Showing papers in "Process Safety and Environmental Protection in 2001"
TL;DR: In this paper, a new index named Safety Weighted Hazard Index (SWeHI) was proposed to measure the impact of safety measures on the values of the hazard indices, which can be used to identify the more hazardous units from the less hazardous ones so that greater attention can be paid to the former.
Abstract: Indices are extensively used for ranking various units of a chemical process industry on the basis of the hazards they pose of accidental fires, explosions and/or toxic release. This type of ranking enables the professionals to identify the more hazardous units from the less hazardous ones so that greater attention can be paid to the former. The available indices—including the well-known Dow and Mond indices, and the author's HIRA (hazard identification and ranking analysis, Khan and Abbasi, 1 )—rank chemical process units mainly in terms of the hazardous substances and operating conditions associated with the concerned units. Dow and Mond indices do consider some factors (‘off setting index values’ in the case of the Mond Index and ‘credits factor’ in the case of the Dow index) to account for the safety measures existing or planned in the unit, but much greater rigour, accuracy, and precision are needed in quantifying the impact of safety measures on the values of the hazard indices. In this context, an attempt has been made to develop a new index, named here the Safety Weighted Hazard Index (SWeHI). The details are presented in this paper.
TL;DR: In this paper, a cyclic and multibed process for the continuous and energy efficient recovery of CO2 is proposed, which involves an integrated energy recovery step for the generation of steam, which is then used for the recovery of the adsorbed phase.
Abstract: Experimental and theoretical studies on the high temperature recovery of CO2 from flue gases are presented. The work employs a potassium promoted hydrotalcite adsorbent, for which CO2 capacities in excess 0.8 mol kg-1 were measured at temperatures of 481 K and 575 K and in the presence of high concentrations (∼30% (v/v)) of water. Elution profiles from a bench-scale adsorption unit also enabled analysis of adsorption and desorption kinetics. A cyclic and multibed process for the continuous and energy efficient recovery of CO2 is proposed. The process involves an integrated energy recovery step for the generation of steam, which is then used for the recovery of CO2 from the adsorbed phase. A mathematical model for the CO2-hydrotalcite system, based on measured equilibria and kinetic data, is used for the preliminary assessment of the process, e.g. in terms of CO2 product purity and steam consumption. Particular attention is given to CO2 recovery from the stack gas of a typical 10 MW coal-fired power plant. The work has application to existing industrial processes in which recovered CO2 (at elevated temperatures) can be used as a feedstock for further catalytic processing, such as dry methane reforming and carbon gasification. © Institution of Chemical Engineers.
TL;DR: In this article, a series of jar tests using iron (III) chloride were carried out to identify factors affecting phosphorus removal, including mixing conditions and the extent of iron hydrolysis prior to reaction with phosphate ions.
Abstract: A series of jar tests using iron (III) chloride were carried out to identify factors affecting phosphorus removal. Mixing conditions and the extent of iron hydrolysis prior to reaction with phosphate ions were explored using crude sewage as a medium. Somewhat surprisingly, the mixing conditions appeared to have little affect on the phosphorus removal performance. As expected, there was a strong link between phosphorus removal and iron:phosphate ratio during standard jar tests with iron (III) chloride. Total phosphorus removal of 80% was achieved at a dose of 1.48:1 molar ratio Fe:P. When a mixture of pre-hydrolysed iron and iron chloride was added, 80% total phosphorus removal was achievable at a dose of 1.86:1 molar ratio Fe:P. These findings could make a considerable difference to the cost of iron (III) chloride addition for phosphorus removal, if the hydrolysed product is formed preferentially to the phosphate. Increased costs could amount to more than £60,000 for a site treating a population equivalent of 200,000 and requiring a 1 mg l –1 total phosphorus effluent target. In reality, the hydrolysed product is unlikely to form to this extent but the results suggest that the formation of hydroxide may not only take place when the phosphorus removal reactions are complete as the relative reaction rates are more similar than perhaps was previously thought. Metal hydroxides have the capability to remove phosphorus by absorption but less efficiently.
TL;DR: In this paper, the feasibility of a submerged MBR fitted with three pore-sized non-woven poly-propylene (NWPP) membranes has been studied, and the performance was compared with that of a conventional polysulfone (PS) membrane material.
Abstract: Capital costs of a MBR (Membrane Bio-Reactor) process are substantially influenced by the membrane cost itself, which contributes around 50% of the total process capital cost. The feasibility of a submerged MBR fitted with three pore-sized NWPP (Non-Woven Poly-Propylene) membranes has been studied. The performance was compared with that of a conventional polysulfone (PS) membrane material. Both the PS and NWPP membranes demonstrated a drastic reduction in permeate flux at the start of operation. Although the NWPP membrane showed a greater fouling propensity than the PS membrane, the difference in flux decline between the two membranes was not great. All membranes produced an effluent extremely low in organic matter and with a low permeate turbidity (
TL;DR: Coagulation and digestion of tannery wastewater were investigated in this paper, and the results indicated that coagulation considerably reduced the concentration of sulphide and improved the anaerobic treatability.
Abstract: Coagulation and digestion of tannery wastewater were investigated. Coagulation at pH7.5 removed at least 32% of chemical oxygen demand (COD), 64% of suspended solids (SS), 77% of chromium, 80% of sulphide and 85% of colour. The results indicated that coagulation considerably reduced the concentration of sulphide and improved the anaerobic treatability. Both aluminium sulphate and ferric chloride coagulants provided excellent sulphide removal (>71%), even at a low dose of 50 mg l–1. Subsequent anaerobic digestion was carried out on initial samples and supernatants from the coagulation at an hydraulic retention time (HRT) of 10 days with a loading rate of 0.33 kg COD/m3/day. Incorporation of coagulation prior to digestion resulted in an increased capacity of the digesters and improved digestion performance. A methane yield of 0.2 l CH4/(g COD removed) was achieved, while COD removal was 77% and COD removal rate was 0.24 kg COD/m3/day. The combined system provided a residual COD of less than 760mg l–1 and a residual sulphide of less than 200 mg l–1. The results also demonstrated that a sulphide concentration in excess of 260 mg l–1 completely inhibited methane production. These results may lead to a reduction in waste disposal costs for tannery companies.
TL;DR: In this paper, the authors describe work undertaken by Environmental Resources Management (ERM), in association with subconsultants Rowan Williams Davies & Irwin Inc. and the Health and Safety Laboratory (HSL) to model the dispersion of chlorine in complex terrain.
Abstract: The EU Seveso II Directive requires operators of major hazard facilities to prepare safety reports for sites storing quantities of dangerous substances in excess of specified levels. The safety report should include an assessment of the risk associated with the facility, which will include an evaluation of the effects of releases of dangerous substances to the environment. The models commonly used for assessing the dispersion of dense gases in the atmosphere are based on the ‘ideal’ of flat, unobstructed terrain. For ‘real’ situations such models may be unduly pessimistic in their predictions and, in certain circumstances, may even be optimistic. This paper describes work undertaken by Environmental Resources Management (ERM), in association with sub-consultants Rowan Williams Davies & Irwin Inc. (RWDI) and the Health and Safety Laboratory (HSL) to model the dispersion of chlorine in complex terrain. The work involved physical modelling of releases in a Boundary Layer Wind Tunnel (BLWT) and the use of Computational Fluid Dynamics (CFD). The paper focuses on the key findings of the study, which provide a dramatic insight into how terrain and buildings can fundamentally alter the dispersion behaviour of dense gases. The results show how flat terrain models may overestimate the chlorine hazard range by as much as a factor of 5, whilst the predicted direction of travel of the cloud may err by up to 90°. This has implications not only for the assessment of risks associated with major hazard facilities, but also for land-use planning in the vicinity of the site and emergency preparedness.
TL;DR: In this paper, a theoretical discussion of the key characteristics of such assessment procedures, selected methods are applied to nine different processes and the results show that if two different assessment methods are used for comparing two processes in order to identify the more dangerous one, in 75% of the cases both methods deliver the same result.
Abstract: A large variety of methods exist for identifying and assessing the hazard potential of chemical processes during the design phase. These methods vary significantly in goal, scope, structure and the exact way of considering safety aspects. After a theoretical discussion of the key characteristics of such assessment procedures, selected methods are applied to nine different processes. The results show that if two different assessment methods are used for comparing two processes in order to identify the more dangerous one, in 75% of the cases both methods deliver the same result. In general, good agreement was obtained between methods assessing the energy that can be potentially released, as long as the methods consider not only fire and explosion but also reaction and decomposition. Results from toxicity assessment vary significantly depending on the toxicological endpoint considered and on the substance property used for assessing toxic effects. Furthermore, the disadvantages of using discrete qualitative instead of continuous quantitative properties are highlighted using mass as an example. The results clearly show the high dependence of the results on the selected assessment method. Thus, the selection of a method for a given purpose has to be made carefully and the user should be aware of its characteristics and their influence on the results obtained.
TL;DR: In this article, the authors investigated the kinetics of reductive degradation of two different azo dyes by zero-valent iron in aqueous solution using a laboratory-scale slurry reactor system.
Abstract: The kinetics of reductive degradation of two different azo dyes by zero-valent iron in aqueous solution were investigated using a laboratory-scale slurry reactor system. Both reductive degradations show pseudo first order reaction kinetics. A typical rate constant for the reactions is 0.735 min−1 for Acid Orange II and 0.694 min−1 for Acid Blue 113 at mixing speeds of 2000 revolutions per minute. The apparent rate constant (k) increased with both mixing speed and iron concentration but decreased with increased initial dissolved oxygen content and pH. The increase with iron concentration for both Acid Orange II and Acid Blue 113 is linear with correlation coefficients of 3 × 10−5mgl−1. The rate constant increases linearly with the inverse square root of mixing speed for both dyes—corresponding directly with increasing reaction rate with decreasing boundary layer thickness. Half lives for Acid Orange II correlate well with values reported in the literature. These figures demonstrate the mass transfer limitation and surface dependency of these heterogeneous reactions and show the trends that it is necessary to understand in order to address them for commercial application. The effect of mass transfer on reaction rate is described qualitatively in terms of mass transfer theory and quantitatively in terms of the empirical Sherwood number and thickness of the stagnant boundary layer that adheres to the iron particle. The effect of surface passivation is shown quantitatively in terms of initial dissolved oxygen content of the aqueous phase.
TL;DR: In this article, the authors used design information to build a dynamic operator training simulator (DOTS) which can be used to explore start-up, shutdown and emergency operations procedures, to experience various operations and to evaluate safety.
Abstract: With the increasing complexities and integration of chemical processes, ensuring safety is becoming more difficult and expensive for new and/or modified plants This inevitably increases the risks of unacceptable environmental impact as well as cost of operation This is especially true where there is no existing plant to train operators It is now possible to use design information to build a dynamic operator training simulator (DOTS) which can be used to explore start-up, shutdown and emergency operations procedures, to experience various operations and to evaluate safety This approach has proved very successful in achieving safe operation of a new MTBE process The paper reports the experience of developing DOTS and using it to ensure safe operation
TL;DR: In this article, a series of batch tests where acid yellow 17 and hydrolysed Reactive Black 5 textile dyes were ozonated to assess the efficacy of partial oxidation and associated decolourization, and parent compound degradation.
Abstract: This work involved a series of batch tests where Acid Yellow 17, and unhydrolysed and hydrolysed Reactive Black 5 textile dyes were ozonated to assess the efficacy of partial oxidation and associated decolourization, and parent compound degradation. Absorbance readings and a decrease in the chemical oxygen demand/total organic carbon (COD/TOC) confirmed that partial oxidation was the predominant degradation mechanism. An applied dose of 0.6 g 1–1 caused 100% colour removal through dye chromophore cleavage whilst higher doses resulted in further degradation. Biodegradability improvement in ozonated hydrolysed Reactive Black 5 was tracked through biological oxygen demand (BOD5) increase and BOD/COD and BOD/TOC ratios. Partial oxidation improved the biodegradability of hydrolysed Reactive Black 5 and the optimal applied dose requirement for maximum biodegradability improvement was 1.8 gl 1–1, which increased the BOD/TOC and BOD/COD ratios from 0 to 0.58 and 0.27, respectively. This suggested that for maximum biodegradability improvement, partial oxidation must proceed beyond decolourization.
TL;DR: In this article, a coal-based activated carbon, Chemviron F400, was oxidized by nitric acid and air, and the results indicated that there was a significant change in the structure of the precursor by oxidation and subsequent treatments.
Abstract: Modified samples of a coal based activated carbon, Chemviron F400, were oxidized by nitric acid and air. Nitric acid oxidized samples were treated to remove humic type by-products of the oxidation process either by washing with sodium hydroxide solution or heating under vacuum. All samples were characterized to investigate the effect of the treatment and the chemical as well as the physical characteristics of these materials. The characterization included scanning electron micrographs (SEM), Brunauer-Emmett-Teller (BET) and Langmuir surface area measurements, Fourier Transform Infra Red spectroscopy (FTIR) analysis, sodium capacity measurement, pH titration and zeta potential measurements. The results indicated that there was a significant change in the structure of the precursor by oxidation and subsequent treatments. The ion exchange capacity of the carbon was markedly enhanced by the addition of oxygen containing weakly acidic surface groups.
TL;DR: In this article, coal-based activated carbon, Chemviron F400, was oxidized by nitric acid and air to enhance their metal sorption capacity, and the kinetic performance of these samples was assessed.
Abstract: Samples of a coal-based activated carbon, Chemviron F400, were oxidized by nitric acid and air to enhance their metal sorption capacity. Acid oxidized samples were either alkali washed or heated under vacuum to remove organic by-products formed during oxidation. Mini-column breakthrough experiments were conducted to determine the sorption performance of the samples for Cu, Ni, Zn and Cd uptake. The kinetic performance of these samples was assessed. Ion exchange performance of activated carbon samples was significantly enhanced on oxidation. Copper uptake capacity of a 24 h acid oxidized sample was increased by a factor of 60 compared to the unoxidized as-received material. Subsequent treatments reduced the metal uptake capacity of the oxidized carbons indicating that by-products produced during oxidation had metal binding ability. The metal sorbed samples were regenerated using 0.1M HCl solution.
TL;DR: In this article, the authors investigated channel formation in a packed bed of fuel solids as a result of the random packing process and derived a general relationship between the bed porosity and the particle size distribution and the proposed methodology is tested against limited experimental data.
Abstract: Obtaining energy from sustainable sources such as waste and biomass has required a significant extension of combustion technology. Many of the advanced technologies are based on thermal treatment in gas-solid packed-bed systems such as gasifiers, incinerators and biomass furnaces. In this paper channel formation in a packed bed of fuel solids as a result of the random packing process has been investigated. Channelling causes a severely uneven distribution of the primary airflow through a packed fuel bed and results in poor combustion performance of the furnace. By assuming Furnas packing, a general relationship is derived between the bed porosity and the particle size distribution and the proposed methodology is tested against limited experimental data. A probability density function (PDF) of truncated Gaussian type is assumed for the random size distribution at local areas within the bed and the local bed porosity is calculated accordingly. Then by solving the fluid flow equations through the porous bed, flow rate profiles are obtained at the top surface of the bed. Two particulate systems were investigated as a function of change in bed height and pressure drop through the grate. Depending on bed height and pressure drop through the grate, maximum local flow rate at the top surface of the bed can be 1.5 ∼ 2 times higher than the minimum flow rate for the particulate system with a narrower size range (2.5 mm–18 mm) while the ratio of the maximum to minimum flow rate can reach as high as 8 ∼ 32 for the particulate system with a wider size range (0.677 mm–20 mm). Visualization of the velocity profile inside the bed reveals that flow passages are slightly curved in some areas but straight in others. The largest channel observed presents a ‘perfect’ straight passage of airflow running from the very bottom of the bed to the very top of the bed. Channelling inside a burning bed of solid waste in a large-scale travelling grate incinerator plant was also investigated using a unique in-house prototype instrument. The result shows that the combustion processes within the bed were dominated largely by the circles of formation and subsequent collapse of channels.
TL;DR: In this article, a multi-zoned physical model and a localized reaction site are proposed to model the solid-state digestion (SSD) process, where methanogenesis occurs only in a thin layer at an interface between rich and lean material.
Abstract: The literature on solid-state digestion (SSD) reveals no convincing physical model of the process. Most of the reported reaction models implicitly assume homogeneity: the heterogeneous nature of the waste substrate may be noted but is rarely modelled. In contrast, this paper proposes an essential role for heterogeneity. A multi-zoned physical model and a localized reaction site are consistent with many characteristics of SSD. The fundamental hypothesis is that methanogenesis requires sites protected from the rapid acidogenesis occurring in the richer elements of the waste. If this protection is provided by mass-transfer resistances within pockets of leaner material, it is essential that their identity is not destroyed by excessive mixing or size reduction. A possible mechanism for such an effect is furnished by the proposed model, with a central role for mass transfer. Reaction is envisaged as occurring only in a thin layer, at an interface between rich and lean material. Acetogenesis and methanogenesis take place in distinct zones, with the latter protected from acid inhibition by mass-transfer resistances in an intervening buffer zone. The rate of waste stabilization is determined by the rate of advance of this multi-zoned reaction front. Several of the mass transfer processes occurring between these zones could be rate-limiting. This model suggests that methanogenesis in a typical landfill gradually spreads from discrete initiation points, with the reaction zones forming an expanding set of concentric shells. Process optimization may thus require maximizing the number of initiation points, subject to a constraint: only the larger seed fragments can develop. Reported failures to replicate the process at laboratory scale might thus be due to the use of homogenized feedstock. The implications of the model for commercial practice are discussed, as are potential methods of experimental verification.
TL;DR: In this article, the effects of five factors, namely, temperature, leaching time, acid normality, solid-to-liquid ratio, stirring rate, and reaction time on leaching yield of the red mud waste from the Etibank Seydisehir Aluminium Plants, Turkey, have been studied using statistically designed experiments.
Abstract: Sulphuric acid leaching of Ti, Al and Fe (which make up the ‘Red mud’ waste from Etibank Seydisehir Aluminium Plants, Turkey), has been studied using statistically designed experiments. The effects of five factors, namely: temperature, leaching time, acid normality, solid-to-liquid ratio, stirring rate on leaching yield of TiO2, Al2O3 and Fe2O3, have been investigated. Experiments have been planned by factorial design and orthogonal central composite design methods. The following models have been obtained by means of variance analysis at 92.5% confidence level. • YTiO2= 64.1087 − 5.2264 X1 + 22.6566 X2 − 1.3085 X3 − 9.2821 X4 + 1.4675 X5 − 7.0354 Xl2 − 5.8515 X22 + 1.2055 X42 + 8.9975 X1X2 - 2.6113 X1X4 − 1.7837 X1X5 + 1.5350 X2X3 + 1.9550 X2X5 + 2.9287 X3X4 − 1.3838 X3X5 • YFe2O3 = 13.2686+ 8.9664 X1+ 16.7172X2 − 10.2664 X4 + 3.2134 X5+ 6.9270 X22 + 4.2107 Xl + 9.9694 X1X2 − 4.7119 X1X4 − 7.6144 X2X4 + 2.5906 X2X5 − 5.5756 X3X5 • YAl2O3 = 68.2351 + 8.4249 X1 + 2.1984 X2 + 1.9705 X3 + 4.0853 X5 + 3.9794 Xl + 4.2312 X1 X2 − 2.7225 X1X4 + 3.1000 X2X3 + 2.5750 X2X5 where X1 is temperature, X2 is acid concentration, X3 is stirring speed, X4 is solid-to-liquid ratio, and X5 is reaction time
TL;DR: In this paper, the authors focus on the glycol dehydration unit for one of the onshore oil and gas processing facilities in Abu Dhabi operated by Abu Dhabi Company for Onshore Oil Operations (ADCO).
Abstract: Recent developments in environmental regulations on the emissions of aromatic compounds including benzene, toluene, ethyl benzene and xylene isomers (BTEX) and other volatile organic compounds (VOCs) have made these emissions a major concern in the natural gas industry. In particular, one of the sources of emissions is glycol dehydration units. During the dehydration of natural gas, the BTEX and VOC compounds in it are absorbed by the glycol solvent, and subsequently emitted to the atmosphere during the thermal regeneration of glycol. As a result, quantification and means of reduction and ultimately elimination of these emissions is gaining importance in the industry. This problem requires careful attention during the design phase. The environmental considerations mentioned above are increasingly driving the selection and operation of process alternatives to reduce the BTEX/VOCs emissions to the atmosphere. This paper focuses on the glycol dehydration unit for one of the onshore oil and gas processing facilities in Abu Dhabi operated by Abu Dhabi Company for Onshore Oil Operations (ADCO). Firstly, the BTEX/VOCs emission levels vented out to atmosphere are quantified, and a description given of the sampling/measurement technique. Secondly, the process parameters associated with all major equipments in the glycol dehydration unit, i.e. the absorber, the flash tank, and the regenerator that may lead to the reduction in BTEX/VOC emissions, are optimized. The optimization study involves building a process simulation model based on actual design data/parameters provided by the glycol unit vendor and verified by operational data.
TL;DR: In this paper, an outflow model is proposed to predict the mass flow rate for releases into the atmosphere from high pressure vessels accurately in a fast and robust manner in the context of the development of a safety assessment package.
Abstract: The prediction of out ow from high pressure vessels or pipework following an accidental failure is required in the safety assessment of industrial plant used to process or store flammable material. In particular, predictions of the mass flow rates of accidental leaks provide source conditions for mathematical models of gas dispersion or accumulation and fires. In this paper, the modelling of outflow from high pressure vessels in the context of the development of a safety assessment package is addressed. For any consequence model implemented as part of a safety assessment package, the issues of model robustness and efficiency as well as accuracy must be considered. The outflow model described in this paper is demonstrated to predict the mass flow rate for releases into the atmosphere from high pressure vessels accurately in a fast and robust manner. The mathematical formulation of the model, the numerical methods used to implement the model and its validation are discussed.
TL;DR: In this paper, the authors used the Integrated Empirical Rate (IER) photochemical kinetic mechanism to determine whether the local photochemistry of ozone events is light-limited (VOC-limited) or NOx-limited.
Abstract: The experimental work of this paper has been conducted over a period of one year, starting in January 1997, for measurement of air pollutants and meteorological parameters in the urban atmosphere of the Khaldiya residential area in Kuwait. The measurements were carried out simultaneously every 5 minutes by using the Kuwait University mobile air pollution monitoring laboratory (Chemical Engineering Department). The main emphasis of the paper has been placed on the problem of ozone for those days that are characterized by events of photochemical smog. The first objective of this paper deals specifically with the use of the Integrated Empirical Rate (IER) photochemical kinetic mechanism that has been developed at the Commonwealth Scientific and Industrial Research Organization (CSIRO) of Australia as a screening tool for photochemical smog assessment. The IER has been used to determine whether the local photochemistry of ozone events is light-limited (VOC-limited) or NOx-limited. Such information is necessary in developing an effective emission control plan and enables the decision as to whether NOx or NMHC emission needs to be controlled. On the other hand, the available models to predict the concentrations of ozone are complex and require a number of input data that are not easily acquired by environmental protection agencies or local industries. Thus, the second objective concerns the short-term forecasting of ozone concentration based on a neural network method.
TL;DR: In this paper, three batch co-digestion trials were undertaken to derive optimum mixtures for the co digestion of poultry manure with molasses, with sheep and goat manure, and with thickened waste activated sludge (A-3).
Abstract: One of the key constraints to development in rural areas of the developing world is the lack of suitable energy supplies. One possible solution is to promote the generation of biogas from agricultural and other organic wastes. In practical terms, the amounts of organic waste generated at particular sites may not be sufficient to make digestion cost-effective. The concept of co-digestion is well established. What is not clear is whether some wastes would have adverse effects when added to a stable digester or when used in conjunction with another waste. This paper examines some initial studies into the use of anaerobic digestion for two-component mixtures. The experiments were designed using mixture design mathematics so that any synergism or antagonism could be identified. Three batch co-digestion trials were undertaken to derive optimum mixtures for the co-digestion of poultry manure with molasses (A-1), with sheep and goat manure (A-2), and with thickened waste activated sludge (A-3). The results from Trial A-1 showed that during the batch co-digestion of poultry manure (a high-nitrogen waste) with molasses (a highly degradable waste) synergistic or antagonistic interactions could not clearly be deduced. The results of Trial A-2 showed that the best results were obtained with a mixture of 75% poultry manure and 25% sheep and goat manure. The conclusions which were drawn from the results of Trial A-3 were that synergistic and antagonistic interactions were not apparent and that the methane yields generally increased with increased substitution of waste activated sludge with poultry manure.
TL;DR: In this paper, four appropriate mathematical model forms were synthesized from extensive published data for UV disinfection of Escherichia coli in reverse osmosis (RO) water with the addition of either a shielding agent or an absorbing agent and evaluated in a comparative study.
Abstract: A present lack of a rigorous quantitative understanding of the kinetics of ultraviolet (UV) inactivation of bacterial contaminants is shown to limit wide application and optimization of UV disinfection efficacy in the provision of potable water and treatment of wastewaters. Four appropriate mathematical model forms were synthesized from extensive published data for UV disinfection of Escherichia coli in reverse osmosis (RO) water with the addition of either a shielding agent or an absorbing agent and evaluated in a comparative study. Celite 503*** (with a median particle size of 23 μm) in suspended solids concentrations in the range 0.0 to 0.3 g l −1 was the UV shielding agent, and powdered coffee (International Roast***) concentrations in the range 0.0 to 0.03 g l −1 was the UV absorbing agent. The models were the classical log-linear, Davey linear-Arrhenius, Ratkowsky- Belehradek or square-root and a third order polynomial model ( n OP). The test criteria for model selection and ranking included goodness of fit and accuracy in prediction; relative complexity (i.e., parsimony ); ease of synthesis and use; and potential for physiological interpretation. The percent variance accounted for (%V ) in prediction was used as a stringent test of goodness of fit. The Davey linear-Arrhenius model explained an overall mean of 97.2% V . This compared with, respectively, 95.6, 93.0 and 86.7% V for the n OP, log-linear and square-root models. The poorer fit of the square-root model suggests that suspended solids concentration and UV dose act independently on disinfection kinetics as implied in the Davey linear-Arrhenius model. This model is quadratic in UV dose and linear in suspended solids concentration. It has three terms: [ dose ]., [ dose ]. 2 and [ conc ]. It best explained deviation in tailing from classically implied log-linear survivor kinetics for the rate of UV disinfection of viable bacterial cells. Overall it best fulfilled the criteria for model selection. Further, from a practical view, it is of a form that is readily integrated with equations describing the rheology and hydrodynamics of liquid flow that permit a simulation of a UV disinfection unit operation for the provision of potable water.
TL;DR: In this article, the authors developed an indoor air quality model based on chemical engineering principles to the movement and potential control of volatile substances in buildings, which incorporates the surface interactions of volatile organic compounds (VOCs) with interior materials.
Abstract: The Indoor Air Quality model developed in this study involves the application of chemical engineering principles to the movement and potential control of volatile substances in buildings. The model incorporates the surface interactions of volatile organic compounds (VOCs) with interior materials. Sorption parameters estimated in a test chamber are then applied to an actual test house in Kuwait as an example building. Model parameters including source emission rates, removal rates by adsorption and surface emission rates by desorption, together with their relationships with air movement in the chamber, have been studied. Adsorption and desorption rate constants for four VOCs have been obtained using polyacrylonitrile, polyester and cotton textiles that are usually present in living room carpets, sofas and curtains of actual houses. The adsorption isotherms obtained by thermogravimetric analysis reveal that Henry's law can be used as an approximate isotherm for VOC concentrations in air below 1000 mg−3. The linear adsorption rate constants (based on bare fibre areas) for the tested fibre materials ranged from 0.02 to 7.3 mh−1 and the linear desorption rate constants ranged from 0.001 to 17.8 h−1. The model developed in this study predicts concentration profiles that fit very well with the concentrations measured in an actual test house located in Kuwait, providing good prediction of ways of improving air quality inside buildings in all locations.
TL;DR: In this paper, the impact of residual iron and aluminium coagulants on secondary biological treatment as a result of pre-precipitation has received little attention, and the results of a laboratory-scale screening experiment are presented.
Abstract: Pre-precipitation is widely used in wastewater treatment to increase the removal of suspended solids (SS) and chemical oxygen demand (COD) in the primary sedimentation process. During pre-precipitation, a portion of the coagulant is removed from the treatment system in the primary settled sludge. However a residual amount will remain in the supernatant which is then treated by the secondary, biological treatment process. The effect of direct coagulant addition to the secondary biological treatment stage, known as simultaneous precipitation, is well documented but the effect of residual coagulant on secondary biological treatment as a result of pre-precipitation has received little attention. Jar tests were optimized with respect to SS, COD and phosphorus (P) removal at influent pH—between pH 7–8. Optimum dose was found to be 25 mgl −1 as metal ion for both alum and ferric sulphate coagulants. The residual metal concentration in the primary settled wastewater from the jar test experiments was identified as being 1.94 and 1.98 mg Fel −1 for ferric sulphate coagulants and 0.90 mg All −1 1 for alum. Primary effluent was fed to a settled activated microbial biomass to give total solids concentration of 2.0–2.5 g1 −1 . The impact of residual metal concentration on (i) respiration rate and COD removal and (ii) species diversity and floc structure were investigated. This paper presents the results of a laboratory-scale screening experiment undertaken to consider the impact of residual iron and aluminium coagulants on the secondary treatment process. Results identify a link between low level concentrations of coagulant, and reduction in microbial activity, changes in species diversity and floc morphology highlighting the importance of a bench/pilot-scale study.
TL;DR: In this paper, a model for the fluidized bed combustion of volatile matter from waste is presented, where a fraction of the volatile content is released within the freeboard, as a result of both pyrolysis and transport of the devolatilizing particles.
Abstract: This paper describes a model for the fluidized bed combustion of volatile matter from waste. This waste is assumed to be composed of wood, cardboard and PVC. The model assumes that a fraction of the volatile content is released within the freeboard, as a result of both pyrolysis and transport of the devolatilizing particles. The model describes precisely the diffusion-controlled combustion of the volatile matter within the bed, on the basis of a hydrodynamic model of the bed, combined with energy and mass balance equations. The results of the model show that the release of volatiles in the freeboard may increase the freeboard temperature by 200 K and may multiply the emissions of NO 25 times.
TL;DR: In this paper, an integrated cloud chamber/combustor capable of systematically producing quasi-monodisperse droplet mists within the combustion transition range for the first time is presented.
Abstract: Combustion of liquid fuel sprays is employed in a diverse range of industrial applications. Aerosol combustion characteristics differ to those exhibited by gaseous combustion primarily due to the heterogeneity of the unburnt aerosol mixture. Simplified models of aerosol burning rate have identified possible laminar burning velocity enhancement for aerosol fuel/air systems comprising droplet sizes within the so-called combustion ‘transition range’—typically understood to be 5–15 μm for mono-disperse aerosols. However, burning velocity enhancement has not been validated to date, and hence understanding of aerosol combustion mechanisms is limited for conditions of considerable practical importance. This paper describes the methodology utilized to design and commission an integrated cloud chamber/combustor capable of systematically producing quasi-monodisperse droplet mists within the combustion ’transition range’ for the first time. The principle of Wilson's cloud chamber is used to produce quasi-monodisperse ethanol aerosol clouds, facilitating systematic cloud generation across the combustion ‘transition range’. The Malvern Mastersizer X™, operating in transient mode, is used to examine droplet growth, final droplet size and mono-dispersity, while Particle Image Velocimetry is used to confirm pre-ignition quiescence. The creation of quasi-monodisperse, quiescent mists comprising droplets within the combustion ‘transition range’ facilitates aerosol combustion studies (e.g. flame propagation, ignition energies, etc.) of importance to explosion hazard quantification as well as other industrial applications such as internal combustion engines.
TL;DR: In this article, a model for determining the cheapest legal treatment paths for a given waste stream has been extended by an assessment measuring the environmental impact resulting from the treatment itself as well as from the remaining emissions, thus allowing a comparison of treatment policies.
Abstract: A model for determining the cheapest legal treatment paths for a given waste stream has been extended by an assessment measuring the environmental impact resulting from the treatment itself as well as from the remaining emissions, thus allowing a comparison of treatment policies. Since uncertainty in stream composition is considered, the results obtained with respect to both objectives are distributions and not single values. The Pareto optimal alternatives are identified automatically, and the possibly resulting trade-offs between the economic and environmental objectives can be displayed and analysed. The model has been applied to several case studies. While one case study showed that the cheapest treatment path might well be the environmentally most benign, in the other case studies trade-offs between cost and environmental impact became evident. The model showed in detail which treatment operations and/or pollutants cause a high environmental impact, a finding that could be used as a basis for elaborating modifications of the process that produced the waste stream. From the detailed results provided by the model the basic principle of waste treatment in the light of environmental assessment was also highlighted: the reduction of one environmental impact generally accompanies an increase in another impact. For example, the emission of harmful compounds might be reduced at the expense of energy consumption. In summary, the model proved to be a valuable tool in analysing treatment options for a given waste stream from an economic as well as an environmental point of view.
TL;DR: In this paper, a set of elemental conversion efficiencies for production of gases such as hydrogen chlorine and sulphur dioxide is recommended for fire hazard analysis, and the toxicity of the resulting smoke plume is calculated as the sum of dangerous dose fractions for each toxic component irrespective of its action on the body.
Abstract: The combustion products released by fires in agrochemical warehouses are reviewed and a set of elemental conversion efficiencies for production of gases such as hydrogen chlorine and sulphur dioxide is recommended for fire hazard analysis. In the absence of better data, it is recommended that the toxicity of the resulting smoke plume is calculated as the sum of dangerous dose fractions for each toxic component irrespective of its action on the body. It is argued that the hazard from combustion products released by many warehouse fires is at least as great as that from vaporized parent compounds, but that actual hazard range is a complex function of warehouse inventory, the way it is distributed throughout the warehouse, the location of the seat of the fire and the rate of spread of the fire.
TL;DR: In this paper, two selected metal hydroxide cakes from the on-site wastewater treatment of nickel and chromium electroplating activities and the anodizing of aluminium materials were treated with Portland cement and mixed with clay, offering two possibilities of solidification/stabilization prior to landfilling, and reutilization in ceramic products, respectively.
Abstract: Metal hydroxide sludges from the wastewater treatment of metal finishing effluents are complex wastes, mainly inorganic, with a high content of heavy metals and anions. This makes it necessary to employ careful environmental management. In this work, two selected metal hydroxide cakes from the ‘on site’ wastewater treatment of nickel and chromium electroplating activities and the anodizing of aluminium materials were treated with Portland cement and mixed with clay, offering two possibilities of solidification/stabilization prior to landfilling, and reutilization in ceramic products, respectively. The obtained products were characterized by the determination of ecotoxicity values, EC 50 , of the TCLP leachates and the chemical characterization of DIN-38414-S4 leachates. The unconfined compressive strength (UCS) was determined in all derived products. Cement formulations show values of EC 50 higher than 3000mg l -1 and high concentrations of chromium in the DIN 38414-S4 leachates, due to the alkaline medium resulting from the cement addition. The clay/waste products are non-hazardous based on the EC 50 and the low concentrations of heavy metals in the leachates. The paper establishes environmental characterization of both kind of products, showing that there are environmental benefits of waste dosification in ceramic materials.
TL;DR: In this article, the authors apply methods of time series and survival analysis to assess the frequency of major accidents at fixed industrial installations in Europe and analyze the effectiveness of current information reporting requirements in the respective EU legislation (Seveso II Directive) intended to increase safety in the European process industry.
Abstract: This paper applies methods of time series and survival analysis to assess the frequency of major accidents at fixed industrial installations in Europe. In a wider sense, the effectiveness of current information reporting requirements in the respective EU legislation (‘Seveso II Directive’), intended to increase safety in the European process industry, is analysed. The quantitative results show that the information currently available at a European level is not sufficient to come to reliable conclusions regarding the frequency of such events.
TL;DR: In this paper, a compact wet scrubber was developed that consists of several venturi scrubbers working in self-priming mode, which is located at the bottom of a multistage packed tower.
Abstract: Up-to-date exhaust gas cleaning systems of waste incineration plants are highly effective, yet expensive in terms of equipment and other expenses. Aiming at a simpler, but nevertheless effective system, a compact wet scrubber was developed that consists of several venturi scrubbers working in self-priming mode. The venturi scrubbers are located at the bottom of a multistage packed tower. This compact apparatus incorporates several of the steps of a conventional exhaust gas cleaning process, such as dust separation, quench, acid and basic wet cleaning. Therefore, investment and running costs for the gas cleaning process are reduced without any loss of separation efficiency. The design concept and important experimental results of the compact scrubber are reported. The scrubber has been employed at a hazardous waste incineration plant in order to test its applicability under real conditions. The experiments were used to identify benefits and drawbacks of the scrubber, and to improve the scrubber design concept. It is shown that the developed scrubber is highly effective in separating fine dust particles and inorganic-gaseous pollutants (HCl, HF, SO 2 ). Additionally, the concentration of polychlorinated dioxins and furans (PCDD/F) is significantly reduced in the off-gas of the scrubber. These compounds are adsorbed into plastic packing materials.