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Rimozione di nutrienti e microinquinanti attraverso un processo a fanghi attivi assistito da membrana e carboni attivi

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Chapter 1 – Membranes and membrane bioreactors 15 The traditional materials used in the fabrication of membranes included cellulose acetate, polyamide and polysulfone. Other polymers are now used in the manufacturing of membranes and include polypropylene, nylon, polyacronitrile (PAN), polycarbonate, polyvinyl alcohol (PVA) and polyvinylidene fluoride (PVDF). In addition, ceramic and metallic membranes are used for MF and UF applications. Membrane materials are typically polymer- or ceramic-based (Tab.1). Table 1. Materials used for the manufacture of membranes. Material MF UF Material MF UF RO Alumina X Ceramic composites X X Carbon-carbon composites X Polyacrylonitrile (PAN) X X Cellulose esters (mixed) X Polyvinyl alcohol (PVA) X X Cellulose nitrate X Polysulfone (PS) X X Polyamide, aliphatic X Polyethersulfone (PES) X X Polycarbonate (track-etch) X Cellulose acetate (CA) X X X Polyester (track-etch) X Cellulose triacetate (CTA) X X X Polypropylene X Polyamide, aromatic (PA) X X X Polytetrafluoroethylene (PTFE) X Polyimide (PI) X X Polyvinyl chloride (PVC) X Composites X Polyvinylidene fluoride (PVDF) X Composites, polymeric thin film X Sintered stainless steel X Polybenzimidazole (PBI) X Cellulose (regenerated) X X Polyetherimide (PEI) X Polymeric spiral membranes are generally used when a high throughput is required, while polymeric tubular membranes, which can often be mechanically cleaned, are more suited for low-maintenance operations, highly viscous products or fluids with suspended material. Hostile environments, high levels of solvents, wide pH ranges and other process considerations may dictate the use of ceramic membranes. This technology is normally adopted for ultrafiltration and microfiltration applications and typically uses an alumina or zirconium coating that is applied to the inside surface of a ceramic support. The capital cost of ceramic membranes is much higher than conventional polymeric membranes but in some applications they are the only viable proposition. Ceramic membranes often provide a longer operational lifetime, offsetting the high initial cost. Ceramics are not resistant to abrasion although polymerics may be. Organic membranes Cellulose acetate (CA) is the classic membrane material used by the pioneers of modern membrane technology to create skinned membranes. There are several advantages to the use of CA and its derivatives as membrane materials such as hydrophilicity (to minimize fouling of the membrane), wide range of pore sizes that can be manufactured (from RO to MF) with reasonably high fluxes, low cost. Among the disadvantages of CA membranes are a fairly narrow temperature range (maximum temperature 30-35°C), a rather narrow pH range (preferably 3-6), poor resistance of CA to chlorine (less than 1 mg/l of free chlorine under continuous exposure and 50 mg/l in a shock dose), risk of creep or compaction phenomenon to a slightly greater extent than other materials, highly biodegradability. Polyamide membranes (PA) overcame some of the problems associated with CA membranes, e.g. the pH tolerances are wider. However, PA membranes are much worse with regard to chlorine tolerance and Biofouling tendencies. Polyamides for the contact skin layer in many composite membranes.

Anteprima della Tesi di Laura Innocenti

Anteprima della tesi: Rimozione di nutrienti e microinquinanti attraverso un processo a fanghi attivi assistito da membrana e carboni attivi, Pagina 10

Tesi di Dottorato

Dipartimento: Dipartimento di Scienze Ambientali

Autore: Laura Innocenti Contatta »

Composta da 183 pagine.

 

Questa tesi ha raggiunto 4319 click dal 01/04/2005.

 

Consultata integralmente 4 volte.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.