1,721,209 research outputs found
Influence of indigenous and added iron on copper extraction from soil
No full textExperimental tests of copper leaching from a low permeability soil are presented and discussed. The objective of the experiments was to investigate the influence of indigenous and added iron in the soil towards copper mobilization. Metals' leaching was performed by flushing (column tests) or washing (batch tests) the soil with an aqueous solution of ethylenediaminetetraacetic acid, EDTA. An excess of EDTA was used in flushing tests (up to a EDTA:Cu molar ratio of about 26.2:1), while, in washing tests, the investigated EDTA vs. copper molar ratios were in the range between 1 (equimolar tests) and 8. Copper extraction yield in flushing tests (up to about 85%) was found to depend upon contact time between the soil and the leaching solution and the characteristics of the conditioning solution. The saturation of the soil with a NaNO3 solution before the treatment, favoured the flushing process reducing the time of percolation, but resulted in a lower metal extraction during the following percolation of EDTA. The indigenous iron was competitive with copper to form EDTA complexes only when it was present in the organic and oxides-hydroxides fractions. Artificial iron addition to the soil resulted in an increase of both the exchangeable iron and the iron bonded to the organic fraction of the soil, thus increasing the overall amount of iron available to extraction. In both batch and continuous tests, the mechanism of copper extraction was found to involve the former dissolution of metal salts, that lead to an initial high concentration of both copper and selected competitive cations (essentially Ca2+), and the following EDTA exchange reaction between calcium and copper complexes. The initial metal salts dissolution was found to be pH-dependant. © 2009 Elsevier B.V. All rights reserved
Experimental assessment of a process for the remediation of organophosphorous pesticides contaminated soils through in situ soil flushing and hydrolysis
No full textThis paper presents a treatability study for the remediation of soils contaminated with phosalone. Experimental tests were performed on an artificially contaminated standard soil with medium organic content. Phosalone was removed from the contaminated soil by flushing with an aqueous solution of ethanol. Ethanol concentration was in the range between 5 and 10% vol. Pollutant extraction efficiency, ethanol loss in soil and soil erosion were determined to assess the optimal extraction conditions. The extraction solution was then submitted to an hydrolysis treatment in order to remove phosalone. The degradation kinetic of phosalone during hydrolysis in presence of ethanol was investigated. Experimental tests were performed at several pH and temperature conditions and kinetic constant rate were determined. In addition, the effect of temperature on half-life time and activation energy of hydrolysis reaction was examined
UPGRADING OF A CONVENTIONAL ACTIVATED-SLUDGE PLANT BY MEANS OF A MULTISTAGE AEROBIC SYSTEM WITH STEP SLUDGE RECIRCULATION (SSR)
No full textThe performance of a multi-stage activated-sludge plant with partial biomass recirculation was examined. The system, which was designed to treat domestic sewage, consists of four stages and has two recirculation flows: (a) directly into the anoxic stage, and (b) distributed over all the aerobic stages from the secondary settlement tank. Different values of recirculation flow to each aerobic stage were adopted during the experiments, and the optimal configuration for removing both ammoniacal nitrogen and carbonaceous substrate was determined. The configuration which gave the best performance also improved the sludge settleability
Recupero del rame da terreni contaminati
No full textObiettivo di questo lavoro è mettere a punto un processo per realizzare il recupero del rame da terreni industriali contaminati; a tale scopo sono state eseguite prove sperimentali nelle quali un terreno di composizione standard è stato contaminato con una soluzione di cloruro di rame. Il rame è stato quindi estratto dal terreno con una soluzione acquosa 0.1 M di un sale sodico dell’EDTA. L’efficienza massima di estrazione ottenuta con un solo passaggio è pari al 60%; la riutilizzazione della soluzione estratta ha consentito un ulteriore incremento del rendimento di estrazione. Il rame è stato quindi precipitato mediante aggiustamento del pH e aggiunta di solfato di ferro
Simulazione e verifica sperimentale di impianti a fanghi attivi a ricircolo parzializzato con predenitrificazione
No full textUna soluzione particolarmente valida per la realizzazione dell’upgrading degli impianti di depurazione è costituita dal sistema multistadio a ricircolo parzializzato (SSR), nel quale il primo stadio, non aerato, costituisce un reattore di predentirificazione.
Una vasca a fanghi attivi tradizionale può essere trasformata in un reattore SSR semplicemente mediante l’inserimento di pareti divisorie e di un sistema di distribuzione per la parzializzazione della corrente di ricircolo dei fanghi tra i vari stadi, fermo restando l’invio della corrente di ricircolo della miscela aerata in testa all’impianto.
La corrente di ricircolo fanghi può così essere opportunamente ripartita in funzione del carico organico affluente a ciascuno stadio in modo da realizzare le condizioni depurative migliori in ogni comparto: in particolare, una sperimentazione condotta su un impianto reale, ha evidenziato come le migliori condizioni si realizzino quando la corrente di ricircolo fanghi è inviata per l’80% direttamente allo stadio finale, e solo in piccola quantità nei primi stadi.
Lo stadio di denitrificazione in testa all’impianto, assoggettato in tal modo ad un valore elevato del carico organico, esercita le funzioni di selettore anossico. In tal modo sono garantite le condizioni per una crescita bilanciata delle varie specie di microrganismi nell’impianto
Simulazione e verifica sperimentale di impianti a fanghi attivi a ricircolo parzializzato della biomassa
No full textUna soluzione particolarmente valida per migliorare le prestazioni degli impianti di depurazione a fanghi attivi tradizionali è costituita dal sistema multistadio a ricircolo parzializzato della biomassa (step sludge recirculation, S.S.R). La presente sperimentazione, condotta su un impianto reale, riguarda un impianto a fanghi attivi multistadio costituito da quattro stadi disposti in serie nel quale il primo stadio, non aerato, costituisce un reattore di predentirificazione.
La corrente di ricircolo fanghi è stata ripartita in funzione del carico organico affluente a ciascuno stadio in modo da realizzare le condizioni di reazione ottimali in ogni comparto. La sperimentazione ha evidenziato che le migliori condizioni si realizzano quando la corrente di ricircolo fanghi è inviata per l’80% direttamente allo stadio finale, e il rimanente 20% distribuito nei primi stadi.
Lo stadio di denitrificazione in testa all’impianto esercita le funzioni di selettore anossico: in tal modo sono garantite le condizioni per una crescita bilanciata delle varie specie di microrganismi nell’impianto
Kinetic study of nitrate removal from aqueous solutions using copper-coated iron nanoparticles
No full textNitrates are considered hazard compounds for human health due to their tendency to be reduced to nitrites, in particular in reducing environment. Nano zero valent iron (nZVI) represents an efficient and low-cost adsorbent/reductive agent for nitrate removal from groundwater and wastewaters and a little addition of a second metal species (Cu, Pd, Ni, Ag) has proven to increase process effectiveness, by enhancing stability and oxidation resistance of nanoparticles. In this work Cu/Fe nanoparticles were loaded in a NO3 (-) solution (100 mg L(-1)) and the removal efficiency was tested by monitoring nitrate concentration at selected time intervals. Results showed that the nitrate removal process involves both reduction and adsorption processes: the removal mechanism has been investigated, and the pseudo-first-order and pseudo-second-order-adsorption kinetic models were successfully tested
Limiting factors for the leaching of chromium in aqueous solution
No full textThis paper illustrates the results of experiments performed in order to assess the immobilization capacity of trivalent chromium in aqueous solution. To this end, the standard techniques of solidification/stabilization were employed. Compressive strength and porosity of the inertization matrix were measured together with the amount of embedded chromium leached in an aqueous solution
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