Aggregation and Fouling Impacts in Determining Organic and Clay Removal by Electropositive Filtration

Abstract

Electropositive filtration (EPF) uses a macroporous filter media with a strong positive charge to achieve high separation factors for substances many times smaller than its nominal pore size; however, the variables that affect its performance are poorly understood. The objective of this work was to elucidate the significance of filter fouling and particle size in relation to electroadhesion in determining material removal by an electropositive filter. EPF performance was evaluated using humic acid (HA) and montmorillonite clay in adsorption and dead-end filtration experiments. Comparative analyses were done with a negatively charged microglass filter of similar nominal pore size. The electropositive filter had a higher selectivity for HA and clay because of favorable charge–charge interactions. HA and clay removal were governed by aggregate size and filter fouling. For the HA, accumulation of negatively charged material on the electropositive filter resulted in decreased removal as filtration progressed because of screening of the charge interactions. For the clay, rapid fouling resulted in high removal but plugging of the filter. Precoagulation resulted in optimum performance conditions—high selectivity and low headloss development.