Growth with high planktonic biomass in Shewanella oneidensis fuel cells

Shewanella oneidensis MR-1 grew for over 50 days in microbial fuel cells, incompletely oxidizing lactate to acetate with high recovery of the electrons derived from this reaction as electricity. Electricity was produced with lactate or hydrogen and current was comparable to that of electricigens which completely oxidize organic substrates. However, unlike fuel cells with previously described electricigens, in which cells are primarily attached to the anode, at least as many of the S. oneidensis cells were planktonic as were attached to the anode. These results demonstrate that S. oneidensis may conserve energy for growth with an electrode serving as an electron acceptor and suggest that multiple strategies for electron transfer to fuel cell anodes exist.     

Reuse potential of agricultural wastes in semi-arid regions: Egypt as a case study

Agricultural wastes represent an important source of bio-energy and valuable products. In Egypt, 18% of the agricultural wastes is used directly as fertiliser. Another 30% is used as animal food. The remainder is burnt directly on the fields or is used for heating in the small villages, using low efficiency burners. These wastes can be used more efficiently as a source of energy and as organic fertiliser. The anaerobic bioconversion of these materials will result in a net energy production. The utilisation of agricultural wastes for the production of energy and compost, combined with using solar energy will save fossil fuel, improve health conditions and the general life quality in the villages. This revised version was published online in June 2006 with corrections to the Cover Date.     

Advanced monitoring of high-rate anaerobic reactors through quantitative image analysis of granular sludge and multivariate statistical analysis

Four organic loading disturbances were performed in lab-scale EGSB reactors fed with ethanol. In load disturbance 1 (LD1) and 2 (LD2), the organic loading rate (OLR) was increased between 5 and 18.5 kg COD m(-3) day(-1), through the influent ethanol concentration increase, and the hydraulic retention time decrease from 7.8 to 2.5 h, respectively. Load disturbances 3 (LD3) and 4 (LD4) were applied by increasing the OLR to 50 kg COD m(-3) day(-1) during 3 days and 16 days, respectively. The granular sludge morphology was quantified by image analysis and was related to the reactor performance, including effluent volatile suspended solids, indicator of washout events. In general, it was observed the selective washout of filamentous forms associated to granules erosion/fragmentation and to a decrease in the specific acetoclastic activity. These phenomena induced the transitory deterioration of reactor performance in LD2, LD3, and LD4, but not in LD1. Extending the exposure time in LD4 promoted acetogenesis inhibition after 144 h. The application of Principal Components Analysis determined a latent variable that encompasses a weighted sum of performance, physiological and morphological information. This new variable was highly sensitive to reactor efficiency deterioration, enclosing variations between 27% and 268% in the first hours of disturbances. The high loadings raised by image analysis parameters, especially filaments length per aggregates area (LfA), revealed that morphological changes of granular sludge, should be considered to monitor and control load disturbances in high rate anaerobic (granular) sludge bed digesters.     

Community dynamics within a bacterial consortium during growth on toluene under sulfate-reducing conditions

A sulfate-reducing bacterial consortium was enriched from an anoxic aquifer contaminated with BTEX compounds, using toluene as a growth substrate. Total cell counts, protein contents and sulfide production were determined to follow growth at the in situ temperature (14 °C) and at 25 °C, respectively. Community members were identified by 16S rRNA gene cloning and sequencing. Phylogenetic analysis revealed 12 sequence types belonging to Deltaproteobacteria (several groups) , Epsilonproteobacteria, Bacteroidetes, Spirochaetaceae and an unclassified bacterial clade. The most prominent phylotype comprising 34% of all clones was affiliated to the Desulfobulbaceae and closely related to environmental clones retrieved from hydrocarbon-contaminated aquifers. Flow-cytometric methods were applied to analyze the community dynamics and to identify key organisms involved in toluene assimilation. Flow-cytometric measurement of DNA contents and scatter behavior served to detect and quantify dominant and newly emerging clusters of subcommunities. Up to seven subcommunities, two of them dominant, were distinguished. Cell sorting was used to facilitate the analysis of conspicuous clusters for phylogenetic identity by terminal restriction fragment length polymorphism profiling of the 16S rRNA genes. The Desulfobulbaceae phylotype accounted for up to 87% in proliferating subcommunities, indicating that it represents the key organism of toluene degradation within this complex anaerobic consortium.     

Comparison of static,in-vessel composting of MSW with thermophilic anaerobic digestion and combinations of the two processes

The biological stabilisation of the organic fraction of municipal solid waste (OFMSW) into a form stable enough for land application can be achieved via aerobic or anaerobic treatments. To investigate the rates of degradation (e.g. via electron equivalents removed, or via carbon emitted) of aerobic and anaerobic treatment, OFMSW samples were exposed to computer controlled laboratory-scale aerobic (static in-vessel composting), and anaerobic (thermophilic anaerobic digestion with liquor recycle) treatment individually and in combination. A comparison of the degradation rates, based on electron flow revealed that provided a suitable inoculum was used, anaerobic digestion was the faster of the two waste conversion process. In addition to faster maximum substrate oxidation rates, anaerobic digestion (followed by post-treatment aerobic maturation), when compared to static composting alone, converted a larger fraction of the organics to gaseous end-products (CO₂ and CH₄), leading to improved end-product stability and maturity, as measured by compost self-heating and root elongation tests, respectively. While not comparable to windrow and other mixed, highly aerated compost systems, our results show that in the thermophilic, in-vessel treatment investigated here, the inclusion of a anaerobic phase, rather than using composting alone, improved hydrolysis rates as well as oxidation rates and product stability. The combination of the two methods, as used in the DiCOM^® process, was also tested allowing heat generation to thermophilic operating temperature, biogas recovery and a low odour stable end-product within 19 days of operation.     

Complete genome sequence of Anaerococcus prevotii type strain (PC1)

Anaerococcus prevotii (Foubert and Douglas 1948) Ezaki et al. 2001 is the type species of the genus, and is of phylogenetic interest because of its arguable assignment to the provisionally arranged family 'Peptostreptococcaceae'. A. prevotii is an obligate anaerobic coccus, usually arranged in clumps or tetrads. The strain, whose genome is described here, was originally isolated from human plasma; other strains of the species were also isolated from clinical specimen. Here we describe the features of this organism, together with the complete genome sequence and annotation. This is the first completed genome sequence of a member of the genus. Next to Finegoldia magna, A. prevotii is only the second species from the family 'Peptostreptococcaceae' for which a complete genome sequence is described. The 1,998,633 bp long genome (chromosome and one plasmid) with its 1852 protein-coding and 61 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.     

Biodegradation performance of an anaerobic hybrid reactor treating olive mill effluent under various organic loading rates

The primary objective of this study was to evaluate the performance of a 20 l lab scale anaerobic hybrid reactor (AHR) combining sludge blanket in the lower part and filter in the upper part under varying organic loading rates (OLRs) in order to study biodegradation of olive mill effluent (OME). For this purpose, some parameters, such as total phenols, effluent chemical oxygen demand (COD), suspended solids (SS), volatile fatty acids (VFAs), and pH in the influent and effluent, and removal efficiencies for those parameters (except pH) were continuously monitored throughout the experimental period of 477 days. Eleven different organic loadings between 0.45 and 32 kg COD m⁻³ day⁻¹ were imposed by either varying influent COD or hydraulic retention time (HRT). The results demonstrated that the AHR reactor could tolerate high influent COD concentrations. Removal efficiencies for the studied pollution parameters were found to be as follows: COD, 50–94%; total phenol, 39–80%; color, 0–54%; and suspended solids, 19–87%. The levels of VFAs in the effluent, which was principally acetate, butyrate, iso-butyrate, and propionate, varied between 10 and 2005 mg l⁻¹ depending upon OLRs. A COD removal efficiency of 90% could be achieved as long as OLR is kept at a level of less than 10 kg COD m⁻³ day⁻¹. However, a secondary treatment unit for polishing purposes is necessary to comply with receiving media discharge standards.     

Synergetic effect of pH and biochemical components on bacterial diversity during mesophilic anaerobic fermentation of biomass-origin waste

Aims: To investigate the synergetic effect of pH and biochemical components on bacterial community structure during mesophilic anaerobic degradation of solid wastes with different origins, and under acidic or neutral conditions. Methods and Results: The bacterial community in 16 samples of solid wastes with different biochemical compositions and origins was evaluated during mesophilic anaerobic degradation at acidic and neutral pH. Denaturing gradient gel electrophoresis (DGGE) and single‐strand conformation polymorphism (SSCP) were used to compare the communities. Multivariate analysis of the DGGE and SSCP results revealed that most of the dominant microbes were dependent on the content of easily degradable carbohydrates in the samples. Furthermore, the dominant microbes were divided into two types, those that preferred an acid environment and those that preferred a neutral environment. A shift in pH was found to change their preference for medium substrates. Although most of the substrates with similar origin and biochemical composition had similar microbial diversity during fermentation, some microbes were found only in substrates with specific origins. For example, two microbes were only found in substrate that contained lignocellulose and animal protein without starch. These microbes were related to micro‐organisms that are found in swine manure, as well as in other intestinal or oral niches. In addition, the distribution of fermentation products was less sensitive to the changes in pH and biochemical components than the microbial community. Conclusions: Bacterial diversity during anaerobic degradation of organic wastes was affected by both pH and biochemical components; however, pH exerted a greater effect. Significance and Impact of the Study: The results of this study reveal that control of pH may be an effective method to produce a stable bacterial community and relatively similar product distribution during anaerobic digestion of waste, regardless of variation in the waste feedstocks.     

Reactor performance and microbial community of an EGSB reactor operated at 20 and 15°C

Aims:  To investigate the effects of low temperatures on the performance and microbial community of anaerobic wastewater treatment.
Methods and Results:  An expanded granular sludge bed (EGSB) reactor was employed to treat synthetic brewery wastewater at 20 and 15°C. Reactor performance was represented by chemical oxygen demand (COD) removal efficiency, while the microbial community was analysed using denaturing gradient gel electrophoresis (DGGE) and clone technology. When the hydraulic retention time (HRT) was maintained at 18 h, COD removal efficiencies above 85% were obtained at both 20 and 15°C, with influent COD concentrations up to 7300 and 4100 mg l⁻¹, respectively. At 15°C, the COD removal efficiency was more easily manipulated by increasing the influent COD concentration. DGGE and clone results for both temperatures revealed that Methanosaeta and Methanobacterium were two dominant methanogens, and that the majority of the eubacterial clones were represented by Firmicutes . When the temperature decreased from 20 to 15°C, both archaeal and eubacterial communities had higher diversity, and the proportion of Methanosaeta (acetate-utilizing methanogens) decreased markedly from 60·0% to 49·3%, together with an increase in proportions of hydrogen-utilizing methanogens (especially Methanospirillum ).
Conclusions:  The feasibility of psychrophilic anaerobic treatment of low and medium strength organic wastewaters was demonstrated, although lower temperature could significantly affect both reactor performance and the anaerobic microbial community.
Significance and Impact of the Study:  The findings enrich the theory involving the microbial community and the application of anaerobic treatment in a psychrophilic environment.     

酸碱调控污泥厌氧发酵实现乙酸累积及微生物种群变化

摘要：【目的】通过对污泥厌氧发酵pH调控,研究挥发性脂肪酸的累积、产酸微生物种群变化及产氢产乙酸菌群对乙酸产生的贡献。【方法】测定不同pH条件下污泥厌氧发酵过程中挥发性脂肪酸的累积;分别应用末端限制性片段长度多态性（T-RFLP）和荧光原位杂交技术（FISH）分析产酸系统中微生物种群结构的变化及产氢产乙酸菌的数量。【结果】 pH为10.0时,有机酸和乙酸的产率在发酵结束时分别达到652.6 mg COD/g-VS和322.4 mg COD/g-VS,显著高于其它pH条件。T-RFLP结果表明,pH值为12