1,721,304 research outputs found
Aerobic Granular Sludge for Leachate Treatment
Full text linkThe treatment of municipal landfill leachate by means of aerobic granular sequencing batch reactors (GSBRs) was investigated. The paper reports the results from an experimental campaign lasted 100 days, which has been divided into three periods: cultivation of granular sludge (70 days), operation with semi-fresh (15 day) and diluted landfill leachate (15 day). Two different GSBR configurations were used: a Sequencing Batch Bubble Column reactor and a Sequencing Batch Airlift Reactor. All reactors were operated at Volume Loading Rates (VLRs) between 4.8 and 7.2 g COD /(m 3 ·d). The Chemical Oxygen Demand (COD) removal efficiency varied between 80% and 90% under operation with synthetic wastewater feeding. On the other hand, the COD removal performance decreased to 40-50 % with semi-fresh leachate and to 50-60% with diluted leachate. Regarding nitrogen removal, after granules formation, the performance were satisfactory only when the reactors were fed with synthetic wastewater. Contrarily, the obtained results underline that a specific pre-treatment of ammonium must be applied in order to optimize nitrogen removal. However, the observed results indicate that the landfill leachate can be potentially treated in GSBR bioreactors
Simultaneous nitrogen and organic carbon removal in aerobic granular sludge reactors operated with high dissolved oxygen concentration
Full text linkSimultaneous nitrification and denitrification (SND) together with organic removal in granules is usually
carried out without Dissolved Oxygen (DO) concentration control, at ‘‘low DO’’ (with a DO < 30–50% of
the saturation value, about 3–4 mg/L) to promote anoxic conditions within the aggregates. These
conditions can sometimes be in detrimental of the stability of the granules itself due to a lack of shear
force. In this work, the authors achieved SND without oxygen control with big sized granules. More spe-
cifically, the paper presents a experimentation focused on the analysis of two Sequencing Batch Reactors
(SBRs), in bench scale, working with different aerobic sludge granules, in terms of granule size, and high
DO concentration, (with concentration varying from anoxic conditions, about DO 0 mg/L, to values close
to those of saturation, >7–8 mg/L, during feast and famine conditions respectively). In particular, different
strategies of cultivation and several organic and nitrogen loading rate have been applied, in order to eval-
uate the efficiencies in SND process without dissolved oxygen control. The results show that, even under
conditions of high DO concentration, nitrogen and organic matter can be simultaneously removed, with
efficiency >90%. Nevertheless, the biological conditions in the inner layer of the granule may change sig-
nificantly between small and big granules, during the feast and famine periods. From point of view of
granule stability, it is also interesting that with a particle size greater than 1.5 mm, after the cultivation
start-up, the granules are presented stable for a long period (about 100 days) and, despite the variations
of operational conditions, the granules breaking was always negligible
Analisi sperimentale e modellistica di formazione del fouling delle membrane nei sistemi MBR
No full textThe SND process in two granular sequencing batch reactors with different mean granule sizes: a case study.
Full text linkFoaming in membrane bioreactors: Identification of the causes
Full text linkMembrane bioreactors (MBRs) represent by now a well established alternative for wastewater treatment.
Their increasing development is undoubtedly related to the several advantages that such technology is
able to guarantee. Nevertheless, this technology is not exempt from operational problems; among them
the foaming still represents an “open challenge” of the MBR field, due to the high complexity of phe-
nomenon. Unfortunately, very little work has been done on the foaming in MBRs and further studies are
required. Actually, there is not a distinct difference between conventional activated system and MBR: the
main difference is that the MBR plants can retain most Extracellular Polymeric Substances (EPSs) in the
bioreactor. For these reason, unlike conventional activated sludge systems, MBRs have experienced
foaming in the absence of foam-forming micro-organisms. Nevertheless, the actual mechanisms of EPS
production and the role of bacteria in producing foam in activated sludge in MBRs are still unclear. In this
paper, the authors investigated the roles of EPS and foam-forming filamentous bacteria by analyzing
samples from different pilot plants using MBRs. In particular, in order to define the macroscopic features
and the role of EPS and filamentous bacteria, a Modified Scum Index (MSI) test was applied and pro-
posed. Based on the MSI and the foam power test, the causes of biological foaming were identified in
terms of the potential for foaming, the quality and the quantity of the foam. The results indicated that the
MBR foaming was influenced significantly by the concentration of bound EPSs in the sludge. In addition,
the quantity and stability of MBR scum increased when both bound EPSs and foam-forming filamentous
bacteria were present in the activated sludge
comparing two start-up strategies for MBRs: experimental study and mathematical modelling
No full textThe performance of a membrane bioreactor (MBR), and mechanisms of fouling formation, may differ
due to the start-up. Therefore, the start-up can constitute an aspect that critically influences MBR performance
during its lifespan. Indeed, the start-up can influence the mechanisms of membrane fouling,
which is of paramount importance in an MBR. In order to gain insights on the effects of the start-up,
both experimental and mathematical modelling studies were carried out on an MBR pilot plant. The MBR
pilot plant constituted of a hollow fibre membrane module, in a submerged configuration, was fed by
real wastewater. Two experimental periods were carried out, lasting 65 days each, characterised by two
different MBR start-ups: without inoculum of activated sludge, and with inoculum of activated sludge.
An integrated MBR mathematical model was applied to the two periods in order to combine the insights
gained from the experimental survey. The MBR model simulates both biological and physical processes
simultaneously, taking into account the interactions between them. Two MBR model calibrations were
carried out for the two different experimental start-ups. Model calibration was carried out by means of
an innovative calibration protocol, based on the global sensitivity analysis, and the Generalised Likelihood
Uncertainty Estimation. Thus, two sets of model parameters were assessed and compared. Both
experimental and mathematical model results were analysed to quantify the effects of the two start-ups
on membrane fouling. The results showed only slight differences in terms of total pollutant removal
efficiency. However, relevant differences appeared with respect to the fouling phenomenon between the
two start-ups. The results demonstrated that the best choice, in terms of the start-up of MBR systems,
comes from a compromise between minimisation of the fouling issues and high system performance
Heavy metals and persistent organic pollutants in marine organisms from two sicilian protected areas: Strait of Messina and Cape Peloro lakes
No full textThis paper reviews several scientific articles regarding levels of organic and inorganic contaminants in a variety of marine species coming from two Sicilian protected areas: the Strait of Messina and Cape Peloro lakes (Ganzirri and Faro). Moreover, different analytical techniques for the determinations of organic and inorganic contaminants, and the procedures adopted for the analyses, are summarized. Quantitative and qualitative determination of organic pollutants was performed by High Resolution Gas Chromatography-Electron Capture Detection and confirmed by Gas Chromatography-Mass Spectrometry. The concentrations of inorganic elements were determined by Atomic Absorption Spectrophotometry, derivative Stripping Chronopotentiometry, Inductively Coupled Plasma-Optical Emission Spectrometry and Inductively Coupled Plasma - Mass Spectrometry. Results provide evidence that organic and inorganic residues found in some of the examined samples were mostly below the Maximum Residue Levels (MRLs). In conclusion, species analyzed in these studies were safe for human consumption and, consequently the investigated environments were estimated as free from toxicological risk
Analisi sperimentale e modellistica di formazione del fouling delle menbrane negi sistemi MBR
No full textLa tecnologia MBR è una realtà consolidata e la sua applicazione è considerata una valida alternativa ai sistemi convenzionali, soprattutto ove il refluo depurato assuma pienamente il ruolo di “risorsa” riutilizzabile. Tuttavia, la diffusione dei bioreattori a membrana è frenata prevalentemente dall’elevato costo di investimento su cui grava, inoltre, l’impossibilità di prevedere correttamente la durata della vita utile delle membrane a causa dell’incompleta conoscenza del fouling, della sua evoluzione e delle sue conseguenze. Il fenomeno di sporcamento, infatti, è estremamente complesso e la conoscenza dei meccanismi di deposito e le proprietà sporcanti di tutti gli agenti presenti nella miscela da filtrare è lungi dall’essere completa. In questo contesto, le caratteristiche della particolare miscela filtrata (fango attivo) hanno un ruolo essenziale nella definizione qualitativa e quantitativa del fouling; tuttavia, a causa dell’estrema complessità della sua composizione, è praticamente impossibile scorporare l’influenza di ogni elemento, fisico o biologico, nei confronti della formazione dei fenomeni di sporcamento (dimensione dei fiocchi biologici, dispersione cellulare, presenza di composti organici ed inorganici, grado di attività e maturazione batterica, etc.). Per quanto detto sopra, allo scopo di migliorare le conoscenze sul fouling, buona parte delle ricerche concentrano l’analisi sperimentale sullo studio degli effetti causati dalle singole componenti (soprattutto batteri, proteine e colloidi) sul processo di micro o ultrafiltrazione. Parallelamente all’analisi delle componenti più sensibili, la letteratura focalizza l’attenzione sui principali parametri tecnico-gestionali che possono condizionare il processo: carico inquinante, idrofobicità della membrana e della miscela aerata, flusso di permeato e dimensioni dei pori della membrana. La complessità del fenomeno viene aggravata dalla natura estremamente labile di alcune sostanze (EPS, sostanze umiche, ecc...) che possono influenzare negativamente i meccanismi di deposito in funzione delle variazioni delle condizioni operative e gestionali. Inoltre, l’interazione tra colloidi in sospensione e cake depositato sulla membrana è influenzata da moltissime variabili che sono legate alle numerosissime componenti presenti nella miscela biologica, e alle loro correlazioni, di conseguenza possono manifestarsi significative differenze, in termini di permeabilità e persistenza dello stato di deposito, anche in due impianti funzionanti con la stessa configurazione e con le stesse apparenti condizioni di funzionamento. Da un punto di vista teorico, si può affermare che lo sporcamento della membrana è dovuto a due fenomeni fondamentali: il deposito di colloidi, batteri, protozoi e virus all’interno dei pori (sporcamento interno) e il deposito superficiale (deposizione esterna) dei fiocchi biologici e delle particelle sospese che hanno dimensioni mediamente superiori a quelle dei pori. Sebbene i meccanismi di sporcamento siano stati studiati a lungo, in letteratura ci sono molte contraddizioni sull’effettivo ruolo di molti foulants (agenti sporcanti); molti autori, infatti, assegnano un peso totalmente opposto al ruolo esercitato dai singoli agenti responsabili dello sporcamento, o all’effetto che questi hanno sul tipo di deposito (reversibile, irreversibile, irremovibile ...) . Una recente review sui sistemi MBR, distingue tre diversi tipi di intasamento delle membrane (Meng et al., 2009): il fouling reversibile, irreversibile e irremovibile. Il primo può essere rimosso tramite lavaggio idraulico, ad esempio controlavaggio e azione idrodinamica; il fouling irreversibile non può essere rimosso per semplice pulizia idraulica, ma richiede una pulizia più intensa (cioè chimica); infine il fouling irremovibile non può essere rimosso da ogni approccio. Ulteriori motivi di contraddizione sono evidenziati nell’attribuzione del peso maggiore o minore nella formazione del fouling tra solidi disciolti, solidi sospesi e colloidali (Wisniewski e Gransmick,1998; Defrance et al., 2000). Queste contraddizioni evidenziano la complessità del fenomeno e la difficoltà della sua determinazione. Tuttavia il parametro fondamentale, che sembra accomunare i diversi meccanismi di sporcamento, è rappresentata dalle dimensioni medie dei foulants in relazione alle dimensioni medie dei pori della membran
Natural Fiber-Reinforced Composites
No full textOver the last decade, composites of polymers reinforced with natural fibres have received increasing attention, both from the academic world and from several industries. There is a wide range of natural fibres which can be applied as reinforcements or fillers thanks to their properties and availability; i.e. flax, hemp, jute, kenaf and sisal.
Natural fibres are mainly attractive for the following reasons: specific properties, price, health advantages and recyclability.
Particularly, industry is getting more and more interested in environment-friendly products and therefore the research on natural fibre based on composite materials is gaining importance.
Some of the benefits linked to the usage of such natural composites are their low density and good specific properties. Furthermore, they are renewable and have a CO2-neutral life cycle, in contrast with their synthetic opponents (i.e. glass and carbon). Despite such good premises, these fibres have also some negative characteristics: they are highly hydrophilic and their properties may vary in time. The natural fibres have a complex structure of elementary fibres, consisting of cellulose, hemicellulose, pectin, lignin and others and thus they should not be considered as monofilament fibres.
Mechanical, physical and even chemical properties of these fibres are strongly harvest-dependent, influenced by climate, location, soil characteristics, and weather circumstances. They are affected also by fibre processing (i.e. retting, scutching, bleaching, spinning) and by their incorporation into composites: handling, impregnation and consolidation may introduce supplementary changes. Obviously, such variability complicates the prediction and the evaluation of the composite properties. Another known problem in natural fibre reinforced composites is the poor interface quality between the fibres and the polymer matrix; chemical pre-treatments are often applied in order to enhance the adhesion between these components,.
In the last few years several new components based on natural fibre composites have been mainly developed by industries in the automotive field; i.e. in 2003 around 43,000 tonnes of natural fibre have been used by the European automotive industry as composite reinforcement. This interest is due to the excellent tensile mechanical properties of fibre obtained from plants such as flax, hemp and the stinging nettle.
Other main applications of the natural fibres are in the following fields: nautical and biomedical ones. The aim of this work is to present a review on the main natural fibres investigated by researchers and to report the results of some original studies performed by the Authors
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