How It Started

Outdoor air pollution is a serious threat to human health; approximately 4.2 million people die every year due to it.^[2] This issue touches Serbia in particular, as estimates show that Serbia has at least 75% of its citizens breathing polluted air, with official World Air Quality reports labeling some of its cities as exceeding the WHO’s (World Health Organization) recommended air quality by x7-10.^[3][4] So, Dr. Ivan Spasojevic, joined by some of his peers, designed the Liquid3, uniquely integrating photobioreactor systems with modern infrastructure, and placed it in Makedonska Street, Belgrade.^[5]

How It Works

The Liquid3 urban photobioreactor is a glass tank filled with tap water and microalgae. The glass tank is embedded into a structure that acts as a bench and is outfitted with utilities like charging ports for passing citizens. The other notable components of the Liquid3 design include a pressure pump, a bubble column, and a couple of solar panels. The pressure pump is used to pump the polluted surrounding air into the tank. From there, the microalgae, with the help of natural sunlight, perform photosynthesis and convert the water in the tank, along with carbon dioxide pollution from the pumped-in air, into fresh oxygen, which is carried and released into the atmosphere through the bubble column. Microalgae also have a property called biosorption, which allows them to passively filter out heavy metal contaminants in the air by binding them to their complex chemical structure. And the solar panels act as a renewable energy power supply for the whole system. While a solid amount of the energy will be allocated towards operating the pumps, there is enough energy gathered to supply energy to the other utilities of the Liquid3 structure, like a night light lamp, a couple of charging ports, and a temperature regulation system that would be necessary if climate conditions were to become too extreme for sustaining microalgae life.^[3][6][7]

Advantages

Most notably, when there isn’t enough space for fresh exposed soil, like in malls or other dense urban areas, or the surrounding environment is just outright too polluted, trees are unable to grow while the Liquid3 photobioreactor tank  is unbothered by both of these problems and can still function effectively. Another glaring advantage of implementing Liquid trees instead of real trees is that microalgae are much more efficient at photosynthesis than trees and it is said that one Liquid3 tank is able to replace two 10-year old trees or 200m of lawn.^[1][8] Microalgae are also much better at filtering heavy toxic metals out of the air than regular trees giving us better purification of the air per capita. Trees also come with pollen that can lead to a faster spread of allergies, asthma, and hayfever.^[8]  Microalgae, through photosynthesis, produce biomass which can be repurposed for many different uses such as:^[1][9][7]

• Excellent fertilizer
• Wastewater treatment
• Compost for green areas
• Production of biofuels

Challenges

Trees have many benefits that photobioreactor infrastructure like Liquid3 do not provide. Architecturally, trees offer color and natural characteristics. They help expand and shape our landscapes, they soften the harsh scenery of metal, stone, and glass of cities and they are said to be able to help improve the moods of onlookers. Trees also conserve water and reduce soil erosion. They lower the air temperature through shade, reduce noise pollution and reduce wind speeds. They increase property values and also help create wildlife and plant diversity in your area.^[10] All of these are irreplaceable, important features that trees intrinsically have and Liquid trees don't. Liquid trees also have maintenance costs(estimated around $70 per month per Liquid3 unit) and are estimated to need replacement every couple of years with the current model.^[8] And finally, since microalgae have a small  temperature range where they can survive, if the climate gets too hot or too cold there needs to be more money and energy dedicated to preserving them.

Public Discussion

There have been a lot of people voicing their concerns about implementing Liquid trees into their cities. The cost of losing trees is truly great. However, scientists and the creators of Liquid3 themselves have adamantly reinforced the goal of liquid trees is “not to replace forests but to use this system to fill those urban pockets where there is no space for planting trees.”^[11] And with that said, advocators for biotechnology commend Liquid3 as it is a concrete example of successful and practical integration photobioreactor systems with modern architecture.

Ideally, a lot of people hope that the existence of Liquid3 will also act as an advertisement for the importance of environmental protection.