[Impact Mechanisms of Carboxyl Group Modified Cathode on Acetate Production in Microbial Electrosynthesis Systems].

Microbial electrosynthesis systems (MESs) can convert carbon dioxide into added value compounds using microorganisms as catalyst, which is expected to help achieve conversion of greenhouse gases into resources. However, the synthetic efficiency of MESs is far behind the industry requirements. In this study, carbon cloth surfaces were bonded with carboxyl groups by electrochemical reduction of aryl diazonium salts and then used as a cathode in MESs reactors. The results showed that the hydrophilicity of the carbon cloth surfaces improved after the carboxyl groups were modified. However, weaker current of cyclic voltammetry was obtained in the modified cathode. Significant differences were observed between modified (CA-H, CA-M, CA-L) and non-modified cathode (CK) during the start-up period. After 48h, the hydrogen production rate of CA-H, CA-M, CA-L was 21.45, 28.60, and 22.75 times higher than CK. After 120h, the acetate accumulation concentration of CA-H, CA-M, CA-L was 2.01, 2.43, and 1.44 times higher than CK. After 324h, there was little difference in the electrochemical activity of cathodic biofilm and protein content (about 0.47 mg·cm-2) in all groups. The analysis of the community structure of cathodic biofilm showed that, in the genus level, Acetobacterium, Norank_p_Saccharibacteria, and Thioclava were the dominant species, accounting for 59.6% to 82.1%. There was little difference in the relative abundance of Acetobacterium in all groups (31.3% to 40.1%). However, the relative abundance of norank_p_Saccharibacteria in CA-H, CA-M, CA-L, and CK were 16.1%, 24.6%, 31.1%, and 37.5%, respectively. The carboxyl modified cathode had a great influence on the start-up stage of MESs, which could be a new idea for the rapid start-up of MESs.

[Sulfate Reduction and Microbial Community of Autotrophic Biocathode in Response to Externally Applied Voltage].

The removal efficiencies of environmental pollutants in a microbial electrolysis system (MES) with a biocathode are highly affected by the externally applied voltage. Although the cathode biofilm plays a key role in the pollution removal, its response to the applied voltage is still unknown. A two-chambered MES with a biocathode was constructed to study the impact of the different applied voltages (0.4, 0.5, 0.6, 0.7, and 0.8 V) on the sulfate reduction, extracellular polymer formation, and cathodic bacterial community. The results show that the current output and coulomb and COD removals of the MES are positively correlated with the applied voltage ranging from 0.4 to 0.8 V. The sulfate reduction rate first increases and then decreases with increasing voltage in the MES. The maximum sulfate reductive rate[78.9 g·(m3·d)-1] and maximum S2- production (31.9 mg·L-1±2.2 mg·L-1) were achieved at 0.7 V. The highest electron recovery efficiencies of the MES are 41.8%; hydrogen production may be a pathway leading to electron loss. The polysaccharide and protein contents of the cathode biofilm increase with increasing voltage. The cathode biomass at 0.8 V is 70% higher than that at 0.4 V. The high throughput sequencing results show that Proteobacteria and Dsulfovibrio are dominant in the cathodic microbial community at the phylum and genus levels, respectively. The relative abundance of Desulfovibrio shows little variation with the increasing voltage, indicating that Desulfovibrio is of advantage for using the cathode as electron donor for the respiratory metabolism. With the increasing voltage, the distribution of Desulfovibrio at species level indicates that the changes of Desulfovibriox magneticus RS-1 and s_unclassified_g_Desulfovibrio are contrary.

[Influence of substrate COD on methane production in single-chambered microbial electrolysis cell].

The chemical oxygen demand (COD) of substrate can affect the microbial activity of both anode and cathode biofilm in the single-chamber methanogenic microbial electrolysis cell (MEC). In order to investigate the effect of COD on the performance of MEC, a single chamber MEC was constructed with biocathode. With the change of initial concentration of COD (700, 1 000 and 1 350 mg x L(-1)), the methane production rate, COD removal and energy efficiency in the MEC were examined under different applied voltages. The results showed that the methane production rate and COD removal increased with the increasing COD. With the applied voltage changing from 0.3 to 0.7 V, the methane production rate increased at the COD of 700 mg x L(-1), while it increased at first and then decreased at the COD of 1000 mg x L(-1) and 1350 mg x L(-1). A similar trend was observed for the COD removal. The cathode potential reached the minimum (- 0.694 ± 0.001) V as the applied voltage was 0.5 V, which therefore facilitated the growth of methanogenic bacteria and improved the methane production rate and energy efficiency of the MEC. The maximum energy income was 0.44 kJ ± 0.09 kJ (1450 kJ x m(-3)) in the MEC, which was obtained at the initial COD of 1000 mg x L(-1) and the applied voltage of 0.5 V. Methanogenic MECs could be used for the treatment of wastewaters containing low organic concentrations to achieve positive energy production, which might provide a new method to recover energy from low-strength domestic wastewater.

[Characterization of biocatalysed sulfate reduction in a cathode of microbial electrolysis system].

In order to improve H2 utilization efficiency and to reduce energy consumption during the hydrogenotrophic sulfate reduction process, a two-chambered microbial electrolysis system (MES) with a biocathode was constructed. The performance of MES in terms of sulfate removal and the electron utilization was studied. With an applied voltage of 0.8 V, biocathode removed about 109.8 mg x L(-1) of SO4(2-) from the wastewater within 36 h of operation, and average reductive rate reached 73.2 mg x (L x d)(-1). The highest current density obtained from the MES was 50-60 A x m(-3). The total coulomb efficiency achieved in a cycle was (43.3 +/- 10.7)%, and around 90% of the effective electrons were used by the cathode bacteria for SO4(2-) reduction. During the operation of MES, the major products of SO4(2-) bio-reduction are sulfide and hydrogen sulfide. With an applied voltage of 0.4 V, both the SO4(2-) removal rate and electron output decreased compared with that of 0.8 V; however, the electric charge efficiency obtained by the MES increased and reached 70% when 0.4 V was applied. Meanwhile, ignorable H2 gas was detected at the end of the cycle, indicating bacteria might directly use cathode as the electron donor thus enhanced energy efficiency. The bacteria could use cathode of the MES as electron donor to reduce SO4(2-) effectively, which may provide a new method to lower energy consumption of the hydrogenotrophic sulfate reduction process, making advanced treatment for sulfate containing wastewater more affordable for practical applications.

[Effect of polycyclic aromatic hydrocarbons on the vertical distribution of denitrifying genes in river sediments].

To establish the relationship between polycyclic aromatic hydrocarbons (PAHs) and various stages of denitrification under denitrifying conditions in sediments, we examined the impact of PAHs on the vertical distribution of special denitrifying genes. In March of 2011, sediment samples were collected from three representative locations along the Pearl River. The characteristics of vertical distribution of PAHs as well as denitrifying genes in the sediment samples were analyzed. Based on these vertical characteristics, relationships between PAHs and special denitrifying genes (narG, nirS, nosZ and nrfA) were established using the multivariate method. Results of canonical correspondence analysis (CCA) showed a close correlation between high ring PAHs and dissimilatory nitrate reduction. The impact of PAHs on nosZ was the most significant, namely PAHs imposed strong inhibition on the nitrite reduction stage. Except for the nitrite reduction stage, denitrifying bacteria from other stages of denitrification acclimatized themselves to the high ring PAHs. Especially, bacteria containing nrfA may have the potential to anaerobically degrade high ring PAHs. Besides this, the special role of nirS remains to be studied further.

[Impact of microbial aggregating agents on soil aggregate stability under addition of exogenous nutrients].

In this study, we investigated the effects of biological aggregating agents (fungal hyphae and microbial extracellular polysaccharides) soil aggregate (with different sizes) stability under addition of exogenous nutrients. The exogenous nutrients included glucose and ammonium nitrate. Experiments were conducted in a 30 d incubation period with three treatments: (1) the control (0.5 mg x g(-1) soil); (2) CN5 (0.5 mg x g(-1) soil, 0.1 mg x g(-1) soil, C/N = 5); (3) CN10 (0.5 mg x g(-1) soil, 0.05 mg x g(-1) soil, C/N = 10). Results showed that soil respiration rates were not significantly different among the three treatments, with maximums being about 3.10 mg x (h x kg)(-1), indicating that the impact of inorganic nitrogen fertilizer was not obvious in a short term. Aside from 5 d, macroaggregates amount of CK (15.67%) was observably lower than those of CN5 (25.32%) and CN10 (24.63%), there were no remarkable discrepancies among 3 treatments in other incubation period. The insignificant difference in the aggregate amounts among the three treatments suggested that the influence of glucose on microbial activities surpassed the inorganic nitrogen fertilizer in shortterm in the study.

[Electricity generation and quinoline degradation of pure strains and mixed strains in the microbial fuel cell].

Microbial flora composition of microbial fuel cells (MFC) is important to the electricity generation. Four bacterium strains Q1, b, c and d which represent all different morphology of culturable bacterium were isolated from a MFC using 200 mg x L(-1) quinoline as the fuel and operating for at least 210 days. Strains Q1, c and d were Pseudomonas sp. based on 16S rDNA sequence analysis, while strain b was Burkholderia sp. Double-chamber MFCs using 200 mg x L(-1) quinoline and 300 mg x L(-1) glucose as the fuel and potassium ferricyanide as the electron acceptor were constructed. Results showed that strain b, c and d were non-electrogenesis. The electrical charges of MFC inoculated electrogenesis strain Q1 with non-electrogenesis strain b, c and d respectively were 3.00, 3.57 and 5.13C, and the columbic efficiency were 3.85%, 4.59% and 6.58%, which were all lower than that inoculated with pure Q1, because of the interspecific competition of electrogenesis and non-electrogenesis bacteria. Combinations of Q1 with the other three strains respectively resulted in 100% of quinoline degradation rates within 24h, which is better than pure cultures, that is, mixed microbial populations perform better in MFC when complex organics are used as the fuel. GC/MS analyses showed that only 2(1H)-quinolinone and phenol existed in the effluent of the MFC, which was inoculated with only Q1 or mixed bacteria.

[Factors affecting the DAPI fluorescence direct count in the tidal river sediment].

The factors affecting the DAPI (4', 6-diamidino-2-phenylidole) fluorescence direct count in the tidal river sediment were examined. Sediment samples were collected from the Guangzhou section of the Pearl River. Besides sediment texture and organic matter, an improved staining procedure and the involved parameters were analyzed. Results showed that the procedure with the sediment with 2000 fold dilution and ultrasonic water bath for 10 min, and with a final DAPI concentration of 10 microg x mL(-1) and staining time for more than 30 min produced the optimum results of DAPI direct count in the sediment. The total bacterial number was correlated to the proportion of the non-nucleoid-containing cells to the total bacterial number (r = 0.587, p = 0.004). The organic matter content also correlated to the ration. The clay content had a strong correlation with the organic matter, through which the clay content also affected the ratio. A multiple regression analysis between the ration versus the organic matter, the total bacterial number, and the clay content showed that the regression equation fit the measure values satisfactorily (r = 0.694). These results indicated that the above factors needed to be considered in the applications of the DAPI fluorescence direct counting method to the tidal river sediment.

[Biosorption of Cd(II), Cu(II), Pb(II) and Zn(II) in aqueous solutions by fruiting bodies of macrofungi (Auricularia polytricha and Tremella fuciformis)].

Batch experiments were conducted to study the ability of fruiting bodies of Auricularia polytricha and Tremella fuciformis to adsorb Cd(II), Cu(II), Pb(II) and Zn(II) from aqueous solutions, including biosorption ability of the biomass to remove heavy metals from solutions with different concentrations, kinetics of adsorption, influence of co-cations, and biosorption affinity in multi-metalsystem. Results showed that in the solutions with individual metal, the maximum biosorption amounts of Cd(II), Cu(II), Pb(II), Zn(II) by A. polytricha were 18.91, 18.69, 20.33, 12.42 mg x g(-1), respectively, and the highest removal rates for all cases were more than 85%. The maximum biosorption amounts of Cd(II), Cu(II), Pb(II), Zn(II) by T. fuciformis were 19.98, 20.15, 19.16, 16.41 mg x g(-1), respectively, and highest removal rates for all cases were more than 75%. In the solutions with initial concentrations of 10, 50 and 100 mg x L(-1), the biosorption amounts increased but the removal rates decreased as the initial concentrations increasing. The pseudo-second-order reaction model described adsorption kinetics of heavy metal ions by fruiting bodies of A. polytricha and T. fuciformis better than the pseudo-first-order reaction model. In the solutions with multi metals, the biosorption amounts of heavy metals by two biosorbent were in the order of Ph(II) > Cd(II) > Cu(II) > Zn(II). The ions with more negative charges were preferential to be sorbed. The biosorption ability of A. polytricha was inhibited in multi-metal solutions. In multi-metal solutions, T. fuciformis sorbed a higher amount of Pb(II) but lower amounts of other three ions than that in the individual metal solutions. The results indicated that both fruiting bodies of A. polytricha and T. fuciformis were potential biosorbents.

[Power generation from glucose and nitrobenzene degradation using the microbial fuel cell].

By constructing a dual-chamber microbial fuel cell (MFC), experiments were carried out using an initial glucose concentration of 1 000 mg/L with different nitrobenzene (NB) concentrations (0, 50, 150 and 250 mg/L) as the MFC's fuel. Results showed that with an external resistance of 1 000 omega, the initial glucose concentration of 1 000 mg/L and the initial NB concentrations of 0, 50, 150, 250 mg/L, the operation periods were 55.7, 51.6, 45.9 and 32.2 h, respectively, the maximum voltage outputs were 670, 597, 507, and 489 mV, the maximum volumetric power densities were 28.57, 20.42, 9.29, and 8.47 W/m3, and the electric charges were 65.10, 43.50, 35.48, and 30.32 C. The MFC could use the NB and glucose mixtures as fuel and generated stable electricity outputs. The degradation rates of NB in the MFC in all cases reached up to 100% and COD removals in the MFC were 87% - 98%. However, the electricity generation was negligible when using 250 mg/L NB as the sole fuel. Denaturing gradient gel electrophoresis (DGGE) profiles demonstrated that the presence of NB resulted in changes of the dominant bacterial species on the electrodes.

[Power generation from pyridine and glucose using microbial fuel cell].

Different organics have different effects on the power generation of microbial fuel cell. A packing-type MFC was constructed to investigate organic matter degradation and power generation. Experiments were conducted using an initial pyridine concentration of 500 mg/L with different glucose concentrations (500, 250, and 100 mg/L) as the MFC fuel. Results showed that maximum voltages decreased with the decrease of concentration of glucose and the maximum voltage was 623 mV. The cycle time were 49.5, 25.7, 25.2 h respectively. Correspondingly, the maximal volumetric power densities were 48.5, 36.2, 15.2 W/m3. Pyridine removal rate reached 95% within 24 h using MFC, which was not affected by concentration of glucose. Power generation using glucose was not affected in the presence of high concentration of pyridine. However, the phenomenon of electricity production was not obvious when using 500 mg/L pyridine as sole fuel. The results clearly demonstrated the feasibility of using the MFC to generate electricity when using pyridine and glucose mixture as fuel and simultaneously enhanced pyridine degradation.

[Isolation and characterization of electrochemical active bacterial Pseudomonas aeruginosa strain RE7].

Microbial components of the microbial fuel cells (MFCs), including species constitution and metabolic mechanism of the anodic microorganisms, are critical to the optimization of electricity generation. An electrogenesis baterium strain (designated as RE7) was isolated from an MFC that had been running in a fed batch mode for over one year. The isolate was identified as a strain of Pseudomonas aeruginosa based on its physiological, morphological characteristics and 16S rRNA sequence analysis. Direct electron transfer from RE7 to an electrode was examined using cyclic voltammetry and MFC. Results of both methods showed the electrochemical activity of the bacterium without any electrochemical mediator. The P. aeruginosa strain RE7 was inoculated into the anode chamber of a packing-type MFC and the maximal voltage output was 352 mV with 1 500 mg/L glucose as the fuel. Correspondingly, the maximal area and volumetric power densities were 69.2 mW/m2 and 6.2 W/m3, respectively. Bacteria-producing soluble redox mediators, such as phenazine derivatives, are possible mechanism to facilitate the direct electron transfer to the electrode from the bacterial cells.

[Comparison of power generation in microbial fuel cells of two different structures].

Low electricity productivity and high cost are two problems facing the development of microbial fuel cell (MFC). Comparative studies on electricity generation in MFCs of different designs while under the same conditions are important in enhancing the power output. Single-chamber MFC and dual-chamber MFC were constructed and acetate was used as the fuel. Power outputs in these MFC were compared side by side with a resistance of 1,000 Omega connected to each. Experimental results showed that the electricity was generated continuously and steadily in the MFCs. The average maximum output voltages obtained by the single-chamber and dual-chamber MFCs were 600 and 650 mV, respectively. The electric cycles were operated for 110 and 90 h for the single-chamber and dual-chamber MFCs, respectively. From the single-chamber and dual-chamber MFCs, the maximum area power densities were 113.8 and 382.4 mW/m2 respectively, and the maximum volumetric power densities were 1.3 and 2.2 mW/m3 respectively. The internal resistances of single-chamber and dual-chamber MFC were 188 and 348 Omega, respectively. Results indicated that the dual-chamber MFC had a better performance than the single-chamber MFC. The effective area of anode and the proton exchange membrane had a significant effect on the performance of MFCs.