Mechanisms and models for anaerobic granulation in upflow anaerobic sludge blanket reactor

Upflow anaerobic sludge blanket (UASB) reactor has been employed in industrial and municipal wastewater treatment for decades. However, the long start-up period required for the development of anaerobic granules seriously limits the application of this technology. In order to develop the strategy for rapid UASB start-up, the mechanisms for anaerobic granulation should be understood. This paper attempts to provide a up-to-date review on the existing mechanisms and models for anaerobic granulation in the UASB reactor, which include inert nuclei model, selection pressure model, multi-valence positive ion-bonding model, synthetic and natural polymer-bonding model, Capetown's model, spaghetti theory, syntrophic microcolony model, multi-layer model, secondary minimum adhesion model, local dehydration and hydrophobic interaction model, surface tension model, proton translocation-dehydration theory, cellular automaton model and cell-to-cell communication model. Based on those previous works, a general model for anaerobic granulation is also proposed. It is expected that this paper would be helpful for researchers to further develop a unified theory for anaerobic granulation and technology for expediting the formation of the UASB granules.     

Effect of temperature on removal of heavy metals from contaminated river sediments via bioleaching

The aim of this study was to determine the effect of temperature on the solubilization of heavy metals from contaminated river sediment by sulfur oxidizing bacteria taken from Ell-Ren River sediment. Of three temperatures tested (25 degrees C, 37 degrees C and 55 degrees C), pH decrease was greatest at 37 degrees C, indicating that, after acclimation, bacterial oxidizing activity is greatest at this temperature. At 55 degrees C, pH change was similar to that which occurred with no inoculum added. The increase in sulfates and high pH at 55 degrees C indicate that the indirect mechanism was not initiated at this temperature. Solubilization efficiency of total extractable Ni, Zn, Cu and Cr was high (>90%) at 37 degrees C, whilst that of Pb was only 60.4%. Except for Pb, the optimal temperature for solubilization of total extractable heavy metal was 37 degrees C. The order of average solubilization efficiency of total extractable heavy metals was Ni, Zn, Cu>Cr>Co, Pb. The solubilization efficiency of Pb and Co was markedly less than that of other heavy metals. Transfer of heavy metals between binding fractions was most apparent at 55 degrees C before and after bioleaching.     

Influence of loosely bound extracellular polymeric substances (EPS) on the flocculation, sedimentation and dewaterability of activated sludge

Laboratory experiments on the activated sludge (AS) process were carried out to investigate the influence of microbial extracellular polymeric substances (EPS), including loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), on biomass flocculation, sludge settlement and dewaterability. The heat EPS extraction method was modified to include a mild step and a harsh step for extracting the LB-EPS and TB-EPS, respectively, from the sludge suspension. Six lab-scale AS reactors were used to grow AS with different carbon sources of glucose and sodium acetate, and different sludge retention times (SRTs) of 5, 10 and 20 days. The variation in the bioreactor condition produced sludge with different abundances of EPS and different flocculation and separation characteristics. The sludge that was fed on glucose had more EPS than the sludge that was fed on acetate. For any of the feeding substrates, the sludge had a nearly consistent TB-EPS value regardless of the SRT, and an LB-EPS content that decreased with the SRT. The acetate-fed sludge performed better than the glucose-fed sludge in terms of bioflocculation, sludge sedimentation and compression, and sludge dewaterability. The sludge flocculation and separation improved considerably as the SRT lengthened. The results demonstrate that the LB-EPS had a negative effect on bioflocculation and sludge-water separation. The parameters for the performance of sludge-water separation were much more closely correlated with the amount of LB-EPS than with the amount of TB-EPS. It is argued that although EPS is essential to sludge floc formation, excessive EPS in the form of LB-EPS could weaken cell attachment and the floc structure, resulting in poor bioflocculation, greater cell erosion and retarded sludge-water separation.     

Soluble microbial products formation in anaerobic chemostats in the presence of toxic compounds

Anaerobic chemostats fed on glucose (approximately 10 g chemical oxygen demand (COD)/L) were used to investigate the effects of toxicity on soluble microbial product (SMP) formation. Addition of the toxic compounds chloroform and chromium increased the net accumulation of SMP, despite reducing the percentage of SMP in the effluent due to the overwhelming production of volatile fatty acids (VFAs). In the reactor spiked with chloroform the normalized accumulation of SMP (SMP/So) increased from 2% to 8%, whereas in the reactor spiked with Cr (VI) the SMP/So ratio reached as high as 20% after the spike, and in both cases SMP net accumulation was proportional to the concentration of toxicant. After the chloroform and chromium spikes biomass seemed to produce more extra cellular polymeric substances (EPS) suggesting that this might have helped them to cope with the stress. Chromatography results indicate that some of the high MW compounds present in the SMP might have been due to EPS release into the bulk solution, and that other compounds, probably released as a result of cell lysis, were also present. Hydrolysis of EPS did not seem to contribute to SMP accumulation in the presence of toxic compounds, and DNA analysis suggested that cell lysis products was an important contribution to SMP accumulation, in the presence of chromium.     

“一带一路”油气资源潜力及合作前景

"一带一路"是国家重大战略,本文着重从"一带一路"油气资源潜力、贸易量及线路、我国石油企业对外合作权益等方面分析"一带一路"国家油气资源潜力与合作前景,指明油气资源主要合作方向是中东、中亚和俄罗斯等大型含油气区。在此基础上,结合中国油气资源形势,提出相关合作建议:一是巩固和加强与中亚国家的油气合作;二是扩大与中东国家油气合作的领域与规模;三是抓住机遇,力争在俄罗斯油气上游市场取得突破。     

Exposure assessment of carcass disposal options in the event of a notifiable exotic animal disease: application to avian influenza virus

We present a generalized exposure assessment of 28 disposal options for poultry carcasses in the event of a highly pathogenic avian influenza (HPAI) outbreak. The analysis supports a hereto unverified disposal hierarchy for animal carcasses, placing waste processing (e.g., incineration and rendering) above controlled disposal (e.g., landfill), above uncontrolled disposal (e.g., burial on-farm). We illustrate that early stages of the disposal chain (on-farm) pose greater opportunities for exposure to hazardous agents than later stages, where agents are generally contained, wastes are treated, and residues are managed by regulated processes. In selecting carcass disposal options, practitioners are advised to consider the full range of hazards rather than focusing solely on the HPAI agent, and to give preference to technologies that (i) offer high destruction efficiencies for target pathogens; (ii) do not give rise to significant releases of other pathogenic organisms; and (iii) do not release unacceptable concentrations of toxic chemicals. The approach offers an exposure assessment perspective for carcass disposal, thus providing a risk-informed basis for contingency planning and operational intervention. The authors recognize that relevant legislation, public perception, available capacity, and cost also need to be considered when selecting disposal options in the event of HPAI.     

肉松生产的新方法

前言肉松是在中国很普及的半干肉制品,其水分活度(a_w)大约在0.60～0.65。由于肉松的生产至今主要依靠经验,所以缺乏对加工过程中温度和时间的控制。传统的加工方法是用炒锅将肉块慢慢炒干打松;本试验运     

Natural products from marine organisms and their associated microbes

The marine environment is distinguished by unique groups of organisms being the source of a wide array of fascinating structures. The enormous biodiversity of marine habitats is mirrored by the molecular diversity of secondary metabolites found in marine animals, plants and microbes. The recognition that many marine invertebrates contain endo- and epibiotic microorganisms and that some invertebrate-derived natural products are structurally related to bacterial metabolites suggests a microbial origin for some of these compounds. Other marine natural products, however, are clearly located in invertebrate tissue and microbial involvement in the biosynthetic process seems unlikely. The complexity of associations in marine organisms, especially in sponges, bryozoans and tunicates, makes it extremely difficult to definitively state the biosynthetic source of many marine natural products or to deduce their ecological significance. Whereas many symbiotic marine microorganisms cannot be isolated and cultured, numerous epi- and endobiotic marine fungi produce novel secondary metabolites in laboratory cultures. The potent biological activity of many marine natural products is of relevance for their ecological function but is also the basis of their biomedical importance.     

Multiple-input microcantilever sensors

A surface-micromachined micro-electro-mechanical-system (MEMS) process has been used to demonstrate multiple-input chemical sensing using selectively coated cantilever arrays. Cantilever motion due to absorption-induced stress was readout using a custom-designed, eight-channel integrated circuit. Combined hydrogen and mercury vapor detection was achieved with a palm-sized, self-powered module with spread-spectrum telemetry reporting.     

Computerized detection and segmentation of mitochondria on electron microscope images

Mitochondrial function plays an important role in the regulation of cellular life and death, including disease states. Disturbance in mitochondrial function and distribution can be accompanied by significant morphological alterations. Electron microscopy tomography (EMT) is a powerful technique to study the 3D structure of mitochondria, but the automatic detection and segmentation of mitochondria in EMT volumes has been challenging due to the presence of subcellular structures and imaging artifacts. Therefore, the interpretation, measurement and analysis of mitochondrial distribution and features have been time consuming, and development of specialized software tools is very important for high-throughput analyses needed to expedite the myriad studies on cellular events. Typically, mitochondrial EMT volumes are segmented manually using special software tools. Automatic contour extraction on large images with multiple mitochondria and many other subcellular structures is still an unaddressed problem. The purpose of this work is to develop computer algorithms to detect and segment both fully and partially seen mitochondria on electron microscopy images. The detection method relies on mitochondria's approximately elliptical shape and double membrane boundary. Initial detection results are first refined using active contours. Then, our seed point selection method automatically selects reliable seed points along the contour, and segmentation is finalized by automatically incorporating a live-wire graph search algorithm between these seed points. In our evaluations on four images containing multiple mitochondria, 52 ellipses are detected among which 42 are true and 10 are false detections. After false ellipses are eliminated manually, 14 out of 15 fully seen mitochondria and 4 out of 7 partially seen mitochondria are successfully detected. When compared with the segmentation of a trained reader, 91% Dice similarity coefficient was achieved with an average 4.9 nm boundary error.