ADVANCED OXIDATION PROCESSES: ASSESSMENT OF NATURAL ORGANIC MATTER REMOVAL AND INTEGRATION WITH MEMBRANE PROCESSES

Abstract

Stringent water quality regulations and general aesthetic issues have urged drinking water industry to apply advanced water treatment technologies that can meet multiple treatment objectives. Removal of significant amount of natural organic matter (NOM), including colour causing organics, to meet stringent disinfection by product (DBP) regulations from source water with low alkalinity and low turbidity is very challenging with conventional water treatment processes. Membrane filtration processes are effective in removing significant amount of NOM thus minimizing the formation of carcinogenic DBPs. However, fouling of membrane is a major problem affecting system performance. Improved pretreatment of feed water helps reduce or eliminate membrane fouling.

This study characterized source water, examined fouling in nanofiltration (NF) membranes and explored various pretreatment options to reduce NF fouling. Resin fractionation was performed to characterize NOM and to identify the major fractions responsible for DBP formation in natural source water of the Tatamagouche water treatment plant (WTP) in Nova Scotia. The source water primarily comprised of hydrophilic neutrals (HIN) and hydrophobic acid (HOA) compounds, with the latter being a major contributor to the DBP formation. Fouling behaviour of the NF membranes was examined at bench- and full-scale levels to understand the impact of source water quality on membrane fouling in the Tatamagouche and Collins Park WTPs. Bench- and full-scale results revealed higher fouling in the Collins Park WTP which together supported ongoing membrane cleaning practices in the plant. Surface enhanced Raman spectroscopy (SERS), demonstrated here as a novel technique, suggested that carbohydrates and proteins are the main foulants in the source water. Bench-scale experiments conducted to evaluate the performance of ozone (O3), ultraviolet (UV), hydrogen peroxide plus ozone (H2O2/O3), H2O2 plus UV (H2O2/UV) and O3 plus UV (O3/UV) for reducing NOM and DBP precursors suggested that the O3/UV AOP offers the optimum reduction of NOM. Integrating AOP pretreatments with NF membrane resulted in an improved permeate flux but not permeate quality of the NF membrane.