Dynamic Growth Rates of Microbial Populations in Activated Sludge Systems

Results of mathematical modeling and whole cell 16S ribosomal RNA-targeted fluorescence in situ hybridizations challenge the widely held perception that microbial populations in “steady-state” activated sludge systems share a common net growth rate that is proportional to the inverse of the mean cell residence time. Our results are significant because they encourage bioprocess engineers to appreciate the differences in growth physiology among individual microbial populations in complex mixed microbial communities such as suspended growth activated sludge bioreactor systems.     

Bacterial Leaching of Metals from Tannery Sludge by Indigenous Sulphur-Oxidizing Bacteria—Effect of Sludge Solids Concentration

An investigation on the effect of sludge solids concentration on bioleaching of Cr(III) and other metals from tannery sludge by indigenous sulphur-oxidizing bacteria was carried out. The sludge solids concentrations ranged from 13 to 60 g/L. The concentration of elemental sulphur was fixed at 30 g/L. The results showed that the lowest pH reached after 25 days of bioleaching at all studied sludge solids concentration was about 1.3. The optimum sludge solids concentration for maximum metal leaching from tannery sludge was 40 g/L and about 87% of Cr(III), 73% of Al, 72% of Fe, 62% of Mg, and 73% of Zn could be leached in this case. During bioleaching, the concentrations of total and volatile suspended solids of the tannery sludge significantly decreased. The sulphur-oxidizing bacteria could tolerate a Cr(III) concentration as high as 5,930 mg/L at pH 1.3. The leaching efficiencies of Cr(III), Al, and Fe for both chemical leaching and bioleaching of tannery sludge were similar at pH 1.3. The leaching efficiency of Ca, Mg, and Zn in both leaching processes were identical for pH values in the range of 1.3 to 3.0.     

European Research into Sewer Sediments and Associated Pollutants and Processes

Research investigating all aspects of solids in sewer systems has been underway in Europe for nearly two decades. Due to the early development of European sewer systems, originally as part of the industrialization process more than 100 years ago, urbanization has caused the original sewer networks to become overloaded and unable to function efficiently. Operational problems of interest include loss of ability to convey (designed) flows and the performance of “overflows” to relieve the high flows discharging directly into rivers and other watercourses. Research has characterized the nature of the solids getting into sewer systems, how they behave in terms of transport, and some of the main aspects of their effects. It has been possible to demonstrate that much of the pollutants found in suspension during storms, and likely to be discharged from overflows, originate from the predominantly organic “near bed solids” which accumulate in systems during dry weather. New ideas for the way in which the sediments are transported and the importance of the transformation processes, are leading toward the development of a unified and integrated understanding of the way in which sewer solids behave and the associated biochemical transformation processes.     

Linking social change and developmental change: Shifting pathways of human development.

P. M. Greenfield's new theory of social change and human development aims to show how changing sociodemographic ecologies alter cultural values and learning environments and thereby shift developmental pathways. Worldwide sociodemographic trends include movement from rural residence, informal education at home, subsistence economy, and low-technology environments to urban residence, formal schooling, commerce, and high-technology environments. The former ecology is summarized by the German term Gemeinschaft (“community”) and the latter by the German term Gesellschaft (“society”; T?nnies, 1887/1957). A review of empirical research demonstrates that, through adaptive processes, movement of any ecological variable in a Gesellschaft direction shifts cultural values in an individualistic direction and developmental pathways toward more independent social behavior and more abstract cognition—to give a few examples of the myriad behaviors that respond to these sociodemographic changes. In contrast, the (much less frequent) movement of any ecological variable in a Gemeinschaft direction is predicted to move cultural values and developmental pathways in the opposite direction. In conclusion, sociocultural environments are not static either in the developed or the developing world and therefore must be treated dynamically in developmental research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

New Alternative To Cyanidation: Biocatalyzed Bisulfide Leaching

Abstract

Metallurgists have long sought cost-effective techniques for recovering precious metals from their ores. They are increasingly called upon to design processes for ores refractory to conventional recovery techniques. Adding environmental costs (including site remediation) to the total cost of mining has also stimulated a search for alternative to conventional processes. This paper describes progress in development of an alternative to cyanidation, bisulfide leaching, for extracting gold, silver from refractory ores and concentrates. While bisulfide leaching can be implemented abiolically, significant benefits accrue from its practice as a bioprocess integrating precious-metals liberation and extraction steps. Bisulfide leaching appears to offer advantages over the traditional cyanidation process, including lower reagent costs and toxicity as well as an ability to leach “preg-robbing” ores and other ores not amenable to cyanidation. Bisulfide leaching may also offer advantages over cyanidation for selective dissolution of precious metals from base-metal concentrates.     

Perspective from the United States: Tensions between “Getting It Done” and “Getting It Right”

For over 2 decades, and in response to complaints that arbitration was too expensive and too time consuming, the American construction bar has been energetic and innovative in developing a broad array of dispute resolution tools for resolving construction disputes. These “tools” have included “partnering,” mandatory negotiations, interim decision making by design professionals, mediation, standing neutrals and dispute resolution boards, minitrials, early neutral evaluation, and expert determinations, all developed as alternatives to arbitration and litigation. More recently, in 2006, a voluntary “fast track” process for resolving construction disputes within 100?days has been proffered by the CPR Institute for Conflict Prevention and Resolution. Yet, there are certain dynamics or “tensions” inherent within, and associated with, all construction disputes that continue to resist efforts to speed up dispute resolution processes; these tensions must be reconciled or taken into account before any fast track or “adjudication”-type process will be generally accepted in the United States construction industry. Thus, for now and in the foreseeable future, there will continue to be a smorgasbord of dispute resolution processes for resolution of construction disputes. This is a good thing, because parties to construction disputes come with a great variety of appetites and needs. The focus of attention should be, not so much on development of the ideal or best dispute resolution tool, but having a willingness to select the “best tool for the job,” after the nature of the dispute is known.     

Exploring Factors for Ethical Decision Making: Views from Construction Professionals

The construction industry has experienced malpractice, which is a significant cause for concern. Does the nature of the industry provide some hint for tracing the underlying reasons of the relatively severe ethical problems in construction? Can one of the most influential stakeholders in the industry, the professionals, improve the situation? This study was conducted in Hong Kong to investigate what kinds of ethical problems are faced by construction professionals, and to explore the factors influencing their ethical decision making. Statistical factor analyses identified six intuitive underlying factors that affect ethical decision making when construction professionals are facing ethical dilemmas in the industry. Four of them influencing decision making are “deontological factor,” “consequential factor—egoism,” “consequential factor—utilitarianism,” and “legal requirement.” Two other factors are “oneself/family” and “stakeholders.” Results show that construction professionals’ ethical behavior is guided by legal requirements. When making ethical decisions, they adopt an egoism approach that prioritizes their self-interest and their families’ interests higher than the public’s interest; they would consciously evaluate the consequences of any unethical behavior.     

Use of Total Suspended Solids in Characterizing the Impact of Spent Filter Backwash Recycling

Recycling of spent filter backwash water is a widely practiced residual management approach throughout the United States for drinking water utilities. The United States Environmental Protection Agency (USEPA), under the 1996 Safe Drinking Water Act Amendments, has recently proposed regulations governing the recycle of this waste stream. Considering this new regulation, a comprehensive study was conducted by researchers at Colorado State University, and a suspended solids mass balance model was developed to characterize the impact of backwash water recycling on the overall treatment process. Online particle count data indicated that certain recycle practices could impact the overall treatment process. Data from pilot-scale experiments showed that total suspended solids (TSS) is a useful tool for characterizing the impacts of the backwash recycle processes. TSS can be used to assess whether solids loading or suboptimal coagulation conditions are the cause of recycle related issues. For the study described here, filter breakthrough occurred at about the same total influent solids load, regardless of the manner in which backwash recycling was performed, indicating that recycle of backwash solids did not impact the overall treatment process.     

基于Lotka-Volterra的生物浸铀微生物生长动力学模型研究

前人研究表明,生物浸铀过程中浸矿和辅助浸矿微生物两者间存在协同作用,两者相互促进提高生物浸铀效率。浸矿和辅助浸矿微生物是如何相互促进,使彼此更好地得到生长,两者相互促进生长动力学模型是什么?Lotka-Volterra模型被广泛应用在两种间相互作用下生物数量增长模型研究中,对于生物浸铀中浸矿和辅助浸矿微生物生长动力学模型研究具有借鉴意义。由Lotka-Volterra模型得出了浸矿和辅助浸矿微生物独立共生和竞争共生方程,根据浸矿和辅助浸矿微生物协同特性建立了其生长动力学模型,由模型再推导出浸矿和辅助浸矿微生物协同作用稳定态点,该稳定态点与试验结果相差较小,说明生物浸铀浸矿和辅助浸矿微生物生长动力学模型拟合效果较好。将Lotka-Volterra模型应用到生物浸铀中,具有新颖性,提供了新的研究视角,对完善生物浸铀中微生物协同问题、提高生物浸铀效率具有重要的理论与实际意义。     

Application and Experiment on the Least-action Principle of Explosive Welding of Stainless Steel/Steel

In nature, many physical phenomena follow the least-action principle, which is also abided by the course of explosive welding of stainless steel/steel. The optimal welding interface can be obtained with the least explosive charge by theoretical analysis and interface test. The bonding energy can be acknowledged as the ＂action＂ in explosive welding. To minimize the bonding energy, these rules must be followed such as the lower limit of explosive charge, the upper limit of span and the explosive of critical explosion velocity. The principle of least-action is achieved in the course of explosive welding, and the interface will be optimum.     

Wisdom and compassion: What the Buddha taught a psycho-poetical analysis.

Wisdom and compassion are the two cardinal virtues of Buddhism. This article answers the following questions: What is wisdom? What is compassion? How can they be developed? What is the relevance of the Buddhist teachings in the modern world? How can they be applied to alleviate the stresses and anxieties of everyday life? Can they help solve the global crises we face today? The authors contends that wisdom and compassion are necessary virtues for our happiness as well as for our survival. Unfortunately, believing this is not enough. Knowing it to be true is not enough. Understanding it is not enough. We must practice it. We must become wisdom and compassion in our everyday life. And no one can do it for us. We must do it ourselves, and we must start now. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Measuring Sludge Network Strength Using Rheology and Relation to Dewaterability, Filtration, and Thickening—Laboratory and Full-Scale Experiments

Researchers ?rmeci and Abu-Orf used rheology; a fundamental character of sludge, to arrive at a standard protocol for measuring network strength in terms of energy required to break up the structure of a certain volume of sludge. A mathematical derivation showed that the area under the rheograms indicated energy dissipation within the sludge system, which was related to the network strength. The research described in this paper investigates the use of this protocol for measuring sludge network strength at different polymer doses and relates the results to filtration, thickening, and dewatering. Laboratory tests used anaerobically digested sludge and both capillary suction time and filtration tests to indicate dewaterability and filtration. Network strength measurements used a torque rheometer. At full scale, dose response testing was used to correlate the measured network strength of the conditioned sludge to both centrifugation and gravity belt thickening performance as indicated by solids output. Both laboratory and full-scale testing showed that the network strength could be used to identify the optimum polymer conditioning to achieve good water removal from the sludge. The network strength increased with increasing the polymer dose, however, within the optimum dose range, a “drop” in the network strength occurred. This paper also discusses how to use the sludge network strength information to achieve the desired dryness from a dewatering device, and ultimately automate conditioning and dewatering processes.     

THE DENSITY OF PACKING OF TWO-COMPONENT POWDER MIXTURES

Abstract

The problem of the bulk density attained by a mixture of two powders, of uniform particle size, is considered. It is shown that there are three limiting cases for which the bulk density may easily be calculated and that, from these cases, the bulk density corresponding to a wide range of conditions may be deduced.

It is suggested that a clear distinction must be maintained between a perfect ordered mix, designated a “hyperperfect” mix, and a perfect randomized mix, the randomized mix being the only type attainable by use of a practical mixing machine. The perfection of the mixing of the two component powders is an important factor in the problem and, for mixes as obtained from practical mixing machines, the bulk density is considerably lower than would be the case with the theoretically perfect randomized mix.

The assumption upon which most of the work on the density of mixtures is based, namely that of a “hyperperfect mix”, is inappropriate to industrial mixing processes, so that such treatments are invalid.     

Accretion of Pollutants in Snow Exposed to Urban Traffic and Winter Storm Maintenance Activities. I

Urban snow is impacted by traffic activities and winter maintenance practices that result in significant accretion of dissolved, colloidal, and suspended solids in a complex heterogeneous snow matrix that includes heavy metals, inorganic, and organic compounds. Extended residence times of snow as a roadway snowbank exposed to these pollutant-generating activities lead to significant pollutant accretion and partitioning in the snow matrix. This study analyzed four highway sites in urban Cincinnati with respect to specific water quality indices for the residence time of roadway snow. Chloride levels in roadway snow illustrate a direct correlation to application of de-icing salts. While accretion of total dissolved solids (TDS) was initially rapid with a decrease late in the event, total suspended solids (TSS) accretion demonstrated a more gradually increasing trend for the duration of roadway snow, approaching 105?mg/L. Temporal trends towards increasing total chemical oxygen demand (CODt) exerted by roadway snow are similar to TSS, with CODt values approaching 105?mg/L. Applications of 2.2×105?kg of de-icing salt containing cyanide as an anticaking agent, along a 27-km section of interstate, resulted in approximately 6 kg of cyanide discharged along this major north-south interstate in the study area. Results indicate that traffic activities and winter storm management practices can have a significant impact on pollutant accretion in urban snow.     

Thermodynamic study on calcium treatment of “liquid phase window” and inclusions modification

It is important to study the “liquid phase window” and control non metallic inclusions modification for prevention of submerged entry nozzle blocking during continuous casting. Based on the production practice of medium and high carbon steel in a steel plant, the “liquid phase window” during calcium treatment was studied by combining thermodynamic theoretical calculation and industrial test, which was based on considering the influence of silicon element and temperature on the “liquid phase window”. The results show that the “liquid phase window” varies with T［O］, T［Al］, ［S］ content and temperature, and the low temperature “liquid phase window” must be within the range of high temperature “liquid phase window”, and the silicon content in molten steel has a great influence on the “liquid phase window”. The concepts of “partial liquid phase window” and “complete liquid phase window” are proposed, and the optimum calcium content range of S50C production in a steel plant is determined to be (18-27)×10-6。     

Bioleaching of Sulfide Mineral in Stirred Tank Reactors Operated in a Variety of Modes

Abstract

This paper reviews analysis and modeling for the bioleaching of pyrite in stirred tank reactors operated in a variety of modes: batch, repeated-batch and continuous flow. In a batch reactor, rate data were consistent with a kinetic model assuming that the growth rate of adsorbed bacteria on the mineral surface is proportional to the product of the concentration of adsorbed cells and the fraction of adsorption sites unoccupied by cells. In this modeling, the adsorbed cell concentration was related to the free cell concentration in liquid medium through the Langmuir adsorption isotherm. The reactor model for batch operation is used to investigate the effect of solution replacement on bioleaching rate in repeated-batch reactor. Moreover, the batch model is extended to analyze and model the bioleaching in a continuous-flow tank reactor.     

Constructing a Complex Precast Tilt-Up-Panel Structure Utilizing an Optimization Model, 3D CAD, and Animation

This paper presents the concept used to construct a complex residential tilt-up-panel structure utilizing three-dimensional (3D) modeling and animations. The residence comprises of 108 precast concrete panels of varying rectangular shapes with “dog legs” and window and door “cutouts” that look like an assembled jigsaw puzzle. The erection and installation procedure called for a maximum panel-to-panel joint tolerance of 1.27?cm (0.5?in.), often in 90° joints between panels. 3D animations were used to experiment with the construction process on the computer screen prior to construction in order to avoid potential costly on-site errors. In addition, the 3D animations were also used as a training tool for the contractors. This paper focuses on describing the methodology used to integrate a crane selection algorithm and optimization model with 3D modeling and animation for the selection, utilization, and location of cranes on construction sites. Analytical optimization processes were used to decrease the traveling time and distance of the selected crane, to improve the crane lifting sequence and to minimize the use of panel casting slabs.     

Ca处理“液相窗口”及夹杂物变性热力学研究

摘要：研究“液相窗口”控制钢液中非金属夹杂物变性对于防止连铸过程浸入式水口堵塞具有重要意义。基于某钢厂中高碳钢生产实践,在重点考虑Si元素和温度对“液相窗口”影响的基础上,通过热力学理论计算与工业试验相结合,对Ca处理过程“液相窗口”进行了研究。结果表明：“液相窗口”随钢液中T［O］、T［Al］、［S］含量及温度变化而变化;低温“液相窗口”一定位于高温“液相窗口”范围内;钢液中［Si］含量在某些条件下对“液相窗口”影响较大;并提出了“部分液相窗口”和“完全液相窗口”的概念;确定了某钢厂S50C生产最佳Ca质量分数范围为（18~27）×10-6。     

Towards a Novel Bioleaching Mechanism

Abstract

Research on the chemistry of pyrite bioleaching demonstrated-contradictory to the text book theory on direct or indirect leaching mechanisms-that only the indirect one is functioning. Cells of Thiobacillus ferrooxidans and Leptospirillum ferrooxidans primarily attach to the surface of pyrite particles by electrostatic interactions caused by iron(III) ion containing extracellular polymeric compounds. If sufficient free iron(III) ions are available (0.2 g/l) pyrite degradation starts. The first degradation products are thiosulfate and iron(II) ions. Thiosulfate will be rapidly oxidized by iron(lll) ions to tetrathionate. Tetrathionate adsorbs to the pyrite surface and is hydrolized to sulfane-monosulfonic acid and sulfate plus one proton. From the sulfane-monosulfonic acid several polythionales and elemental sulfur may arise. Consequently, the function of the leaching bacteria is “only” the maintenance of a high redox potential by keeping the iron(III) ions mainly in the oxidized state to optimize the indirect attack on the metal sulfide.     

Combined Removal of Carbon and Nitrogen in an Integrated UASB-Jet Loop Reactor Bioreactor System

An innovative anaerobic–aerobic integrated bioreactor system consisting of an upflow anaerobic sludge blanket (UASB) and a jet loop reactor was developed to investigate the feasibility of combined removal of carbon and nitrogen for a low-strength wastewater at different hydraulic retention times (HRTs) and recycle ratios. Total chemical oxygen demand (COD) removal of the integrated system increased from 87 to 92%, at a combined system HRT of 44?h, when the recycle ratio was increased from 100 to 400%, respectively. Denitrification efficiency of the integrated system increased from 49 to 86%, at all HRTs, when the recycle ratio was increased from 100 to 400%. The integrated system, on average, achieved more than 78% of total nitrogen at all HRTs. Nitrogen content of the biogas produced from the UASB reactor increased with increase in recycle ratios while the methane content exhibited a reverse trend, irrespective of the HRTs. Sludge volume index of the UASB reactor increased from 15?to?42?mL/g total suspended solids at the end of the study. Specific methanogenic activity of the granular sludge decreased from 1.3 to 0.8 g CH4–COD/g volatile suspended solids per day at the end of the study. Nitrogen and COD mass balance of the integrated system indicated that a substantial amount of influent nitrogen and COD was lost in the effluent as dissolved form.