Monitoring the removal of 1-µm Microplastics and Bacteria from secondary-treated wastewater in Spent Coffee Ground Biochar columns with Flow Cytometry

This study investigates the influence of pyrolysis temperature on spent-coffee-grounds biochar’s surface and chemical characteristics and its impact on the removal of small microplastics (1 µm), a size range challenging to both capture and measure with conventional systems. High-throughput flow cytometry was used to rapidly and accurately quantify traceable 1-µm microplastic spikes, alongside enumerating stained bacterial cells naturally present in secondary-treated wastewater. Filtration column tests at a flow rate of 1 mL/min were performed, with effluent samples collected every 2 min for a real-time analysis of microplastics and bacteria removal. Biochar produced at 500˚C exhibited the highest removal capacity, with almost no microplastics detected after filtration tests and over 50% of bacteria retained. In contrast, 300˚C biochar showed the lowest removal efficiency for both microplastics and bacteria, while 700˚C biochar demonstrated intermediate performances.