On a hotel rooftop in Bangkok, dozens of barrels of green liquid bubble under the sun – the latest innovation in urban farming.

Proponents of the edible algae known as spirulina say it could help provide a sustainable source of protein as an alternative to meat.

Three times a week, Patsakorn Thaveeuchukorn harvests the green algae in the barrels.

“The algae is growing so fast, normally the doubling time is around 24 hours,” said Patsakorn, whose employer EnerGaia uses Bangkok’s rooftops to grow spirulina.

With its high levels of protein and nutrients, “it is beneficial to food security,” he told AFP.

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