Developing advanced analysis methods for the preparation, characterisation and quantification of microplastics in wastewater streams

The early 2000s saw the beginning of wastewater treatment plants (WWTPs) being seen as a potential source of microplastics (MPs) in the environment. During this time, the first study investigating the prevalence of microplastics pollution in the environment was conducted. Research into the extent of microplastics emissions from WWTPs has gained popularity over the last decade. Microplastics are known to enter living organisms, including humans, and while the toxicological mechanism of microplastics is still under investigation, microplastics are small enough to act as a vector for pathogens to enter the body and increase risk to disease.

To understand the extent of microplastics pollution and determine whether existing methodologies for the removal of microplastics from wastewater streams are suitable, accurate and consistent methods for the analysis of microplastics from major potential sources such as WWTPs is needed. Researchers in microplastics analysis recognise the importance of reliable identification, full characterisation, and accurate quantification of microplastics, and all the current available techniques have their own specific limitations. Common analytical techniques such as FTIR and Raman spectroscopies are popular for microplastics analysis, but more advanced methods are emerging as technology advances. However, the complicated nature of microplastics analysis goes beyond the instrument of choice.

Comparison across studies is made more complicated by the extensive variety in methodology for sample collection, treatment, and preparation all the way through to data processing, reporting and dissemination. The need for unified methods and standardisation is apparent and recognised across the field. The variety of methods used, from sampling to data analysis, make results difficult to compare and therefore, the extent of microplastics escaping WWTPs remains uncertain.

This project will focus on method development and validation for the accurate identification, characterisation and quantification of microplastics in wastewater. Firstly, a systematic literature review will be conducted to evaluate the current knowledge surrounding microplastics in wastewater and ascertain the extent of lack of method standardisation.

The first step of the experimental work is to evaluate the effect of different sample preparation procedures such as chemical treatment on the characteristics of model 'microplastics in wastewater' samples. Current literature-recommended methods will be used and developed to limit the impact of sample preparation on microplastics characteristics. This work will include determination of the optimal chemical or physical conditions for deactivating bacteria (a necessary step in wastewater sample treatment) without causing significant damage to microplastics. The characteristics and integrity of the samples will be determined using Fourier-Transform Infrared spectroscopy, Raman spectroscopy, and Scanning Electron Microscopy. The suitability of flow cytometry will be investigated as a quantification technique for microplastics.
Secondly, WWTP conditions will be mimicked in the laboratory, where selected parameters can be controlled and monitored to identify the specific aspects of wastewater treatment systems that have potential impacts on microplastics. Maintaining the integrity of the sample throughout the method is important for accurate identification, characterisation and quantification.

Thirdly, the optimised sample treatment methods will be applied to fully characterise and quantify microplastics in real wastewater effluent and sludge. This will be used to confirm that the methods are applicable to real life, and the results will provide further insight into the impact that WWTP systems have on the fate and prevalence of microplastics. The subsequent results can thus provide an evidence-based approach to steer future research in microplastics and WWTP systems.