A team of scientists from Chinese research institutes has made a breakthrough in using bacteria to purify wastewater and produce chemical compounds for the semiconductor industry. This pioneering process has the potential to revolutionize the sustainable and eco-friendly production of valuable semiconductor materials. The study, which was published in the peer-reviewed journal Nature Sustainability on October 16, demonstrated the successful use of genetically modified bacteria to convert wastewater pollutants into semiconductor biohybrids, comprised of both biological and non-biological components.
Led by Professor Gao Xiang from the Shenzhen Institute of Synthetic Biology of the Chinese Academy of Sciences and Professor Lu Lu from the Harbin Institute of Technology in Shenzhen, the research team specifically targeted marine microorganism Vibrio natriegens as the starting point for their bacteria modification. This bacterium is exceptionally fast-growing, thriving in high-salt environments, and highly resistant to wastewater. It has the ability to use over 200 types of organic materials as nutrients, including sugars, alcohols, amino acids, and organic acids, making it an ideal candidate for this research.
The scientists successfully initiated the sulfate reduction mechanism in Vibrio natriegens by training the strain to absorb sulfate directly from the environment and produce hydrogen sulfide. This hydrogen sulfide was then combined with metal ions in the wastewater to create semiconductor nanoparticles. This method proved to be versatile and capable of working with various metal ions, resulting in compounds like cadmium sulfide, lead sulfide, and mercury sulfide.
The nanoparticles synthesized were attached to the surface of the bacteria, forming semiconductor biohybrids. When exposed to light, these biohybrids absorbed solar energy and converted it into electrons, providing the bacteria with additional energy. In a laboratory experiment where biohybrids were used to treat wastewater, 99% of the cadmium ions were successfully recovered as cadmium sulfide particles.
These semiconductor nanoparticles, also known as quantum dots, were a significant discovery that earned another group of scientists the Nobel Prize in Chemistry this year. Gao Xiang explained that after a complete cycle, the biohybrids in the wastewater can be collected through filtration or sedimentation to extract the semiconductor materials. This system offers an efficient and cost-effective method for producing highly valuable quantum dots.
Furthermore, as the biohybrids grow in the wastewater, they also convert organic pollutants into 2,3-butanediol (BDO), a valuable chemical used widely in cosmetics, agriculture, and healthcare. Laboratory tests showed that under artificial light, biohybrids produced BDO at twice the rate of unmodified bacteria, with a 26% increase in carbon conversion.
The additional energy generated by the nanoparticles through light absorption enhances the efficiency of biohybrid synthesis and increases the rate of organic substance conversion in wastewater. Traditionally, bacteria rely on self-metabolism and the digestion of organic matter to provide all the energy necessary for growth and BDO production. However, the additional energy gained from light absorption accelerates these processes, as Gao explained.
During an experiment conducted in a 5-liter reactor, the researchers successfully grew biohybrids using real industrial wastewater, achieving a BDO productivity of 13 grams per liter, surpassing the results of all previous studies.
Currently, scientists are exploring ways to scale up this process. The main challenge lies in the poor transparency of industrial wastewater, which requires reactors with a larger surface area to provide sufficient illumination for active bacterial activity.
The scientists stated that semiconductor biohybrids combine the best attributes of biological whole-cell catalysts and semiconductor nanomaterials, allowing non-photosynthetic industrial microbial cell factories to harness solar energy for chemical production.
