jen00214_prn 148..156 - Journal of Environmental Sciences
Transcription
jen00214_prn 148..156 - Journal of Environmental Sciences
Journal of Environmental Sciences Volume 30 2015 www.jesc.ac.cn Highlight articles 129 Rice: Reducing arsenic content by controlling water irrigation Ashley M. Newbigging, Rebecca E. Paliwoda and X. Chris Le 132 Apportioning aldehydes: Quantifying industrial sources of carbonyls Sarah A. Styler Review articles 30 Application of constructed wetlands for wastewater treatment in tropical and subtropical regions (2000–2013) Dong-Qing Zhang, K.B.S.N. Jinadasa, Richard M. Gersberg, Yu Liu, Soon Keat Tan and Wun Jern Ng 47 Stepwise multiple regression method of greenhouse gas emission modeling in the energy sector in Poland Alicja Kolasa-Wiecek 113 Mini-review on river eutrophication and bottom improvement techniques, with special emphasis on the Nakdong River Andinet Tekile, Ilho Kim and Jisung Kim Regular articles 1 Effects of temperature and composite alumina on pyrolysis of sewage sludge Yu Sun, Baosheng Jin, Wei Wu, Wu Zuo, Ya Zhang, Yong Zhang and Yaji Huang 9 Numerical study of the effects of local atmospheric circulations on a pollution event over Beijing–Tianjin–Hebei, China Yucong Miao, Shuhua Liu, Yijia Zheng, Shu Wang and Bicheng Chen, Hui Zheng and Jingchuan Zhao 21 Removal kinetics of phosphorus from synthetic wastewater using basic oxygen furnace slag Chong Han, Zhen Wang, He Yang and Xiangxin Xue 55 Abatement of SO2–NOx binary gas mixtures using a ferruginous active absorbent: Part I. Synergistic effects and mechanism Yinghui Han, Xiaolei Li, Maohong Fan, Armistead G. Russell, Yi Zhao, Chunmei Cao, Ning Zhang and Genshan Jiang 65 Adsorption of benzene, cyclohexane and hexane on ordered mesoporous carbon Gang Wang, Baojuan Dou, Zhongshen Zhang, Junhui Wang, Haier Liu and Zhengping Hao 74 Flux characteristics of total dissolved iron and its species during extreme rainfall event in the midstream of the Heilongjiang River Jiunian Guan, Baixing Yan, Hui Zhu, Lixia Wang, Duian Lu and Long Cheng 81 Sodium fluoride induces apoptosis through reactive oxygen species-mediated endoplasmic reticulum stress pathway in Sertoli cells Yang Yang, Xinwei Lin, Hui Huang, Demin Feng, Yue Ba, Xuemin Cheng and Liuxin Cui 90 Roles of SO2 oxidation in new particle formation events He Meng, Yujiao Zhu, Greg J. Evans, Cheol-Heon Jeong and Xiaohong Yao 102 Biological treatment of fish processing wastewater: A case study from Sfax City (Southeastern Tunisia) Meryem Jemli, Fatma Karray, Firas Feki, Slim Loukil, Najla Mhiri, Fathi Aloui and Sami Sayadi CONTENTS 122 Bioreduction of vanadium (V) in groundwater by autohydrogentrophic bacteria: Mechanisms and microorganisms Xiaoyin Xu, Siqing Xia, Lijie Zhou, Zhiqiang Zhang and Bruce E. Rittmann 135 Laccase-catalyzed bisphenol A oxidation in the presence of 10-propyl sulfonic acid phenoxazine Rūta Ivanec-Goranina, Juozas Kulys, Irina Bachmatova, Liucija Marcinkevičienė and Rolandas Meškys 140 Spatial heterogeneity of lake eutrophication caused by physiogeographic conditions: An analysis of 143 lakes in China Jingtao Ding, Jinling Cao, Qigong Xu, Beidou Xi, Jing Su, Rutai Gao, Shouliang Huo and Hongliang Liu 148 Anaerobic biodegradation of PAHs in mangrove sediment with amendment of NaHCO3 Chun-Hua Li, Yuk-Shan Wong, Hong-Yuan Wang and Nora Fung-Yee Tam 157 Achieving nitritation at low temperatures using free ammonia inhibition on Nitrobacter and real-time control in an SBR treating landfill leachate Hongwei Sun, Yongzhen Peng, Shuying Wang and Juan Ma 164 Kinetics of Solvent Blue and Reactive Yellow removal using microwave radiation in combination with nanoscale zero-valent iron Yanpeng Mao, Zhenqian Xi, Wenlong Wang, Chunyuan Ma and Qinyan Yue 173 Environmental impacts of a large-scale incinerator with mixed MSW of high water content from a LCA perspective Ziyang Lou, Bernd Bilitewski, Nanwen Zhu, Xiaoli Chai, Bing Li and Youcai Zhao 180 Quantitative structure–biodegradability relationships for biokinetic parameter of polycyclic aromatic hydrocarbons Peng Xu, Wencheng Ma, Hongjun Han, Shengyong Jia and Baolin Hou 191 Chemical composition and physical properties of filter fly ashes from eight grate-fired biomass combustion plants Christof Lanzerstorfer 198 Assessment of the sources and transformations of nitrogen in a plain river network region using a stable isotope approach Jingtao Ding, Beidou Xi, Qigong Xu, Jing Su, Shouliang Huo, Hongliang Liu, Yijun Yu and Yanbo Zhang 207 The performance of a combined nitritation–anammox reactor treating anaerobic digestion supernatant under various C/N ratios Jian Zhao, Jiane Zuo, Jia Lin and Peng Li 215 Coagulation behavior and floc properties of compound bioflocculant–polyaluminum chloride dualcoagulants and polymeric aluminum in low temperature surface water treatment Xin Huang, Shenglei Sun, Baoyu Gao, Qinyan Yue, Yan Wang and Qian Li 223 Accumulation and elimination of iron oxide nanomaterials in zebrafish (Danio rerio ) upon chronic aqueous exposure Yang Zhang, Lin Zhu, Ya Zhou and Jimiao Chen 231 Impact of industrial effluent on growth and yield of rice (Oryza sativa L. ) in silty clay loam soil Mohammad Anwar Hossain, Golum Kibria Muhammad Mustafizur Rahman, Mohammad Mizanur Rahman, Abul Hossain Molla, Mohammad Mostafizur Rahman and Mohammad Khabir Uddin 241 Molecular characterization of microbial communities in bioaerosols of a coal mine by 454 pyrosequencing and real-time PCR Min Wei, Zhisheng Yu and Hongxun Zhang 252 Risk assessment of Giardia from a full scale MBR sewage treatment plant caused by membrane integrity failure Yu Zhang, Zhimin Chen, Wei An, Shumin Xiao, Hongying Yuan, Dongqing Zhang and Min Yang 186 Serious BTEX pollution in rural area of the North China Plain during winter season Kankan Liu, Chenglong Zhang, Ye Cheng, Chengtang Liu, Hongxing Zhang, Gen Zhang, Xu Sun and Yujing Mu J O U RN A L OF E N V I RO N ME N TA L S CI EN CE S 30 (2 0 1 5 ) 1 48–1 5 6 Available online at www.sciencedirect.com ScienceDirect www.journals.elsevier.com/journal-of-environmental-sciences Anaerobic biodegradation of PAHs in mangrove sediment with amendment of NaHCO3 Chun-Hua Li1,2 , Yuk-Shan Wong3 , Hong-Yuan Wang5 , Nora Fung-Yee Tam2,4,⁎ 1. State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China. E-mail: lich@craes.org.cn 2. Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China 3. Department of Biology, The Hong Kong University of Science and Technology, Hong Kong, China 4. State Key Laboratory on Marine Pollution, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China 5. Key Laboratory of Nonpoint Source Pollution Control, Ministry of Agriculture/Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China AR TIC LE I N FO ABS TR ACT Article history: Mangrove sediment is unique in chemical and biological properties. Many of them suffer Received 30 May 2014 polycyclic aromatic hydrocarbon (PAH) contamination. However, the study on PAH Revised 1 September 2014 biological remediation for mangrove sediment is deficient. Enriched PAH-degrading Accepted 5 September 2014 microbial consortium and electron acceptor amendment are considered as two effective Available online 27 January 2015 measures. Compared to other electron acceptors, the study on CO2, which is used by Keywords: the anaerobic biodegradation of four mixed PAHs, namely fluorene (Fl), phenanthrene (Phe), Anaerobic biodegradation fluoranthene (Flua) and pyrene (Pyr), with or without enriched PAH-degrading microbial Electron acceptor amendment consortium in mangrove sediment slurry. The trends of various parameters, including PAH Mangrove sediment concentrations, microbial population size, electron-transport system activities, electron NaHCO3 amendment acceptor and anaerobic gas production were monitored. The results revealed that the Polycyclic aromatic hydrocarbon inoculation of enriched PAH-degrading consortium had a significant effect with half lives methanogens, is still seldom. This study investigated the effect of NaHCO3 amendment on shortened by 7–13 days for 3-ring PAHs and 11–24 days for 4-ring PAHs. While NaHCO3 amendment did not have a significant effect on the biodegradation of PAHs and other parameters, except that CO2 gas in the headspace of experimental flasks was increased. One of the possible reasons is that mangrove sediment contains high concentrations of other electron acceptors which are easier to be utilized by anaerobic bacteria, the other one is that the anaerobes in mangrove sediment can produce enough CO2 gas even without adding NaHCO3. © 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. Introduction Polycyclic aromatic hydrocarbon (PAH) has been shown to induce a number of toxic effects, such as respiratory stimulation, genotoxicity, mutagenic, tumorigenicity and carcinogenicity (USEPA, 1993). Because of their low water solubility and hydrophobicity, PAHs are persistent in the environment and tend to adsorb readily onto particulate matter in air and water, with sediments becoming their ultimate repository. High PAH concentrations have been found near urban and industrialized coastal regions (Ke et al., 2005). Mangrove ecosystems commonly found in the inter-tidal zone of tropical and subtropical regions are often under pollution ⁎ Corresponding author. E-mail: bhntam@cityu.edu.hk (Nora Fung-Yee Tam). http://dx.doi.org/10.1016/j.jes.2014.09.028 1001-0742/© 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. J O U RN A L OF E N V I RO N M EN TA L S CI EN CE S 30 (2 0 1 5 ) 1 4 8–1 5 6 stress and are sinks, or receivers, of various man-made pollutants (Zheng et al., 2002). In addition to contaminated tidal water, inputs from rivers or streams, storm-water run-off, sewage discharges and atmospheric deposition are possible sources of PAHs (Ke et al., 2005). Although many PAHs are known to be biodegraded under oxic conditions, most contaminated sediments are anoxic. Hence, anaerobic bacteria should play a more important role in biodegradation of PAHs in the natural environment (Levett, 1990). With recent results demonstrating that some PAHs could be degraded without oxygen, anaerobic electron acceptors, such as NO−3, SO2− 4 and Fe(III) could be used by bacteria to biodegrade PAH contaminants (Coates et al., 1996; Ambrosoli et al., 2005; Chang et al., 2008). Furthermore, anaerobic biodegradation seems to make a complete breakdown by converting PAHs to CO2 (Hutchins et al., 1991; Macrae and Hall, 1998; Nieman et al., 2001), while most aerobic biodegradation would leave incomplete breakdown products in the polluted environment (Chang et al., 2008). Biodegradation could also be enhanced with the amendment of electron acceptors. Recent studies have demonstrated that anaerobic biodegradation of PAHs can be improved by adding electron acceptors, which are utilized by anaerobes (Coates et al., 1996; Chang et al., 2003). As for methanogens, they use CO2 or carbonate as a terminal electron acceptor. And CO2/bicarbonate (Genthner et al., 1997) or sodium bicarbonate (Chang et al., 2008) is often used as an electron acceptor source. The latter was chosen in the present study because it can produce CO2 easily when dissolves in water and it is more applicable in in-situ remediation. The present study aims to: (1) evaluate the effect of NaHCO3 amendment on the anaerobic biodegradation of mixed PAHs comprising fluorene (Fl), phenanthrene (Phe), fluoranthene (Flua) and pyrene (Pyr) in mangrove sediment slurry; (2) examine the effect of enriched PAH-degrading microbial consortium and (3) monitor the trend of various parameters during the biodegradation period, including PAH concentrations, microbial population size, electrontransport system (ETS) activities, electron acceptor and anaerobic gas production. 149 was about 5 μg/g dry weight (dw) and the dominant electron acceptors were sulfate (1939.9 μg/g dw), followed by Fe(III) (333.5 μg/g dw), nitrate (20.3 μg/g dw) and Mn(IV) (2.5 μg/g dw). The sediment was sieved through a 2 mm sieve to remove materials, such as stones and plant debris, before use. 1.4. Microbial growth medium The mineral salt medium (MSM) was used as the medium for microbial growth. It contains the following compounds (g/L): K2HPO4, 0.27; KH2PO4, 0.35; NH4Cl, 2.7; MgCl2·6H2O, 0.1; CaCl2·2H2O, 0.1; FeCl2·4H2O, 0.009; MnCl2·4H2O, 0.004; ZnCl2, 0.0014; CoCl4·6H2O, 0.001; and (NH4)6 Mo7O24·4H2O, 0.001. The medium pH and salinity were adjusted to 7.2 and 25‰, respectively. The freshly prepared 0.8 mL Na2S·9H20 (0.5 mol/L) solution was aseptically added into 1000 mL autoclaved MSM through a 0.25 μm pore size filter. 1.5. Electron acceptor amendment Sodium bicarbonate (1.68 g) was added to 1 L MSM to form 20 mmol/L, and the CO2 gas concentration developed in the headspace was 13.3% (0.65 mmol per flask) at the beginning of experiment. 1.6. PAH biodegradation experiment The four PAH compounds (Fl, Phe, Flua and Pyr) used in this study were purchased from Sigma Chemicals, USA (purity > 96%). A stock solution containing 5 g/L of each PAH was dissolved in distilled acetone. Five treatments were included, they were (1) indigenous bacteria (IB): without sodium bicarbonate amendment and inoculums of enriched consortium, only PAHs, MSM and sediment; (2) indigenous bacteria plus sodium bicarbonate amendment (IB + NaHCO3): sodium bicarbonate amendment was applied to IB treatment; (3) enriched bacteria (EB): the enriched PAH-degrading consortium was inoculated in to IB treatment; (4) EB + NaHCO3: sodium bicarbonate amendment was applied to EB treatment and (5) sterile control (SC): same as IB but the sediment was sterilized by autoclaving at 121°C and a pressure of 1 bar for one hour, for three consecutive days; 0.2 mL NaN3 (0.15 g/mL) was added to ensure the microorganisms in the sediment were inactive. Quickfit conical flasks (100 mL), with silicone suba-seal septa (Sigma-Aldrich) and wrapped with aluminum foil, were used to perform the biodegradation experiment. Mixed PAH stock (50 μL; 5000 mg/L for each PAH) was spiked into the flask and placed in a sterile fume hood for 30 min for acetone vaporization. Fresh sediment (25 g) was transferred into the flask to obtain an initial concentration of 10 mg/kg (fresh weight) for each PAH. MSM (25 mL) was then added to the flask. The flasks were shaken at 150 r/min and 28°C for 125 days under non-oxygen condition, which was maintained following the same method described in our former publication (Li et al., 2009). In brief, the gas in the headspace of flask was replaced with high purified N2 gas. The flasks were shaken at 150 r/min and 28°C for 125 days. 1.3. Collection of sediments 1.7. Analytical methodology Subsurface sediment was freshly collected by PVC cores from a depth of 10–15 cm in Ma Wan mangrove swamp, Hong Kong, China. The total concentration of the 16 US EPA priority PAHs Six replicates of samples were sacrificed every 25 days, three of which were used for PAH analysis and the others for the determination of the population sizes of different microbial 1. Materials and methods 1.1. Enriched anaerobic PAH-degrading microbial consortium The enriched anaerobic PAH-degrading microbial consortium was used. The dominant microbial species included Bacillus sp., Clostridium sp., Geobacillus sp., Methanobacterium formicium, Delftia sp., and Bacillus acidicola sp. The enriched consortium was incubated at 28°C under non-oxygen condition, until a microbial population size of about 106 mL−1 was reached. The suspension was used as inoculums in some treatments described below. 1.2. Chemicals 150 J O U RN A L OF E N V I RO N ME N TA L S CI EN CE S 30 (2 0 1 5 ) 1 48–1 5 6 groups, the microbial activity under PAH stress, concentrations of electron acceptors used by anaerobic bacteria. Sediment slurries in the flasks were freeze-dried, extracted and concentrated to determine the residual PAHs following the standard method described by Li et al. (2009). The PAHs were quantified by a Hewlett Packard 7890ATHB gas chromatography with a flame ionization detector (GC-FID), using a HP-5MS fused silica capillary column (30 m × 0.25 mm × 0.25 μm) (Restek, Bellefonte, Pennsylvania, USA). The chromatographic conditions were as follows: carrier gas: helium (1 mL/min); injection mode: splitless; injector and detector temperature: 280°C and 300°C, respectively. The oven temperature program was as follows: held at 80°C for 1 min, increased to 190°C at 30°C/min, increased to 225°C at 1.8°C/min and then increased to 280°C at 30°C/min and held at 280°C for 3 min. The recovery rates of Fl, Phe, Flua and Pyr using this analytical approach were 92.2%, 99.4%, 99.1% and 100.1% respectively. Their detection limits were 0.23, 0.23, 0.49 and 0.45 ng/g dry sediment, respectively. A modified most probable number (MPN) method (Li et al., 2009) was used to estimate the population sizes of total heterotrophic anaerobic bacteria (THB) and PAH-degrading bacteria (PDB) grown on brewer agar (Fluka, BioChemika, Steinheim, Germany) plates and R2A plates coated with Phe film, respectively. The positive growth of THB was based on the presence of a colony on the agar plate, and that for PDB was identified by the colony surrounded by a clear zone on the white PAH film, respectively. The plates were placed inside an anaerobic jar (Becton, Dickinson and Company, Franklin Lakes, New Jersey, USA) and incubated at 28°C in an incubator (BD240, Binder, Ulm, Germany) for 4–6 weeks. The population size of methanogen was enumerated according to MPN method described by Jain et al. (1991) with PBBM medium containing 0.7 g KH2PO4, 0.9 g K2HPO4, 0.9 g NaCl, 0.2 g MgCl2·6H2O, 0.1 g CaCl2·2H2O, 1.0 g NH4Cl, trace mineral solution (FeCl2·4H2O, 0.009 mg/L; MnCl2·4H2O, 0.004 mg/L; ZnCl2, 0.0014 mg/L; CoCl4·6H2O, 0.001 mg/L; (NH4)6 Mo7O24·4H2O, 0.001 mg/L) 10 mL, DI water 1000 mL. The pH was adjusted to 7.2. After autoclaving, 10 mL vitamin solution and 0.8 mL Na2S·9H20 (0.5 mol/L) solution was added into 1000 mL autoclaved PBBM medium aseptically by injecting the solution through a 0.25 μm pore size filter. The composition of vitamin solution (per liter) was: 0.002 g biotin, 0.002 g folic acid, 0.010 g B6 (pyridoxine) HCl, 0.005 g B1 (thiamine) HCl, 0.005 g B2 (riboflavin), 0.005 g nicotinic acid, 0.005 g pantothenic acid, 0.001 g B12 crystalline, 0.005 g PABA (p-aminobenzoic acid), 0.005 g lipoic acid, DI water 1000 mL. Five-tube MPN method was applied. Cultivation was performed using 20 mL screw tubes sealed with butyl-rubber stoppers and aluminum caps, the gas phase in these sealed tubes was replaced with N2:CO2 (80:20, V/V). These tubes were incubated at 37°C for 30 days. Methane gas production in the gas phase of each tube was measured for the detection of methanogens. Methane gas determination followed the method described in the following paragraph. The microbial activity under PAH stress was evaluated by a modified electron-transport system (ETS) method (Li et al., 2009) with 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazoliumchloride (INT) as the electron acceptor. The detailed method has been described in another paper (Li et al., 2011). The PAH-stress was also produced by adding 20 μL (5000 mg/L in distilled acetone) mixed PAHs comprising Fl, Phe, Flua and Pyr. The concentrations of different electron acceptors, includ− ing Fe(III), Mn(IV), sulfate (SO2− 4 ) and nitrate (NO3) were measured according to Lovley and Li (Lovley and Phillips, 1986; Li et al., 2009). The gas (10 μL) in the headspace of each Quickfit conical flask or MPN tube was sampled by an air-tight syringe, and the concentrations of CH4 and CO2 were determined by a Hewlett Packard 5890A gas chromatography with a thermal conductance detector (GC-TCD), equipped with a Porapak Q column (80–100 mesh; 6′ × 1/8″; stainless steel) (Alltech, Chicago, Illinois, USA). The chromatographic conditions were as follows: carrier gas: helium (20 mL/min); reference gas: helium (30 mL/ min); injector and detector temperature: 80°C. The oven temperature program was as follows: held at 50°C for 2.5 min. Oxidation–reduction potential (ORP) and pH values were measured with ORP & pH meter (TPS WP-81, Brisbane, Australia) by inserting the probe into the flask immediately after moving off its septum and sealing with parafilm. 1.8. Biodegradation kinetics The biodegradation of all four PAHs was described by the first order kinetics (Chen et al., 2008): C ¼ C 0 e−kt ð1Þ where, C0 (μg/g) is the concentration of PAH at time zero, C (μg/g) is the concentration of PAH after subtracting the abiotic loss at time t (day) and k is the first order rate constant (biodegradation rate in the present study) of the reaction. t1/2, the half life for each PAH compound, was calculated by the formula: t 1=2 ¼ ðln 2Þ=k: ð2Þ 1.9. Statistical analyses A two-way multiple analysis of covariance (MANCOVA) method at p ≤ 0.05, with NaHCO3 amendment and inoculums as two fixed factors, biodegradation time as the covariate, the lnC values of Fl, Phe, Flua and Pyr as the multivariates, was used to test any significant differences from NaHCO3 and inoculums on the biodegradation rate (k). Their effects on other parameters, including microbial population sizes, ETS, electron acceptors and anaerobic gases were analyzed by a two-way analysis of covariance (ANCOVA) method at p ≤ 0.05, with NaHCO3 amendment and inoculums as two fixed factors, biodegradation time as the covariate, ln(parameter value) as the independent variable. All statistical analyses were conducted using the software of SPSS 16.0 (SPSS Inc., Chicago, IL, USA). 2. Results 2.1. PAH biodegradation The anaerobic biodegradation of the four PAHs all followed the same temporal pattern (Fig. 1). The abiotic losses of the four PAHs were relatively few, ranging from 6% to 14%. The biodegradation kinetics was best fitted by the first-order rate 151 J O U RN A L OF E N V I RO N M EN TA L S CI EN CE S 30 (2 0 1 5 ) 1 4 8–1 5 6 SC IB+NaHCO3 IB EB 10 Residual Phe concentration (µg/g) Residual Fl concentration (µg/g) 10 EB+NaHCO3 8 6 4 2 0 0 25 50 75 100 8 6 4 2 0 125 0 25 Biodegradation time (day) Residual Pyr concentration (µg/g) 10 Residual Flua concentration (µg/g) 50 75 100 125 Biodegradation time (day) 8 6 4 10 8 6 4 2 2 0 0 25 50 75 100 0 125 25 0 Biodegradation time (day) 50 75 100 125 Biodegradation time (day) Fig. 1 – Polycyclic aromatic hydrocarbon (PAH) biodegradation and the best fit kinetic models under methanogenic condition (mean and standard deviation of triplicates are shown; the lines show the best fit kinetic models C = C0e−kt; SC: sterile control; IB: with indigenous bacteria; IB + NaHCO3: with indigenous bacteria and NaHCO3 addition; EB: with enriched consortium addition and EB + NaHCO3: with enriched consortium and NaHCO3 addition). model, with regression coefficients (r2) varying from 0.8319 to 0.9895 (p < 0.05). The biodegradation rates and the half-lives of the four PAHs are shown in Table 1. The half lives of the 3-ring PAHs varied between 29.8 and 43.1 days, while the respective values of the 4-ring PAHs were 59.8–86.6 days. These findings indicated that the low molecular weight PAHs (Fl, Phe) had faster biodegradation than the high molecular weight ones (Flua, Pyr). According to MANCOVA analysis results, the inoculation of the enriched PAH-degrading consortium significantly enhanced the biodegradation rates of all four PAHs, with F = 14.916, p = 0.001 for Fl, F = 18.596, p = 0.000 for Phe, F = 11.633, p = 0.003 for Flua, and F = 5.473, p = 0.030 for Pyr; while the amendment of NaHCO3 had no significant effect (p > 0.05). The inoculation of enriched PAH-degrading consortium had significant effect with half lives shortened by 7– 13 days for 3-ring PAHs and 11–24 days for 4-ring PAHs. While with the amendment of NaHCO 3 , the anaerobic biodegradation half lives of PAHs of IB + NaHCO 3 and EB + NaHCO 3 treatments were either shorten very few days or even prolonged (Fl) comparing with IB and EB treatments, respectively. Table 1 – The first order rate constant (k, day− 1) of PAH degradation, half-lives (t1/2, days) and r2 (correlation coefficient). Fl IB IB+ NaHCO3 EB EB + NaHCO3 Phe 2 Flua 2 Pyr 2 k t1/2 r k t1/2 r k t1/2 r k t1/2 r2 0.0166 0.0161 0.0223 0.0233 41.8 43.1 31.1 29.8 0.9659 0.9060 0.9642 0.9424 0.018 0.0185 0.0226 0.0232 38.5 37.5 30.7 29.9 0.9886 0.9895 0.9803 0.9566 0.0087 0.0095 0.0114 0.0116 79.7 73.0 60.8 59.8 0.9692 0.8945 0.9324 0.8319 0.008 0.0095 0.0108 0.0111 86.6 73.0 64.2 62.5 0.9429 0.8987 0.9078 0.9663 152 J O U RN A L OF E N V I RO N ME N TA L S CI EN CE S 30 (2 0 1 5 ) 1 48–1 5 6 IB 6 Total heterotrophic bacteria (THB) IB+NaHCO3 EB EB+NaHCO3 Methanogen 8 5 4 3 2 7 log(MPN) log(MPN) 5 log(MPN) PAH-degrading bacteria (PDB) 6 6 4 3 2 5 1 0 1 0 25 50 75 100 125 4 0 Biodegradation time (day) 25 50 75 100 125 0 0 25 50 75 100 125 Biodegradation time (day) Biodegradation time (day) Fig. 2 – Population sizes of heterotrophic anaerobic bacteria (THB), methanogen and PAH-degrading bacteria (PDB) during polycyclic aromatic hydrocarbon (PAH) biodegradation (mean and standard deviation of triplicates are shown). about one order of magnitude higher than those of IB and IB + NaHCO3 (Fig. 2). The population sizes of the PDB were significantly enhanced with the inoculation of the enriched consortium (Table 2). The sizes of treatments EB and EB + NaHCO3 declined from 106 MPN/mL slurry at day 0 to about 104 MPN/mL slurry at day 25, then kept at 103–104 MPN/mL slurry from day 50 to day 125. These values were still higher than those in the treatments without inoculums. However, the amendment of NaHCO3 had no significant effect on the population sizes of PDB (Table 2). PAH biodegradation rates of all the four treatments with amendment of NaHCO3 were relative lower than those of nitrate, sulfate and Fe(III) amendments according to our previous published or un-published results (Li et al., 2010). However, compared to other studies on PAH biodegradation under methanogenic condition, the mangrove sediment slurry used in the present experiment demonstrate much higher biodegradation ability. For example, Kraig (2000) found that under methanogenic condition low molecular weight PAHs were biodegraded, but high molecular weight ones did not decreased, even two six-ring PAHs increased in concentration almost 50%. Genthner et al. (1997) detected active methanogenesis in creosote-contaminated sediment but only limited degradation of a few PAHs was observed and none of the 4, 5-ring PAHs was degraded. 2.3. Microbial activity under PAH stress The inoculation of enriched consortium had significant effect on ETS activity, but the amendment of NaHCO3 had no significant effect (Table 2). EB and EB + NaHCO3 treatments always maintained higher microbial activities (100– 160 μg/(mL·hr) INTF) compared to the treatments without inoculums. They had comparable trends, with slight decreases from day 0 to day 25, then some increases until day 75, followed by declines thereafter. In the treatments without inoculums, IB and IB + NaHCO3, ETS activities were very low in the first 50 days, reaching the peak at day 75 then declined towards to the end of experiment (Fig. 3). 2.2. Microbial population sizes The population sizes of THB, methanogen and PDB during the biodegradation period are shown in Fig. 2. THB had relative stable population sizes for all treatments (ranged from 103 to 104 MPN/mL slurry), and the inoculation of enriched consortium significantly increased THB population size, especially at the beginning period, but NaHCO3 amendment had no significant effect according to ANCOVA analysis (Table 2). Large population sizes of the methanogen were found in all treatments, ranging from 106 to 108 MPN/mL slurry (Fig. 2). Similar to THB, the inoculation of enriched consortium also significantly increased the population size of methanogen but the amendment of NaHCO3 had no significant effect. The population sizes of treatments EB and EB + NaHCO3 had 2.4. Electron acceptors As enough reducing reagent (Na2S) was added in the experimental slurry, Fe(III) and Mn(IV) react with it and form FeS and MnS, respectively, and almost no Fe(III) and Mn(IV) were detected during biodegradation. Fig. 4 shows the sulfate Table 2 – Two-way analysis of covariance (ANCOVA) analysis results showing the effects of NaHCO3 amendments, inoculation of enriched PAH-degrading consortium on the population sizes of total anaerobic heterotrophic bacteria (THB), methanogen and PAH-degrading bacteria (PDB), and bacterial activity under PAH stress [electron-transport system (ETS)], with time as the covariate. Factors Bacterial population sizes THB NaHCO3 Inoculum ETS activity Methanogen PDB F p F p F p F p 0.020 17.977 0.890 0.000 0.842 41.175 0.370 0.000 0.011 75.996 0.918 0.000 0.086 101.784 0.772 0.000 153 J O U RN A L OF E N V I RO N M EN TA L S CI EN CE S 30 (2 0 1 5 ) 1 4 8–1 5 6 IB IB+NaHCO3 EB EB+NaHCO3 NaHCO3 whatever for the whole biodegradation and the time after day 50. For nitrate concentration, similar temporal trends among all treatments were displayed and the result of two-way ANCOVA indicated that both the inoculation of enriched consortium and the NaHCO3 amendment had no significant effects on the utilization of nitrate (Table 3). The nitrate concentrations of the experimental treatments reached their peak values at Day 50 because some water soluble nitrate was released from sediment due to continuous shaking and microbial activity. The values then declined rapidly until day 100 and remained almost unchanged till day 125. INTF (mg/(mL.hr)) 160 120 80 40 0 0 25 50 75 100 125 2.5. Anaerobic gases Biodegradation time (day) Fig. 3 – Microbial activities of PAH-degrading microbes during polycyclic aromatic hydrocarbon (PAH) biodegradation (mean and standard deviation of triplicates are shown). concentration, with peak concentrations of all the treatments at day 50, about 1500 mg/L slurry for IB and IB + NaHCO3 treatments, and around 700 mg/L slurry for EB and EB + NaHCO3 treatments. The lower peak values in the treatments with inoculums indicated faster utilization rate of sulfate than without inoculums. These results also suggested that the sulfate concentrations in the first 50 days were due to the combined effect of both utilization by anaerobic microbes and the release of sulfate from sediment matrix. After day 50, microbial utilization became the dominant activity. The effects of the inoculums and NaHCO3 amendment on sulfate concentration were examined under two periods, the whole experimental period (0–125 days) and after day 50 (50–125 days), using the two-way ANCOVA analysis. The results showed that the inoculums had significant effect on the utilization of sulfate after day 50, but not for the whole experimental period (Table 3). No significant effects were detected with the amendment of IB The temporal changes of CH4 gas were similar between IB and IB + NaHCO3, as well as between EB and EB + NaHCO3 (Fig. 5). According to two-way ANCOVA results, the amendment of NaHCO3 had no significant effect on the residual concentration of CH4 gas (p > 0.05) but significantly higher amounts of CH4 were found in the treatments with inoculums during the biodegradation period (F = 173.782, p = 0.000). More and more CH4 gas was detected in the headspace as time proceeded, with 0 at day 0, and about 0.67 mmol per culture flask at day 125 for EB and EB + NaHCO3 treatments. The treatments IB and IB + NaHCO3 showed relative low CH4 gas production, around 0.21 mmol per culture flask at day 50 and then remained from 0.06 to 0.16 mmol per culture flask until the end of the experiment (Fig. 5). The residual CO2 gas in the flask was mainly influenced by two factors, the final production of anaerobic respiration and the electron acceptor utilized by methanogens. With the same initial CO2 concentration, the flask with less residual CO2 concentration indicates it has higher utilization rate by methanogens. Both the inoculums and the amendment of NaHCO3 had significant effects on the residual gas in flasks with F = 4.932, p = 0.042 for inoculums and F = 10.798, p = 0.004 for NaHCO3, respectively. Fig. 5 shows that with the amendment of NaHCO3, the treatments IB + NaHCO3 and EB + NaHCO3 had significant higher initial CO2 gas concentration (0.65 mmol per flask) in the headspace at the IB+NaHCO3 EB EB+NaHCO3 Nitrate concentration (mg/L) Sulfate concentration (mg/L) 1500 1200 900 600 300 0 0 25 50 75 100 Biodegradation time (day) 125 50 40 30 20 10 0 0 25 50 75 100 125 Biodegradation time (day) Fig. 4 – Electron acceptor concentrations in the slurry during polycyclic aromatic hydrocarbon (PAH) biodegradation (mean and standard deviation of triplicates are shown). 154 J O U RN A L OF E N V I RO N ME N TA L S CI EN CE S 30 (2 0 1 5 ) 1 48–1 5 6 Table 3 – Two-way analysis of covariance (ANCOVA) analysis results showing the effects of NaHCO3 amendment and inoculation of enriched PAH-degrading microbial consortium on the concentrations of electron acceptors (nitrate and sulfate) with time as the covariate. Factors Electron acceptors Nitrate NaHCO3 Inoculum Sulfate (0–125 days) Sulfate (50–125 days) F p F p F p 0.038 0.051 0.847 0.823 0.000 3.161 0.994 0.091 0.001 53.000 0.973 0.000 sampling time. The addition of NaHCO3 had relative lower pH values compared to other treatments (Fig. 6). ORP values showed some decreases as biodegradation proceeded but the decrease was relatively small. ORP values declined from − 280 mV to around − 330 mV (Fig. 6). Both the inoculation of enriched consortium and NaHCO3 amendment had no significant effects on ORP changes according to ANCOVA analysis (p > 0.05). 3. Discussion 3.1. Effect of NaHCO3 amendment on PAH-degrading ability beginning time. The CO2 gas of EB + NaHCO3 treatment had a rapid decrease from day 0 to day 100, and kept at a similar level till day 125. However, the CO2 gas of IB + NaHCO3 treatment did not change so much until day 75, followed by a sharp decline (Fig. 5). On the other hand, IB and EB treatments showed different trends with IB + NaHCO3 and EB + NaHCO3 treatments, their CO2 gas reached peak values at day 50, followed by a marked decrease at day 75, then kept at similar values till the end of the experiment. The peak value of EB treatment was more than two times higher than that of IB treatment, and always had higher CO2 gas concentration until day 125. 2.6. pH and ORP The pH values in all treatments decreased from about 7.0 to 5.0–6.0 with the increase of biodegradation time (Fig. 6). At the same sampling date, IB treatment showed the highest pH values. Both the inoculums of enriched consortium and NaHCO3 amendment had significant effects on the change of pH, with F = 16.350, p = 0.001, and F = 13.941, p = 0.001, respectively. The inoculation of enriched consortium showed lower pH values than the treatments without it at the same IB The amendment of NaHCO3 did not have any statistically significant on the biodegradation of PAHs and other parameters except CO2 gas in the headspace of experimental flasks. These results suggested that NaHCO3 could not improve PAH-degrading ability when added as electron acceptor (CO2 from NaHCO3) for methanogens in the mangrove sediment with high concentrations of other electron acceptors. Because methanogenic process is known to be the least exergonic microbial reaction that produces only a limited amount of energy when compared to aerobic or other anaerobic respiration processes (Schink, 1997). When other efficient terminal electron acceptors, such as sulfate, nitrate and oxidized forms of metals, are present in the environments, methanogenesis occurs in a very low rate (Zehnder, 1988). In the present study, other electron acceptors, including sulfate, nitrate, Fe(III) and Mn(IV), were present in different amounts. All of them are more preferred by anaerobes than CO2. What is more, sulfate was the dominant electron acceptor from initial till the end of the experiment (Fig. 4), and it could be an important electron acceptor source for anaerobes. Another possible reason was that with large population sizes of anaerobic bacteria and methanogens (Fig. 2), large amount of CO2 gas was produced IB+NaHCO3 EB 0.8 Production of CO2 (mmol/culture flask) Production of CH4 (mmol/culture flask) 0.8 0.6 0.4 0.2 0.0 EB+NaHCO3 0 25 50 75 100 Biodegradation time (day) 125 0.6 0.4 0.2 0.0 0 25 50 75 100 125 Biodegradation time (day) Fig. 5 – Anaerobic gas production during polycyclic aromatic hydrocarbon (PAH) biodegradation (mean and standard deviation of triplicates are shown; IB: with indigenous bacteria; IB + NaHCO3: with indigenous bacteria and NaHCO3 addition; EB: with enriched consortium addition and EB + NaHCO3: with enriched consortium and NaHCO3 addition). 155 J O U RN A L OF E N V I RO N M EN TA L S CI EN CE S 30 (2 0 1 5 ) 1 4 8–1 5 6 IB IB+NaHCO3 EB EB+NaHCO3 -250 7.0 ORP (mV) pH 6.5 6.0 -300 5.5 -350 5.0 4.5 0 25 50 75 100 125 Biodegradation time (day) 0 25 50 75 100 125 Biodegradation time (day) Fig. 6 – pH and oxidation-reduction potential (ORP) in the slurry during polycyclic aromatic hydrocarbon (PAH) biodegradation (mean and standard deviation of triplicates are shown). in a very short time (Fig. 5) and it can provide enough electron acceptor for the respiration of methanogens. 3.2. Effect of enriched PAH-degrading microbial consortium on PAH-degrading ability with NaHCO3 amendment The positive effect of enriched PAH-degrading microbial consortium had already been demonstrated in previous studies (Tam and Wong, 2008; Li et al., 2011), and this effect was also observed in the present study. The biodegradation rates of PAHs, especially for 4-ring PAHs were significantly enhanced by the inoculation of enriched PAH-degrading consortium. The enriched consortium had higher microbial activity under PAH-stress and larger population sizes of THB, methanogen and PDB compared to IB and IB + NaHCO3 treatments. The inoculation of enriched consortium caused a significantly faster utilization of sulfate than other electron acceptors, suggesting that the consortium was sulfate-dependent. Besides, the treatments with inoculums showed significantly higher CH4 concentration in the headspace, further suggesting a higher efficiency and more completeness of the decomposition of PAHs and other organic matter in the slurry. 3.3. Influence of pH and ORP The decrease of pH value was due to the production of some anaerobic products, including CO2 gas, H2S and simple organic acids, during anaerobic biodegradation (Levett, 1990; Jain et al., 1991). Additionally, NaHCO3 amendment also caused a lower pH value, which could be explained by the following equilibrium in slurry system: HCO−3 = H+ + CO23 −. pH values decreased to near 5.0 at the end of experiment, but no significant correlation was found between pH and microbial activity or the population size of total anaerobic heterotrophic bacteria according to Pearson correlation coefficient analysis (2-tailed test), suggesting that the microbes in the mangrove sediment slurry had a good adaptability to lower pH range. ORP values in the present experiment decreased to some extent but not so dramatically as the Fe-reducing or Mnreducing conditions (Li et al., 2010, 2011), probably because the initial ORP values were already very low (−280 mV), much lower than those initial values in Fe-reducing or Mn-reducing conditions, which were 120–130 mV. According to Pearson correlation coefficient analysis (2-tailed test), no significant correlation was found between ORP and microbial activity or the population size of total anaerobic heterotrophic bacteria, indicating that the change of ORP had no significant effect on the anaerobic bacteria. Similar results were observed by previous publications (Onderdonk et al., 1976; Chang et al., 2008). For instance, Chang et al. (2008) reported that ORP value decreased from an initial − 310 mV to a steady range of − 400 to −420 mV between days 20 and 50 of the incubation period under methanogenic condition, but no significant relationship was found between ORP value and bacteria activity. 4. Conclusions On the basis of the results we conclude that: (1) NaHCO3 amendment did not improve PAH-degrading ability in the mangrove sediment. The probable reason could be that concentrations of other electron acceptors in mangrove sediment are high, and enough CO2 was produced because of the activity of anaerobes even without adding NaHCO3. (2) The inoculation of the enriched PAH-degrading consortium supported higher microbial activity and larger population sizes of the PAH-degrading bacteria than the treatments without inoculums, leading to more rapid and complete biodegradation with the half lives of the target PAHs being shortened significantly. 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