1,721,014 research outputs found
Reclaiming cigarette butts: biorefinery technologies toward circular waste valorization
Full text linkCigarette butts (CBs) are among the most abundant forms of anthropogenic litter, with about 5 trillion units
discarded each year, corresponding to more than 800,000 tons of waste. Composed primarily of cellulose acetate
(CA), accounting for 95% of the filter mass, CBs exhibit low biodegradability and act as carriers of toxic substances
such as nicotine, heavy metals, and polycyclic aromatic hydrocarbons. Their persistence in the environment
has raised growing concerns across terrestrial and aquatic ecosystems. This review critically examines
the potential integration of CBs into circular waste management strategies through biorefinery technologies. Key
processes include deacetylation to increase hydrolytic accessibility, enabling conversion into fermentable sugars
for bioethanol production, as well as thermochemical routes like pyrolysis for fuel and activated carbon generation.
Additional valorization options, such as enzymatic degradation and transformation into nanostructured
carbon materials, are discussed with respect to their feasibility and environmental impact. Legislative gaps,
technological barriers, and limited scalability are identified as major constraints to industrial implementation.
Nonetheless, the inclusion of CBs as a non-conventional feedstock offers a promising opportunity to reduce the
environmental footprint of CBs while recovering energy and materials within a biorefinery loop
Esame di Chimica - Simulazioni Risolte degli Esami di Chimica
No full textL'esame di Chimica, insieme ad Analisi Matematica I, rappresenta uno dei primi scogli dei ragazzi che hanno appena intrapreso gli studi universitari in campo scientifico-ingegneristico. Questo testo è stato pensato per dare una risposta alle richieste degli studenti che ricercano continuamente nuovi esercizi con cui studiare meglio e verificare il proprio livello di preparazione. In particolare, la necessità predominante degli studentiè risultata quella di avere un modello della prova scritta dell'esame di chimica che negli ultimi anni segue uno schema uguale a tutti i corsi di Ingegneria e Architettura. Le prove che si trovano nel libro sono infatti composte da 20 domande: 17 quesiti a risposta multipla e 3 esercizi numerici. Tutti i quesiti e gli esercizi sono corredati da relativa soluzione, commentata ove necessari
Optimization of the Anaerobic Digestion from Olive Oil Production's wastes
No full textThe aim of this thesis is the optimization of the anaerobic digestion of wastes derived from olive oil production, which represent one important economic sector of all the Mediterranean Countries. The main byproducts of this activity are the semi-solid Olive Pomace (OP), characterized by low pH, high content of organic matter and in particular of ligno-cellulosic materials, and a liquid one, the Olive Mill Waste Water (OMWW) which have a dark color, low pH and high content of polyphenolic substances. Because their features, these wastes are very polluting and not recommended with the traditional methods, which consists essentially to dispose on the soil with the consequent alteration of the chemical characteristics of the ground and the possibility to contaminate the groundwater. For these reasons anaerobic digestion represents the most sustainable method to treat these wastes, which permits the production of a gas rich in methane and a stabilized sludge poor in organic matter, the digestate usable as fertilizer. A first test, conducted in laboratory scale (about 100 ml) was made in order to evaluate the biogas production from a 10% w/w mixture composed by OP and OMWW. The biogas production was very low (0.22 NL/L) and consequentially the efficiency of process resulted of 0.3%. The high poly-phenols content in the OMWW are responsible of the inhibition of the methanogenic bacteria activity and owing the lignocelluloses nature of the largest organic structures determined the low biodegradability of the OP and OMWW. The first part of the thesis' work consisted in the identification of the effects of chemical and physical pretreatments by AD fermentation tests in order to evaluate the biogas and methane production, abatement of the organic matter and reduction of the lag phase of 133 pretreated OP and OMWW to score the best one. In addition, considering that AD is aimed to produce energy, operational energy costs to perform the pretreatments were investigated, based on the consumption of direct energy (heat and electricity) as well as the indirect energy spent to produce the chemicals used. To this aim an Energy Sustainability Index (ESI) were introduced and applied to select the most efficient pretreatment method from an energy sustainability perspective. The simply dilution of OP with tap water (WP) has a beneficial effect in the anaerobic digestion, improving over 57 times the energy production respect to un-treated waste (NP). However considering the CH4 production, the best pretreatments resulted to be the CaCO3, FeCl3 addition and the ultrasonic pretreatment, which had an efficacy of 108, the highest among the tested pretreatment processes. Between the three best pretreatments the addition of 5g/L of CaCO3 to the reaction medium, resulted the only one able to give a positive energy balance between the energy obtained and that spent, due to the low energy required for the CaCO3 production. The CaCO3 pretreatment permits to pass from an efficiency of 0.3% to about 21%. After the identification of the CaCO3 addition as the best pretreatment, a test including the same OP- OMWW mixture with 5 g/L of CaCO3 has been conducted in a CSTR reactor having a volume of 2 Liters. Since the beginning of the prove, it was evident a problem with the mixing system due to a elevate value of the mixture's viscosity, 160- 200 cP. The Rushton impeller resulted totally unable to guarantee an homogenous mixing of the reactor medium. In fact, the Rushton impeller can give a boost to the fluid only in a radial direction, resulting to be inefficient along the axial one and not able to guarante the circulation of the solid present in the feed, derived mainly from the breaking of the olive seeds during the olive oil production's process. To improve the mixing of the reaction medium, four different impellers were tested: Pelton Impeller; Rushton impeller with six 45° inclined blades; Marine Impeller with 3 blades; Anchor Impeller. The best performances were obtained with the marine and the anchor impellers. The first is designed to guarantee mainly an axial movement to the fermenting fluid, which, at constant rpm, results to be superior than the Rushton with inclined blades. it guarantees also a radial movement to the reaction medium, which consents to involve in the mixing all 134 the reactor volume. Conversely, the optimal performances of the test conducted with the anchor impeller can be explained observing the presence of a well mixed region in the superior part of the reactor where anchor impeller was located, for the effect of the tangential movement given to the fluid, and a less agitated, but no stagnant, part in the inferior part of the reactor. This more quiet zone resulted ideal for the methanogenic bacteria' conditions which do not tolerate intense mechanical stress derived from the impeller rotation. In this way their growth, reproduction and metabolism activity was favored with a consequent increasing of the methane production. An ulterior attempt to increase the efficiency of the AD process consisted in the simultaneous experimentation of the two best impellers (the marine and the anchor) with the two stage AD configuration, based on the separation into two interconnected steps, of the two distinctly different groups of bacteria (acidogens and methanogens), in order to maximize their growth by maintaining optimum conditions in each step for each particular group of bacteria. The two stage configuration resulted advantageous only for the AD conducted with the marine impeller using a reactor with a semi spherical bottom to improve the solids circulation. In this test the efficiency passed from 22.64% (mono-stage) to 30.24% (two stage configuration) with an improvement of rhe efficacy (η) of 1.34 times. Conversely, the two stage has worsened the efficiency of the AD with the anchor impeller whose efficiency dropped down from over 33% to 17.5%, which corresponds to η = 0.52. The marine impeller, in fact, gives an axial boots to the reaction medium which permits to the gas bubbles to leave the reaction volume, preventing the inhibition of the reactions involved in the AD. The semi-spherical bottom of the reactor also had a beneficial effect on the AD, permitting a better homogenization of the biomass and of the substrates into the reaction medium. Conversely, the anchor impeller which give a strong radial impulse and only a gentle axial movement to the reaction medium. This configuration gives a behavior, which can be similar to an UASB reactor, permits the growth, the reproduction and the activity of the methanogenic microorganisms which are not disturbed by strong mechanical stress transmitted by the mixing system. Although this good aspect, the quasi stagnant region does not consent the complete degassing of the hydrogen gas in the first acidogenic phase from the reaction medium. On the contrary the anchor impeller has not any impact on the mono-stage configuration where the biogas is formed essentially by methane, but has a strong inhibiting effect on the two stage configuration where the formed hydrogen is a reaction intermediate products. Lastly, a continuous test has been conducted using a pilot reactor having a working volume 135 of 1,800 liters. The olive oil production's wastes were fed with milk whey, a byproduct form dairy activity. The codigestion was conducted in mesophilic conditions and had a duration of 75 days. The system reached a stationary condition with a biogas production of 1.4 L/L and a methane content of 70-75% v/v. This gas flow has an energetic annual potential of 55 GJ. Taking in account that Puglia' s annual energetic consumption is of 375,000 GJ (Piano Energetico Ambientale Regionale - Regione Puglia, 2004), the anaerobic digestion of olive oil and dairy's waste is able to cover the 0.015% of the regional energetic deman
Some critical aspects of the enzymatic hydrolysis at high dry-matter content: a review
No full textEnzymatic hydrolysis represents the crucial phase in bioethanol production. Its aim is to convert pretreated lignocellulosic polymers in hexose sugars for fermentation into bioethanol. To be economically advantageous, the enzymatic hydrolysis should operate with a high concentration of dry matter. The drawback of this is the increase in the reaction medium’s viscosity and consequently bad mixing within the bioreactor due to the complexity of the lignocellulosic polymers. Another critical aspect of the enzymatic hydrolysis is enzyme deactivation, which is mainly due to two factors: the presence of lignin by-products, originating from the pretreatment of lignocellulosic biomass, and the accumulation of glucose in the reaction medium by cellulose hydrolysis. This review details these two critical aspects of enzymatic hydrolysis conducted with high dry-matter content. The most relevant milestones and technological solutions to improve rheological performance and to reduce enzyme deactivation have been investigated
Exploitation of Solar Energy for Ammonium Sulfate Recovery from Anaerobic Digestate of Different Origin
No full textDigestate represents the semi-liquid byproduct of the anaerobic digestion process. It was estimated that 56 Mtonnes of digestate are annually produced only in Europe. Digestate composition depends on the initial total solids (TS) mixture fed to the digester and by its origin (manure, food wastes, agricultural residues, wastewater sludge). Typical values for the different components include a stabilized organic matter content between 20 and 50 g/L, a good content of nitrogen compounds (2-8 g/kg) and of phosphorous compounds (up to 3 g/kg). In particular, ammonia presence in digestate is interesting for ammonium sulfate production, a fertilizer which favors plants' growth. Traditional ammonium sulfate synthesis is conducted by stripping followed by sulfuric acid absorption, a process which requires high energy and chemicals consumptions. This work investigates the exploitation of solar energy to evaporate the liquid phase of digestate in a lab-scale greenhouse. Digestate vapors, rich in ammonia, are sent in a Drechsler trap, filled with 38% w/w sulfuric acid solution, through three solar air fans. The process has been tested on digestates differing for TS content and origin. It emerged that the process is favored by digestates with high ammonia content, as those originated from manure, and a TS content of about 10% w/w, which allowed to obtain an ammonium sulfate concentration of about 2 M in the final solution
Beyond Anaerobic Digestion: New Perspectives for the Development of a Biorefinery Platform for the Simultaneous Production of Medium-Chain Fatty Acids by Chain Elongation and Biogas from Food Wastes
No full textThe medium chain fatty acids (MCFAs) obtained via chain elongation of short chain fatty acids are becoming a trend topic in the field of biorefinery research. Their synthesis can be implemented in the over 150 000 full-scale anaerobic digestion plants around the world, increasing the economic revenues derived from the mere biogas production. This paper offers a critical insight into the needed actions for the creation of biorefinery model for the simultaneous production of the MCFAs and biogas from the organic fraction of municipal solids wastes and the most abundant food wastes, such as brewery wastes, grape pomace, and cheese whey. A three-stage chain elongation process was suggested with the aim to optimize the operational parameters and the pretreatments for the production and purification of all the compounds involved in the process: (i) the electron donor, (ii) the electron acceptor compounds, and (iii) their reaction into a separate reactor for the synthesis of MCFAs. The remaining organic matter from the fermentation steps for the electron donor and the electron acceptor molecules can be sent to the already-existing AD plant for biogas production. Specifically, it was emphasized that the molar ratio between the electron donor (ethanol or lactate) and electron acceptor compounds (volatile fatty acids, VFAs) in the ranges of 3:1 and 6:1 can optimize the MCFAs yield. Regarding the reactor configuration, batch mode was not able to ensure high yield, while the continuous mode operating at hydraulic retention time (HRT) of 5-10 days and at neutral or slightly acidic pH led to high conversion of food wastes in MCFAs (25-50% (w/w)). Nanofiltration and pertraction were the best techniques to recover the MCFAs from the other organic compounds, with very high yields in the range of 75%-95%. The applications for MCFAs involved different fields: from the production of jet and diesel fuels to polyhydroxyoctanoate and polyhydroxydecanoate biosynthesis. Finally, the main challenges for a full-scale implementation of the chain elongation process were discussed and emphasized: among them, the low concentration of the MCFAs in the reaction medium and the need to increase the technology readiness level of the recovery and purification techniques were considered to be priorities
Integrated biorefinery for the planet’s future
No full textEditorial paper of the Renewable Energy's special issue "Integrated biorefinery for the planet's future
Optimization of biogas production from coffee production waste
No full textThis study was conducted to investigate the effects of chemical pretreatments on biogas production from coffee waste. After the preparation of a mixture of coffee waste with a TS concentration of 10% w/w, basic and acid pretreatments were conducted in batch mode and their performances were compared with the biogas produced from a mixture without any pretreatment stage. The basic pretreatment demonstrated a very good action on the hydrolysis of the lignin and cellulose, and permitted a biogas production of about 18 NL/L with a methane content of almost 80% v/v. Thus, the basic pretreatment has been used to scaleup the process. The coffee refuse was has been carried out in a 45 L anaerobic reactor working in continuous mode and in a mesophilic condition (35 C) with a Hydraulic Retention Time (HRT) of about 40 days. A high biogas production of 1.14 NL/L d, with a methane percentage of 65% v/v was obtained, thus permitting a process yield of about 83% to be obtained
On semidefinite lift-and-project of combinatorial optimization problems
No full textFinding the stability and the chromatic number of a graph are two among the fundamental problems in combinatorial optimization. Given a graph, the first calls for a stable set of maximum cardinality, i.e. a subset of vertices such that no two are adjacent; the latter asks for a partition of the nodes into the minimum number of stable sets (i.e. colors).
Both the stable set and graph coloring problems are well-known to be NP-hard, hence no
polynomial time algorithm to solve them exactly is expected to exists unless P=NP. Thus, the study of strong relaxations of these two problems is a well-researched topic. In particular, the Lov\'asz theta function provides at the same time a good upper bound on the stability number of a graph and a lower bound on the chromatic number of its complement. It can be computed in polynomial time by solving a semidefinite program, which in addition turns often out to be fairly tractable in practice. As a consequence, achieves a hard-to-beat trade-off between computational effort and strength of the bound. Hierarchies of relaxations to strengthen both towards the stability and chromatic number have been documented, but in general such improvements come at a heavy computational burden with off-the-shelf SDP algorithms and require highly specialized methods to be addressed.
In the last decades, Lift-and-Project methods have gained a lot of attention, being able to generate strong relaxations for combinatorial optimization problems. In particular, starting from any linear relaxation \lov\ and \sch's Lift-and-Project framework generates a semidefinite relaxation. Its application to the fractional stable set polytope showed its potential, producing bounds stronger than but in general they come at a nontrivial computational cost.
In this thesis we introduce a new semidefinite relaxation for the stable set problem obtained by the lifting of a more compact linear formulation than the classical one. Then, we characterize some classes of valid inequalities for the stable set polytope which are implied by our proposal. We then discuss how to face the computational burden arising from these semidefinite programs by the employment of a general purpose solver for SDPs.
Despite Lift-and-Project applications have been widely studied on the Stable Set problem, to the best of our knowledge none on the Graph Coloring problem have been presented. We investigate its employment in this problem, showing that the resulting SDP can yield bounds above the fractional chromatic number, a remarkable threshold not so straightforward to cross with semidefinite programming.
Although interior-point methods achieve good accuracy in reasonable time for small and medium size SDPs, their scalability to large instances is often compromised by memory requirements.
On the other hand, Alternating Direction Methods of Multipliers currently represent the most popular first-order alternatives, being suited to scale to much larger semidefinite programs. This of course at some cost in accuracy, that should be correctly addressed when bounding the optimal solution of some combinatorial optimization problem. In this work we focus on an ADMM designed for SDPs in standard form and extend it to deal with inequalities. Moreover, we report different methods to compute a valid bound on the optimal value of the SDP starting from a medium accuracy solution and we discuss the employments of these methodologies within ADMMs
Volatile fatty acids production from waste rich in carbohydrates: Optimization of dark fermentation of pasta by products
No full textPasta is one of the most appreciated Italian products around the world. The 31% of the global production of pasta is made by Italian companies: here, about 120 companies assure an annual production of 5.3 million tons of pasta. The pasta not compliant with the required selling standards (for example size, weight) is usually crushed, grounded to power, and used for animals feeding. This study offered a more advantageous alternative for the valorization of pasta by-products, whose mono-fermentation for Volatile Fatty Acids (VFAs) production was not investigated before. In particular, we considered pasta residues to optimize the operational parameters both in batch and in continuous conditions. The first round consisted in batch tests at different Total Solids (TS) con- centration (1.5–10% TS w/w). The 2% TS w/w emerged as the best one, able to assure a VFAs yield close to the 80%. Consequently, this concentration was chosen for the conduction of continuous tests dedicated to the optimization of the best HRT and SRT for the process. The HRT of 3 d and a SRT of 4.4 d allowed the best process performances with a VFAs productivity of 3.48 gVFAs_COD per L of reactor and per day. The optimization of the process conditions for VFAs production led to a greater concentration of butyric acids (about 10% w/w) instead of the mere acetic acid production. Because of the economic value of butyric acid, this result is of particular interes
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