Il progetto degli impianti MBR: configurazione dei reattori, componenti e particolari costruttivi.

Vengono discussi alcuni aspetti della progettazione degli impianti MBR, come la scelta della configurazione, la scelta delle membrane, delle dotazioni elettromeccaniche e delle opere accessorie degli impianti MBR. Inoltre sono riportati dei cenni sulle soluzioni tecnologiche più innovative atte a minimizzare le disfunzioni dei sistemi MBR e di conseguenza dei costi operativi. La scelta di sistemi con flusso a pistone in impianti MBR ha impatti negativi sia sulla per quanto concerne il fenomeno del foaming che quello del fouling. Per la scelta delle membrane risulta che quelle piane siano utilizzate sia per applicazioni industriali che civili, quasi esclusivamente in impianti a configurazione sommersa a servizio di comunità medio-piccole, mentre quelle a fibre cave sono utilizzate anch’esse in impianti a configurazione sommersa, vengono maggiormente utilizzate per installazioni di grandi dimensioni. Le tipologie di griglie vanno scelte in maniera opportuna in funzione della tipologia di membrana installata. In particolare, i costruttori suggeriscono di adottare una grigliatura grossolana a coclea a monte di quella fine o dell’unità di stacciatura, indicata se sono installate membrane a fibre cave. Come sistema di miscelazione si adottano mixer compatti dotati di anello convogliatore orientati in modo da evitare la formazione di zone morte e di innescare dei moti rotatori che consentono di ottenere un'adeguata miscelazione, contenendo al contempo i costi energetici. Il sistema di aerazione deve avere il duplice ruolo di fornire l'ossigeno necessario alla biomassa per ossidare la sostanza organica e l'azoto ammoniacale, nonché di garantire una sufficiente turbolenza in corrispondenza delle fibre della membrana (scouring) per attenuare il fenomeno del fouling. L'ottimizzazione dei costi di aerazione tuttavia, passa necessariamente anche attraverso la scelta di macchine elettriche altamente efficienti. In particolare alcuni costruttori di membrane suggeriscono l'utilizzo di compressori centrifughi che consentono un maggiore controllo delle portate erogate anche al variare della viscosità della miscela aerata. Nella progettazione dei reattori, si consiglia sempre di prevedere dispositivi di evacuazione superficiale della schiuma, utilizzando stramazzi laterali a livello di sfioro regolabile o mediante inghiottitoi dotati di galleggiante. La scelta di soluzioni tecnologicamente avanzate, quali membrane con flusso elicoidale, i sistemi pulsanti e le membrane rotative, consentono un’efficace minimizzazione del fenomeno del fouling consentendo di ottenere notevoli vantaggi in termini di qualità dell'effluente rispetto ai sistemi convenzionali. La progettazione degli impianti MBR deve essere effettuata attuando delle soluzioni volte alla minimizzazione dei costi, sia di investimento che operativi, attraverso scelte progettuali oculate, che vanno dalla scelta della configurazione dei reattori all'impiantistica di processo

Fate of aerobic granular sludge in the long-term: The role of EPSs on the clogging of granular sludge porosity

This work aims to investigate the stability of aerobic granular sludge in the long term, focusing on the clogging of the granular sludge porosity exerted by the extracellular polymeric substances (EPSs). The effects of different cycle lengths (short and long-term cycle) on the granular sludge stability were investigated. Results obtained outlined that during the short duration cycle, the formation and breakage of the aerobic granules were continuously observed. During this period, the excess of EPS production contributed to the clogging of the granules porosity, causing their breakage in the long run. During the long-duration cycle, the extended famine period entailed a greater EPSs consumption by bacteria, thus limiting the clogging of the porosity, and allowed obtaining stable aerobic granules. Reported results demonstrated that an excess in EPSs content could be detrimental to the stability of aerobic granular sludge in the long-term

Biopolymer Recovery from Aerobic Granular Sludge and Conventional Flocculent Sludge in Treating Industrial Wastewater: Preliminary Analysis of Different Carbon Routes for Organic Carbon Utilization

The recovery of biopolymers from sewage sludge could be a crucial step in implementing circular economy principles in wastewater treatment plants (WWTP). In this frame, the present study was aimed at evaluating the simultaneous production of polyhydroxyalkanoates (PHA) and extracellular polymeric substances (EPS) obtainable from the treatment of agro-industrial wastewater. Two biological enrichment systems, aerobic granular sludge (AGS) and a conventional activated sludge operating as a sequencing batch reactor (SBR), were monitored for 204 and 186 days, respectively. The maximum biopolymers accumulation capacity was close to 0.60 mgPHA-EPS gVSS−1 in the AGS when operating at 3 kgCODm−3d−1, whereas in the SBR, it was about half (0.35 mgPHA-EPS gVSS−1). Biopolymers extracted from the AGS were mainly constituted by EPS (>70%), whose percentage increased up to 95% with the OLR applied in the enrichment reactor. In contrast, SBR enabled obtaining a higher PHA production (50% of the biopolymers). Results suggested that organic carbon was mainly channeled toward metabolic pathways for extracellular storing in AGS, likely due to metabolic stressors (e.g., hydraulic selection pressure, shear forces) applied for promoting aerobic granulation

Treatment of high strength industrial wastewater with membrane bioreactors for water reuse: Effect of pre-treatment with aerobic granular sludge on system performance and fouling tendency

In this study, the treatment of citrus wastewater with membrane bioreactors (MBRs) under different configurations was investigated for water reuse. In particular, one MBR and one aerobic granular sludge MBR (AGS+MBR) bench scale plants were operated for 60 days. The experimental campaign was divided into two periods. In Phase I, a conventional hollow fiber MBR was employed for the treatment of the raw high strength wastewater, whereas in Phase II a combination of in-series reactors (AGS plus MBR) was adopted for the treatment of the high strength citrus wastewater The results demonstrated that both plant configurations enabled very high COD removal, with average values close to 99%. Respirometric batch tests revealed a considerable high metabolic activity of the biomass in both plant configurations, with higher values in the AGS+MBR. It was speculated that the MBR reactor enriched in active biomass deriving from the erosion of the external granule layers in the upstream reactor. In terms of fouling tendency, higher resistance to filtration was observed in the AGS+MBR plant, also characterized by higher irremovable resistance increase compared to the MBR plant that might severely affect the membrane service life

The role of extracellular polymeric substances on aerobic granulation with stepwise increase of salinity

A granular sequencing batch reactor (GSBR) worked for 164 days to study the effect of salinity on aerobic granulation. The feeding had an organic loading rate (OLR) of 1.6 kg COD c5m 123 c5d 121 and a gradual increase of salinity (from 0.30 to 38 g NaCl 12 c5L 121) to promote a biological salt-adaptation. First aggregates (average diameter 48 0.4 mm) appeared after 14 days. Extracellular polymeric substances (EPSs) analyses revealed that proteins were mainly higher than polysaccharides, and microorganisms metabolized EPSs as additional carbon source, mostly in feast phase, to face the energy demand for salinity adaptation. No significant worsening of organic matter removal was observed. The initial decrease of nitrification (from 58% to 15%) and the subsequent increase (up to 25%), confirmed the acclimation of AOBs to saline environment, while the accumulation of nitrites suggested NOBs inhibition. The nitrogen removal initially decreased from 58% to 15%, due to the inhibitory effect of salinity, and subsequently increased up to 29% denoting a simultaneous nitrification\u2013denitrification. The dimensions of mature granules (higher than 1 mm) probably involved PAOs growth in the inner anaerobic layers. Nitrites caused a temporary deterioration of phosphorous removal (from 60% to almost zero), that increased up to 25% when nitrites were depleted

Simultaneous nitritation-denitritation for the treatment of high-strength nitrogen in hypersaline wastewater by aerobic granular sludge

Fish processing industries produce wastewater containing high amount of salt, organic matter and nitrogen. Biological treatment of such wastewaters could be problematic due to inhibitory effects exerted by high salinity level. In detail, as is known, high salt concentration leads to accumulation of nitrite due to inhibition of nitrite-oxidizing bacteria. The feasibility of performing simultaneous nitritation and denitritation in treating of fish canning wastewater by aerobic granular sludge was evaluated, and simultaneous nitritation-denitritation was successfully sustained up to 50 gNaCl L-1. Nitritation collapsed above which nitritation, and the only nitrogen removal mechanism was represented by heterotrophic synthesis. Conversely, organic matter removal was not affected by salinity, but rather by organic loading rate (OLR). COD fractionation analysis highlighted that aerobic granules exhibited excellent removal capacity toward particulate organic matter. Finally, results obtained in this work pointed out that aerobic granular sludge had excellent ability of adapting in adverse environmental conditions

Transapical off-pump mitral valve repair with Neochord Implantation (TOP-MINI): step-by-step guide

open10openColli, Andrea; Zucchetta, Fabio; Torregrossa, Gianluca; Manzan, Erica; Bizzotto, Eleonora; Besola, Laura; Bellu, Roberto; Sarais, Cristiano; Pittarello, Demetrio; Gerosa, GinoColli, Andrea; Zucchetta, Fabio; Torregrossa, Gianluca; Manzan, Erica; Bizzotto, Eleonora; Besola, Laura; Bellu, Roberto; Sarais, Cristiano; Pittarello, Demetrio; Gerosa, Gin

The Ipsilateral Interhemispheric Transprecuneal Approach to the Atrium: Technical Considerations and Clinical Outcome on a Series of 7 Patients

Surgical removal of tumors of the atrium is challenging due to their deep location, vascularization, and to their complex three-dimensional relationships with the highly functional white matter fibers of the region. To assess the feasibility and the effectiveness of the ipsilateral interhemispheric transprecuneus approach (IITA) for tumors involving the atrium and the posterior third of the temporal horn, a retrospective chart review of all patients who had undergone a surgical treatment for intraventricular tumors between January 2008 and January 2017 was performed, and the step-by-step approach is described. Ten patients affected by lesions of the atrium of the lateral ventricle underwent surgical treatment, seven of which were approached through the IITA. The mean age was 42.8 years (range 6-63 years). The symptoms presented included severe, drug-resistant headache (90%), lateral homonymous hemianopsia (50%), seizures (30%), and speech disturbances (30%). Histological examinations revealed seven patients with meningioma (70%), one with a metastasis (10%), one with a choroid plexus papilloma (10%) and one with a cavernoma (10%). In all cases, a gross total removal was obtained. All patients had a significant improvement in their headache. Two patients experienced a worsening of the pre-operative visual disturbances, while two patients had a significant improvement. No patients without pre-operative visual disturbances described a post-operative worsening of visual symptoms. The IITA represents a feasible approach for tumors of the atrium. The three-quarter prone position facilitates the enlargement of the interhemispheric fissure by increasing the working angle and facilitating the exposure of the lateral wall of the atrium

Study of aerobic granular sludge stability in a continuous-flow membrane bioreactor

A granular continuous-flow membrane bioreactor with a novel hydrodynamic configuration was developed to evaluate the stability of aerobic granular sludge (AGS). Under continuous-flow operation (Period I), AGS rapidly lost their structural integrity resulting in loose and fluffy microbial aggregates in which filamentous bacteria were dominant. The intermittent feeding (Period II) allowed obtaining the succession of feast and famine conditions that favored the increase in AGS stability. Although no further breakage occurred, the formation of new granules was very limited, owing to the absence of the hydraulic selection pressure. These results noted the necessity to ensure, on the one hand the succession of feast/famine conditions, and on the other, the hydraulic selection pressure that allows flocculent sludge washout. This preliminary study shows that the proposed configuration could meet the first aspect; in contrast, biomass selection needs to be improved