Wastewater treatment plants could soon do more than just purify water — they could become hubs of industrial innovation. A recent study suggests that wastewater treatment is ready for an industrial-scale transformation, enabling the harvesting of valuable biopolymers and minerals like phosphorus. This innovation could drastically reduce reliance on petroleum-derived polymers.

“The perspective is enormous, because you’re taking something that is currently waste and making high-value products from it,” says Professor Per Halkjær Nielsen from Aalborg University in Denmark

Wastewater vs oil

We rely heavily on fossil fuels not just for energy, but for a vast array of materials used in everyday products — from plastics and textiles to adhesives and paints. Many synthetic polymers, essential for manufacturing, are derived from petrochemicals, which come from crude oil. The development of biopolymers from wastewater treatment plants presents an exciting solution, as it offers a renewable, eco-friendly replacement for petroleum-based materials.

This is where wastewater comes in.

Wastewater from industrial processes, mining, and municipal systems contains biopolymers — long molecular chains produced by bacteria and microorganisms.

“Every single day, many tons of biomass are produced, depending on how big the treatment plant is, and this is typically converted in a biogas reactor so that you get energy out of it. A large part of the bacteria consists of biopolymers, i.e. the adhesive material around them, and biopolymers are in demand in the industry as a sustainable alternative to oil-based polymers,” says Nielsen.

Researchers suggest building extraction plants alongside wastewater facilities to harvest useful products.

“We can take 20–30 percent of the biomass and turn it into biopolymers that can replace petroleum products, but it actually also replaces seaweed. Today, many biopolymers are produced from seaweed from large kelp forests that are endangered. So, if we can find other ways to extract biopolymers, it is a clear advantage for the environment and biodiversity as well,” Per Halkjær Nielsen points out.

“There is great potential if companies can see that the product can be used for something and thus want to invest in testing and developing it. And this requires that we build pilot scale plants so that we can produce not just grams, but kilograms and in a few years’ time, many tons.

It gets even better. In addition to biopolymers, wastewater contains trace amounts of precious and industrially important metals like gold, silver, copper, and rare earth elements (REEs). New technologies now allow these materials to be reclaimed and reintroduced into the economy, offering both environmental and economic benefits.

How this would work

Several methods have been developed to recover valuable metals from wastewater, each tailored to the low concentrations typically present. Common techniques include chemical precipitation, adsorption, ion exchange, membrane filtration, and biological methods. Each, naturally, has its own strengths and limitations depending on the metals being targeted.

Chemical precipitation is one of the most established techniques, where chemical agents are added to wastewater to form insoluble metal compounds that precipitate out of the solution.

Membrane filtration is another prospective process. It involves techniques like reverse osmosis and nanofiltration. These retain metal ions while allowing water to pass through. These methods are also well-suited for large-scale wastewater treatment. Still, membrane fouling can reduce efficiency over time, necessitating further development of fouling-resistant materials.

Meanwhile, biological methods involve the use of microbes, algae, and plants to accumulate metals from wastewater. Certain bacteria and fungi can reduce metal ions to form insoluble compounds, while hyperaccumulating plants show potential for absorbing significant amounts of metals. These bio-based methods are an exciting area of research with significant promise for sustainable metal recovery.

Can this be economically practical?

While the potential for metal recovery from wastewater is immense, this isn’t exactly easy to accomplish.

One of the primary challenges in metal recovery from wastewater is the low concentration of metals present. Wastewater typically contains only trace amounts of valuable metals, making it difficult to justify the cost of recovery. To overcome this, technologies must be highly selective and efficient, capable of capturing metals even at very low concentrations. This is a bit better for biopolymers, but we’re still talking about small concentrations.

Then, there’s the contaminants. Industrial wastewater often contains a complex mixture of contaminants, including organic compounds, suspended solids, and various metal ions. This complexity can interfere with metal recovery processes, reducing efficiency and increasing the cost of treatment. Developing technologies that can selectively target specific metals in complex mixtures is a key area of ongoing research.

Ultimately, the big challenge is to make this extraction cost-effective. Although the recovery of valuable metals from wastewater has clear environmental benefits, the cost of implementing and maintaining metal recovery systems can be high, particularly when dealing with low concentrations of metals. For widespread adoption, recovery technologies must be both cost-effective and scalable.

Ultimately, though, researchers are confident in scaling these processes up.

The field of metal recovery from wastewater is rapidly evolving, driven by advances in materials science, biotechnology, and environmental engineering. As the global demand for metals continues to rise — particularly with the growth of renewable energy and electric vehicles — recovering metals from non-traditional sources like wastewater will become increasingly important.

Sasmitha A Zahra et al, Rethinking characterization, application, and importance of extracellular polymeric substances in water technologies, Current Opinion in Biotechnology (2024). DOI: 10.1016/j.copbio.2024.103192