Water Research 87 (2015) 127e136 Contents lists available at ScienceDirect Water Research journal homepage: www.elsevier.com/locate/watres Effects of octahedral molecular sieve on treatment performance, microbial metabolism, and microbial community in expanded granular sludge bed reactor ** Fei Pan a, , Aihua Xu a, Dongsheng Xia a, Yang Yu a, Guo Chen b, Melissa Meyer c, * Dongye Zhao d, Ching-Hua Huang c, Qihang Wu e, Jie Fu c, a School of Environmental Engineering, Wuhan Textile University, Wuhan 430073, China b Department of Radiation Oncology, Winship Cancer Institute, Emory University School of Medicine, Atlanta, GA 30322, USA c School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA d Environmental Engineering Program, Department of Civil Engineering, Auburn University, Auburn, AL 36849, USA e Collaborative Innovation Center of Water Quality Safety and Protection in Pearl River Delta, Guangzhou University, Guangzhou 510006, China article info abstract Article history: This study evaluated the effects of synthesized octahedral molecular sieve (OMS-2) nanoparticles on the Received 18 April 2015 anaerobic microbial community in a model digester, expanded granular sludge bed (EGSB) reactor. The Received in revised form addition of OMS-2 (0.025 g/L) in the EGSB reactors resulted in an enhanced operational performance, i.e., 7 September 2015 COD removal and biogas production increased by 4% and 11% respectively, and effluent volatile fatty acid Accepted 11 September 2015 (VFA) decreased by 11% relative to the control group. The Biolog EcoPlate™ test was employed to Available online 14 September 2015 investigate microbial metabolism in the EGSB reactors. Results showed that OMS-2 not only increased the microbial metabolic level but also significantly changed the community level physiological profiling Keywords: Manganese of the microorganisms. The Illumina MiSeq high-throughput sequencing of 16S rRNA gene indicated Nanoparticles OMS-2 enhanced the microbial diversity and altered the community structure. The largest bacterial Lactic acid bacteria genus Lactococcus, a lactic acid bacterium, reduced from 29.3% to 20.4% by abundance in the presence of High-throughput sequencing 0.25 g/L OMS-2, which may be conducive to decreasing the VFA production and increasing the microbial Anaerobic digestion diversity. OMS-2 also increased the quantities of acetogenic bacteria and Archaea, and promoted the Microbial metabolism acetogenesis and methanogenesis. The X-ray photoelectron spectroscopy illustrated that Mn(IV)/Mn(III) with high redox potential in OMS-2 were reduced to Mn(II) in the EGSB reactors; this in turn affected the microbial community. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction et al., 2015), catalytic combust exhausts (Wang et al., 2015), and remediate contaminated soil (Xie et al., 2014). However, with the Nanoparticles (NPs) have been increasingly applied in industries increasing uses of nanotechnology, more and more man-made NPs such as manufacture, medical devices and diagnostics, construc- are released into our atmosphere, soil, or water environments tion, electronics, and water/wastewater treatment (Meyer et al., during their life-time. Consequently, this has caused a heated 2009; Reinhart et al., 2010; Yang et al., 2013). Their excellent debate on the environmental and health risks of engineered NPs in physiochemical properties can be attributed to their high surface- the environment (Hristozov and Malsch, 2009). to-volume ratio. Among these NPs, metallic/metal oxide NPs have NPs can reach the wastewater treatment plants (WWTPs) been some of the most important materials. In environmental ap- through discharges from industrial plants and from various con- plications, these NPs have been employed to treat wastewater (Luo sumer products. In typical secondary biological wastewater treat- ment processes, most of the NPs are associated with the biomass. For example, a mass balance for metallic silver NPs (Ag-NPs) in a * Corresponding author. Daniel Lab 304, School of Civil and Environmental En- WWTP indicated that more than 95% of the entering Ag-NPs were gineering, 200 Bobby Dodd Way NW, Atlanta, GA 30332, USA. sequestered into the wastewater biomass and removed along with ** Corresponding author. 1 Fangzhi Rd, Wuhan 430073, China. biomass sedimentation from the effluent stream (Shafer et al., E-mail addresses: [email protected] (F. Pan), [email protected] (J. Fu). http://dx.doi.org/10.1016/j.watres.2015.09.022 0043-1354/© 2015 Elsevier Ltd. All rights reserved. 128 F. Pan et al. / Water Research 87 (2015) 127e136 1998). Metallic/metal oxide NPs can affect the microorganisms and microbial ecosystems in WWTPs due to their various nano-toxic effects. The antimicrobial mechanisms of metallic/metal oxide NPs include cell membrane disruption (Lee et al., 2008), release of metal ions (Li et al., 2008), and generation of oxidative stress (e.g., reactive oxygen species, ROS) (Xia et al., 2008). Typically, the aerobic biological treatments (e.g., activated sludge and membrane reactor) are the dominant processes in WWTPs. The impacts of metallic/metal oxide NPs on aerobic pro- cesses have been well studied, and the most investigated NPs are Ag-NPs (Choi et al., 2008), nano-ZnO (Zheng et al., 2011), nano-TiO2 (Xia et al., 2006), and nano-zero valent iron (NZVI) (Lee et al., 2008). Due to the growing need for sustainable energy, anaerobic treat- ment has been rapidly developed and applied in past 20 years, of which anaerobic granular sludge (AGS) reactors have been widely used (Rajeshwari et al., 2000). Upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors are the most popular AGS reactors and employed to treat different types of organic wastewater, such as food, beverage, and pulp and paper industry wastewater (van Lier, 2008). Recent research found that NZVI can increase the rate of anaerobic granulation and organic removal in a UASB reactor treating coking wastewater (Liu et al., 2011). Mu and coworkers indicated a high dose of nano-ZnO (>100 mg/g-TSS) decreased the productions of extracellular poly- Fig. 1. Schematic diagram of the expanded granular sludge bed (EGSB) reactor device. 1 feed tank, 2 peristaltic pump, 3 reactor, 4 circulating pump, 5 water bath tank, 6 re- meric substances (EPS) and methane in the UASB reactor (Mu et al., circulating pump, 7 sampling ports, 8 water-sealed bottle, and 9 wet gas flow meter. 2012). However, the impacts of diverse NPs on anaerobic digestion are still largely unknown and the effects of metallic/metal oxide NPs on the anaerobic microbial metabolism and communities shows the schematic diagram of an EGSB reactor. The reactor was remain unexplored. made up of a plexiglass column with an internal diameter of The octahedral molecular sieve (OMS-2) is a form of manganese 70 mm, an overall height of 850 mm, and an effective volume of dioxide having a tunnel size of 0.46 nm  0.46 nm (Ding et al., 3.6 L. The exterior of the reaction zone was coated with a water 2005). OMS-2 NPs exhibit unique features like mixed-valence of jacket and the top of the reactor was equipped with a settling manganese (Mn) and acidic sites, and have extensive applications chamber and a three-phase separator. The EGSB reactor was (Luo et al., 2015; Suib, 2008). However, the potential health risks operated under the mesophilic conditions (approximately 35 C) and environmental impacts of OMS-2 are unknown. The dissimi- and its temperature was maintained by circulating the warm water latory Mn reduction is known to promote the growth of several through the reactor jacket. The influent wastewater entered the microorganisms in anaerobic environment (Nealson and Saffarini, reactor from the bottom via a peristaltic pump. A part of the 1994). The redox circle between different Mn species in OMS-2 effluent returned to the bottom of the reactor by a re-circulating may provide some benefits for the anaerobic microbial community. pump and the other part was discharged through the overflow. A This study aimed to test the effect of synthetic OMS-2 NPs on the liquid upflow velocity of 3.0 m/h was maintained. The produced gas operational performance of the EGSB reactor by evaluating the was separated by the three-phase separator and determined by a chemical oxygen demand (COD) removal, biogas production, and wet gas flow meter. the effluent volatile fatty acid (VFA) concentration. We employed the Biolog EcoPlate™ test (Garland and Mills, 1991) to distinguish 2.3. Inoculated sludge and synthetic wastewater spatial and temporal changes in microbial metabolism. The high- throughput microbial community analysis was further carried out The inoculated sludge, taken from the anaerobic digester of the on the Illumina MiSeq platform. The information will aid in our sewage treatment plant in Wuhan Textile University (Wuhan, understanding of the NPs' effects and the action mechanisms on China), had a grain size of 0.6e2.0 mm, volatile suspended solids anaerobic microorganisms and the digestion process. (VSS) of 7.4 g/L, and suspended solids (SS) of 11.75 g/L. The influent organic wastewater was synthesized using the following stock so- 2. Materials and methods lution: sucrose 90 g/L, NH4HCO3 14.1 g/L, KH2PO4 0.97 g/L, K2HPO4$3H2O 1.62 g/L, and NaHCO3 33.3 g/L. The chemical oxygen 2.1. Preparation of OMS-2 demand (COD) of the stock wastewater was approximately 100 g/L. OMS-2 was synthesized by a reflux method, which has been 2.4. Operation scheme reported elsewhere (Luo et al., 2015). The details in synthesis and characterization of OMS-2 are described in Text S1 and Fig. S1 of Before experiments, the stock wastewater was diluted to the Supporting information (SI). desired concentration of COD and appropriate amounts of trace elements were added, including the following chemicals (all in mg/ 2.2. Experimental setup L): H3BO3 100, CuSO4$5H2O 58, ZnSO4$7H2O 100, NiSO4$6H2O112, MgSO4$7H2O 5000, FeSO4$7H2O 750, yeast 3000, MnSO4$H2O 188, Four groups of EGSB reactors (G1eG4, each group had two NaMo7O24$2H2O 50, CaCl2$2H2O 7500, and FeSO4$7H2O 50.