Preventing the flow of microplastics via effluent into surface water

Frank Oesterholt MSc, Patrick Bäuerlein PhD

  • Start date
  • End date
  • Principal
    Topsector Water en Maritiem
  • collaborating partners
    The Great Bubble Barrier, Hoogheemraadschap Hollands Noorderkwartier, KWR, PWN Technologies

Microplastics are small, synthetic particles that can have a big impact if they flow into large surface water bodies. Larger pieces of plastic waste cause harm to river and marine life, where for example animals mistake them for food or become tangled up in them.  The longer the plastic remains in the water, the more sunlight degrades it into ever smaller particles that can more easily be taken up in the food chain. These small plastic particles bind to organic micropollutants in the surface water and have already been detected in the food chain. Bubble Barriers could offer a solution to prevent the flow of microplastics into surface water.


The traditional wastewater treatment plants (WWTPs) remove nitrate, phosphate and suspended particles from wastewater. At this moment not much is known about the presence of microplastics in WWTP effluent. Larger pieces of plastic and other materials are filtered out from the water, but few solutions are as yet available to intercept microplastics in the water treatment, and no single solution enables the retention and removal of microplastics over the whole width and depth of wastewater.

The application of the Great Bubble Barrier is an effective way of removing macroplastics from flowing rivers and canals. The Bubble Barrier’s tube contains small holes through which air is pumped out, creating a wall of bubbles. Thanks to the river’s natural current and the diagonal positioning of the Bubble Barrier, the plastic waste is guided to the river bank. There, it can then be removed from the water, without interfering with the vessels or the fish. A similar set-up is now going to be used in Wervershoof to examine whether the barrier also has an impact on microplastics.

At different moments over the course of the project water samples will be taken at various locations, following the (adapted) measurement protocol to determine the number of plastic particles per litre, which was developed in the TRAMP-project. Based on three sub-studies, the Tramp project is mapping the extent to which Dutch inland waters are polluted with extremely small plastic particles. TRAMP is being funded by the Open Technology Programme of the NWO Domain Applied and Engineering Sciences (AES).

For this project, 600-1000 litres of water will be filtered and all particles larger than circa 10 µm, and possibly also smaller, will be intercepted. The samples will be processed as described in the TRAMP project, and then measured using an FT-IR microscope (Fourier-Transform Infrared). These measurements provide information about the number of plastic particles, the type of plastic found and its size.


The Great Bubble Barrier (TGBB), water utility PWN, PWN Technologies (PWNT), Hollands Noorderkwartier Water Authority (HHNK), and KWR Watercycle Research Institute have jointly begun a research project aimed at measuring the degree to which microplastics are present in a WWTP’s effluent, and how effectively a Bubble Barrier can prevent microplastics from being discharged with the effluent.


This research project involves three cornerstones:

  1. Determining the physical factors involved in the use of a Bubble Barrier to retain microplastics for the protection of surface water.
  2. Further developing the existing measurement method for microplastics to encompass plastic particles of 10 µm and larger, so that their presence can be better quantified. This will produce a dataset on the presence and character of microplastics in WWTP effluent.
  3. Determining the effectiveness of a Bubble Barrier in intercepting microplastics.