A team of researchers, under the leadership of Prof. Xiang Gao from the Shenzhen Institute of Advanced Technology (SIAT) of the Chinese Academy of Sciences and Prof. Lu Lu from the Harbin Institute of Technology, has put forward an innovative approach to convert wastewater contaminants into valuable chemicals using sunlight.
Green chemical manufacturing makes a greener life. Image Credit: SIAT
This breakthrough has the potential to open doors for sustainable and environmentally friendly chemical production. The findings from their study were published in Nature Sustainability on October 16th, 2023.
Traditional chemical manufacturing heavily depends on energy-intensive processes. Semiconductor biohybrids, which combine efficient light-harvesting materials with high-performing living cells, have emerged as an exciting development in harnessing solar energy for chemical production. Nonetheless, the primary challenge lies in finding an economically viable and eco-friendly method to scale up this technology.
In this study, the researchers aimed to directly transform pollutants from wastewater into semiconductor biohybrids within the wastewater environment. The concept involves using the organic carbon, heavy metals, and sulfate compounds naturally found in wastewater as the foundational materials for constructing these biohybrids, which can then be converted into valuable chemicals.
However, real industrial wastewater typically exhibits significant variations in its composition of major organic pollutants, heavy metals, and complex pollutants. These constituents are often toxic to bacterial cells and present challenges for efficient metabolism.
Additionally, industrial wastewater often contains high levels of salt and dissolved oxygen, necessitating the use of bacteria with the capacity for aerobic sulfate reduction. Consequently, using wastewater as a feedstock for bacteria becomes a complex and challenging task.
To address these challenges, the researchers opted for Vibrio natriegens, a rapid-growing marine bacterium known for its remarkable tolerance to high salt concentrations and its ability to metabolize a variety of carbon sources.
They incorporated an aerobic sulfate reduction pathway into V. natriegens and trained the genetically modified strain to utilize different metal and carbon sources. This allowed them to produce semiconductor biohybrids directly from the complex composition of wastewater.
Their primary goal was to produce 2,3-butanediol (BDO), a valuable commodity chemical.
To achieve this, they engineered a strain of V. natriegens that produced hydrogen sulfide. This compound played a crucial role in facilitating the generation of CdS nanoparticles, which are highly efficient at absorbing light. These nanoparticles, known for their biocompatibility, allowed for the in-situ formation of semiconductor biohybrids, enabling non-photosynthetic bacteria to utilize light in the process.
The findings demonstrated that these sunlight-activated biohybrids achieved a substantial improvement in BDO production, surpassing the yields attainable with bacterial cells alone. Additionally, the process proved to be scalable, as it enabled solar-driven BDO production on a considerable 5 l scale using real wastewater as the raw material.
The biohybrid platform not only boasts a lower carbon footprint but also reduces product costs, leading to an overall smaller environmental impact when compared to both traditional bacterial fermentation and fossil fuel-based BDO production methods. Remarkably, these biohybrids could be produced using a variety of wastewater sources.
Xiang Gao, Professor, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences
Journal Reference
Pi, S., et al. (2023). Solar-driven waste-to-chemical conversion by wastewater-derived semiconductor biohybrids. Nature Sustainability. doi.org/10.1038/s41893-023-01233-2.