Method of monitoring and optionally controlling removal of microplastics from microplastic containing waters

A method of monitoring and optionally controlling removal of microplastics from microplastic containing water selected from raw water, drinking water, storm water, water originating from melted snow, surface water, effluent of industrial wastewater treatment plants, effluent of municipal wastewater treatment plants, industrial process water, said method comprising the steps of:

• admixing at least one coagulant and polymer to the microplastic containing water, and allowing the at least one coagulant and polymer to interact with the microplastic containing water to form flocs and/or aggregates containing microplastic particles;
• and
• removing the formed flocs and/or aggregates in a separation process to provide treated water with decreased microplastic content;
• wherein the addition amount of said at least one coagulant and polymer is controlled in relation to a predetermined reference input value;
• wherein the number of microplastic particles of the microplastic containing water before and/or after addition of said at least one coagulant and polymer is determined using an optical measurement method which measures light scattering and fluorescence of particles in a predetermined volume of the microplastic containing water, by:
• a) measuring light scattering and fluorescence of particles in said predetermined volume of the microplastic containing water before and/or after addition of said at least one coagulant and polymer,
• b) measuring light scattering and fluorescence of particles in a predetermined volume of a reference water sample comprising microplastics, before and/or after addition of said at least one coagulant and polymer, wherein said reference water sample is doped with predetermined microplastics,
• c) combining the measured light scattering intensities and fluorescence intensities of each measurement in a) and b),
• d) identifying particle populations measured which represent microplastic particle populations, and
• e) determining the number of microplastic particles in the microplastic containing water before and/or after addition of said at least one coagulant and polymer, and further wherein:
• (i) the size of the microplastic particles ranges from 0.1-100 μm;
• (ii) the coagulant is added in an amount which results in a concentration of metal derived from the coagulant in the microplastic containing water which ranges from 0.01-1.5 mmol/l;
• (iii) the amount of active polymer added to the water ranges from 0-50 mg/l;
• and
• (iv) the optical measurement is made using flow cytometry.