Simultaneous Bioreduction of Multiple Oxidized Contaminants Using a Membrane Biofilm Reactor Haixiang Li 1,2 , Hua Lin 1 , Xiaoyin Xu 2 , Minmin Jiang 2 , Chein-Chi Chang 1,3* , Siqing Xia 2* ABSTRACT: This study tests a hydrogen-based membrane biofilm reactor (MBfR) to investigate simultaneous bioreduction of selected oxidized contaminants, including nitrate (NO  3 -N), sulfate (SO 2 4 ), bromate (BrO  3 ), chromate (Cr(VI)) and para- chloronitrobenzene (p-CNB). The experiments demonstrate that MBfR can achieve high performance for contaminants bio- reduction to harmless or immobile forms in 240 days, with a maximum reduction fluxes of 0.901 g NO  3 -N/m 2 d, 1.573 g SO 2 4 /m 2 d, 0.009 g BrO  3 /m 2 d, 0.022 g Cr(VI)/m 2 d, and 0.043 g p-CNB/m 2 d. Increasing H 2 pressure and decreasing influent surface loading enhanced removal efficiency of the reactor. Flux analysis indicates that nitrate and sulfate reductions competed more strongly than BrO  3 , Cr(VI) and p-CNB reduction. The average H 2 utilization rate, H 2 flux, and H 2 utilization efficiency of the reactor were 0.026 to 0.052 mg H 2 /cm 3 d, 0.024 to 0.046 mg H 2 /cm 2 d, and 97.5% to 99.3% (nearly 100%). Results show the hydrogen-based MBfR may be suitable for removing multiple oxidized contaminants in drinking water or ground- water. Water Environ. Res., 89, 178 (2017). KEYWORDS: Oxidized contaminants, bioreduction, membrane biofilm reactor (MBfR), hydrogen. doi:10.2175/106143016X14609975746686 Introduction In recent years, several oxidized compounds including nitrate (NO 3 - -N), sulfate (SO 2 4 ), bromate (BrO  3 ), para-chloronitro- benzene (p-CNB), and chromate (Cr(VI) as CrO 2 4 ) have emerged as serious drinking water or groundwater contami- nants. Nitrate and sulfate are common oxidized contaminants in surface water or groundwater, and concentrations of nitrate and sulfate have reached 0.5 to 70mg N/L and 4 to 100 mg SO 2 4 in some lakes, rivers, and wells (Almasri, 2007; Showers et al., 2008; Liu and Lu, 2008; Fu and Jin, 2009). Bromate can form directly in drinking water via a molecular ozone pathway by oxidation of bromide to hypobromite. Following ozonation, bromate concentrations in potable waters typically range from 0.4 to 60 lg/L (Butler et al., 2005). In China, p-CNB was detected in many surface waters, and reached concentrations of 0.005 to 3.7 mg/L in lakes and rivers close to chemical factories (Li et al., 2014). In the natural environment, chromate concentration was approximately 1–40 lg/L. However, Cr(VI) compounds were frequently present in surface water or groundwater at relatively high concentrations because of widespread use of chromate in industries (Chung et al., 2006). These contaminants are of wide concern because of their potential risk for human health. Although nitrate and sulfate have caused long-standing water quality problems, the other compounds are considered emerging contaminants. Therefore, the maximum contaminant levels (MCL) for drinking water are 10 mg NO  3 -N/L, 250 mg SO 2 4 /L, 10 lg BrO  3 /L and 50 lg Cr(VI) /L (CMH, 2006). The p-CNB concentration in drinking water supply source is regulated at 50 lg/L in China (CMH, 2001). In many cases, two or more of the oxidized contaminants occur together, and several technologies can treat them. Some advanced separation treatment processes, such as reverse osmosis, ion exchange, and membrane filtration are effective, but are expensive and generate secondary pollutants that require subsequent disposal (Lee et al, 2011; Li and Zou, 2011). Biological reduction to harmless or immobile forms may be a desirable outcome to detoxify or remove all of the oxidized contaminants together. For example, NO  3 -N, SO 2 4 and BrO  3 can be reduced to N 2 ,S 2  , and Br  ; while reduction of CrO 2 4 can lead to insoluble Cr(OH) 3 which can be removed by filtration (Nerenberg and Rittmann, 2004). Anaerobic microbial reduction is an important transformation pathway for p-CNB 1 Collaborative Innovation Center for Water Pollution Control and Water Safety in Karst Area, Guilin University of Technology, Guilin, China. 2 State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, China. 3 Department of Engineering and Technical Services, District of Columbia Water and Sewer Authority, Washington, D.C. * Collaborative Innovation Center for Water Pollution Control and Water Safety in Karst Area, Guilin University of Technology, Guilin 541004, China; e-mail: chang87@gmail.com. * State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092; e-mail: siqingxia@tongji.edu.cn. 178 WATER ENVIRONMENT RESEARCH  February 2017