Designing a Robust Lab Scale Electrocoagulation Reactor For Removal of Micro- and Nanoplastics from Drinking Water

The widespread occurrence of micro and nanoplastics in drinking water sources could cause serious public health issues. These plastics particles, products of industrial operations and weathering of larger plastics, can interact with other contaminants in the environment, leading to more severe environmental pollution. Present drinking water treatment technologies were designed to remove suspended colloids. However, due to the distinct chemical and physical properties of micro and nanoplastics from conventional colloids, it is challenging for traditional chemical coagulation/flocculation/sedimentation process to achieve satisfying removal performance. This report investigates a design of a lab-scale electrocoagulation reactor for the removal of nanoplastics from drinking water sources. Synthesized polystyrene nanoplastics (246.50 ± 16.12 nm, spheres) were added to a 200 ml solution of 5 mM sodium chloride to a concentration of 1.585 mg/l. Electrode holders, printed in 3D using acrylonitrile butadiene styrene (ABS) filament (1.75 mm), were specifically designed, and made with an adjustable bar to hold the electrodes in precise, measurable vertical positions. A DC power supply and multimeter were used for precise voltage and current control during electrocoagulation. Two aluminum plates with an active surface area of 1.0 x 10-3 m2 were used as the electrodes. The design was tested under a constant voltage (5 V) but varying currents (10 mA, 25 mA, and 50 mA). After 2 hr electrocoagulation and 2 hr settling, the concentration of nanoplastics in the water column was determined using a turbidity meter. Electrocoagulation reduced the nanoplastics concentration by 83.6 %, 90.8 % and 93.9 % (n=3 x 3 trials for each current) with a current of 10 mA, 25 mA, and 50 mA, respectively, without the addition of a flocculant or coagulant. The impact of current was statistically significant. It was also observed that the pH increased in the solution from 5.5 to a stable pH of 8.3, which facilitates aluminum hydroxide formation for removal of the nanoplastics through hetero aggregation. The distribution of nanoplastics in the produced foam and the settled phase were also determined, and mass balance analysis on total nanoplastics were performed. While the volume of foam produced correlated with the current intensity, nanoplastic content in foam increased first then appeared to reach a peak. The mass balance performed across the systems with different currents recorded an average percentage recovery of 114 ± 2.2 (std error). These findings demonstrate that electrocoagulation can be employed for removing nanoplastics from drinking water sources. This study lays the groundwork for the systematic evaluation of the impact of different water chemistries (different ionic strengths, concentration and types of dissolved organic matter, pH buffering capacity) and different plastic type (size, shape, and surface morphology) on the effectiveness of electrocoagulation. Future studies will aid in process scale up and further improving drinking water safety addressing this crucial environmental and public health problem.