Pretreatment by a novel photo-electro reactor to control organic and biofouling during reverse osmosis filtration of reclaimed water

Abstract

This study reports the performance of a novel photo-electro filtration (PEF) reactor consisting of an IrO2/RuO2 coated anodic filter and UV lamp to pretreat biologically treated wastewater effluent prior to reverse osmosis (RO) filtration. Synthetic model solutions and biologically treated wastewater effluent were used for systematic evaluation of the PEF reactor performance in terms of organic degradation, bacterial inactivation, biofilm formation reduction, and ultimately RO fouling mitigation. Experiments with model solutions containing proteins (Bovine Serum Albumin) and bacteria (Pseudomonas aeruginosa) show that UV irradiation and electrochemical treatment with increasing voltage input resulted in superior bacterial inactivation, biofilm formation reduction, and effective organic degradation. When the PEF reactor was used to pretreat biologically treated wastewater effluent, electrochemical treatment at 3 V alone and the combination of electrochemical treatment at 3 V and UV could achieve near complete bacterial inactivation and good fouling reduction during subsequent RO operation. However, the combination of electrochemical treatment at 3 V and UV was superior over electrochemical treatment at 3 V alone in several aspects including fouling reduction and reduced risk of membrane degradation due to chlorine residue. The underlying mechanisms responsible for effective PEF pretreatment performance were elucidated by monitoring the fate of free chlorine, hydroxyl radicals (indirectly monitored by measuring concentration of the quenching chemical N-n-dimethyl-p-nitrosoaniline), H2O2, quorum sensing signal molecules, and organic fractions during UV irradiation and electrochemical treatment. Effective bio and organic fouling mitigation by PEF pretreatment was attributed to the enhanced bacterial inactivation and degradation of organic compounds (primarily protein-like and humic-like substances) by hydroxyl radicals (∙OH) produced from photo-electrochemical treatment.