(663b) Integrated Membrane Bioreactor Process for Water Reclamation and Groundwater Recharge Applications

Among various technologies, integrated systems such as membrane bioreactor (MBR) processes have shown excellent potential for water reclamation, water reuse, groundwater recharge, and similar applications. Superior membranes with better aqueous transport and anti-fouling characteristics can make the technology more efficient and economical. In fact, they can significantly reduce energy costs that constitute a substantial fraction of total operation costs. The continuous flow hybrid MBR system offers several technical advantages over conventional biological processes in environmental applications:  small size or footprint requirements for reactor systems, long solids retention times, and efficient retention of particulates, colloids, contaminants and microorganisms. The application of an adsorbent such as powder activated carbon (PAC) will defoul the membranes and maintain high permeate fluxes. An added advantage will be the ability of the PAC adsorbent to remove most trace-level or residual micro-pollutants during water reclamation.  The micro-pollutants often include many endocrine disrupting chemicals (EDCs) such as pharmaceutical and personal care products (PPCPs), pesticides, and toxic heavy metals.

The treated effluent from such hybrid MBR processes must be generally low in suspended solids, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC) and most pathogens, and must be so as to meet groundwater recharge requirements. Water reclamation for reuse and  groundwater recharge requires that tertiary treatment standards for various components be met, that can be briefly summarized as follows: (i) virus removal or inactivation must exceed  5 logs; (ii) total coliform levels  must be below  2.2 coliforms/100 mL; (iii) turbidity must be below 2 NTU; (iv) TOC concentrations must not exceed 0.5 mg/L (of wastewater origin); (v) organic and inorganic contaminants must meet drinking water maximum contaminant levels (MCLs) (specified by the United States Environmental Protection Agency and/or the State Water Quality Control Board); (vi) lead and copper concentrations must conform to actions levels, and (vii) nitrate limits are based on the treatment technology. The general belief is that these standards could be achieved with high efficiency and favorable economics by the MBR technology using hollow fiber ultrafiltration (UF) membranes instead of employing more energy intensive processes such as nanofiltration and reverse osmosis.

The purpose of this study is to evaluate the performance of the MBR process in the tertiary treatment of reclaimed wastewater obtained from a wastewater treatment plant after secondary treatment.  The study investigates the evaluation for characteristics of polyether sulfone (PES) UF hollow fiber membrane by measuring permeate flux patterns and organic removal measured in terms of TOC and ultraviolet absorbance at 254 nm (UV₂₅₄). The work also includes membrane fouling studies to evaluate the effect of surface fouling and internal pore fouling attributable to organic fouling. The influence of advanced oxidation processes (AOPs) such as ozonation and ozone/hydrogen peroxide oxidation on membrane fouling is also evaluated. A major concern is the influence of AOPs on the TOC removal by the membrane as well as on the permeate flux under different oxidation conditions.  Under the influence of AOPs organic molecules are broken down into smaller fragments, due to free-radical reactions mostly pertaining to the hydroxyl radical. The fragmentation of organic molecules generally leads to the formation of more hydrophilic products. It is possible that pretreatment the application of AOPs may lower the surface fouling due to sorption and consequently lead to lower organic rejection. However, the smaller fragments have a larger propensity to pass through the membrane pores, causing marginally greater internal pore fouling and slightly reducing the permeate flux. These mechanistic aspects attributed to the breakdown of organic molecules by AOPs will be discussed. The study also investigates the effect of PAC at different concentration levels (ranging from 40 to 100 mg/L) on the organic removal and the control of permeate flux decline due to organic and biological fouling. The work further evaluates the effect of biofilm formation on the membrane at different concentration of Escherichia coli (E.coli) with regard to TOC removal and permeate flux decline pattern. Additionally the study also evaluates the use of membrane cleaning strategies using caustic cleaning for permeate flux recovery. Most importantly, the study also provides a comprehensive understanding of flux decline and TOC removal patterns under the influence of PAC with E. colias well as those of AOPs.

Note: Corresponding author is Professor Massoud Pirbazari, pirbazar@usc.edu, 213-740-0592.