When an Indian engineering student visited a traditional brick kiln, he was appalled at what he saw. "My moment of reckoning came during that field trip," says Abhishek Banerjee, recalling the 2016 visit. "We saw that the workers there were being treated very inhumanely. And the working conditions of that brick kiln were very improper -- people were digging clay with their bare hands." Working conditions in brick kilns can be harsh and bonded labor is widespread -- a type of modern slavery where employees are made to work to pay off loans at usurious interest rates. But India's 140,000 brick kilns also have an environmental cost. As well as creating dust and sulfur dioxide, which can cause respiratory diseases and put stress on local crops and wildlife, one study estimated that India's brick kilns burn 15 - 20 million tons of coal each year. This releases over 40 million tons of climate-warming carbon dioxide into the atmosphere.

While a student at Jadavpur University, Banerjee wanted to find a creative and socially beneficial alternative to the brick kilns. Along with his classmates Agnimitra Sengupta, Ankan Podder and Utsav Bhattacharyya, Banerjee created a social enterprise called Qube in 2017. Its product is the Plastiqube -- an alternative brick made from waste plastic.

Banerjee and his team work with waste collectors in West Bengal to gather garbage -- including water bottles and disposable bags. The detritus is then cleaned, shredded and pressed into blocks manually. Each Plastiqube brick costs 5 - 6 rupees (about 8 cents) to make, while the average clay brick sells for about 10 rupees (14 cents), Banerjee says. What's more, unlike traditional bricks, Plastiqubes don't use any mortar. "They are basically like Lego bricks," explains Banerjee, now aged 22. "There have interlocking grooves on the bottom and the top, and they lock between each other." India is estimated to throw away over 25,000 tons of plastic waste every day. Around 40% of it is left uncollected. "We're building something sustainable, literally out of garbage," Banerjee says.