Effect of oxidation with coagulation and ceramic microfiltration pre-treatment on reverse osmosis for desalination of recycled wastewater

Abstract

Oxidation and coagulation before ceramic microfiltration (CMF) greatly increases membrane flux, but is unconventional for reverse osmosis (RO) pre-treatment. Impacts to RO and the wastewater recycling scheme operating CMF at high flux conditions is little understood. In this work, wastewater was treated with ozone or ultraviolet/hydrogen peroxide (UVH) oxidation, coagulation, then CMF, to explore RO membrane performance at bench scale. Sustainable high CMF fluxes were confirmed using coagulation with either ozone or UVH. Uniquely for ozone, dosing 13 mg-O3/L for 15 minutes greatly increased toxic by-product Nnitrosodimethylamine (NDMA) to 33 ng/L. Dosing chloramine (common for RO biofouling control) added only up to 7 ng/L NDMA. RO tests on all pre-treated waters showed little variation to flux but oxidation significantly altered texture of RO fouling material from smooth and dense to porous and granular. Biofouling studies with model bacteria strain RO 22 (Pseudoalteromonas spp) showed higher organic biodegradability but biofilm analysis 2 revealed ozone-coagulant-CMF greatly limited extension of bacteria communities from the membrane surface suggesting oxidation reduces RO biofouling. The novel findings of reduction of RO biofouling risk with oxidation and coagulation for high flux CMF pretreatment identified in this work need to be demonstrated on different wastewater types over longer term.

Comparison of the effects of ozone, biological activated carbon (BAC) filtration and combined ozone-BAC pre-treatments on the microfiltration of secondary effluent

“…The removal effect of ozone is attributed to the transformation of BPs into smaller compounds [64]. However, ozonation also reduced significant quantity of HS ( Figure 5c) which was observed in previous studies [65]. The significant removal of this fraction is believed to be due to the high aromaticity of HS [66].…”

Membrane processes

“…Myat et al. (2018) conducted a testing study to evaluate the pretreatment of oxidation and coagulation on ceramic microfiltration (CMF) and subsequently reverse osmosis (RO) in an advanced treatment train for water reuse. The use of coagulation with either ozone (O 3 ) or ultraviolet/ hydrogen peroxide (UV/H 2 O 2 ) and coagulation with poly aluminum chloride helped to sustain a high flux for the CMF and stable transmembrane pressure (TMP).…”

Online monitoring of N-nitrosodimethylamine for the removal assurance of 1,4-dioxane and other trace organic compounds by reverse osmosis

“…In particular, much of the recent attention has been given towards two specific TOrCs namely N-47 nitrosodimethlyamine (NDMA) and 1,4-dioxane. [8][9][10][11] The former is a disinfection by-product occurring ubiquitously in reclaimed wastewater, 9,12 while the latter is a common industrial 49 solvent often accidentally released into the sewer and the environment. 13 Both NDMA and 1,4-dioxane are probable carcinogens and thus are regulated in potable water reuse applications.…”