Waste management represents an important issue in our society and Waste-to-Energy incineration plants have been playing a significant role in the last decades, showing an increased importance in Europe. One of the main issues posed by waste combustion is the generation of air contaminants. Particular concern is present about acid gases, mainly hydrogen chloride and sulfur oxides, due to their potential impact on the environment and on human health. Therefore, in the present study the main available technological options for flue gas treatment were analyzed, focusing on dry treatment systems, which are increasingly applied in Municipal Solid Wastes (MSW) incinerators. An operational model was proposed to describe and optimize acid gas removal process. It was applied to an existing MSW incineration plant, where acid gases are neutralized in a two-stage dry treatment system. This process is based on the injection of powdered calcium hydroxide and sodium bicarbonate in reactors followed by fabric filters. HCl and SO2 conversions were expressed as a function of reactants flow rates, calculating model parameters from literature and plant data. The implementation in a software for process simulation allowed the identification of optimal operating conditions, taking into account the reactant feed rates, the amount of solid products and the recycle of the sorbent. Alternative configurations of the reference plant were also assessed. The applicability of the operational model was extended developing also a fundamental approach to the issue. A predictive model was developed, describing mass transfer and kinetic phenomena governing the acid gas neutralization with solid sorbents. The rate controlling steps were identified through the reproduction of literature data, allowing the description of acid gas removal in the case study analyzed. A laboratory device was also designed and started up to assess the required model parameters.

L’accoppiamento di diverse operazioni unitarie può in certi casi portare ad una cosiddetta “intensificazione di processo”, cioè ad un aumento sostanziale delle rese, dell’efficienza e della sostenibilità. Nel presente lavoro sono state pertanto analizzate le potenzialità di accoppiamento della fotocatalisi, il più studiato tra i “processi di ossidazione avanzata”, sia con alcuni processi a membrana per la sintesi verde di aromi sia con l’ozonizzazione per la depurazione di acque. È stato dimostrato che in entrambi i casi l’ottenimento di una significativa intensificazione di processo dipende in gran parte dai parametri operativi, in particolare dal rapporto, delta, tra la velocità caratteristica di fotocatalisi e quella del processo accoppiato. Nel caso della sintesi di aromi, in cui la fotocatalisi viene accoppiata con la pervaporazione o con la dialisi ricircolando al reattore il retentato dalla cella con la membrana. Il parametro delta dipende dalla velocità di reazione, dalle proprietà di trasporto delle membrane e naturalmente dal volume del rettore e dall’area della membrana. La reazione fotocatalitica produce l’aroma, ad esempio vanillina da acido ferulico, per ossidazione parziale e grazie al recupero del prodotto se ne evita l’ulteriore ossidazione aumentandone pertanto la resa. L’operare in apparati separati offre diversi vantaggi come la possibilità di variare senza vincoli il rapporto tra area della membrana e volume del reattore, ma impone di considerare anche il grado effettivo di accoppiamento dei processi. In questo caso, come evidenziato dal modello matematico, un sufficientemente elevato rapporto di ricircolo consente comunque di integrare efficacemente i processi. Nell’ozonizzazione fotocatalitica si hanno due importanti vantaggi: l’aumento della velocità di degradazione grazie alla sinergia tra i processi e la capacità di controllare la formazione di prodotti pericolosi. La sinergia viene massimizzata ad un valore ottimale di delta, mentre la formazione dei prodotti indesiderati viene controllata operando secondo le procedure che sono state individuate. / The coupling of different unit operations can generate the so called “process intensification”, giving a substantial increase of yield, efficiency and sustainability. Photocatalytic oxidation is one of the best known Advanced Oxidation Processes and in the present work it is shown which are the possibilities arising by the coupling of photocatalysis both with two membrane separation processes for the green synthesis of aromas and with ozonation for water purification. It has been demonstrated that process intensification depends mainly on the operating condition, one of which is the ratio delta, between the characteristic rate of the photocatalytic reaction and the characteristic rate of the second process. In the synthesis of aromas, photocatalysis has been coupled with pervaporation or dialysis. The integraion has been achieved recirculating the retentate flow of the membrane separation module. The delta parameter and the process enhancement depends on rate of reaction, transport properties of the membranes, accordingly from the volume of reactor and membrane surface. The partial oxidation given by the photocatalytic reaction can yield the vanillin aroma starting from ferulic acid. The recovery of the product, using the membrane separation can avoid a further oxidation and the yield increase. Working with separated apparatuses gives some advantages, the ratio between the volume of the reactor and the membrane surface area can be changed freely, but more attention has to be paid to integration effectiveness. In this case a sufficiently high recirculation rate can guarantee the process integration, as shown by the mathematical model. Photocatalytic ozonation can achieve two important results: the rate of reaction increase by processes synergy and the control of hazardous substances formation. This synergy is maximized at an optimal value of delta. An optimal value of delta exist that maximizes the synergy and the formation of hazardous substances is controlled according to given procedures.

The so called cascading events, which lead to high-impact low-frequency scenarios are rising concern worldwide. A chain of events result in a major industrial accident with dreadful (and often unpredicted) consequences. Cascading events can be the result of the realization of an external threat, like a terrorist attack a natural disaster or of “domino effect”. During domino events the escalation of a primary accident is driven by the propagation of the primary event to nearby units, causing an overall increment of the accident severity and an increment of the risk associated to an industrial installation. Also natural disasters, like intense flooding, hurricanes, earthquake and lightning are found capable to enhance the risk of an industrial area, triggering loss of containment of hazardous materials and in major accidents. The scientific community usually refers to those accidents as “NaTechs”: natural events triggering industrial accidents. In this document, a state of the art of available approaches to the modelling, assessment, prevention and management of domino and NaTech events is described. On the other hand, the relevant work carried out during past studies still needs to be consolidated and completed, in order to be applicable in a real industrial framework. New methodologies, developed during my research activity, aimed at the quantitative assessment of domino and NaTech accidents are presented. The tools and methods provided within this very study had the aim to assist the progress toward a consolidated and universal methodology for the assessment and prevention of cascading events, contributing to enhance safety and sustainability of the chemical and process industry.

Il progetto di ricerca è finalizzato allo sviluppo di una metodologia innovativa di supporto decisionale nel processo di selezione tra alternative progettuali, basata su indicatori di prestazione. In particolare il lavoro si è focalizzato sulla definizione d’indicatori atti a supportare la decisione negli interventi di sbottigliamento di un impianto di processo. Sono stati sviluppati due indicatori, “bottleneck indicators”, che permettono di valutare la reale necessità dello sbottigliamento, individuando le cause che impediscono la produzione e lo sfruttamento delle apparecchiature. Questi sono stati validati attraverso l’applicazione all’analisi di un intervento su un impianto esistente e verificando che lo sfruttamento delle apparecchiature fosse correttamente individuato. Definita la necessità dell’intervento di sbottigliamento, è stato affrontato il problema della selezione tra alternative di processo possibili per realizzarlo. È stato applicato alla scelta un metodo basato su indicatori di sostenibilità che consente di confrontare le alternative considerando non solo il ritorno economico degli investimenti ma anche gli impatti su ambiente e sicurezza, e che è stato ulteriormente sviluppato in questa tesi. Sono stati definiti due indicatori, “area hazard indicators”, relativi alle emissioni fuggitive, per integrare questi aspetti nell’analisi della sostenibilità delle alternative. Per migliorare l’accuratezza nella quantificazione degli impatti è stato sviluppato un nuovo modello previsionale atto alla stima delle emissioni fuggitive di un impianto, basato unicamente sui dati disponibili in fase progettuale, che tiene conto delle tipologie di sorgenti emettitrici, dei loro meccanismi di perdita e della manutenzione. Validato mediante il confronto con dati sperimentali di un impianto produttivo, si è dimostrato che tale metodo è indispensabile per un corretto confronto delle alternative poiché i modelli esistenti sovrastimano eccessivamente le emissioni reali. Infine applicando gli indicatori ad un impianto esistente si è dimostrato che sono fondamentali per semplificare il processo decisionale, fornendo chiare e precise indicazioni impiegando un numero limitato di informazioni per ricavarle. / The research project was finalized to develop an innovative decision support system based on key performance indicators for the choice among process alternatives. In particular, the project was focused on the definition of indicators able to support decisions in the debottlenecking of a process plant. Two indicators that allow evaluating the need and the potentialities for debottlenecking, identifying the causes of production losses and the utilisation of the equipment, were developed. The practical value and the potentialities of such indicators were evaluated analyzing the section of a production process of a high molecular weight organic substance. As a following step, the issue of deciding among process alternatives for debottlenecking was afforded. A methodology based on sustainability indicators was applied to select the best alternative. The methodology, that allows comparing the alternatives through the analysis of environmental, social and economic impacts, was further developed within the present study. Two area hazard indicators aiming at the assessment of the impacts of fugitive emissions were developed to integrate these aspects in the sustainability analysis of process alternatives. To increase the accuracy in the quantifications of these impacts, a new predictive model, based on available data in design phase, considering the different categories of emission sources, the mechanism of losses, and the maintenance, was developed to estimate the fugitive emissions in a process plant. The comparison between the experimental measurements of fugitive emissions rate in a process plant and the model results confirmed that this new predictive model was needed for an adequate comparison of the process alternatives, because the existing predictive models overestimate the real emission rate. Finally applying the indicators on a real process plant it was confirmed that these indicators are very important to simplify the decisional process, because they provide accurate indications based on a limited number of information.

In this work, different biorefineries strategies were used in order to produce different fuels and chemicals from agro – industrial by product, focusing in particularly on microbial fermentation processes. Mixed consortia and pure culture of Thermotoga neapolitana were used to produce biomethane (through anaerobic digestion) and biohydrogen, respectively from grape pomace and milk whey. Due to the lignocellulosic nature of this by products, white and red grape pomaces in the anaerobic digestion process were tested alone, or in co – digestion, in batch, fed – batch and continuous tests in a 29 L CSTR bioreactor. Furthermore, inhibition experiments were performed in order to better characterize the biochemical process and to evaluate the effect of, oxygen, acetic acid and lignocellulosic derived compounds to the biomethanization process. Besides that, the possibility to enrich this biorefinery to produce propanol from the mixture of VFAs originated in the first steps of AD was evaluated. Bio – H2 tests were performed with milk whey alone or in co – digestion with molasses both in a 116 ml microcosms – scale, both in a 19 L SPCSTR reactor, coupled to a membrane module separation system, to enrich the hydrogen purity. Milk whey was also investigated as only carbon source for the production of succinic acid, one of the Top 12 building block according to the U.S.A Department of Energy, using Actinobacillus succinogenes pure culture in a collaborative project between or department and the Flemish Institute For Technological Research. Besides batch and continuous fermentations, different aspects were studied, as an innovative procedure for a biofilm fermentation in 1 L PFR – type reactor, and the possibility to couple the fermenter to an innovative electrodialysis plant, used as ISPR (In Situ Product Recovery) technique without cell retention steps in between.

Due to the negative environmental impact of the Olive Mill Wastewaters (OMW), research is done in order to treat and valorize them. In this work, different OMW from different Italian regions (Liguria and Puglia) and harvests (from 2012 to 2014) were tested in order to recover polyphenols (PCs), molecules with a high added value because of their beneficial properties. The solid phase used for PCs recovery was the resin Amberlite XAD16; the desorption solvent was acidified ethanol. An HPLC method for total PCs content quantification was developed using a C18 column. A new, repeatable and reliable column packing method was developed. The packing quality was evaluated with step-change fluid dynamic analysis tests using NaCl 0.04M as tracer. Also, to avoid clogging problems in the packed columns an OMW pre-treatment was designed, capable to remove 98% of the solids. Several breakthrough tests were performed to evaluate the influence of linear velocity and column length (0.52m and 2.0m). A repeatability test was performed in order to evaluate the stability of the process. The process was modeled using a plug flow with axial dispersion model with solid-liquid mass transfer; implemented in COMSOL3.5a. The desorption curves were obtained with subsequent solvent regeneration. Antioxidant activity tests were performed with the desorption product using the ABTS method. On the basis of economic considerations, two new ion-exchange resins were tested (IRA958Cl and IRA 67Cl). IRA958Cl showed the best performance. Two breakthrough tests at different linear velocities were conducted with this resin. In order to recover specific high added value molecules (tyrosol and hydroxytyrosol) from the actual OMW, experiments were performed in collaboration with the Fachhoschule Nordwestschweiz (FHNW) using a Cyclodextrin-based polyurethane polymer, synthetized by the FHNW research group. Then, in order to increase the purity of tyrosol in the desorption fractions several organic solvents were tested.

This research aims at deepening the knowledge of the hydrodynamics developing within some specific mixing system configurations. In particular, a standard geometry stirred vessel, an unbaffled stirred vessel of unconventional geometry and a shaken bioreactor are studied. Optical techniques (LDA, PIV) are employed in order to obtain detailed information on the mean and turbulent characteristics of the flow developing within the different lab-scale reactors, while subsequent data analysis addresses the comprehension of the principal macro and micro phenomena occurring in the flow. When studying the standard geometry stirred reactor, the evolution of trailing vortices on the wake of a PBT turbine is investigated for the first time under laminar regime. A three-dimensional characterization of the vortical structures is carried out in terms of vorticity levels and locus. The second case study regards an unbaffled stirred tank of low liquid height-to-tank diameter ratio. Due to the unconventional geometry of the system, peculiar interactions arise between the strong tangential motion of the flow, the impeller discharge stream and the flow free surface. Big efforts are devoted to the characterization of this phenomenon which strongly influences the flow, and a mathematical model able to predict it is sought for. In the last part of this research, the operation of shaken bioreactors is explored. Particularly, the suspension dynamics occurring in the presence of solids within a flat-bottomed cylindrical system are investigated, and the associated two-phase flow is assessed by means of 2D-PIV. Also, the influence of a conical bottom on the single-phase flow is examined. A comparative study of the different bioreactors typologies allowed to identify interesting affinities never detected before in the fluid dynamic behaviour of unbaffled stirred tanks and shaken bioreactors, revealing that these two types of reactors can induce very similar flows, although being technologically very different.

The purpose of the first part of the research activity was to develop an aerobic cometabolic process in packed bed reactors (PBR) to treat real groundwater contaminated by trichloroethylene (TCE) and 1,1,2,2-tetrachloroethane (TeCA). In an initial screening conducted in batch bioreactors, different groundwater samples from 5 wells of the contaminated site were fed with 5 growth substrates. The work led to the selection of butane as the best growth substrate, and to the development and characterization from the site’s indigenous biomass of a suspended-cell consortium capable to degrade TCE with a 90 % mineralization of the organic chlorine. A kinetic study conducted in batch and continuous flow PBRs and led to the identification of the best carrier. A kinetic study of butane and TCE biodegradation indicated that the attached-cell consortium is characterized by a lower TCE specific degredation rates and by a lower level of mutual butane-TCE inhibition. A 31 L bioreactor was designed and set up for upscaling the experiment. The second part of the research focused on the biodegradation of 4 polymers, with and with-out chemical pre-treatments: linear low density polyethylene (LLDPE), polyethylene (PP), polystyrene (PS) and polyvinyl chloride (PVC). Initially, the 4 polymers were subjected to different chemical pre-treatments: ozonation and UV/ozonation, in gaseous and aqueous phase. It was found that, for LLDPE and PP, the coupling UV and ozone in gas phase is the most effective way to oxidize the polymers and to generate carbonyl groups on the polymer surface. In further tests, the effect of chemical pretreatment on polyner biodegrability was studied. Gas-phase ozonated and virgin polymers were incubated aerobically with: (a) a pure strain, (b) a mixed culture of bacteria; and (c) a fungal culture, together with saccharose as a co-substrate.

No description available.

The increasing aversion to technological risks of the society requires the development of inherently safer and environmentally friendlier processes, besides assuring the economic competitiveness of the industrial activities. The different forms of impact (e.g. environmental, economic and societal) are frequently characterized by conflicting reduction strategies and must be holistically taken into account in order to identify the optimal solutions in process design. Though the literature reports an extensive discussion of strategies and specific principles, quantitative assessment tools are required to identify the marginal improvements in alternative design options, to allow the trade-off among contradictory aspects and to prevent the “risk shift”. In the present work a set of integrated quantitative tools for design assessment (i.e. design support system) was developed. The tools were specifically dedicated to the implementation of sustainability and inherent safety in process and plant design activities, with respect to chemical and industrial processes in which substances dangerous for humans and environment are used or stored. The tools were mainly devoted to the application in the stages of “conceptual” and “basic design”, when the project is still open to changes (due to the large number of degrees of freedom) which may comprise of strategies to improve sustainability and inherent safety. The set of developed tools includes different phases of the design activities, all through the lifecycle of a project (inventories, process flow diagrams, preliminary plant lay-out plans). The development of such tools gives a substantial contribution to fill the present gap in the availability of sound supports for implementing safety and sustainability in early phases of process design. The proposed decision support system was based on the development of a set of leading key performance indicators (KPIs), which ensure the assessment of economic, societal and environmental impacts of a process (i.e. sustainability profile). The KPIs were based on impact models (also complex), but are easy and swift in the practical application. Their full evaluation is possible also starting from the limited data available during early process design. Innovative reference criteria were developed to compare and aggregate the KPIs on the basis of the actual sitespecific impact burden and the sustainability policy. Particular attention was devoted to the development of reliable criteria and tools for the assessment of inherent safety in different stages of the project lifecycle. The assessment follows an innovative approach in the analysis of inherent safety, based on both the calculation of the expected consequences of potential accidents and the evaluation of the hazards related to equipment. The methodology overrides several problems present in the previous methods proposed for quantitative inherent safety assessment (use of arbitrary indexes, subjective judgement, build-in assumptions, etc.). A specific procedure was defined for the assessment of the hazards related to the formations of undesired substances in chemical systems undergoing “out of control” conditions. In the assessment of layout plans, “ad hoc” tools were developed to account for the hazard of domino escalations and the safety economics. The effectiveness and value of the tools were demonstrated by the application to a large number of case studies concerning different kinds of design activities (choice of materials, design of the process, of the plant, of the layout) and different types of processes/plants (chemical industry, storage facilities, waste disposal). An experimental survey (analysis of the thermal stability of isomers of nitrobenzaldehyde) provided the input data necessary to demonstrate the method for inherent safety assessment of materials.