(101e) Efficacy of Membrane Bioreactor Process Combined With Advanced Oxidation Processes for Organic Removal in Water Reclamation and Reuse

Authors: 
Ravindran, V., University of Southern California
Kim, W., University of Southern California
Pirbazari, M., University of Southern California



An increasing number of public owned wastewater treatment and water reclamation utilities and several municipalities have recognized the importance of recycled water as a new water source, particularly in arid areas of the United States.  These utilities have developed a wide variety of options for water reuse, and have considered water recycling water for indirect potable reuse, or discharge into surface waters or infiltration into subsurface environments for augmenting potential water supply sources. They have considered membrane technologies such as microfiltration (MF) followed by nanofiltration  (NF) or reverse osmosis (RO) for this purpose.  In the present context, our study compares the performance of membrane bioreactor (MBR) process using ultrafiltration (UF) membranes integrated with the application of powder activated carbon (PAC) as adsorbent.

            The major concerns of the U.S. Environmental Protection Agency and local regulatory agencies are health problems arising from the introduction of pathogens (protozoa, bacteria, viruses and other parasites), anthropogenic organic or inorganic chemicals into groundwater or surface water sources.  Additionally, organic matter  or natural organic matter (NOM) already present in drinking water or those formed during wastewater treatment due to decomposition of organic matter could significantly affect water quality in terms of dissolved organic carbon (DOC) concentrations, or can act as precursors to the formation of disinfection byproducts (DBPs) such as trihalomethanes, haloacetic acids, aldehydes, ketones and others, many of which are well known carcinogens.  Therefore, the proposed environmental regulations in the State of California (more stringent than those of the US EPA) include a goal of achieving TOC levels not exceeding 1 mg/L originating from reclaimed waters.

            The purpose of this study was to evaluate the performance of the MBR process regarding the fate of organics in the treated effluent, when reclaimed water is used as the feed.  The intention was to compare the performance of the MBR system (using the UF membrane) with those of  other advanced membrane treatment systems such as  NF or RO processes,  that have been reported in several earlier studies.  The present work considered the application of advanced oxidation processes (AOPs) such as ozonation, ozone-hydrogen peroxide oxidation and UV-hydrogen peroxide oxidation to render the organic matter more easily amenable to biodegradation in the MBR system.  These evaluations also included the evaluation of permeate fluxes and effluent quality pertaining to the MBR system.

            Extensive characterization of organics (or DOC) in the reclaimed water and the treated effluent (MBR) effluent was necessary for the following reasons.  Quality issues for residual compounds arise from their resistance to sorption and biodegradation.  Some of these organic constituents exhibit potentials for forming DBPs during disinfection.   Hydrophilic constituents are poorly sorbed on adsorbents and cannot be easily removed.  Large molecular weight compounds are resistant to degradation, while low molecular weight compounds and polar compounds are sometimes not well rejected during membrane filtration (NF or RO processes), and some have significant health concerns. Hence RO filtration and size fractionation using resins is important for organics classification.  

            The organics characterization strategies  require state-of-the-art analytical techniques including chromatographic and spectroscopic methods.  These techniques focused on several aspects including the bulk organic carbon characteristics including hydrophobicity/hydrophilicity, molecular weight or size distributions, elemental analysis, organic carbon functional groups, potential formation of trace organics and DBPs, and identification of fluoropores.  The gas chromatography/mass spectrometry (GC/MS) analysis provided the qualitative and quantitative assessments of the trace organics and DBPs present.  The RO filtration and resin adsorption methods determine the hydrophobicity and polarity of the constituents. The size exclusion chromatography (SEC)  methods provided details on molecular weight and size distributions of the product, while the carbon-13 nuclear magnetic resonance spectroscopy (13C-NMR) after size separation techniques showed the functional group characteristics of the DOC as well as their polar and non-polar fractions. The UV absorbance (UVA) measurements provide information on the natural of NOM present and the types of products formed after the application of AOPs.   These advanced techniques for organics characterization provided an in-depth evaluation of the MBR system with reference to the effluent characteristics and removals of various organic constituents.

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