Some molecular aspects of hydrogen production by marine Chlorella pyrenoidosa under nitrogen deprivation condition in natural seawater

In this study, marine microalgae Chlorella pyrenoidosa produced 186 ml H₂/l under nitrogen deprivation in natural seawater, and adding 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) to medium reduced the total volume of hydrogen production by 85%. This suggested water was the main electron donor for hydrogenase. An active starch accumulation was observed during the first two days in nitrogen deprivation. But the starch content in cell decreased only by 7% at the end of the hydrogen evolution stage. This was shown the absence of a large contribution of starch to the hydrogen production by C. pyrenoidosa in nitrogen deprivation. Different from the hydrogen production by Chlamydomonas reinhardtii under sulfur deprivation condition, the concentration of acetate in the medium decreased not only at the stage of oxygen consumption but also during the stage of hydrogen evolution by C. pyrenoidosa. Thus, acetate is involved not only in the establishment of anaerobiosis but also plays an important role in the production of hydrogen by C. pyrenoidosa as an exogenous electron donor.     

Effect of microbial hydrogen consumption on the hydrogen permeation behaviour of AISI 4135 steel under cathodic protection

The feasibility of microbial hydrogen consumption to mitigate the hydrogen embrittlement (HE) under different cathodic potentials was evaluated using the Devanathan-Stachurski electrochemical test and the hydrogen permeation efficiency η. The hydrogen permeation efficiency η in the presence of strain GA-1 was lower than that in sterile medium. The cathodic potential inhibited the adherence of strain GA-1 to AISI 4135 steel surface, thereby reducing the hydrogen consumption of strain GA-1. The adherent GA-1 cells were capable of consuming ‘cathodic hydrogen’ and reducing the proportions of absorbed hydrogen, indicating that it is theoretically possible to control HE by hydrogen-consuming microbes.     

海洋中石油烃类降解与微生物腐蚀关系研究

在工程实践中,国家重要的海洋工程设施（如海底输油管线和船舶燃料系统等）发生的腐蚀破坏案例常常涉及到油水环境,并与微生物腐蚀作用密切相关,而了解海洋含油环境中石油烃类的生物转换机制是了解微生物腐蚀的关键。阐述了海洋环境中降解石油烃类的主要微生物及其降解机制,其在有氧和无氧条件下呈现不同的特点。微生物降解石油烃类过程中非常重要的一步即为接受电子,该过程将生物无法直接利用的化学能转换成可直接利用的能量形式,即腺苷三磷酸（ATP）。有氧条件下的烃类降解以氧气作为最终电子受体,而在缺氧条件下可利用硝酸盐、铁离子、硫酸盐等作为电子受体。海洋环境中的石油烃类会促进腐蚀性硫化物的生成,因此油水环境下的微生物腐蚀机理以硫化物的腐蚀破坏为主。此外,烃类降解过程产生的琥珀酸等酸性中间代谢物也会加剧腐蚀的发生。但目前关于海洋油水环境中微生物群落作为一个整体展现出的功能性及其对钢铁设施的破坏机理,仍然缺乏系统性的研究,而基于高通量测序的微生物组学研究技术将成为有效解决这些问题的手段之一。     

Corrosion rate of ordinary and high-performance concrete subjected to chloride attack by AC impedance spectroscopy

Corrosion of reinforcing steel in concrete is studied by using AC impedance. Subjected to different conditions and chloride concentrations, a laboratory study was conducted to estimate the corrosion rate of reinforcing steel embedded in ordinary Portland concrete (OPC) and high-performance concrete (HPC).One hundred and four OPC and HPC concrete cylinders embedded with a single reinforcing steel bar were exposed to sodium chloride solution with 0%, 1%, 3% and 5% concentrations. Specimens were also subjected to pre-conditioning and drying-wetting cycles.The AC Impedance technique (IS) was used to determine the corrosion rate of the reinforced concrete cylinders. In order to interpret the AC impedance spectra, several electrical equivalent circuits were employed.This investigation aims to compare IS with commonly used corrosion assessment techniques, such as Tafel plot (TP) and linear Polarization (LP).Results confirm that data obtained from AC impedance can be used to calculate the corrosion rate of reinforcing steel. A reasonable agreement with the results of TP and LP techniques is demonstrated. It is found that the corrosion rates obtained by AC impedance technique are lower than TP by 5–20%, while results of LP are 20–30% higher than those of TP.     

Comparison of photobioreactors and optimal light regime for rapid vegetative propagation of transgenic Undaria pinnatifida gametophytes

BACKGROUND: Previously, tachyplesin gene (tac) has been successfully transferred into Undaria pinnatifida gametophytes using the method of microprojectile bombardment transformation. The objectives of this study were to compare and evaluate the performance of bubble‐column and airlift bioreactors to determine a preferred configuration of bioreactor for vegetative propagation of transgenic U. pinnatifida gametophytes, and to then investigate the influence of light on vegetative propagation of these gametophytes, including incident light intensity, photoperiod and light quality to resolve the problems of rapid vegetative propagation within the selected bioreactor. RESULTS: Experimental results showed that final dry cell density in the airlift bioreactor was 12.7% higher than that in the bubble‐column bioreactor under the optimal aeration rate of 1.2 L air min^?1 L^?1 culture. And a maximum final dry cell density of 2830 mg L^?1 was obtained within the airlift bioreactor using blue light at 40 µmol m^?2 s^?1 with a light/dark cycle of 14/10 (h). Polymerase chain reaction (PCR) analysis indicated that genes (bar and tac) were not lost during rapid vegetative propagation within the airlift bioreactor. CONCLUSION: The airlift bioreactor was shown to be much more suitable for rapid vegetative propagation of transgenic U. pinnatifida gametophytes than the bubble‐column bioreactor in the laboratory. The use of blue light allows improvement of vegetative propagation of transgenic U. pinnatifida gametophytes. Copyright © 2009 Society of Chemical Industry     

The effect of feed withdrawal on Escherichia coli shedding in beef cattle

Ten beef cattle feeding on silage were orally administered a marker organism (nalidixic acid resistant Escherichia coli K12) daily over six days. Subsequently, the administration of the marker organism was stopped, and the animals were divided into two groups (five animals each). The feed was removed from one group (i.e. fasted group) for 48 h, while the feeding of the control group was continued during that period, until both groups were subsequently slaughtered. During this pre-slaughter period, faecal shedding of total E. coli and E. coli K12, as well as of background flora (total aerobes, total anaerobes, and lactobacilli), was monitored in faecal material obtained by rectal swabs from each animal. After both 24 and 48 h of fasting, the levels of total E. coli shed significantly increased (P<0.01) in the fasted group compared with the control group; total anaerobes shed also increased (after 48 h fasting; P<0.05); while shedding of total aerobes and total lactobacilli did not change significantly. After slaughter of animals, the pH values and the levels of bacterial groups mentioned above were examined in contents of different sections of the gastrointestinal (GI) tract (rumen, abomasum, caecum, small intestine, colon). The pH values were significantly increased in rumen and decreased in abomasum (P<0.05) of the fasted animals compared with controls, but did not differ significantly in other GI sections. Significant decreases of total E. coli population (P<0.05) in abomasums and lactobacilli (P<0.01) in small intestines were observed in fasted animals, while other bacterial groups in other GI sections did not change significantly compared with controls. The marker organism E. coli K12 was not sufficiently competitive within the bovine GI tracts as it was pre-slaughter shed by, and post-slaughter isolated from, only a minority of animals regardless of the group. Overall, the results indicate that key fasting-induced changes of enteric E. coli populations, and influencing its faecal shedding, could have occurred within the relatively short caudal colon–rectum–anus region of the bovine GI tract.     

g-C3N4 doping TiO2 recovered from spent catalyst for H2 evolution from water

Spent catalysts of selective catalytic reduction (SCR) contain a high content of TiO₂ (>70 wt%). The effective recovery of TiO₂ from spent SCR catalysts and its reuse in photocatalytic hydrogen production is of great importance for environmental protection. In this study, the recovered TiO₂ from the spent SCR catalyst was recovered by the alkali washing method, and the purity of the recovered TiO₂ reached 94.7%. g-C₃N₄ as a co-catalyst and enhanced the separation efficiency of the photogenerated electron-hole pairs of the TiO₂ photocatalyst. The composite photocatalyst R–TiO₂/g-C₃N₄ prepared by directly mixing the recovered TiO₂ with g-C₃N₄ significantly improved the photocatalytic activity. The experimental design of the photocatalyst synthesis was optimized using the Design Expert software. The results showed that the recovered TiO₂ was 0.334 g when the g-C₃N₄ was 0.046 g and the ultrasonic time was 163 min. Moreover, the hydrogen production rate reached 443.105 μmol g⁻¹ h⁻¹ within 4 h.     

Design of a furnace for refining copper prior to fusion

The design of a furnace for the removal of copper impurities prior to smelting is presented here. Impurities such as arsenic, antimony, bismuth, lead, and zinc are removed by heating the concentrate below 1000°C in an indirect way using the thermal energy from the gases of fusion and conversion. The concentrate heats up while sliding down along a hermetically sealed vacuum tunnel. After passing through filters, the volatilized substances are conducted along a tunnel with a decreasing temperature profile which induces a step-wise condensation and recovery of the different substances. The main operating cost of the furnace is due to the electric energy required by the vacuum pumps and the liquid air condensers. This cost turns out to be very small as compared to the overall operating cost of the smelter.     

镀锌钢腐蚀行为的研究进展

镀锌是保护钢铁腐蚀最经济有效的方法之一,研究镀锌钢在不同环境中的腐蚀规律、腐蚀机理和腐蚀特性显得尤为重要。综述了镀锌钢发生电化学腐蚀的基本原理及其在大气、海水和钢筋混凝土介质中的腐蚀行为,同时叙述了pH值、温度和Cl-等环境因素对镀锌钢腐蚀性能的影响。