The system design of UV-assisted catalytic oxidation process--degradation of 2,4-D

Unlike the conventional first- or second-order model, a novel approach to design for the removal of 2,4-dichlorophenoxy (2,4-D) by the UV-catalytic oxidation process (UVCOP) was investigated. Two distinctive parameters, initial decay rate and maximum oxidative capacity, were characterized. By using these parameters, the performance of the degradation of 2,4-D by UVCOP regarding to the reagent dosages could be successfully predicted. Low concentrations of ferrous ion was found to be a rate-limiting factor for the process while the dosage of hydrogen peroxide was concluded as a dominant species in determining the maximum oxidation capacities. This information can be used to optimize the treatment process and achieve the expected performance target; an "optimal-dose model" was developed accordingly. The model is an intelligent and useful tool to evaluate the optimal doses of hydrogen peroxide with the minimum dose of ferrous ion, which leads to a better design of the treatment process.     

Oxygen transfer in a full-depth biological aerated filter

The City of San Diego, California, evaluated the performance capabilities of biological aerated filters (BAFs) at the Point Loma Wastewater Treatment Plant. The City conducted a 1-year pilot-plant evaluation of BAF technology supplied by two BAF manufacturers. This paper reports on the first independent oxygen-transfer test of BAFs at full depth using the offgas method. The tests showed process-water oxygen-transfer efficiencies of 1.6 to 5.8%/m (0.5 to 1.8%/ft) and 3.9 to 7.9%/m (1.2 to 2.4%/ft) for the two different pilot plants, at their nominal design conditions. Mass balances using chemical oxygen demand and dissolved organic carbon corroborated the transfer rates. Rates are higher than expected from fine-pore diffusers for similar process conditions and depths and clean-water conditions for the same column and are mostly attributed to extended bubble retention time resulting from interactions with the media and biofilm.     

Dry FGD at United Power Association’s Stanton Station

The United Power Association’s dry FGD system at Stanton, North Dakota was the first utility-operated lime spray dryer to be put into service in the United States. At 60 MW in size, it utilizes a single spray dryer vessel with three rotary atomizers and a ten-compartment fabric filter. It is currently operating at better than expected efficiency and Is meeting state and federal air quality requirements. Start-up and operation have shown that certain areas of design and operating conditions are critical to reliable operation. Flue gas, slurry, and water distribution and mixing must be carefully controlled if reliable, long term operation is to be achieved. Likewise, water chemistry Is Important in the reagent preparation equipment. Start-up of the system was accomplished In a step-wise fashion to bring the baghouse on line first, followed by the spray dryer. The spray dryer was operated at gradually lower outlet temperatures until design conditions were met. Measures taken since start-up to ensure reliable operation, and operation over an eighteen month period are discussed. Both particulate and SO₂ emission performance are evaluated.     

Removal of arsenic from drinking water by chemical precipitation--a modeling and simulation study of the physical-chemical processes.

A dynamic mathematical model was developed for removal of arsenic from drinking water by chemical coagulation-precipitation and was validated experimentally in a bench-scale set-up. While examining arsenic removal efficiency of the scheme under different operating conditions, coagulant dose, pH and degree of oxidation were found to have pronounced impact. Removal efficiency of 91-92% was achieved for synthetic feed water spiked with 1 mg/L arsenic and pre-oxidized by potassium permanganate at optimum pH and coagulant dose. Model predictions corroborated well with the experimental findings (the overall correlation coefficient being 0.9895) indicating the capability of the model in predicting performance of such a treatment plant under different operating conditions. Menu-driven, user-friendly Visual Basic software developed in the study will be very handy in quick performance analysis. The simulation is expected to be very useful in full-scale design and operation of the treatment plants for removal of arsenic from drinking water.     

The risk-effective sustainability of policies: the small business credit environment in Korea

Current ecological or environmental risks, such as air pollution, are usually analysed in an economic system. Existing studies show that small businesses are exposed to environmental risks and thus need to be supported by public financing for the risk-effective sustainability of regional economic performance. However, some critics argue that the acceptable performance may result from methodological bias, instead of theoretical reasons or empirical data. It is not enough to say that 'something is better than nothing' for marginally risky businesses, in terms of the sustainability of policies. Thus, this study analyses whether public-financing support, such as credit guarantees, is sustainable in practice. Empirical results reveal that innovation in governance is required.     

Uncertainty analysis of integrated gasification combined cycle systems based on Frame 7H versus 7F gas turbines

Integrated gasification combined cycle (IGCC) technology is a promising alternative for clean generation of power and coproduction of chemicals from coal and other feedstocks. Advanced concepts for IGCC systems that incorporate state-of-the-art gas turbine systems, however, are not commercially demonstrated. Therefore, there is uncertainty regarding the future commercial-scale performance, emissions, and cost of such technologies. The Frame 7F gas turbine represents current state-of-practice, whereas the Frame 7H is the most recently introduced advanced commercial gas turbine. The objective of this study was to evaluate the risks and potential payoffs of IGCC technology based on different gas turbine combined cycle designs. Models of entrained-flow gasifier-based IGCC systems with Frame 7F (IGCC-7F) and 7H gas turbine combined cycles (IGCC-7H) were developed in ASPEN Plus. An uncertainty analysis was conducted. Gasifier carbon conversion and project cost uncertainty are identified as the most important uncertain inputs with respect to system performance and cost. The uncertainties in the difference of the efficiencies and costs for the two systems are characterized. Despite uncertainty, the IGCC-7H system is robustly preferred to the IGCC-7F system. Advances in gas turbine design will improve the performance, emissions, and cost of IGCC systems. The implications of this study for decision-making regarding technology selection, research planning, and plant operation are discussed.     

生物滴滤器净化低浓度甲苯废气的非稳态工况研究

生物法处理大气污染物时,经常会遇到条件波动或污染物间歇排放等非稳态工况。在不同非稳态条件下,考察了甲苯废气间歇排放对生物滴滤器净化性能的影响。实验方案分3种情况:无甲苯废气排放、无循环液供应或同时没有甲苯废气和循环液的供应。间歇排放时间从2~47 d不等。结果表明,不管何种形式的停运或故障,甲苯净化能力4 d以内基本不下降;停运时间超过5 d,则甲苯去除能力严重下降,仅为原来的1/3~1/2;停运时间在10 d以内,24 h内即可恢复,47 d的长期停运,3 d内也可恢复净化能力。     

Evaluating factors that influence microbial phenanthrene biodegradation rates by regression with categorical variables

To advance the accuracy of bioremediation measurements, it is useful before specific experiments to attribute or estimate the influence of both experimental as well as field conditions on the expected magnitudes of microbial degradation rate coefficients. This paper analyzes the numerical contribution, or influence, of categories of conditions, such as bacterial adaptive state, electron acceptor type, mixing, generalized sorption conditions, and biodegradation temperature, on published phenanthrene biodegradation rates as an example of our regression approach. A fundamental microbial degradation rate equation is transformed to an additive model, then using multiple linear regression on published data, coefficients (of categorical variables) and a linear model are presented that estimate first-order biodegradation rate coefficients to within a factor of 3. Numerical estimates of how much bacterial adaptive state and presence of a sorption phase, the two most statistically significant factors, alter the phenanthrene biodegradation rate are presented. The influence of some measurement or field conditions, for example, the influence of oxygen reduction versus optimal nitrate reduction, cannot be distinguished statistically given the available data and range. The regression model is tested using conditions from newly published papers to estimate a priori the expected rate, which compares very favorably to measurements reported in the papers. Due to limited published data and range for extreme cases, the current coefficients do not apply to degradation of very aged phenanthrene nor very low concentrations of electron acceptors. As estimating tools, however, the coefficients themselves and the regression approach have very beneficial roles in design of experiments for both laboratory and field settings. Our method can be applied to other PAHs as sufficient data become available.     

运用模糊层次分析法优选制浆造纸废水深度处理方案

制浆造纸废水最适深度处理方案的选择是一个多准则决策问题,本文通过建立评价指标体系,从经济费用、技术性能、管理效果和社会效益4个方面,对混凝沉淀（气浮）＋过滤、Fenton氧化和生态法3种深度处理方案进行分析;采用层次分析法确定指标体系权重,其中技术性能（0.5333）权重最高;结合模糊数学法开展综合评判,评估各方案的优缺点,最后通过方案总排序确定工程优选方案。同时,针对2个具有代表意义的制浆造纸企业废水深度处理工程案例,在方案隶属度的确定时增加了决策者的期望值和企业的实际情况,分别选取了最适的制浆造纸废水深度处理方案：混凝沉淀（气浮）＋过滤法（A企业）和生态法（B企业）,这样可以更客观地指导决策者选取最合适的制浆造纸废水深度处理方案。     

Flux Force/Condensation Scrubbing

Considerations for the engineering design of flux force/condensation (FF/C) scrubbers are reviewed. Fine par-ticulate removal in multiple sieve plate FF/C scrubbers is predicted, using mathematical design models. Results of experimental studies of two multiple sieve plate scrubbers for the removal of submicron particles are given. The published experimental data on FF/C scrubber performance are summarized. A preliminary analysis of the economics of FF/C scrubbers, compared to the conventional high energy scrubbers, defines the most favorable operating conditions for the application of FF/C scrubbers.     

The accuracy of plume trajectories forecast using the U.K. Meteorological Office operational forecasting models and their sensitivity to calculation schemes

Studies into the various errors associated with long-range 950 mb trajectories computed using the Meteorological Office numerical weather prediction suite are presented. In the absence of observational data, trajectory error is measured using a verification computed from the model analysed and short-period forecast wind fields. While it is safest to assume that errors determined in this way are the minimum to be expected in relation to “true” trajectories, they nonetheless provide a useful diagnostic of model performance under different synoptic conditions and for trajectory releases at different stages of the forecast. Absolute and directional errors are analysed and the effect of altering the trajectory calculation schemes considered. The possible implications of the results for acid precipitation control strategies are discussed in some detail.     

Comparison of the results obtained by four receptor modelling methods in aerosol source apportionment studies

In this work the performance and theoretical background behind two of the most commonly used receptor modelling methods in aerosol science, principal components analysis (PCA) and positive matrix factorization (PMF), as well as multivariate curve resolution by alternating least squares (MCR-ALS) and weighted alternating least squares (MCR-WALS), are examined. The performance of the four methods was initially evaluated under standard operational conditions, and modifications regarding data pre-treatment were then included. The methods were applied using raw and scaled data, with and without uncertainty estimations. Strong similarities were found among the sources identified by PMF and MCR-WALS (weighted models), whereas discrepancies were obtained with MCR-ALS (unweighted model). Weighting of input data by means of uncertainty estimates was found to be essential to obtain robust and accurate factor identification. The use of scaled (as opposed to raw) data highlighted the contribution of trace elements to the compositional profiles, which was key to the correct interpretation of the nature of the sources. Our results validate the performance of MCR-WALS for aerosol pollution studies.     

Carbon dioxide mineralization process design and evaluation: concepts,case studies,and considerations

Numerous carbon dioxide mineralization (CM) processes have been proposed to overcome the slow rate of natural weathering of silicate minerals. Ten of these proposals are mentioned in this article. The proposals are described in terms of the four major areas relating to CM process design: pre-treatment, purification, carbonation, and reagent recycling operations. Any known specifics based on probable or representative operating and reaction conditions are listed, and basic analysis of the strengths and shortcomings associated with the individual process designs are given in this article. The processes typically employ physical or chemical pseudo-catalytic methods to enhance the rate of carbon dioxide mineralization; however, both methods have its own associated advantages and problems. To examine the feasibility of a CM process, three key aspects should be included in the evaluation criteria: energy use, operational considerations as well as product value and economics. Recommendations regarding the optimal level of emphasis and implementation of measures to control these aspects are given, and these will depend very much on the desired process objectives. Ultimately, a mix-and-match approach to process design might be required to provide viable and economic proposals for CM processes.     

Design and performance characterization strategy using modeling for biofiltration control of odorous hydrogen sulfide

Biofilter, dynamic modeling software characterizing contaminant removal via biofiltration, was used in the preliminary design of a biofilter to treat odorous hydrogen sulfide (H2S). Steady-state model simulations were run to generate performance plots for various influent concentrations, loadings, residence times, media sizes, and temperatures. Although elimination capacity and removal efficiency frequently are used to characterize biofilter performance, effluent concentration can be used to characterize performance when treating to a target effluent concentration. Model simulations illustrate that, at a given temperature, a biofilter cannot reduce H2S emissions below a minimum value, no matter how large the biofilter or how long the residence time. However, a higher biofilter temperature results in lower effluent H2S concentrations. Because dynamic model simulations show that shock loading can significantly increase the effluent concentration above values predicted by the steady-state model simulations, it is recommended that, to consistently meet treatment objectives, dynamic feed conditions should be considered. This study illustrates that modeling can serve as a valuable tool in the design and performance optimization of biofilters.     

Effect of Bag Failure on Baghouse Outlet Loading

One of the most important considerations in baghouse operation is the effect of bag failure on outlet loading. This information would be Of use to equipment manufacturers, users, and regulatory officials. Unfortunately, little information is available in the literature on this aspect of baghouse performance. Equations describing changes in outlet loading resulting from the sudden rupture of one or more bags are developed from first principles. Calculated results from these equations are presented in the form of a chart which can very quickly and simply be used to obtain a numerical value for a revised outlet loading resulting from bag failure(s) for a variety of system conditions. Due to an assumption made in the derivation, the new outlet loading thus obtained represents the maximum increase (worst case conditions) to be expected from the rupture of one or more bags. The following variables are included in the analysis: inlet loading, outlet loading (prior to bag failure), number of bag failures, bag diameter, system pressure drop; and gas temperature.     

Design and Performance Characterization Strategy Using Modeling for Biofiltration Control of Odorous Hydrogen Sulfide

Abstract

Biofilter, dynamic modeling software characterizing contaminant removal via biofiltration, was used in the preliminary design of a biofilter to treat odorous hydrogen sulfide (H₂S). Steady-state model simulations were run to generate performance plots for various influent concentrations, loadings, residence times, media sizes, and temperatures. Although elimination capacity and removal efficiency frequently are used to characterize biofilter performance, effluent concentration can be used to characterize performance when treating to a target effluent concentration. Model simulations illustrate that, at a given temperature, a biofilter cannot reduce H₂S emissions below a minimum value, no matter how large the biofilter or how long the residence time. However, a higher biofilter temperature results in lower effluent H₂S concentrations. Because dynamic model simulations show that shock loading can significantly increase the effluent concentration above values predicted by the steady-state model simulations, it is recommended that, to consistently meet treatment objectives, dynamic feed conditions should be considered. This study illustrates that modeling can serve as a valuable tool in the design and performance optimization of biofilters.     

Polycyclic aromatic hydrocarbon emissions from clinical waste incineration

Since the introduction of the Environmental Protection Act in the UK, there are few reports of PAH emissions from clinical waste incinerators (CWIs) operating to improved performance standards. The main aim of this study is to determine PAH emissions from a state-of-the-art CWI focusing on the effects of reactive gases and operating variables on emissions. This was carried out by collection of stack samples over three phases of operation.

At stack conditions, most PAHs are predicted to be in the vapour phase. Reactive losses of PAHs were closely correlated by rank with expected reactivities from laboratory studies. Estimates of emissions incorporating sampling losses were derived, although no correlation was found between PAH losses and the modest levels of reactive stack gases. PAH concentrations were one to two orders of magnitude lower than earlier reports from incinerators without effective air pollution control equipment (APCE). The low levels of carbon monoxide recorded were not correlated with any PAHs.

This study demonstrates the impact of efficient combustion conditions and APCE on PAH emissions from a CWI.     

Energy budget in <Emphasis Type="Italic">Daphnia magna</Emphasis> exposed to natural stressors

Background, aim, and scope  

Climate changes are nowadays an important issue of concern, and it is expected that in the near future it will be intensified, leading to extreme environmental conditions. These changes are expected to originate additional sources of stress; therefore, the exposure of organisms to natural stressors is receiving an increased importance in risk assessment. Organisms tend to avoid extremely environmental conditions looking for optimum conditions. This work aimed to evaluate the effects of natural stressors on the energetic reserves of Daphnia magna using the quantification of lipids, proteins, and sugars.     

Review of the complexation of tetravalent actinides by ISA and gluconate under alkaline to hyperalkaline conditions

Isosaccharinic (ISA) and gluconic acids (GLU) are polyhydroxy carboxylic compounds showing a high affinity to metal complexation. Both organic ligands are expected in the cementitious environments usually considered for the disposal of low- and intermediate-level radioactive wastes. The hyperalkaline conditions imposed by cementitious materials contribute to the formation of ISA through cellulose degradation, whereas GLU is commonly used as a concrete additive. Despite the high stability attributed to ISA/GLU complexes of tetravalent actinides, the number and reliability of available experimental studies is still limited. This work aims at providing a general and comprehensive overview of the state of the art regarding Th, U(IV), Np(IV), and Pu(IV) complexes with ISA and GLU.In the presence of ISA/GLU concentrations in the range 10^− 5–10^− 2 M and absence of calcium, An(IV)(OH)_x(L)_y complexes (An(IV) = Th, U(IV), Np(IV), Pu(IV); L = ISA, GLU) are expected to dominate the aqueous speciation of tetravalent actinides in the alkaline pH range. There is a moderate agreement among their stability, although the stoichiometry of certain An(IV)-GLU complexes is still ill-defined. Under hyperalkaline conditions and presence of calcium, the species CaTh(OH)₄(L)₂(aq) has been described for both ISA and GLU, and similar complexes may be expected to form with other tetravalent actinides.In the present work, the available thermodynamic data for An(IV)–ISA/GLU complexes have been reviewed and re-calculated to ensure the internal consistency of the stability constants assessed. Further modelling exercises, estimations based on Linear Free-Energy Relationships (LFER) among tetravalent actinides, as well as direct analogies between ISA and GLU complexes have also been performed. This approach has led to the definition of a speciation scheme for the complexes of Th, U(IV), Np(IV) and Pu(IV) with ISA and GLU forming in alkaline to hyperalkaline pH conditions, both in the absence and presence of calcium.     

AERMOD performance evaluation for three coal-fired electrical generating units in Southwest Indiana

An evaluation of the steady-state dispersion model AERMOD was conducted to determine its accuracy at predicting hourly ground-level concentrations of sulfur dioxide (SO₂) by comparing model-predicted concentrations to a full year of monitored SO₂ data. The two study sites are comprised of three coal-fired electrical generating units (EGUs) located in southwest Indiana. The sites are characterized by tall, buoyant stacks, flat terrain, multiple SO₂ monitors, and relatively isolated locations. AERMOD v12060 and AERMOD v12345 with BETA options were evaluated at each study site. For the six monitor–receptor pairs evaluated, AERMOD showed generally good agreement with monitor values for the hourly 99th percentile SO₂ design value, with design value ratios that ranged from 0.92 to 1.99. AERMOD was within acceptable performance limits for the Robust Highest Concentration (RHC) statistic (RHC ratios ranged from 0.54 to 1.71) at all six monitors. Analysis of the top 5% of hourly concentrations at the six monitor–receptor sites, paired in time and space, indicated poor model performance in the upper concentration range. The amount of hourly model predicted data that was within a factor of 2 of observations at these higher concentrations ranged from 14 to 43% over the six sites. Analysis of subsets of data showed consistent overprediction during low wind speed and unstable meteorological conditions, and underprediction during stable, low wind conditions. Hourly paired comparisons represent a stringent measure of model performance; however, given the potential for application of hourly model predictions to the SO₂ NAAQS design value, this may be appropriate. At these two sites, AERMOD v12345 BETA options do not improve model performance.

Implications:

A regulatory evaluation of AERMOD utilizing quantile-quantile (Q–Q) plots, the RHC statistic, and 99th percentile design value concentrations indicates that model performance is acceptable according to widely accepted regulatory performance limits. However, a scientific evaluation examining hourly paired monitor and model values at concentrations of interest indicates overprediction and underprediction bias that is outside of acceptable model performance measures. Overprediction of 1-hr SO₂ concentrations by AERMOD presents major ramifications for state and local permitting authorities when establishing emission limits.