Real-time imaging and photocatalysis mediated biodegradability of microplastics in a continuous flow system

Project Information

RealIMP

Grant agreement ID: 101130832

DOI

10.3030/101130832

Project closed

EC signature date 29 September 2023

Start date 1 March 2024

End date 28 February 2026

Funded under

• Widening participation and spreading excellence

Total cost

No data

EU contribution

€ 156 778,56

Coordinated by

INSTITUTO SUPERIOR TECNICO
Portugal

Periodic Reporting for period 1 - RealIMP (Real-time imaging and photocatalysis mediated biodegradability of microplastics in a continuous flow system)

Reporting period: 2024-03-01 to 2026-02-28

Summary of the context and overall objectives of the project

Plastic pollution has become one of the most pressing environmental challenges of our time. Microplastics (particles smaller than 5 millimeters) are now widely detected in oceans (including the deep ocean), rivers, lakes and drinking water sources. They are highly persistent and can accumulate in ecosystems and living organisms, posing potential risks to environmental and human health. Despite growing awareness, major scientific and technological gaps remain in our ability to detect, monitor and safely remove microplastics and other contaminants of emerging concern from water.
Current methods for detecting and analyzing microplastics are time consuming and complex, requiring specialized equipment and expertise and often limited to laboratory settings. Conventional water treatment technologies are not specifically designed to degrade microplastics or address their interactions with other pollutants. These limitations hinder the development of effective and scalable solutions to protect water resources, ecosystems and public health.
The project addressed these challenges by attempting innovative approaches to detect, monitor and enhance the degradation of microplastics in water. The main objective was to establish new scientific and technological pathways for improving microplastic detection in maritime conditions and enabling their transformation into less harmful substances. To achieve this goal, the project pursued three key objectives: 1) to develop a novel imaging method based on ultrasonic acoustic sensing to detect and monitor microplastics in water under both static and continuous flow conditions; 2) to design and optimize a solar-driven photocatalytic reactor capable of operating under realistic continuous-flow conditions; and 3) to investigate how different parameters of photocatalytic reaction set-up can influence the degradation of microplastics.
Scientifically, the project aimed to assess new methodologies for monitoring and degrading emerging contaminants in aquatic environments. Technologically, it supported the development of innovative, scalable and environmentally friendly water treatment solutions that can be adapted for use in wastewater treatment facilities and other applications. At a broader level, the project aimed to contribute to European and global efforts to protect water resources, reduce pollution and promote sustainable environmental management. These advances support key European priorities, including environmental protection, technological innovation and the transition toward a more sustainable and resilient society.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Early efforts focused on using TiO2-based photocatalysts in powder form inside a custom-built 200 mL reactor inspired by membrane and moving-bed bioreactors. The design would allow water containing microplastics to circulate while retaining the catalyst. However, even at very low flow rates and with anti-clogging measures (back-pulsing), the system clogged within minutes, including when using clean water. Replacing the membrane with a sedimentation tank also failed, as the catalyst particles broke down during circulation and could no longer be separated efficiently. These results showed that slurry-based photocatalysts are impractical for continuous-flow operation at lab scale. Experiments were then conducted under real sunlight using immobilized catalysts. Results showed only limited signs of polymer chain damage and no clear evidence of chemical oxidation of polyethylene, even when hydrogen peroxide or a solar simulator was used.
The project shifted to higher-energy UV-C lamps. A 45 cm tubular photoreactor design was conceptualized but attempts to create functional TiO2 coatings on the reactor walls were repeatedly unsuccessful. A 1 L batch reactor using suspended TiO2 and UV-C light was developed. Three common plastics (polyethylene, polypropylene and PET) were exposed to treatment for over one week. The plastics had different shapes and sizes to facilitate their separation and post-treatment analysis. Polyethylene particles had an average diameter of 500 microns while polypropylene and PET pellets had average diameters of 4 and 3 mm, respectively. Thermogravimetry results had opposite responses depending on the target plastic. Different treatment methods (e.g. photolysis, photocatalysis, addition of H2O2, use of UVA instead of UVC light) showed little to no difference on degradation results. Optical microscopy revealed no visible physical changes before and after treatment apart from yellowing of polypropylene particles.
The project also explored ultrasonic sensors as a method to detect and measure microplastics in water. Signals generated by a function generator in the 500–5000 Hz frequency range were transmitted through the medium and recorded using an oscilloscope connected to receiving sensors. A tomography-inspired acoustic sensing approach was investigated by distributing transmitters and receivers in three-dimensional configurations to probe the composition and spatial characteristics of the aquatic environment. However, tests at small scale produced noisy and unreliable signals. Plastic particles tend to float and does not distribute homogenously in water. Attempts of stirring the system only increased the disturbances in the oscilloscope’s read. Alternative approaches, including enclosing particles in mesh and mapping other submerged solid objects, also yielded inconclusive results due to sensor limitations. The use of different water vessels (glass cylindrical, plastic rectangular and glass hexagonal) could not solve that issue.
Overall, these results show that photocatalysis is not currently an effective or practical solution for microplastic degradation, at least for the size of the microplastics employed photoreactor set-up and reaction conditions. The strong persistence of plastics and the technical challenges encountered highlight the need for alternative approaches and improved detection methods. A reliable and easy method for plastic detection and quantification in water could not be obtained.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project generated new knowledge on the detection and photocatalytic treatment of microplastics in water, while identifying important technical and scientific limitations that remain insufficiently addressed in the current state of the art. A key outcome was the experimental evaluation of photocatalytic reactor designs intended for continuous operation using slurry catalysts. The project identified major practical barriers, including catalyst instability (crumbling of its particles due to set-up vibrations, stirring and flow), separation difficulties and flow limitations, which prevented reliable operation at laboratory scale. These findings highlight the gap between conceptual photocatalytic systems and their practical implementation as well as the need for improved reactor design and catalyst immobilization and doping strategies.
Photocatalytic degradation experiments confirmed the high resistance of common plastics to photocatalytic oxidation. Longer exposure times and smaller plastic particle sizes would potentially lead to a more efficient photodegradation. These results provide experimental evidence of the strong persistence of microplastics and the limited effectiveness of current photocatalytic approaches, under both solar and UV irradiation, at the experimental conditions employed, regarding particle size and treatment duration.
The project also explored ultrasonic acoustic sensing as a novel multidisciplinary, ambitious and cutting-edge method for microplastic detection. Although reliable detection was not achieved at laboratory scale due to signal noise and sensitivity limitations, the work identified key technical challenges and methodological requirements for future development, including the need for improved sensor performance and larger-scale testing.