RMIT engineers mixed 1% recycled cigarette butts into fired-clay bricks, and the bricks matched standard strength while cutting firing energy by 10%

Smokers around the world throw away enough cigarette butts to circle the globe many times over, and almost none of it ever gets recycled. Now, engineers in Melbourne think they've found a second life for that waste: baking it straight into the bricks that build our homes. According to RMIT University in Melbourne, more than 6 trillion cigarettes are produced worldwide every year, and most of the filters end up as litter, adding up to roughly 1.2 million tonnes of toxic waste dumped into the environment annually. In the 2016 study titled 'A practical proposal for solving the world's cigarette butt problem: Recycling in fired clay bricks', the team led by Associate Professor Abbas Mohajerani found that bricks made out of fired clay and only 1% cigarette butt content had the same compressive strength as common bricks. Further RMIT analysis found that the same mixture reduces brick production energy consumption by 10%.

Why cigarette butts are such a big problem

Cigarette filters may appear small, but they quickly add up and are one of the most littered items in the world. It is made from cellulose acetate, which is a type of plastic. Halenur Kurmus and Abbas Mohajerani found in their study, 'Leachate Analysis of Heavy Metals in Cigarette Butts and Bricks Incorporated with Cigarette Butts,' that it could take at least 18 months for the filters to decompose, during which they release harmful chemicals into the environment. Mohajerani said in an RMIT University press release that cigarette butts are saturated with hazardous materials, such as over 60 substances that are carcinogenic. These include heavy metals such as arsenic, chromium, nickel, and cadmium, which leach into soil and water over time. RMIT University estimates that in Australia alone, there are between 25 and 30 billion filtered cigarettes that are smoked each year, with some 7 billion ending up as litter.


How the butts actually go into a brick

Cigarette butts are collected and then mixed into the clay used to make standard bricks, at just 1% of the mixture's weight. A 2020 RMIT study titled ‘Implementation of Recycling Cigarette Butts in Lightweight Bricks and a Proposal for Ending the Littering of Cigarette Butts in Our Cities’ published in Materials explains that this can be done by using whole cigarette butts, pre-shredded cigarette butts, or by pre-blending cigarette butts with other raw materials before they are taken to the brickworks. Afterwards, the mixture is formed into bricks and fired in a kiln, similarly to a regular brick. The firing process takes up actual energy and time. Mohajerani has observed that firing a batch may require as much as 30 hours to be completed, meaning that any reduction in energy consumption will pay off fast.

Matching strength while using less energy

The 2016 study found that bricks made with 1% cigarette butts had a compressive strength of 19.53 MPa, similar to standard bricks. At this modest 1% substitution rate, the added porosity from the burned-out filters is small enough to preserve that strength while still measurably reducing firing energy use by 10%, because of the energy content of the remaining tobacco, estimated at 16.5 MJ/kg. The study found that if only 2.5% of annual worldwide brick production used the 1% cigarette-butt mixture, it would be enough to absorb the world's annual cigarette-butt output while saving an estimated 20 billion megajoules of firing energy, equivalent to the annual energy consumption of one million households in Victoria, Australia. An additional benefit is that bricks produced in this manner would be lighter and more insulating than standard bricks.

What happens to the toxins during firing

A key question is whether making bricks from cigarette waste simply shifts the pollution elsewhere. Kurmus and Mohajerani's study answers this question by measuring the leaching rate of heavy metals from both original cigarette butts and bricks made with cigarette waste. Their results show that firing considerably lowers metal leaching compared to unfired bricks, because the high temperature immobilizes these metals and other contaminants inside the brick, unlike discarded cigarette butts, which can be washed into waterways and soil. Separately, the 2020 implementation study also tested used butts for bacteria and found Staphylococcus, Pseudomonas aeruginosa, and Listeria on the samples tested, a reminder that safe handling matters at every stage of collection.

Turning an idea into an industry plan

Since the initial lab results, Mohajerani's team went further. According to the 2020 Materials study, there is a detailed plan on how the brick manufacturing industry can collaborate with the waste management industry to collect and use cigarette butts in their brick production process, including safety measures during the process. "My dream is a dedicated brickmaking recycling facility in every country, that can recycle butts and solve this pollution problem for good," Mohajerani said in RMIT's 2020 release, alongside a call for stronger anti-littering laws.

The bottom line

This doesn’t mean smoking isn’t harmful to your health or the world around you. However, given that trillions of discarded cigarette butts are littered each year, this research offers a more environmentally friendly outcome. Instead of ending up in rivers, on beaches or along streets, the butts could help reduce energy costs in an industry that will continue making bricks. In this case, a construction material and a persistent litter problem might be solving each other, and that’s a rare thing.