Parameter optimization and design aspect for electrocoagulation of silica nano-particles in wafer polishing wastewater

Abstract

A systematic procedure has been proposed for the design of a multi-channel, continuous-flow electrocoagulation reactor of mono-polar configuration for the removal of sub-micron particles from wastewater. Using the chemical-mechanical-planarization (CMP) process as the target source of wastewater, a series of laboratory-scale studies were conducted to determine the required operating conditions for the efficient removal of the ultrafine particles. These operating criteria included charge loading ( >= 8 F m(-3)), current density ( >= 5.7 A m(-2)), hydraulic retention time ( >= 60 min), as well as the initially operational pH (7 similar to 10). Furthermore, a steady-state transport equation with second-order reaction kinetics was employed to describe the rate of coagulation as the rate-limiting factor, The actual kinetic constant determined from the laboratory-scale experiments was approximately 1.2 x 10(-21) m(3) s(-1), which was three orders of magnitude smaller than that calculated based on Brownian diffusion during the coagulation. The model was subsequently validated with a series of experiments using a pilot-scale electro-coagulation reactor geometrically similar to the laboratory-scale reactor with nearly twenty times volumetric scale-up.