Handles to determine the occurrence of microplastics in the urban water cycle

Our knowledge about the number and types of microplastics (MP) in the freshwater environment is fragmentary. Svenja Mintenig’s recently completed doctoral research throws light on the determination of the occurrence of MP in the urban water cycle. ‘More precise information about MP types and concentrations is required to assess the hazard they represent, trace their origins, and control the sources’, writes Mintenig in her dissertation.

Svenja Mintenig studied the analytical requirements for the identification of micro- and nanoplastics.

Micro- and nanoplastics

Mintenig studied the analytical requirements for the identification of micro- and nanoplastics. The researcher then applied these findings in two field studies. At several WWTPs that discharge into the Meuse and Dommel rivers, Mintenig determined the identity and number of MP in the effluent, and how their concentrations changed in time and space. Twenty-six polymer types were identified. The greatest diversity was seen in the smallest size class. The MP concentrations at practically all the sampling locations were under the threshold values, at which adverse ecological effects are expected.

Three drinking water treatment techniques tested

Mintenig also used experimental simulations to investigate whether nanoplastics (NP) can be removed from surface water by current drinking water treatment techniques. She focused on three commonly used techniques: coagulation-flocculation-sedimentation (CFS), rapid sand filtration and granular activated carbon (GAC). All of the tested techniques are able to partially remove NP of 50 to 200 nm with variable surface charges from the surface water.  Rapid sand filtration was the least effective in removing plastic particles. CFS was the most efficient technique for the larger NP (>200 nm), while smaller NP (50 nm) are better removed by GAC filtration. The total removal percentage was considerable.

All of the tested techniques are able to partially remove NP of 50 to 200 nm with variable surface charges from the surface water.

Clearer picture needed

Drinking water treatment plants in the Netherlands employ different treatment processes. For this reason, Mintenig expects that a large portion of the NP are removed from the surface water during drinking water production. However, she does not rule out that a portion of these plastic particles might remain behind in the drinking water. Further research is therefore needed to gain a clearer picture of the NP removal percentages so that human exposure to them is minimized as much as possible.