It takes 45 minutes to pick up all the milk cartons that have washed up on Long Hai beach overnight. “I feel like all I do is collect them,” says Nguyen Thi Ngoc Tham, gesturing towards the quiet length of sand that fronts her beach house in the south of Vietnam. “I fill about three or four bags every morning, but then there will be a big wave, and when I look back over my shoulder the sand is covered again.”

Facebook Twitter Pinterest Nguyen Thi Ngoc Tham and her son, Phuc Thinh, at Long Hai beach in the south of Vietnam

Milk cartons aren’t the only rubbish that washes up on her shores; bottles of Coca-Cola float in the shallows next to odd shoes, bin bags and sodden bits of cardboard. Once or twice a year, there’s a dead body. “The milk cartons are the most difficult,” she explains. “I can get rid of everything else. Local waste pickers will buy the plastic and the paper from me, and I call the police for the corpses. Nobody will take the milk cartons from me.”

Milk consumption in Vietnam has almost doubled in the past 10 years, as the dairy industry shifts its focus from “saturated” western markets in favour of Asian expansion and is now valued at $4.1bn (£3.1bn). But one of the biggest beneficiaries of this growth seems to be the dairy industry’s principal packaging supplier, Tetra Pak. Last year, 8.1bn of Tetra Pak’s individual cartons were sold across Vietnam. Yet a comprehensive country-wide recycling programme is yet to be implemented. Now, as cartons pile up on beaches and in landfills up and down the country, that’s having a devastating effect on the environment.

Facebook Twitter Pinterest Shop worker Hong An at a Vinamilk store in Ho Chi Minh City

When the Guardian asked Tetra Pak who was recycling their waste, the company told us that there were two facilities in the country: Dong Tien plant in Binh Tanh and Thuan An in Binh Duong. Dong Tien invited the Guardian to come and visit. Thuan An declined to comment.

Tetra Pak told the Guardian that they are recycling 18,000 metric tonnes of cartons a year, with 93,000 packs per tonne, which would mean that they are currently recycling about 20% of their output. The principal recycling plant, they said, is Dong Tien.

But during a tour of the Dong Tien plant, kindly laid on by vice director Phan Quyet Tien, the Guardian was told that although at its peak in 2016 the plant was processing 300-400 tonnes of Tetra Pak packaging a month, they now only process 100 tonnes in the same time frame. So at its peak Dong Tien was recycling just 5.5%(over a year) of all the cartons sold in Vietnam. Now, according to its vice director, that has sunk to just over 1%. Quyet Tien was not aware of the partnership between Tetra Pak and the Thuan An recycling plant. To his knowledge, there used to be another plant in Long An which was able to recycle the packaging, but is no longer able to do so.

“Recycling Tetra Pak cartons is possible, but only if you have the right systems and technology in place,” he explains. “In the past, we bought Tetra Pak waste directly from Tetra Pak, and we also bought milk cartons from informal collectors and litter pickers across the country. But the latter has proved financially ineffective, and it was impossible for us to make a profit.

Facebook Twitter Pinterest Phan Quyet Tien, vice director of Dong Tien paper recycling plant

These days, the Dong Tien plant only accepts waste materials sent directly by the Tetra Pak-affiliated dairy companies themselves. “Between 30% and 50% of the product is aluminium and plastic, and the rest is paper,” says Quyet Tien. “But it’s not simply a matter of mashing the cardboard down or melting the plastic – we have to extract each separate layer and treat them all in different ways.” The process still isn’t cost-effective he says, but it’s their social responsibility to do what they can to help the environment – even if it’s not enough. “We’d love to be able to recycle the cartons that people use and throw away afterwards – I’m sure many recycling plants would – but we get very little support from Tetra Pak themselves and we’re not a charity.”

The result? A country festooned with empty milk cartons. You’ll see clusters outside primary schools and nurseries: one million primary school children get a free carton of sweetened milk at school every day, thanks to a Tetra Pak-supported governmental project. A waste education programme is being piloted in 30 kindergartens, but what happens to the five million cartons at the end of each school week still depends on the institution. “We try to use as many cartons as we can for our arts and crafts lessons,” says Phung Thi Dung, 38, who has been working as a primary school teacher in the Ba Ria province for ten years. “But the rest just get thrown away. I’m not sure where they end up.”

Facebook Twitter Pinterest Litter on a beach in Bin Thuan province

On Long Hai beach Ngoc Tham isn’t sure what to do with the cartons she gathers. Once a week she burns them after sending her 14-year-old son, Phuc Thinh, inside and instructing him to close all the windows and doors to prevent the fumes from seeping inside. Her nearest neighbours – an elderly couple whose beach hut is 300m away – often come storming down the sand to complain about the smell.

Those at the country’s “informal waste stations” admit they don’t have the answers either. Le Thi Anh, 75, works alongside her teenage grandson to sort through the sacks of rubbish dropped off by litter pickers from across the region. “In around 2013 the number of milk cartons being brought to us began to increase quite dramatically,” she says. “We bought them at the start, because somebody told us that recycling plants would buy them to make roofing tiles. But when we took them to the factory, they said it was impossible and they sent us away.” In the end, she burned the cartons in an unofficial landfill nearby. “The smoke was so strong I was coughing for a week.”

Thi Anh was right about one thing: Tetra Pak cartons can be made into corrugated roofing tiles – utilising between 95% and 97% of the multi-layered packaging in the process. “On average, we produce 5,000 tiles every month,” says Quyet Tien over at Dong Thien. Unfortunately, they’re also twice as expensive as normal roof tiles. “As a result, we have to manufacture to order, because so few construction companies are willing to pay that price and we don’t want to be left with any excess,” he explains.

Facebook Twitter Pinterest Aluminium from Tetra Pak cartons at Dong Tien paper recycling plant

The problem may yet worsen. Next May the company will open Vietnam’s first domestic packaging plant on the outskirts of Ho Chi Minh City. Worth $110m, the factory will be capable of producing 20bn cartons a year – foreshadowing a presumed increase in dairy consumption of yet another 50%.

For now, in the absence of any economically viable recycling solutions, Tetra Pak cartons in urban areas of Vietnam are collected by local authority-licensed municipal rubbish collection services, such as Citenco, to be disposed of in large landfill sites across the country. In Ba Ria, the cartons largely end up in a Korean-owned rubbish dump spanning 30 hectares (74 acres) – the largest in the region. There’s no sorting or recycling involved. It’s estimated that between 76%-82% of non-recyclable urban waste in Vietnam ends up in managed landfills. But for those in rural regions, where only 10% of waste is collected by the licensed authorities, the majority ends up dumped by the side of the road or in the sea.

Facebook Twitter Pinterest Milk adverts in Ho Chi Minh City

Environmental experts are concerned. Mia MacDonald is the executive director of policy research organisation Brighter Green. “I find it strange and unsettling that so little is known about what happens to Tetra Pak packaging when it’s being distributed in such vast quantities across regions such as Vietnam,” she says. “Tetra Pak appear to have seen the potential for growth in south-east Asia, and are now trying to capitalise on that with small, single-use cartons that are quickly consumed and then thrown away. And the packaging appears benign: it’s not obviously plastic or glass or metal – it presents itself as recyclable. ”

Facebook Twitter Pinterest An open-air dump site in La Gi province

“When Tetra Pak came to Vietnam in 1994, drinking milk was almost non-existent,” says the company’s in-country spokesperson, Ta Bao Long. “It was always just sweetened condensed milk … which was given to babies and ill people. We had to educate the customers about the convenience and safety of drinking milk from a portable, disposable carton.”

Facebook Twitter Pinterest The production of roof tiles from recycled Tetra Pak cartons at Dong Tien paper recycling plant

The company concedes that more needs to be done to develop recycling across Vietnam. “We’ve been proactively working on recycling since 2004, scouting for recyclers and seeking support from the government as well as NGOs. We started working with the first recycler in 2006,” Jason Pelz, regional circular economy director for Tetra Pak told the Guardian. “We agree more needs to be done. Over the past few years we have worked with our partners to build a total recycling capacity of 18,000 metric tonnes per year. The bottleneck is collection and segregation. We will continue to work closely with the government as well as other partners to increase the beverage carton collection and recycling in Vietnam.”

“We would like to strengthen recycling ability by discussing with [a] recycler in the north; which would bring more convenience in transportation and logistics,” says Ly Trang, Tetra Pak’s sustainability manager in Vietnam. “We are always looking for partners in the recycling/waste collection sector, who have the same vision … Waste management, segregation and collection in Vietnam [is not] at a mature stage yet so there is a lot of work to do.” Pelz added: “Recyclables are not sorted by consumers to be collected in different streams, and the collection of recyclables is often done voluntarily by waste pickers based on the value they can sell to the junk shops. This adversely impacts the recycling of most recyclables, because clearly you can’t recycle effectively when the waste is mixed. The Vietnamese government sees the need to build the infrastructure … We fully support the government initiative and are actively doing our part.”

“Recycling has to be supported by Tetra Pak and the milk industry, because they’re the ones making huge profits,” says Quyet Tien, adding that the Dong Tien recycling plant needs to upgrade its carton processing technology, but can’t afford it. “If Tetra Pak don’t offer to supply it to us, we will have to drop the programme completely and Tetra Pak can find someone new – or they can try recycling it themselves and see how difficult it is.”

Additional reporting by Trang Bui