LIQUID tree is an urban photo-bioreactor, a compact water-filled system containing microalgae, that performs photosynthesis. These microalgae absorb carbon dioxide (CO2) and release oxygen (O2), functioning like traditional trees, but with 10-50 times greater efficiency per-unit volume.

Liquid trees can be installed in urban spaces where planting trees is difficult due to lack of land, and they are often designed in the form of benches, bus shelters or street furniture.

Many systems also include solar panels, lighting and remote monitoring to ensure round-the-year operation. Along with improving air quality, they can also provide biomass for fertiliser, potential biofuel use, and help in reducing dust particles, toxic gases, and heat effects in crowded cities.

An experiment is being carried out by the Department of Environmental Engineering at the NED University of Engineering and Technology. The project uses microalgae in flat-panel photo-bioreactors to capture atmospheric CO2.

According to early results, a 250-litre reactor can absorb about 0.38kg of CO2 per year, which equals the absorption capacity of nearly five mature neem trees.

This makes it a promising innovation for urban air quality improvement and sustainable biofuel production, especially in cities like Lahore where air pollution is a serious problem.

In simple words, a liquid tree is an artificial, but natural solution that works like a tree in cleaning the air, and expe- riments have shown that it clearly has the potential to play a strong role in combating urban pollution.

It would be wise to use this technology to overcome persistent environmental degradation in Pakistan, and save our cities and future generations from pollution.

Ahsan ul Haq Shaikh
Chunian

Published in Dawn, September 23rd, 2025