Fermentative biohydrogen production II: Net energy gain from organic wastes

Several reports have demonstrated the feasibility of hydrogen production by dark fermentation (DF). However, most reports had resorted to mesophilic or thermophilic conditions to increase hydrogen yield, overlooking the energy input to the process and hence, loss of net energy gain. For net positive energy gain, energy input to the process should be minimized and additional energy should be harvested from the aqueous end products of DF. Our previous study presented an approach to assess the potential for net energy gain from the hydrogen produced by DF, and from the end products of DF via anaerobic digestion (AD) or microbial fuel cells (MFC). In this study, that approach is extended to identify the most promising process configuration and operating conditions to maximize net energy gain possible from liquid and particulate organic wastes. Based on this analysis, DF followed by MFC appears to result in higher net energy gains.     

Plastic Degradation by Extremophilic Bacteria

Intensive exploitation, poor recycling, low repeatable use, and unusual resistance of plastics to environmental and microbiological action result in accumulation of huge waste amounts in terrestrial and marine environments, causing enormous hazard for human and animal life. In the last decades, much scientific interest has been focused on plastic biodegradation. Due to the comparatively short evolutionary period of their appearance in nature, sufficiently effective enzymes for their biodegradation are not available. Plastics are designed for use in conditions typical for human activity, and their physicochemical properties roughly change at extreme environmental parameters like low temperatures, salt, or low or high pH that are typical for the life of extremophilic microorganisms and the activity of their enzymes. This review represents a first attempt to summarize the extraordinarily limited information on biodegradation of conventional synthetic plastics by thermophilic, alkaliphilic, halophilic, and psychrophilic bacteria in natural environments and laboratory conditions. Most of the available data was reported in the last several years and concerns moderate extremophiles. Two main questions are highlighted in it: which extremophilic bacteria and their enzymes are reported to be involved in the degradation of different synthetic plastics, and what could be the impact of extremophiles in future technologies for resolving of pollution problems.     

高效菌种的厌氧-缺氧-膜生物反应器处理焦化废水

采用厌氧-缺氧-膜生物反应器(A~2O-MBR)工艺处理焦化废水,并投入经固定化的高效菌种.采用MBR使污泥含量大为提高,污泥沉降比增大,故采用泥水回流,使MBR的泥水回到缺氧池.厌氧池采用具有蜂窝胞壁结构的纤维滤料.经过3个多月的试验表明,该工艺运行稳定,具有较好的适应能力和抗冲击能力.当进水COD和氨氮质量浓度分别为2 000 mg·L~(-1)和150 mg·L~(-1)左右时,出水分别在120 mg·L~(-1)和9 mg·L~(-1)左右,去除率分别约为94%和93%,均达到GB 8978-1996的一级标准要求.     

电厂循环水杀菌灭藻处理探讨

介绍了电厂循环水处理方法，并对各种方法进行了优缺点比较，对电厂循环水处理有一定的指导意义。     

Predicting Thermophilic Spore Population Dynamics for UHT Sterilization Processes

A mathematical model of Bacillus stearothermophilus spore populations during lethal heating treats activation of dormant spores and inactivation mechanisms affecting dormant/activated spores. Rate constants of activation/inactivation processes were determined from isothermal survivor curves of experiments in 105, 110, 115, and 120°C and corresponding simulations with the model. Variations of rate constants with temperature were incorporated by Arrhenius equations responding to general temperature regimes. Tests demonstrated high correspondence between experimental survivor curves and those generated by simulations with the model for isothermal and dynamic, lethal heating. Tests also indicated Arrhenius rate constants at low lethal temperatures (105-120°C) and the model may apply to ultra high temperature. The new model was more effective than the traditional model in representing and predicting spore population dynamics during lethal heating.     

Characterization and Classification of Streptococcus Thermophilus and Lactobacillus Delbrueckii Subsp. Bulgaricus Strains Isolated from Traditional Greek Yogurts

ABSTRACT Streptococcus thermophilus (74 strains) and Lactobacillus delbrueckii subsp. bulgaricus (75 strains) isolates from traditional Greek yogurts were tested on the basis of their acidification kinetics, acidity, viscosity, and aroma compounds formation in milk pure cultures. Strains of Lb. bulgaricus presented greater viscosity values, higher acidification activity and produced more acetaldehyde at culture pH 4.6 than S. thermophilus strains. Acetoin was formed only by the latter strains, while diacetyl was not detected in either species. Application of cluster and discriminant analysis permitted definition of distinct groups of strains and of the most significant variables to discriminate among them. Finally, classification and regression tree analysis allowed clusters characterization by critical values of the most discriminant variables. Evaluation of results as above could be a useful tool to select, through a large number of screened strains, the suitable starters for specific purposes.     

低温纤维素降解菌的筛选及其产酶研究

从甘南州玛曲县高寒草甸土壤中筛选出一株低温纤维素降解菌M7。通过形态观察、生理生化及16SrRNA序列比对分析,发现菌株M7与Bacillus subtili strain XS6进化距离最近,初步鉴定为枯草芽孢杆菌（Bacillus subtili）。通过Box-Benhnken中心组合设计和响应面分析法（RSM）,对其生长和产羧甲基纤维素酶（CMCase）条件进行优化。结果表明:温度20℃,培养基初始pH5.0,转速175r/min,酵母膏2.5g/L和微晶纤维素2.5g/L,蛋白胨5g/L,菌株M7所产CMCase达到最大值。      

Protease and xylanase activities and thermophilic populations as potential process monitoring tools during thermophilic aerobic digestion

Thermophilic aerobic digestion (TAD) of potato process waste slurry was carried out in a batch process in a continuously stirred tank reactor at 55 °C for a total of 156 h. The pH of the slurry was either unregulated, or regulated at 6.0, 7.0, 8.0, 9.0 and 9.5, and aeration rate was 0.5 vvm. The effect of aeration rate on the digestion process was studied at 0.1, 0.25, 0.5 and 1.0 vvm at pH 7.0 and 55 °C. The development of thermophiles (55 and 65 °C populations) and hydrolytic enzyme activities (protease and xylanase) in the process were monitored. Thermophiles developed rapidly to reach peak populations in 24h or earlier, and remained stable at all fixed pH reactions. The thermophile population was only minimally affected by the aeration rate, and they were present mostly as spores after 96h of digestion. Xylanase enzyme appeared rapidly, reached a peak in approximately 60h, and declined rapidly thereafter. Highest activities were produced in neutral reactions and higher aeration rates. Aeration rates affected protease activity profoundly. The profile of both enzymes closely reflected the development of microbial activity and the overall progress of TAD, in a medium where their substrates were not predominant and not the preferred carbon sources. The relatively simple process of measuring the activities of these enzymes is potentially a more direct measure of the progress of TAD than enumeration of the microbial populations and thus, has greater potential in process monitoring. Copyright © 2003 Society of Chemical Industry     

Corrosion inhibition approach of oil production systems in offshore oilfields

Synthesis and modification of imidazoline were carried out based on review of the corrosion inhibitor development and application for oilfields. A series of imidazoline compounds were synthesised through the solvent dewatering and vacuum dewatering methods. After reaction of imidazoline with ethane oxide, the produced compound was used to react with halogen hydrocarbon and polyphosphoric acid respectively. Finally an agent with performance of corrosion‐inhibition, sterilisation and anti‐scaling was obtained. The structures of the compounds were characterised by the Fourier transformation infrared spectrum. The relationships between corrosion inhibition effectiveness of the compounds and their structures were investigated so as to determine the structure of a novel corrosion inhibitor. The selected corrosion inhibitor was evaluated by a series of experiments to understand the characteristics of imidazoline derivative and some major factors associated with oil production in the oilfields of China. The experimental results showed that this corrosion inhibitor has outstanding performance of corrosion inhibition and sterilization, and is suitable for corrosion inhibition of the oil abstraction systems with high water‐content in the offshore oilfields.     

Removal of dimethyl sulfide in a thermophilic membrane bioreactor

BACKGROUND: Several sources such as the paper and pulp industry and waste treatment plants emit waste gases containing volatile organic sulfur compounds at elevated temperature. Since cooling the hot gases increases the operational cost of biological reactors, application of thermophilic microorganisms could be a cost‐effective solution. The objectives of this study were to investigate the possibility of removal of dimethyl sulfide from waste gases under thermophilic conditions (52 °C) in a membrane bioreactor and to examine the long‐term stability of the reactor at elevated temperature. The effects of operating conditions such as gas residence time, nutrient supply, temperature decrease and short‐term shutdown on elimination capacity were investigated. RESULTS: A maximum elimination capacity of 54 g m^?3 h^?1 (0.108 g m^?2 h^?1) was obtained at a mass loading rate of 64 g m^?3 h^?1 (0.128 g m^?2 h^?1) with a removal efficiency of 84% at a gas residence time of 24 s. The long‐term operation of the thermophilic membrane bioreactor was followed for 9 months. Although the removal efficiency decreased to 50% after 3 months of continuous operation, it recovered (>96%) after the excess biomass was removed by applying high‐velocity liquid recirculation. CONCLUSION: This study demonstrated that the dimethyl sulfide removal is possible in a thermophilic membrane bioreactor with an elimination capacity of 54 g m^?3 h^?1 (0.108 g m^?2 h^?1) at a gas residence time of 24 s. Copyright © 2008 Society of Chemical Industry