Papers by Keyword: Mixed Culture

Abstract: Microbial extracellular electron transfer is a significant process in a microbial fuel cell (MFC). Owing to many potential losses in the electron transfer from microorganism to an electrode, a promotion of microbial attachment to electrode should be a productive solution to this difficulty of MFC. We also introduced here a prior colonization of microbes on electrode instead of a conventional immobilization which entirely occurred in a MFC reactor to expedite an attachment of microorganisms on the electrode surface. Coconut shell-based granular activated carbons (CGACs) used as one of the electrodes in the upflow bio-filter circuit microbial fuel cell were immersed in Lysogeny broth (LB) at pH 7 before an inoculation of anaerobic consortium from a wastewater treatment plant was performed. The immobilization was proceeded in an Erlenmeyer flask at 30°C with a shaking speed of 100 rpm throughout an experiment. CGACs taken from a collection of flasks were examined a surface with scanning electron microscopy (SEM). On the 3^rd day of immobilization, SEM images showed that a colonization was seen obviously in large pores on CGAC surface. There were quite plentiful possessions on a rough surface while smooth surface not supporting well at the beginning got worse in attraction of bacteria on day 9 of immobilization. An addition of fresh LB into immobilization solution was conducted to improve the microbial attachment to smooth surface of CGAC. At 9 days after inoculation, the consequence of fresh medium filling did obviously raise the number of bacteria on the plain surface as opposed to earlier experiment.

Abstract: Iron ore is the raw material for steel production, in addition to iron and slag major component, still contains sulfur and phosphorus compounds and other harmful elements, is the potential adverse effects of factors constitute the steel product quality and environment. Sulfur in iron ores into the steel products will not only produce "heat brittle" phenomenon, but also in the sintering process by roasting produce sulfur dioxide into the air, causing damage to the atmosphere and ecological environment. A typical of the high sulfur iron ore from Inner Mongolia, China, iron grade of 53.06% and sulfur content is 2.76%, the main metal mineral in the ore is magnetite, followed by magnetic pyrite, pyrite and siderite, otherwise a small amount of copper mineral chalcopyrite, bornite. In this work, a mixed culture composed by Sulfobacillus thermotolerans, Leptospirillum ferriphilum and Ferroplasma acidiphilum was used to leach the sulfur in iron ore samples, we investigated the leaching rate of sulfur under different initial pH, temperature and pulp density conditions. The results showed that under the condition of the initial pH of 1.8, the temperature was 33 °C, and pulp density 15%, after 7 days of oxidation, we got a yield of 80.16% product in which iron grade of 62.31% and sulfur content is 0.17%. Compared with original sample, sulfur content decreased 95.06%, iron grade increased by 9.25%, and iron recovery was 94.13%. From the results it can be concluded that this microbial process for high sulfur iron ore lead to a significant effect of sulfur reduction and substantial increase in iron grade.

Abstract: The objective of this work was to identify one bacterial consortium adapted to the cultivation in the presence of trivalent arsenic (AsIII). Samples were cultured in flasks containing modified Postgate C liquid medium (selective for sulfate-reducing bacteria, SRB). Six different As concentrations were used: 0.5, 1.0, 2.0, 4.0, 8.0 and 16 mg l^-1. The growth of sulfate reducing microorganisms was indirectly observed by the formation of an iron sulfide black precipitate and also by the Eh measures.100 ml aliquots of cultured media were centrifuged and stored at-20°C for DNA extraction by phenol/chloroform method. Universal primers 968F-GC 1392R (Bacteria domain) were used for 16S ribosomal DNA amplification. Microbial diversity was evaluated by denaturing gradient gel electrophoresis (DGGE). After DGGE analysis 7 different bands were selected, cut, sequenced and analyzed using the Ribosomal Database Project Release. Consortium microorganisms identified were: Pantoea agglomerans, Enterobacter sp, Citrobacter sp, Cupriavidus metallidurans, Ralstonia sp, Burkholderia cepacia and Bacillus sp. Thus the microbial consortium here identified is a good candidate for bioremediation of arsenic contaminated areas and effluents.

Abstract: A functional luxIR-type Quorum Sensing (QS) system is present in Acidithiobacillus ferrooxidans. However, cell-cell communication among various acidophilic chemolithoautotrophs growing on pyrite has not been studied in detail. These aspects are the scope of this study with emphasis on the effects exerted by the N-acyl-homoserine lactone (AHL) type signaling molecules which are produced by Acidithiobacillus ferrooxidans. Their effects on attachment and leaching efficiency by other leaching bacteria, such as Acidithiobacillus ferrivorans, Acidiferrobacter spp. SPIII/3 and Leptospirillum ferrooxidans in pure and mixed cultures growing on pyrite is shown.

Abstract: The gol aim of this study is to optimize the ability to produce hydrogen sulphide (H₂S) in pure and mixed cultures of sulfate reducing bacteria (SRB) at pH variations from 9 to 5. Hydrogen sulphide produced by SRB reacts with dissolved metals in water or tailings generating highly insoluble metal sulfides and therefore the selective immobilization of different metals. Three strains of SRB were isolated from Orcopampa mine tailings and from the Pantanos de Villa wetlands, both located in Peru. Cultures were identified by microscopy, cultural characteristics and biochemical tests as production of desulfoviridin and growth in different substrates. The production of H₂S by pure and mixed cultures was evaluated at: acid pH (5), neutral pH (7) and alkaline pH (9). The mixed culture consisted of all three isolated species: Desulfobacter sp. from mine tailings and Desulfovibrio desulfuricans and Desulfovibrio sapovorans from wetland sludges. Pure cultures of these three strains grew and produced H₂S at both neutral or alkaline pH. At low pH no pure culture was able to grow and no production of H₂S was detected. A mixed culture formed by the three isolated SRB was the only culture that grew and produced sulphide at the three different pH tested in shorter time (24 hours). The improvement of bacterial activity can be based in the metabolic diversity of the mixed culture able to use lactate and acetate as a result of the joint activity of these species. Energy obtained from the substrate is thus used more efficiently.

Abstract: In a batch mixed culture of Propionibacterium acidipropioniai and Saccharomyces cerevisiae, which could exploit synergistic effects, cell growth and propionic acid production rates of P. acidipropioniai significantly increased, compared with those in pure cultures. Compared with a pure culture, the mixed culture had a significant improvement on the maximal propionic acid (12.1 g/l vs. 10.1 g/l) and glycerol conversion efficiency (60.5% vs. 50.5%). Propionic acid production was further enhanced by an addition of glycerol solution in the fed-batch mixed culture; and the maximal propionic acid yield and glycerol conversion efficiency reached 27.9 g/l and 56.7%, respectively. These results showed that a mixed culture of P. acidipropionici and S. cerevisiae could serve as an excellent alternative to conventional propionic acid fermentation.

Abstract: Island settlement in the South-East of Zhejiang Province is a blend region of a variety of marine habitat development model, its formation, development and evolution are closely related with the local geographical environment, cultural background, sources of material and building way. This paper takes the Ruoshan Islands of Wenling, Zhejiang Province as an example, mixes the cultures of Eastern Fujian and South Zhejiang to analyze the causes and law of the island habitat’s evolution, and puts forward the basic method and strategy for construction of the marine habitat with mixed culture character.

Abstract: The removal of sulfur in coal before its combustion can reduce its environmental pollution, and microbial desulfurization should have good application prospects. Some species of bacteria have been used in the process of coal desulfurization, and our previous study demonstrated that mixed culture should be more efficient than pure culture by shaking cultivation. In this study, column leaching was investigated, due to its similarity to the industrial heap leaching. The mixed culture consisted of three strains of bacteria, which were Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans respectively. The ratio of the three strains of bacteria was 1: 1: 1. The column (50 cm height, 650 mm Inner Diameter) bioleaching experiments were carried out at ambient temperature. After desulfurization for 18 days, the ultimate desulfurization rate was 28.66% for total sulfur, which was higher than the previous study of J.Cara (with total sulfur desulfurization rate for 24% after 125 days). This study showed that ferric ions should be in proper concentration, and Leptospirillum ferrooxidans might be in lower ratio for reducing the precipitation of jarosite and improving the efficient of coal desulfurization.

Abstract: To reduce the production cost of polyhydroxyalkanoates (PHA) and disposal amount of excess sludge simultaneously, volatile fatty acids (VFAs) from alkaline excess sludge fermentation was used as carbon sources to synthesize PHA by unenriched mixed cultures. Released phosphorus and residual ammonium in the fermentative VFAs was controlled by adding magnesium to form struvite precipitation. Four VFAs liquids obtained was used to test the influence of initial carbon load and carbon to nitrogen ratio (C:N ratio) on the VFAs uptake rate, PHA storage rate and biomass growth rate. Results show that higher initial carbon substrate load results in relatively higher VFAs uptake rate and higher PHA storage rate, while higher initial C:N ratio results in relatively lower biomass growth rate from VFAs. VFAs generated from thermophilic alkaline sludge fermentation were a suitable carbon source for PHA production by mixed cultures.

Abstract: The biodegradation of mixed cultures was analyzed. The paper studied the effects of treat condition (static and shaking), concentration of dye, activities of oxidative enzymes (LiP, laccase and Manganese Peroxidase) and the bioaugmentation effects of the activated sludge system. The results showed that mixed cultures were able to degrade Reactive Brilliant Red X-3B and Direct Blue-6 (100 mg/L) completely within 32 h in shaking condition. As the initial concentration of Reactive Brilliant Red X-3B increased from 100mg/L to 900mg/L, the decolorization rate still maintain a high level only decreased from 99.3% to 83.5%. Induction in the activity of oxidative enzymes (LiP, laccase and Manganese Peroxidase) represented their role in degradation. In augmented experiments, it showed that in the control SBR system with the CODCr of the effluent was in three average levels 848, 1228, and 1550 mg/L, the CODCr degradation rates were 42.3%, 32.8% and 19.7%. In the augmented system treated with the same effluent, the degradation rates of augmented system were 86.5%, 71.8% and 59.8% respectively. It showed that the activated sludge was augmented by the mixed cultures which made the system to be more stable and improve impact resistance.