Can We Use Plants to Filter Wastewater? Apparently Yes

Wastewater is one of the many problems that we need to have a better solution of. After all, the bad things in it which are left untreated could harm us humans and the environment.

Many have tried alternatives to treat wastewater, but maybe they’ve overlooked the most natural things with that capability: plants.

We’ve used plants for so many things, from simple decoration to things that stuff our bellies. Only recently that it’s discovered that we can also use it for wastewater. It’s all thanks to Jacques Brisson, professor in the University of Montreal’s Department of Biological Sciences.

Brisson is a researcher with a specialty in phytotechnologies, the use of plants to solve the environmental problems caused by human activities. His work as a researcher focuses on making use of plants’ natural ability to treat wastewater. And recently, he and his colleagues published studies on the sustainable and cost-effective technologies.

Using plants for evapotranspiration

Published in the journal Water Research, Chloé Frédette who completed her PhD with Brisson has found important findings. With Brisson, they both created a model for maximizing the evapotranspiration potential of plants.

Brisson said, “Chloé’s project developed an original design for a zero-liquid-discharge wetland that treats industrial wastewater. The idea was to completely eliminate all of the contaminated water by evapotranspiration so that none is discharged into the environment.”

What does a zero-liquid-discharge wetland mean? It’s a leakproof artificial basin that contains plants growing in soil and coarse sand. And when contaminated water passes through the sand, the plants will absorb the water and release it into the air as vapor.

“The contaminants are immobilized in the sand, thereby eliminating any danger of leaching into the environment. The plants and the bacteria in their roots can also break down some of the contaminants and render them less toxic,” Brisson said.

Now, this system isn’t actually brand new, since European countries have long used such wetlands to treat wastewater. But, Fredette and Brisson’s work is innovative. The reason for that is the model; their wetland’s parameters can be adjusted to optimize the treatment of leachate, a mixture of rainwater and buried contaminants.

Brisson explained, “The big question was how can we design a zero-liquid-discharge wetland when the quantity of water entering the system is unpredictable because it varies depending on rainfall. In the end, the solution lies in the shape of the wetland, the choice of vegetation and installation of a temporary storage tank for the water.”

Even though the model was developed for Montreal’s climate, it’s adaptable to any climate. What needs to be done is choosing plants with a high evapotranspiration rate and are suited to local conditions.

“This green approach has enormous potential, especially since it is much cheaper than conventional wastewater treatment plants,” Brisson pointed out.


treated wastewater for agriculture in Jordan. Photo by Ghazi Al Jabri Wikimedia Commons


Filtering pesticides with biochar

The other study that Brisson did revolves around the effectiveness of constructed wetlands for treating agricultural runoff. In his experimental research, published in Ecological Engineering, it shows that adding biochar to wetland vegetation is very effective in treating water contaminated with chlorantraniliprole (CAP), a common insecticide.

Biochar itself is a type of charcoal often used to improve soil fertility. Now we know that it’s not only useful for plants, but also for filtering pesticides that usually seep into the environment. “

In our experiment, which ran for three years, adding biochar to the soil in our constructed wetlands removed more than 90% of CAP from the agricultural runoff,” Brisson said. Not only CAP, Brisson got similar results for glyphosate, a widely used herbicide.

It’s not clear if Brisson’s findings are economically feasible in a large scale or not. But at least his research is a good start towards utilizing greener, more organic, and ultimately better methods to treat wastewater that will lessen the ecological damage by human activities.

Other environmentally friendly ways to treat wastewater?

One of the most popular ways to treat wastewater is using membrane filters, due to their less energy needs to purify water. In order to keep them in good condition, common methods to clean it is with large amounts of strong chemicals. However, some of these agents destroy the membranes in the process. Let’s just say that the damage isn’t good.

There are so many things in dirty wastewater filters, and to unclog them, they’re treated with strong acids, bases or oxidants. Chlorine-containing oxidants such as bleach can break down the most stubborn organic debris. But as mentioned, they damage the membranes, which are in most commercial nanofiltration systems. Moreover, they produce toxic byproducts.

Another milder option to clean them is with hydrogen peroxide. Unfortunately, it decomposes contaminants slowly and not as efficient.

Now, it is possible to make it such. Before, hydrogen peroxide is combined with iron oxide to form hydroxyl radicals that improve hydrogen peroxide’s efficiency (called Fenton reaction). It’s just that to make it work, extra hydrogen peroxide and acid are needed, and thus increasing financial and environmental costs.

To tackle this problem, researchers have developed reusable nanoparticle catalysts that incorporate glucose. They help efficiently break down contaminants inside these filters effectively, without the usual risks of damage.

Researcher Jianquan Luo and colleagues combine glucose oxidase and iron oxide nanoparticles into a system that catalyzes the Fenton-based breakdown of contaminants. The result is an efficient and delicate cleaning system for membrane filters.


wastewater treatment plant. Photo by Czeva Wikimedia Commons


How they came up with this discovery

The researchers first compared the removal of organic contaminants from polyamide filters by the glucose oxidase enzyme and iron oxide nanoparticles to other, traditional or conventional cleaning methods.

They discovered that this approach was superior at breaking down the common contaminant bisphenol A and methylene blue, while also preserving more of the membrane structure. After seeing the initial results, the team then combined glucose oxidase and iron oxide into a single nanoparticle, connecting them with an amino bridge.

Next, they tested the new nanoparticle’s ability to clean methylene blue-soaked nanofiltration membranes, which they dirtied and cleaned for three cycles.

After each cleaning cycle, the nanoparticles were retrieved with a magnet and reused with fresh glucose to activate the catalyst. It’s at this point they discovered that the nanoparticles were highly effective at cleaning the membranes, returning them to 94% of their initial water filtration capacity.

Since the nanoparticles don’t require strong chemicals and are easily recoverable, the researchers claim that their new system is a more eco-friendly and cost-effective approach for cleaning nanofiltration membranes.

Do you think it’s better if we use the first method or the second? I personally think that the more eco conscious and cost-effective methods, the better. So, those methods can work together hand-in-hand, and we have more options to treat wastewater. But what do you think?



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