Biohybrid alchemy: Transforming wastewater contaminants into chemicals

Researchers have proposed a novel method for transforming wastewater contaminants into valuable chemicals using sunlight, offering an avenue for sustainable and circular chemical manufacturing.

Conventional chemical manufacturing relies on energy-intensive processes. Semiconductor biohybrids, which combine efficient light-harvesting materials and living cells, have emerged as an exciting possibility for those seeking to use solar energy to produce chemicals, say the authors of this new study.

The challenge now lies in finding an economically viable and environmentally friendly way of scaling-up the technology.

It was published in Nature Sustainability in October.

The work was led by Professor GAO Xiang from the Shenzhen Institute of Advanced Technology (SIAT) of the Chinese Academy of Sciences and Professor LU Lu from the Harbin Institute of Technology.
The researchers set out to convert pollutants from wastewater into semiconductor biohybrids directly in the wastewater environment. The concept involves utilizing the organic carbon, heavy metals, and sulphate compounds present in wastewater as the raw materials for constructing these biohybrids, and subsequently converting them into valuable chemicals.

Nevertheless, real industrial wastewater usually varies in its composition of major organic pollutants, heavy metals, and complex pollutants, all of which are often toxic to bacterial cells and difficult for them to metabolize efficiently. It also contains high levels of salt and dissolved oxygen that require bacteria with an aerobic sulphate reduction capacity. Thus, it’s challenging to use wastewater as bacteria feedstock.

To overcome this, the researchers selected a fast-growing marine bacterium, Vibrio natriegens, which has exceptional tolerance for high salt concentration and a capacity for utilizing various carbon sources. They introduced an aerobic sulphate reduction pathway into V. natriegens and trained the engineered strain to utilize different metal and carbon sources in order to produce semiconductor biohybrids directly from such wastewater.

Their primary target chemical for production was 2,3-butanediol (BDO), a valuable commodity chemical.

By engineering a strain of V. natriegens, they generated hydrogen sulphide, which played a pivotal role in facilitating the production of CdS nanoparticles that efficiently absorb light. These nanoparticles, renowned for their biocompatibility, enabled the in-situ creation of semiconductor biohybrids and enabled the non-photosynthetic bacteria to utilize light.

The results showed that these sunlight-activated biohybrids exhibited significantly enhanced BDO production, surpassing yields achievable through bacterial cells alone. Furthermore, the process displayed scalability, achieving solar-driven BDO production on a substantial 5-liter scale using actual wastewater.

Life-cycle assessment shows that this specific biohybrid route has substantial sustainability gain compared with conventional 2,3-butanediol production routes.

“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,” said Prof. GAO. “Remarkably, these biohybrids could be produced using a variety of wastewater sources.”

The authors say the work can bring solar-driven biomanufacturing and waste-to-wealth conversion one step forward and pave the way to cleaner production and circular economy.