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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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Nutrients and micropollutants removal by a membrane bioreactor (MBR) and activated carbons 6 ABSTRACT The aim of the experimental work carried out during the three-years PhD was to verify the reliability of and advanced biotechnological process for wastewater treatment: the membrane biological reactor (MBR). The need of high quality standards and of the possible reuse of treated wastewater, determines the necessity to adopt advanced wastewater treatment processes. Among the best available technologies in the biotechnological field, the Membrane Biological Reactor (MBR) seems to be the best option for the achievement of such results. In order to gain more information about MBR processes and their proper full scaling-up, a study concerning the pilot-scale application of an ultrafiltration submerged MBR for the treatment of wastewaters has been carrying out since 1999. The membrane utilised in this experimentation was a hollow- fibres type with a nominal pore size of 0.02 Πm, that is the ultrafiltration range. The main goals of the research were the determination of the efficiencies and the study of the related mechanisms for the removal of nutrients and micropollutants and the definition of the best possible treatment option for waste activated sludge produced within the MBR process. During the experimentation, five experimental runs have been carried out. The biomass concentration have been increased from 3.7 g/l (Run 1), to 9.2 g/l (Run 2) to 16.7 g/l (Run 3), to 18.2 g/l (Run 4) and then decreased to 10 g/l (Run 5). During Run 4 also granular activated carbon (GAC) was added within the reactor (1% on a dry weight basis) to investigate the possible improvement on micropollutants removal. The application of the membrane technology gave excellent results in terms of removal of macropollutants: suspended solids and nutrients. In particular, the total suspended solids (TSS) removal was virtually quantitative and a “solids free” effluent was obtained. This aspect is of outmost importance when considering the removal of the fractions of nutrients and micropollutants bound to the solid matter in order to allow an easy reuse of the treated water or the discharging of effluents with high quality standards in water bodies. COD removal was always at good levels, generally in the range 84-94% and the MBR allowed a 30% improvement in the removal of this pollutant compared to a conventional process. This result was mainly tied to the suspended solids removal from the effluent stream of the MBR and to the retention of organic macromolecules exerted by the ultrafiltration membrane. Respiration, that is the conversion of organic substances into CO2, was the main removal mechanism for COD, when biomass concentration in the bioreactor was equal or larger than 9 g/l. Nitrogen was successfully removed, with yields in the range 61-90%, and with a concentration of total nitrogen in the effluent in the range 4.5-11 mgN/l. Denitrification was the main removal process for high biomass concentrations in the bioreactor, when the sludge yield was extremely poor (Yobs equal to 0.1 gMLVSS/gCODremoved or lower). Moreover, ammonia nitrogen concentration in the effluent was constantly below 1 mgN/l. This result has to be ascribed to the perfect retention of nitrifying biomass exerted by the ultrafiltration membrane and thus the improvement of the nitrification process. The MBR biomass showed ammonium utilisation rates (AUR) of 2.5-3 mgN/gVSS h, which are equal to the highest values generally found in the conventional activated sludge processes. Phosphorous removal ranged between 73 and 77%: this effect was mainly due to the retaining of the particulate matter. In fact, the “luxury up-take” mechanism by phosphorous

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 1

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.