy and Environment Innovation Challenge.