Materials of the future extracted from wastewater

Turning harvested biomass from wastewater treatment plants into sustainable products is now possible on an industrial scale, according to researchers based at Aalborg University in Denmark, in collaboration with Aarhus University, and Delft University in the Netherlands.

Utilising surplus biomass in useful ways

Bacteria in wastewater plants help in the water purification process and enable the recycling of resources. The result is partly pure water and partly biomass (bacteria) from which it is possible to extract biopolymer.

In a treatment plant, there are several hundred different kinds of bacteria. Each bacterial species produces its own type of biopolymer with different properties. An ongoing part of the project is to determine which bacteria there are, determine what polymers they make, determine what characteristics they have, and find out what they can be used for.

The researchers believe that biopolymers extracted from biomass can provide a sustainable alternative to oil-based products. The research has also demonstrated that phosphorus, which is on the EU's list of critical raw materials that may be difficult to obtain in the future, and other minerals can also be extracted from wastewater.

Professor Per Halkjær Nielsen, Department of Chemistry and Bioscience at Aalborg University, said: "The perspective is enormous, because you're taking something that is currently waste and making high-value products from it."

In an article published in Current Opinion in Biotechnology, the researchers state their belief that the process is now ready for 'industrial production and use in practice'.

Sustainable alternative to oil-based polymers

The REThiNk (Recovery of extracellular polymers from wastewater treatment residuals as a new circular biopolymer) research project has focused on biopolymers - long chains of molecules that are bound to each other and that are produced by living organisms, including bacteria.

Synthetic polymers produced in the petrochemical industry from crude oil are used globally for plastics, textile fibres, adhesives and paints, among other products that permeate our everyday lives.

However, the researchers have demonstrated that natural polymers can be harvested from biomass produced in wastewater treatment plants, offering sustainable alternatives to oil-based polymers, for example, as binding agents in paper and in building materials. Biopolymers from wastewater treatment plants also appears to be fire-retardant, opening up new markets if they can be produced commercially, and in a sustainable way.

How are biopolymers harvested?

"In short, the work on biopolymers is about producing a lot of biomass in wastewater treatment plants that is actually bacteria that eat everything that enters the treatment plant so that only the pure water remains," explains Professor Per Halkjær Nielsen.

The biopolymers can be used as a material for 'flocculation', where small particles clump together and settle as part of the water purification process, not just of wastewater treatment plants, but also for harbour sludge, lakes and other water bodies.

Often, however, the biomass waste is either converted into energy using a biogas reactor, or used as agricultural fertiliser. However, with demand for alternatives to oil-based products, the researchers have found a way of extracting or harvesting the biopolymers from biomass.

REThiNk's researchers extracted the biopolymers by changing the pH and temperature of the water. This produced cellulose and gelatinous biopolymers that can be used for a variety of industrial products, as mentioned above.

With hundreds of tonnes of biomass bacteria being produced every year in Danish wastewater treatment plants, the researchers believe it will be possible to create factories that produce biopolymers from biomass.

Global scale up and bacterial potential

REThiNk's ultimate goal is to scale the research to industrial and commercial use. However, this requires analysis and mapping of which polymers are produced in different wastewater treatment plants around the world. This is because the physical properties of polymers have an impact on what they can be used for.

As Nielsen explains: "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."

As well replacing oil-based polymers, wastewater harvested alternatives have other environmental benefits.

"We can take 20-30 percent of the biomass and turn it into biopolymers that can replace petroleum products, but it 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," Nielsen concludes.