Pre-chlorination effects on fouling during microfiltration of secondary municipal wastewater effluent

Abstract

Chlorination-induced changes in the physicochemical characteristics of effluent organic matter (EfOM) and their role in fouling of hollow fiber polyvinylidene fluoride (PVDF) microfiltration membranes during wastewater reclamation was mechanistically investigated. Pre-chlorination strongly influenced pressure rise during constant flux forward filtration as well as hydraulically irreversible fouling by backwashing with low doses exacerbating it and high doses alleviating it. Dose-dependent fouling trends originated from alterations in EfOM size and polarity and consequently its interactions with the membrane based on whether applied chlorine concentrations were above or below a threshold value. Variations in macroscopic phenomena such as sorption tendency, streaming potential, and initial fouling upon exposure to pre-chlorinated EfOM were consistent with favorable adhesion energies calculated using the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. Progressive fouling even though XDLVO theory predicted unfavorable EfOM-EfOM cohesive energies under all chlorination conditions demonstrated that hydrodynamics (permeation drag) dominated later stages of fouling. EfOM in the raw wastewater was largely deposited on the membrane surface resulting in compressible cake filtration. In contrast, pre-chlorination fragmented EfOM leading to intrapore fouling (standard blocking) at the beginning stages of filtration later transitioning to surface fouling (intermediate blocking).