CLEANING SEPTIC TANK MADE EASY WITH THE ROBOTS

A team of students is in the way of developing a robot that performs cleaning works in septic tanks. The few mock trials in the lab were scheduled in April and May in the lab. The robot will experience site trials in July and August. The urgent need for such a device is starkly explicit after six persons being killed on Tuesday near Chennai while engaged in cleaning works in a septic tank.

Deepthi Sukumar, national co-convener of the Safai Karamchari Andolan (SKA) have pointed out that nearly 15 deaths have taken place during the month of January 2019.

The number of septic tanks in India runs into hundreds of thousands. It is illegal to send a person down to clean the chamber but it has been common. According to the Census of 2011, nearly 400 million Indians use septic tanks.

“The liquid on top can be drawn out, but the bottom cover has dense residue. People are sent in to remove this thick sludge,” said Ms. Sukumar.

Technical obstacles

Impelling a robot in this environment is a primary objection, explains Prabhu Rajagopal of the Centre for Non-Destructive Evaluation at IIT-Madras. He has been working on this project for four years.

To remove the sludge, a robot needs a propeller but the state of a septic tank have particular obstacles.

Dr. Rajagopal explains, “Using a rotary propeller, like in an aircraft could make the blades congested within the fluid.”

Hence the team opted for bio-inspired fins. Three master’s projects later, they have a standalone six-fin propeller. That was developed by Srikanth, an M.S. student.

To simulate the tank liquid, they are now trying to obtain slime from the oil and gas sector, whose properties are similar to that of septic tank sludge. The team is working with Professor Indumathi Nambi of the Environmental Engineering group at IIT-Madras in this aspect.

The first step is to homogenize the sludge using the cutter developed by the team, later it could be sucked out. Initially, they were working with a simplistic cutter model. Now, they have an umbrella-like cutter. “It can be retracted then put into the septic tank, and it opens again; on rotating it the contents of the septic tank are cut up. Then it can be sucked out using vacuum pumps,” explains Dr. Rajagopal.

The SKA members work with sanitary workers. They have added a sense of responsibility to the group. “We have 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 the cleaning solution does not exist, they are just are expensive. Dr. Rajagopal mentions a cost for the IIT robot of ₹10-30 lakh, admitting that is also far expensive.

But the engineering hurdles remains the same. For example, the robot has to be spark-proof, because the septic tank environment includes gases that are inflammable.

Stand-alone solution

However, usage of the cutter is less expensive and can be a stop-gap solution. Ultimately, a flawless robot will be required that goes inside the septic tank, and that is the plan of the group.

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

The funding for the project was met partially 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.

– SARANYA NAGARAJAN