Materials of the future can be extracted from wastewater

A group of researchers is on the way to revolutionizing what biomass from wastewater treatment plants can be used for. Biopolymers from bacteria can be a sustainable alternative to oil-based products, and phosphorus and other minerals can also be harvested from the wastewater. A new scientific article says that the research is now so far advanced that it is ready for industrial production and use in practice. The study is published in the journal Current Opinion in Biotechnology.

"The perspective is enormous, because you're taking something that is currently waste and making high-value products from it."

This is what Professor Per Halkjær Nielsen, Department of Chemistry and Bioscience at Aalborg University in Denmark, says about the results of a research project that utilizes surplus biomass in wastewater treatment plants in new ways. The focal point is biopolymers, which can be described as long chains of molecules that are bound to each other and that are produced by living organisms, including bacteria.

Today, synthetic polymers produced in the petrochemical industry from crude oil are used in many contexts including plastics, textile fibers, adhesives and paints. But with future production of biopolymers at wastewater treatment plants, it will be possible to extract a sustainable alternative to oil-based polymers through a waste product.

"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 Nielsen.

"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."

The goal of the REThiNk project is to create the foundation for industrial scale-up in the short term so that in the long term there will be a real revolution in recycling biomass from wastewater treatment plants

Biopolymers can be used as a binding agent in paper and in building materials, and they can be used as a material for flocculation where small particles clump together and settle as part of the water purification of harbor sludge, lakes and wastewater treatment plants. An added bonus is that biopolymers from wastewater treatment plants appear to be fire-retardant. Thus, there is a potentially large market for biopolymers if they can be produced commercially in a sustainably way, and there is potential for this, according to the research project REThiNk.

In a wastewater treatment plant, there are several hundred different species of bacteria that produce many types of biopolymers with different properties. These bacteria use the biopolymers as an adhesive to form colonies and adhere to surfaces so they are not just flushed out of the treatment plant.

These biopolymers can be extracted by changing the pH and temperature of the water to produce cellulose and gelatinous biopolymers that can be used for a variety of industrial products. The expectation is that it will be possible to create factories that produce biopolymers from Danish wastewater treatment plants, and the potential is great, since hundreds of thousands of tons of bacteria are produced annually in Denmark alone.

As an added benefit, minerals and other valuable components can be harvested from the wastewater that arrives at the treatment plants, such as phosphorus, which is on the EU's list of critical raw materials that may be difficult to obtain in the future.

The goal of the REThiNk project is to create the foundation for industrial scale-up in the short term so that in the long term there will be a real revolution in recycling biomass from wastewater treatment plants all over the world and not just in Denmark. It also requires mapping bacteria at wastewater treatment plants around the world so that it is possible to predict how each of them can play a role in biopolymer production, phosphorus extraction, etc.

"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.

"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.

In the REThiNk project, Aalborg University is collaborating with Delft University in the Netherlands and Aarhus University.