Huajun Feng

Ecological roles and release patterns of acylated homoserine lactones in Pseudomonas sp. HF-1 and their implications in bacterial bioaugmentation.

To enable development of a better bacterial bioaugmentation system for tobacco wastewater treatment, the roles and release patterns of acylated homoserine lactones (AHLs) in Pseudomonas sp. HF-1 were evaluated. Swarming was found to be induced by N-hexanoyl-homoserine lactone (C(6)-HSL) and N-3-oxo-hexanoyl-homoserine lactone (3-oxo-C(6)-HSL); the formation of extracellular polymeric substances (EPS) was induced by 3-oxo-C(6)-HSL, C(6)-HSL and N-3-oxo-octanoyl-homoserine lactone (3-oxo-C(8)-HSL); and biofilm formation was induced by C(6)-HSL and 3-oxo-C(8)-HSL. When the culture conditions were 25°C, pH 5-6, 3% inoculum, 1.5 g L(-1) nicotine and 1% NaCl, the amount of AHLs released was sufficient for quorum sensing of swarming and EPS formation for strain HF-1, which was beneficial to the startup stage during bioaugmentation. When strain HF-1 was cultured at pH 8 in the presence of 1.2-1.8 g L(-1) of nicotine and 1% NaCl, the threshold for quorum sensing of biofilm formation was reached and the bioaugmentation system showed an efficient performance.

Where are signal molecules likely to be located in anaerobic granular sludge

Quorum sensing is a concentration-sensing mechanism that plays a vital role in sludge granulation. In this study, the regularities of distribution of different signal molecules, including intra- and interspecific signal molecules (diffusible signal factor, DSF), interspecific signal molecules (autoinducter-2, AI-2) and intraspecific signal molecules (acyl-homoserine lactones, AHLs), from three types of anaerobic granular sludge were investigated. The results showed that 70-90% of DSF was distributed in sludge, while AI-2 in the Water phase accounted for over 80% of the total content. Interestingly, there was a positive correlation between DSF and AI-2, which played opposite roles in granulation. Moreover, more than 55% of short and medium acyl chain AHLs tended to spread in aqueous water, while the long acyl chain AHLs were closer to granular sludge than the short and medium acyl chain AHLs. With the exception of one type of sludge, the percentage of long acyl chain AHLs in the sludge phase was greater than 70%. The different distributions of signal molecules were primarily determined based on their physicochemical properties, including molecular weight and solubility in water or organic solutions. In addition, the basic properties of sludge, such as the granular level or the production of EPS, were closely related to the diversity, distribution and concentration of signal molecules. As a medium in granulation, extracellular polymeric substances production was regulated by different signal molecules from different parts of anaerobic granular sludge. This study provides a foundation for investigation of quorum sensing in the system of anaerobic granular sludge.

The effect of C/N ratio on nitrogen removal in a bioelectrochemical system

The effect of C/N ratios of 2, 2.7, and 3.5 on nitrogen removal in a bioelectrochemical system (BES) was investigated. Starch was used as a carbon source for the electrogenesis phenomenon we observed in a previous study. The results showed that an increased C/N ratio helped the BES to remove nitrate and depress nitrite accumulation but did not increase autotrophic denitrification. Nitrate and total nitrogen removal were increased from 0.69±0.02gm(-3)h(-1) to 1.09±0.16gm(-3)h(-1), and from 0.52±0.08gm(-3)h(-1) to 0.97±0.06gm(-3)h(-1), respectively, when the C/N ratio was increased from 2.0 to 3.5. However, the autotrophic denitrification ratio decreased from 72.74% to 50.23% with the same increase in the C/N ratio. High C/N ratios postponed the excretion of soluble microbial products and increased electrogenesis, but did not improve the anode transformation efficiency.

The effect of carbon sources on nitrogen removal performance in bioelectrochemical systems.

In order to ascertain the effects of different carbon sources (methanol, glucose, starch and NaHCO(3)) on denitrification in BESs, the experiment was conducted in a constant current, 3.5 of chemical oxygen demand to nitrate ratio in a greenhouse. Among the four carbon sources investigated in BESs, NaHCO(3) showed the highest nitrite accumulation and the ratio of soluble microbial products to soluble chemical oxygen demand (SMP/SCOD) with a value of 3.68 ± 0.68 mg/L and 94%, respectively. And the addition of organic substrates could reduce SMP production and enhance the denitrification process. In the constant voltage experiment, it was observed that the organics could be used by microbes to generate electrons at the anode. And a maximal current value of 11.0 mA in the BESs fed with starch indicated that the complex carbon source was easier to be used by microorganisms to generate electricity than the simple carbon source.

Effect of weathering treatment on the fractionation and leaching behavior of copper in municipal solid waste incinerator bottom ash

This work describes the effect of weathering of fresh quenched municipal solid waste incinerator (MSWI) bottom ash on the fractionation and leaching behavior of Cu. A sequential extraction procedure was used to characterize the fractionation of Cu in the fresh and weathered MSWI bottom ash samples. It showed that the organic matter bound fraction of Cu decreased drastically from 69% to 37% during the weathering treatment, while the residual fraction, Fe-Mn oxides bound fraction, carbonate bound fraction and exchangeable fraction increased from 24% to 54%, 3% to 4%, 2% to 3% and 2% to 3%, respectively. Furthermore, two standard leaching procedures, synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP), were carried out on the fresh and weathered samples. The leaching of Cu was attenuated with the process of weathering treatment in the SPLP procedure, but was enhanced in the TCLP procedure. The results suggested that the weathering treatment could change the fractionation and leaching behavior of Cu in MSWI bottom ash. Further research is required to correlate weathering of ash and mobility of Cu.

Optimization of Fenton treatment process for degradation of refractory organics in pre-coagulated leachate membrane concentrates

Untreated leachate membrane concentrates are a threat to the environment. In our study, effective removal of contaminants in pre-coagulated leachate membrane concentrates was achieved using the Fenton process. The Fenton process was optimized using the response surface method, and the maximum total organic carbon (TOC), chemical oxygen demand (COD), and chromaticity reduction efficiencies reached 68.9%, 69.6%, and 100% under the conditions pH 2, H2O2 concentration 1mol/L, and Fe2+ concentration 17.5mmol/L. The COD concentration was reduced from 1120 to 340mg/L. The H2O2 concentration was the key factor affecting the TOC removal efficiency. Slow, continuous addition of the Fenton reagents improved the H2O2 utilization rate, which improved the TOC removal efficiency. Fourier-transform infrared and three-dimensional fluorescence spectroscopy showed that the majority compound of the removed organic material was humic acid. Our study provides guidelines for the treatment of leachate membrane concentrates in engineering applications.

Electrical Stimulation Improves Microbial Salinity Resistance and Organofluorine Removal in Bioelectrochemical Systems

ABSTRACT Fed batch bioelectrochemical systems (BESs) based on electrical stimulation were used to treat p-fluoronitrobenzene (p-FNB) wastewater at high salinities. At a NaCl concentration of 40 g/liter, p-FNB was removed 100% in 96 h in the BES, whereas in the biotic control (BC) (absence of current), p-FNB removal was only 10%. By increasing NaCl concentrations from 0 g/liter to 40 g/liter, defluorination efficiency decreased around 40% in the BES, and in the BC it was completely ceased. p-FNB was mineralized by 30% in the BES and hardly in the BC. Microorganisms were able to store 3.8 and 0.7 times more K+ and Na+ intracellularly in the BES than in the BC. Following the same trend, the ratio of protein to soluble polysaccharide increased from 3.1 to 7.8 as the NaCl increased from 0 to 40 g/liter. Both trends raise speculation that an electrical stimulation drives microbial preference toward K+ and protein accumulation to tolerate salinity. These findings are in accordance with an enrichment of halophilic organisms in the BES. Halobacterium dominated in the BES by 56.8% at a NaCl concentration of 40 g/liter, while its abundance was found as low as 17.5% in the BC. These findings propose a new method of electrical stimulation to improve microbial salinity resistance.

Stimulative mineralization of p-fluoronitrobenzene in biocathode microbial electrolysis cell with an oxygen-limited environment

p-Fluoronitrobenzene (p-FNB) is a toxic compound and tends to accumulate in the environment. p-FNB can be effectively removed and defluorinated in a single-chamber bioelectrochemical system (BES). To verify the suppositionally integrated reductive and oxidative metabolism mechanism in the BES, an oxygen-limited environment was used, with pure oxygen and nitrogen environments used as two controls. Under the oxygen-limited condition, the most excellent performance was achieved. The defluorination rate and mineralization efficiency were 0.0132h(-1) and 72.99±5.68% after 96h, with 75.4% of fluorine in the form of the fluoride ion. This resulted from the unique environment that allowed conventionally integrated reductive and oxidative catabolism. Moreover, the oxidation-reduction potential (ORP) had a significant effect on microbial communities, which was also an important reason for performance diversity. These results provide a new method for complete p-FNB treatment and a control strategy by ORP regulation for optimal system performance.

A comparative study on stabilization of available As in highly contaminated hazardous solid waste.

The stabilization of available As was conducted by chemical fixation after Fenton process in a solid waste residual (SWR) from organic arsenic industry. Single as well as combined fixation treatments by using ferric sulfate (FS), magnesium chloride (MC) and calcium hydroxide (CH) were carried out to assess and to evaluate the fixation effect through toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP) and sequential extraction procedure (SEP). The effect of aging treatment on the fixation of available As in SWR was also investigated. Experimental result showed that the optimal molar ratios for Fe:As, Mg:As and Ca:As were 2:1, 3:1 and 2:1, respectively, and the combination fixation FS+MC+CH was found to be the optimal fixation treatment. With respect to the leaching behavior and the speciation migration of As in SWR after stabilization, TCLP, SPLP and SEP represent a pertinent and inseparable system for the fixation effect evaluation. The fixation treatment of available As in SWR could be evaluated directly after 3 days and the aging treatment is not needed though it can further enhance the fixation effect.

A new method for rapid construction of a Pseudomonas sp. HF-1 bioaugmented system: Accelerating acylated homoserine lactones secretion by pH regulation

Pseudomonas sp. HF-1 bioaugmented systems were operated to treat tobacco wastewater under pH 5.5 for three cycles and pH 8.0 for the rest, which was suitable for HF-1 biofilm formation. The results showed that, under pH control, the contents of 3-oxo-C6-HSL, C6-HSL and 3-oxo-C8-HSL were significantly higher than HF-1 thresholds for biofilm formation. Compared with non-pH controlled reactors, HF-1 showed greater colonization in pH controlled reactors, primarily owing to the high extracellular polymeric substances secretion induced by quorum sensing. Accordingly, high indigenous community activity and granular sludge were observed. Sludge granulation occurred from the seventh cycle, and the average diameter was greater than 400 μm. These systems were also highly efficient with nearly 100% nicotine degradation and 60% total organic carbon removal. Overall, the results indicate that pH regulation is a new and feasible method for acceleration of releasing of auto-inducers, which is beneficial to construction of HF-1 bioaugmented systems.