Water Research 150 (2019) 340e348 Contents lists available at ScienceDirect Water Research journal homepage: www.elsevier.com/locate/watres Bioenergy generation and degradation pathway of phenanthrene and anthracene in a constructed wetland-microbial fuel cell with an anode amended with nZVI * Junfeng Wang a, Xinshan Song b, , Qusheng Li a, Heng Bai b, Congyun Zhu a, Baisha Weng c, Denghua Yan c, Junhong Bai d a School of Environment, Jinan University, Guangzhou, 510632, Guangdong, China b College of Environmental Science and Engineering, Donghua University, Shanghai, 201620, China c China Institute of Water Resources and Hydropower Research, Beijing, 100038, China d School of Environment, Beijing Normal University, Beijing, 100875, China article info abstract Article history: The frequent occurrence of polycyclic aromatic hydrocarbons (PAHs) in aquatic environments is of great Received 21 July 2018 concern because of their teratogenicity, toxicity, carcinogenicity, and mutagenicity to plants, animals and Received in revised form human beings. In this study the bioelectricity generation, biodegradation, phytoextraction and substrate 12 November 2018 adsorption of phenanthrene and anthracene in a constructed wetland-microbial fuel cell (CW-MFC) were Accepted 27 November 2018 investigated with an anode electrode amended with or without biochar-nZVI. During a 182-day oper- Available online 30 November 2018 ation period, the average removal efficiency for phenanthrene and anthracene ranged from 88.5% to 96.4%. The concentration of phenanthrene in roots, stems and laminas of T. orientalis was 14.9, 3.9 and Keywords: À1 À1 Polycyclic aromatic hydrocarbons 2.3 ng g respectively, while that of anthracene was 22.2, 3.1 and 1.3 ng g , respectively. In addition, the Bioelectricity generation application of nZVI was conducive to bioelectricity generation and organic compound degradation in the Phytoextraction and phytotransformation CW-MFC reactor. The distribution of the bacterial community indicated that the relative abundance of Nitrogen removal Bacillus, Paludibacter, Desulfovibrio and Lactococcus with a degradation capability for refractory organics Bacterial community distribution was significantly increased. Especially the genus Bacillus for excreting catalase became more abundant. The results of our study indicate how to promote bioelectricity generation and biodegradation of re- fractory organic compounds in a CW-MFC by improving the culture conditions for bacteria. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction the requirements of environmental protection under natural con- ditions (Haritash and Kaushik, 2009; Wild and Jones, 1995). In Polycyclic aromatic hydrocarbons (PAHs) occur frequently in addition, different congeners of the same group (PAHs) can interact aquatic environments such as surface and ground water and even with each other, consequently, reduce their removal efficiency (Lei in effluents of wastewater treatment plants (WWTPs) (Hamdan et al., 2007). Therefore, developing efficient methods to control PAH et al., 2017). Although the concentrations of these compounds are pollution in aquatic environments is an important issue for envi- À À at trace level (ng L 1 to mgL 1)(Qi et al., 2013), they are considered ronmental protection. to pose a serious threat on plants, animals and humans (Goldman A constructed wetland-microbial fuel cell (CW-MFC), which et al., 2001; Paskova et al., 2006). Hence, PAHs are of increasing utilizes natural processes to generate bioelectricity and promotes concern because of their teratogenicity, toxicity, carcinogenicity, the removal efficiency of contaminants within a controlled envi- and mutagenicity (Haritash and Kaushik, 2009; Yu et al., 2017). ronment, has been considered to be a low-cost, easily to maintain Owing to their persistence and stability, the process of volatiliza- and environmentally friendly technology for wastewater treatment tion, chemical oxidation, and photo-oxidation usually do not meet (Wang et al., 2016; Yadav et al., 2012). There are many successful tests using a CW-MFC for the biodegradation of azo dye products and swine slurry remains (Doherty et al., 2015a; Fang et al., 2015). Although these work have demonstrated that the use of a CW-MFC * Corresponding author. fi fi E-mail address: [email protected] (X. Song). can signi cantly enhance the removal ef ciency of contaminants by https://doi.org/10.1016/j.watres.2018.11.075 0043-1354/© 2018 Elsevier Ltd. All rights reserved. J. Wang et al. / Water Research 150 (2019) 340e348 341 oxidation coupled with electron transfer to the anode by an 2.2. Reactor construction, inoculation and operation adapted microbial population (Doherty et al., 2015b). The effect of these factors on the removal performance of PAHs by a CW-MFC has The schematic diagram of a CW-MFC reactor (height 52 cm; never been reported. In addition, most of the reported work on CWs internal diameter 16 cm; material polyvinyl chloride) is shown in for PAH treatment is related to the removal efficiency of these Fig. 1. Foamed nickel (FN), foamed nickel amended with nZVI (FN- contaminants. Since CWs comprise of water, plants, substrate and nZVI), carbon fiber felt (CFF) or carbon fiber felt amended with nZVI microorganisms, it is essential to achieve a comprehensive under- (CFF-nZVI) were selected as anode materials. The cathode materials standing of the mechanisms involving phytoextraction, phyto- were similar with to corresponding anodes without any emenda- transformation, substrate adsorption and biodegradation in CWs tion. The diameter of each electrode was 10 cm and the weight of during wastewater treatment. Biochar-Mt-nZVI in the FN-nZVI and in the CFF-nZVI reactor was In a CW-MFC the metabolic functions of microorganisms play an 3.2 g. The distance of the electrodes was 35 cm. They were con- important role in contaminant removal and electron transfer. It has nected with an external electrical resistor (1000 U). All units were been shown that the increase of the abundance of electrochemi- filled with uniform quartz sand with an average particle size of cally active bacteria (EAB) like Pseudomonas, Dechloromonas, Rho- 2e4 mm and a porosity of 29.2%. After macro-nutrients and dopseudomonas or Desulfuromonas may result in an enhancement Hoagland's trace elements had been added for one month, Typha of bioelectricity generation in a CW-MFC (Corbella et al., 2015; orientalis (T. orientalis) was respectively planted into the CW-MFCs Wang et al., 2016). In addition, many studies demonstrated that the with an initial density of 6 plants per unit. The CW-MFC were bioenergy output from MFCs with mixed microbial cultures is inoculated with a volume of 2.0 L active sludge, collected from a higher than the one with pure cultures (Nevin et al., 2008; Rabaey wastewater treatment plant in Shanghai Songjiang area, which has and Verstraete, 2005). One possible cause may be that synergistic been diluted with tap water. Synthetic municipal wastewater was interactions promote the electron flow among the microbial com- used to adapt the microorganisms and wetland plants for about one munity causing an increased bioelectricity generation (Corbella month. During inoculation and operational periods, synthetic et al., 2015). In addition, it was observed that the use of zero val- wastewater was fed into the CW-MFCs at the top and collected from ent iron (ZVI) in a MFC system can increase electricity generation a perforated collection pipe placed 7 cm above the bottom of and biodegradation of organic compounds because of its function reactor. All CW-MFCs were operated in a fed-batch mode with a as electron donor causing a reduction of the of organic compounds hydraulic retention time (HRT) of 2 d. (Cai et al., 2018; Zhang et al., 2011). These results suggest that an anode amended with nano ZVI (nZVI) might improve the degra- 2.3. Preparation of synthetic wastewater dation of organic compounds as well as electricity production. In this study, phenanthrene and anthracene were selected as The composition of synthetic wastewater is as follows: target PAHs. The control group and the CW-MFC with an anode C6H12O6$H2O, KH2PO4,Na2HPO4$12H2O, NH4Cl, NaNO3,CH3COONa, amended with nZVI were used to investigate their performance in MgCl2$6H2O, ZnCl2, CaCl2, CuSO4$5H2O, FeCl3 and H3BO3. During À biodegradation, phytoextraction and substrate adsorption of the operational period, 1 mL phenanthrene (5 g L 1) and anthra- À phenanthrene and anthracene. We hypothesize that: i) nZVI affects cene (5 g L 1) acetone solution was added to 30 L synthetic the biodegradation and phytoextraction of phenanthrene and wastewater. The chemical oxygen demand (COD), NH3-N, nitrate, anthracene during wastewater treatment; ii) an increased phenanthrene and anthracene concentrations in the influent were À bioelectricity generation of a CW-MFC anode amended with nZVI 211.9,15.0, 38.9, 0.17 and 0.17 mg L 1, respectively. The average À will promote the nitrogen removal of the wastewater; iii) the mi- conductivity and pH of influent water were 670.1 ± 50.0 mScm 1 crobial community will adapt to the nZVI located anode in a CW- and 7.50 ± 0.12, respectively. MFC and change its composition. 2.4. Sampling and analytical methods 2. Materials and methods Influent and effluent samples were collected at the feeding time 2.1. Preparation of Biochar-Mt-nZVI Montmorillonite-nZVI (Mt-nZVI) was prepared by reducing FeSO4$7H2O to zero valent iron using sodium borohydride (NaBH4) reduction (Huang et al., 2014; Zhang et al., 2010). Firstly, 24.88 g of FeSO4$7H2O were dissolved in an ethanolic solution (200 mL) at a volume ratio of 1 (water):4 (ethanol). Then 20 g Mt were added and stirred for 0.5 h. Afterwards, NaBH4 solution (50 mL) was added to the Mt-nZVI under continuous stirring at a mol ratio of þ À 1(Fe2 ):3(BH4 ). Finally, the mixture was stirred for another 0.5 h under the protection of N2. Mt-nZVI was washed with deionized water for several times and dried at À40 C for 24 h in a lyophilizer.