Removal of Disinfection By-product Precursors Using Hybrid Coagulation–Ceramic Membrane Systems

2016 © American Water Works Association JOURNAL AWWA OCTOBER 2016 | 108:10 Microfiltration (MF) membranes are low-pressure membranes that generally have pore sizes in the range of 1 to 0.1 μm. They can effectively reject bacteria, protozoa, and colloidal particles by size exclusion. The physical rejection of viruses and the dissolved fraction of natural organic matter (NOM) by MF (0.1 μm nominal pore size) is expected to be low or negligible because most of the constituents tend to be smaller than the membrane pore size (Bérubé et al. 2002). The presence of NOM can affect coagulation performance, cause color and odor problems, contribute to the fouling of membranes, increase the required effective chlorine dose, adsorb onto particles and increase their stability, provide a pathway for the transport of harmful pesticides and heavy metals, and promote microbial growth in the distribution system (Huang et al. 2009, Huang & O’Melia 2008, Bratby 2006, Edzwald 1993, Dempsey et al. 1985). Furthermore, NOM serves as a precursor for the formation of a number of disinfection by-products (DPBs), such as trihalomethanes (THMs) and haloacetic acids (HAAs). The addition of a coagulation pretreatment stage before membrane filtration has been demonstrated as an effective tool for reducing the impact of fouling agents on membrane permeability and also for increasing the removal of contaminants that are orders of magnitude smaller than the nominal pore size of the membrane (Meyn & Leiknes 2010, Huang et al. 2009, Fiksdal & Leiknes 2006, Loi-Brügger et al. 2006, Matsushita et al. 2005, Matsui et al. 2003, Bérubé et al. 2002, Judd & Hillis 2001). Howe and Clark (2006) observed a linear relationship between the reduction of membrane fouling and the reduction of dissolved organic carbon (DOC) in terms of ultraviolet absorbance at 254 nm (UV254) for three polymeric membranes with coagulation pretreatment. Farahbakhsh and Smith (2002) reported that the removal of DOC and UV254 was higher with a lower concentration of polyaluminum chloride than with aluminum sulfate. Bérubé et al. (2002) found that without coagulation pretreatment, the removal of organics and THM precursors by their investigated polymeric membranes was poor, but they concluded that a dose of 0.3 mg-Al/L was sufficient to achieve the removal of 75% organic material and THM precursors. Ceramic membranes have recently gained considerable attention from the drinking water community because they are thought to be superior in terms of structural, chemical, and thermal stability when compared with polymeric-based membranes. Consequently, ceramic membranes can be operated at higher fluxes and tolerate extreme cleaning procedures without compromising membrane integrity (Hofs et al. 2011, Mueller et al. 2010, Lehman et al. 2008, Loi-Brügger et al. 2006). However, the capabilities of ceramic membranes to meet existing US water quality standards, including organics and inorganics, are not well established. There is also a The goal of this study was to investigate the removal of organics and disinfection by-product (DBP) precursors in an optimized pilot-scale hybrid coagulation–ceramic membrane system treating two surface waters with low specific ultraviolet values (SUVA254 < 3 L/mg-m). The average removal of dissolved organic carbon was 30% with coagulation pretreatment and negligible without coagulation pretreatment. The removal of organics with coagulation pretreatment also resulted in reduction in the formation potential of haloacetic acids, trihalomethanes, and halonitromethanes in the range of 36 to 46%, 18 to 40%, and 10 to 36%, respectively. The removals of dissolved organic nitrogen, haloacetonitriles, and N-nitrosodimethylamine precursors were found to be negligible. Bromide was not removed from water, which led to an increase in the bromine incorporation factors for halogenated DBPs. The results showed that the implementation of an optimized coagulation pretreatment stage reduced the rate of membrane fouling (80 to 95%) while providing some removal (10 to 50%) of regulated halogenated carbonaceous DBPs. Removal of Disinfection By-product Precursors Using Hybrid Coagulation–Ceramic Membrane Systems