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1985 action-adventure TV series MacGyver Showcasing the life of Angus MacGyver, a secret agent who solves problems using the items he has. For example, in one episode, he makes a heat shield out of used refrigerator parts. In another movie, he made a fishing bait with a candy box. More than three decades later, the show is still relevant. verb MacGyverto design something in a temporary or creative way, was added to the Oxford English Dictionary in 2015.
Try putting your MacGyver skills to the test: If you were handed some CDs, what would you make of them? Mirrored wall art, mosaic motifs, or a wind chime, perhaps? How about a mini water treatment plant?
That’s what a team of engineers and researchers at Eden Tech, a company based in Paris, France, that specializes in developing microfluidic technology, is doing. Within their R&D division, Eden Cleantech, they are developing a compact, energy-efficient water treatment system to help tackle the growing presence of micro-pollutants in wastewater. To analyze the performance of their AKVO system (named after the Latin word for water, Aqua), made from CDs, Eden Tech has turned to multi-physics simulations.
Pollutants of Emerging Concern
“There are many ways that fine pollutants can make it into wastewater,” says Wei Zhao, chief chemical engineer and chief product officer at Eden Tech. The appearance of these microscopic chemicals in waste water all over the world is the result of everyday human activities. For example, when we wash our hands with soap, wipe down our sinks with cleaning supplies, or flush medications out of our bodies, many chemicals are washed down the drain and end up in septic systems. Some of these chemicals are classified as fine pollutants, or pollutants of emerging concern (CECs). In addition to household waste, agricultural pollution and industrial waste are responsible for the rise of fine pollutants in our waterways.
Micro pollutants are being added to the world’s lakes, rivers and streams every day. Many conventional wastewater treatment plants are not equipped to remove potentially hazardous chemical residues from wastewater.
Unfortunately, many conventional wastewater treatment plants (WWTPs, Figure 1) are not designed to remove these contaminants. Therefore, they are often reintroduced to various water bodies, including rivers, streams, lakes, and even drinking water. Although the risks they pose to human health and the environment are not fully understood, the increasing number of pollution found in the world’s water bodies is a matter of concern.
Figure 1. Most conventional water treatment plants are unable to remove micro-contaminants.
With this growing problem in mind, Eden Tech worked to develop a solution, and thus AKVO was born. Each AKVO CD core is designed to be 15cm in diameter and 2mm thick. A single AKVO cartridge consists of stacked CDs of various numbers, combined to create a miniature factory. A single AKVO core treats 0.5 to 2 cubic meters of water/day, which means a 10,000-cd AKVO system can handle an average municipality’s needs. This raises the question: How does a device made of CDs disinfect water?
A sustainable wastewater treatment method
The single AKVO system (Fig. 2) consists of a customizable cartridge filled with stacked CDs that each have a small channel grid inserted on them. It removes unwanted elements in wastewater, such as fine pollutants, by circulating the water in its networks of micro-channels. These grids are energy-savvy because they only require a small pump to circulate and clean large volumes of water. Cartridges for the AKVO system are easily replaceable, as Eden Tech takes care of recycling them.
Figure 2. AKVO with labeling of all its components.
AKVO’s revolutionary design combines photocatalysis and microfluidics in one compact system. Photocatalysis, a type of advanced oxidation process (AOP), is a fast and effective method for removing micro-pollutants from wastewater. Compared to other AOPs, it is considered to be safer and more sustainable because it is powered by a light source. During photocatalysis, light is absorbed by photocatalysts that have the ability to form electron-hole pairs, which generate free hydroxyl radicals that are able to interact with and degrade target pollutants. Never before has photocatalysis and microfluidics been combined to treat wastewater. “It’s a very ambitious project,” Zhao said. “We wanted to develop an innovative method in order to provide an environmentally friendly and efficient way to treat wastewater.” Designing the current AKVO hasn’t been easy, as Zhao and his team faced many design challenges along the way.
Overcoming design challenges
When in use, a chemical agent (catalyst) and waste water are dispersed through the microchannel walls of the AKVO. The purpose of the catalyst, titanium dioxide in this case, is to react with micro-contaminants and help remove them in the process. However, the fast flow rate of AKVO complicates this procedure. “The big problem is [AKVO] “It has micro-channels with fast flow rates, and sometimes when we put the chemical agent inside one of the channel walls, the micro-pollutants in the wastewater can’t efficiently react with the agent,” Zhao said. In order to increase the chance of contact between the fine pollutants and the persistent chemical agent, Zhao and his team chose to use a zig zag mixer (SHM) design for AKVO’s microchannel networks (Fig. 3).
To analyze the performance of the SHM design to support chemical reactions for the degradation of micropollutants, Zhao used COMSOL Multiphysics software.
Simulation of chemical reactions for the degradation of micro-pollutants
In his work, Zhao built two different models in COMSOL Multiphysics (Fig. 4), which he named the explicit surface adsorption (ESA) model and the transformed surface concentration (CSC) model. Both models represent chemical and fluid phenomena.
In both models, Zhao found that the SHM structure of AKVO creates eddies in the flow moving through it, allowing the fine pollutant and chemical agent a longer reaction time and enhancing mass transfer between each liquid layer. However, ESA model results showed that the design purifies about 50 percent of the fine pollutants in process, less than Zhao expected.
In contrast to the ESA model (Fig. 5), in the CSC model it is assumed that there is no adsorption limitation. Therefore, as long as the fine contaminants reach the surface of the catalyst, a reaction occurs, which has been discussed in the existing literature (ref. 1). In this model, Zhao analyzed how the design implemented the degradation of six different micropollutants, including gemfibrozil, ciprofloxacin, carbamazepine, clofibric acid, bisphenol A, and acetaminophen (Fig. 6). The results of this model were consistent with what Zhao expected, with more than 95 percent of the micro-contaminants being treated.
“We are really satisfied with the results of COMSOL Multiphysics. My next steps will focus on laboratory testing [of the AKVO prototype]. “We expect our first prototype to be ready by the beginning of 2022,” Zhao said. The prototype will eventually be tested in hospitals and water treatment plants in southern France.
Using simulations for this project helped the Eden Tech team save time and money. Developing a prototype of a microfluidic system, such as AKVO, is expensive. To print the microchannel networks on each of the AKVO CDs, a microchannel photomask is needed. According to Zhao, manufacturing a single photomask will cost around 3,000 euros (3,500 USD). Therefore, it is very important that they are confident that their system works well before it is manufactured. “COMSOL Multiphysics has really helped us validate our models and designs,” said Zhao.
Pioneer in the treatment of micro-pollutants
In 2016, Switzerland introduced legislation that requires wastewater treatment plants to remove micro-pollutants from wastewater. their goal? More than 80 percent of micro-pollutants are filtered out in more than 100 wastewater treatment plants in Switzerland. Following in their footsteps, many other countries are currently considering how to deal with the growing presence of these pollutants in their waterways. AKVO has the potential to provide a compact and environmentally friendly way to help slow down this persistent problem.
Next time you go to the disposal of an old CD, or any other household item for that matter, ask yourself: What would a MacGyver do? Or better yet: What would Eden Tech do? Perhaps you hold the building blocks for their next innovative design.
- CS Turchi, DF Ollis, “Catalytic Decomposition of Organic Water Pollutants: Mechanisms Involving Hydroxyl Radical Attack,” Catalysis Journal, Vol. 122, p. 178, 1990.
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