Microplastics are small pieces of degraded plastic less than 5 mm in size that can travel huge distances in the open sea and remain there at various depths. Research has shown that they are not just in our oceans, affecting marine life, but can also travel through the atmosphere to reach even the remotest corners of the world.
Richard Thompson OBE, Professor of Marine Biology and Director of the University of Plymouth’s Marine Institute, was the first to coin the term ‘microplastics’ in 2004. “Our work has so clearly shown that microplastics are present in every sample of beach sand…We’ve looked in the deep sea, in Arctic ice, in the gut of hundreds of fish from the English Channel, and we’ve found microplastic contamination everywhere.”
According to the UN, plastic production is forecast to more than double by 2050 and the scale of the resulting microplastics pollution is shocking in terms of sheer size. In September 2021, a team of oceanographers led by researchers from Kyushu University in Japan, estimated there are 24.4 trillion pieces of microplastics in the world’s upper oceans. It’s harder to measure microplastics within the atmosphere but one US study in 2020 found that atmospheric microplastics can travel long distances and originate from sources such as roads (84%), the ocean (11%) and agricultural soil dust (5%).
While scientists battle with the potential risks to human and marine life, those in the filtration industry are developing technologies to prevent microplastics from becoming an even bigger problem. Although it is relatively early days in terms of research and development, industry experts are working to tackle this apparently insurmountable problem.
Tyre abrasion & microplastics
Research funded by the German Federal Ministry of Education and Research (BMBF) found links between tyre abrasion and microplastics’ emissions, which then enter the environment through road run off. Its findings informed a joint project between German car manufacturer Audi, specifically its Environmental Foundation and the Technical University in Berlin (TU Berlin) to develop a solution which could prevent tyre particles from being washed into sewers and other water sources when it rains.
Daniel Venghaus, research associate in the Department of Urban Water Management at TU Berlin explains: “One important finding showed up to seven times more tyre wear on inner-city curves than on corresponding straights or inclines. Our research found up to three times more abrasion at traffic lights in the crossing area. This defined the hot spots where our filters can be used in a targeted and effective manner.”
Their response is the development of the UrbanFilter concept which prevents tyre particles from being washed into sewers and other water sources when it rains. The sediment filters consist of nine modules, divided into three zones: the road area with a special runoff channel; the sewer where larger solids are filtered out with a filter skirt, and the drain where a magnet module is used to filter the smallest solids such as microplastics. Up to three of the nine modules (one at each level) can be combined to achieve the best result depending on the location.
Lab and road testing
Tests in the laboratory at TU Berlin have shown that without clogging, the filters can permanently trap microplastics in the form of plastic granulates up to 3mm in size. In-situ testing continues to take place on a busy road in Berlin and the UrbanFilter successfully passed its first test during a series of storms.
Some parts of the development are still presenting the researchers with problems. “A major challenge is being able to retain a wide variety of contaminants of different densities, shapes and sizes. In the event of heavy rainfall, it is particularly challenging to ensure that particles already retained are not flushed out again,” said Venghaus. Testing and development work with the UrbanFilter continues and its major goal is,“to develop a flexible filter concept from technically robust subsystems which, together with the intelligent networking of relevant data…relieve our surface waters and improve water quality.”
Microplastics in wastewater
Everyday activities such as washing clothes and using personal care products mean that microplastics enter wastewater treatment plants (WWTPs), making them the main sources of microplastic contaminants in the aquatic environment. However, they are also where efficient removal can take place.
German wastewater treatment specialist Mann+Hummel Water & Fluid Solutions (previously Microdyn-Nadir) has been working on a pilot project at a municipal sewage plant in Hünxe in North Rhine-Westphalia, Germany. It is one of four projects the company is currently involved in around the country, funded by the Department of Environment, Nature and Consumer Protection of North Rhine-Westphalia, and one of the largest wastewater providers in the country (EGLV).
All the pilot projects are investigating different applications of the BIO-CEL activated carbon process in collaboration with universities, engineering firms and utility companies.
Mann+Hummel’s BIO-CEL activated carbon process is a combination of activated carbon and immersed membrane filtration. Already a physical barrier for solids and bacteria, it also retains microplastics. Typically, WWTPs have a conventional aerated system (CAS) which consists of a mechanical treatment, a biochemical treatment and a sedimentation stage where the overflow is released to a water channel. Tobias Steube, global product manager, Life Sciences & Environment, Mann+Hummel Water & Fluid Solutions, explains the problem with microplastics: “The CAS has no physical barrier for any solids or bacteria that get through the first stage of mechanical separation. Sometimes activated carbon is used downstream but sand filters are also required and while they reduce microplastics in the effluent, costs are high for the operator.” However, “the BIOCEL activated carbon process is able to remove micropollutants, bacteria and microplastics in one process and offers a capacity increase, high saving potential and high safety standards.”
Much more to be done
These are just two of the filtration technologies currently being developed in the fight against microplastics. While the race is on for scientists to collect more data and identify the risks to human and marine health in more detail, another race is taking place within the filtration industry for more research, development and data.