Green innovation: Hong Kong start-ups nurture trillions of tiny algae as carbon-capture tech to address climate change

On a small plot of farmland in Hong Kong’s western New Territories, just across the border from mainland China, a series of pumps directs agricultural waste water from a nearby river into a row of outdoor tanks, providing nutrients for trillions of green microalgae.

The facility is not growing the tiny plants as a crop, but rather for their ability to help solve one of the world’s most pressing issues by absorbing carbon dioxide.

“How they capture carbon dioxide is through photosynthesis,” said Nelson Ng Pok-him, co-founder and CEO of Alcarbo Technologies. “They turn carbon dioxide into something like sugar … and they store it inside their bodies. They are like little carbon-dioxide containers.”

Most plant life on the planet does the same thing, producing oxygen and energy for its own use in the process. But microalgae have a prodigious capacity for carbon dioxide relative to their mass, which is why Alcarbo – and many competitors – are racing to demonstrate that microalgae operations can scale up sufficiently to become a cost-effective carbon-capture solution and help reduce human-induced climate change.

Alcarbo’s team of six set up the facility on a 150-square-metre patch in San Tin in the Yuen Long district over five months in early 2023. The site houses two shipping containers that contain algae cultivation and harvesting equipment, as well as a water filtering system – all powered by solar panels. Nearby is a “wall” of 12 algae photobioreactors, which are capable of absorbing half a tonne of carbon dioxide a year even after factoring in the carbon footprint of electricity consumption and construction, Ng said.

“But it can do much better than that,” Ng said, because adding more capacity increases the carbon-absorbing capacity without significantly adding to the carbon footprint. “When we scale it up we just have to build more reactors.”