1,721,004 research outputs found
Guida alla progettazione dei sistemi di collettamento e depurazione delle acque reflue urbane
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Colour removal in Sequencing Batch Reactors
No full textThe primary objective of this research was to study the biological colour removal from a simulated textile effluent containing an azo reactive dye with a Sequencing Batch Reactor (SBR). Further objectives were to achieve reductions in Ammonia and COD in the effluent wastewater.
Anaerobic/aerobic (ANA/AER) sequential step-treatment could provide the best reductions in colour, ammonia and COD. A lab-scale SBR fed with synthetic wastewater and mono-azo dye was set up in laboratory. At the beginning of the experimentation only the aerobic phase occurred in the reactor in order to acclimate the microorganisms and to study the colour adsorption on the biomass. Later an experimental run with an anoxic/anaerobic phase followed by an aerated phase was carried out in order to study the colour degradation and the nitrification and denitrification processes. Furthermore, the sludge age of the reactor was varied between 10, 20 and 30 days and pH, Temperature, ORP and SST and SSV concentrations were monitored during all experiments. Several samples were also collected within a typical operative cycle during the anaerobic phase to determine the colour removal kinetic
Biological colour removal in Sequencing Batch Reactors
No full textThe primary objective of this research was to study the biological removal of organic azo dyes by using a Sequencing Batch Reactor (SBR). Further objectives were to achieve reductions in Ammonia and COD in the effluent wastewater.
Anaerobic and aerobic treatment systems could be both effective in reducing the wastewater colour; however, anaerobic treatment generally produced the greatest colour removal. Anaerobic/aerobic (ANA/AER) sequential step-treatment could provide the best reductions in colour, ammonia and COD. A lab-scale SBR fed with synthetic wastewater and mono-azo dye was set in laboratory in order to perform
some experimental runs. A first experimental run was performed with only aerobic phase, to acclimate the microorganisms and to study the colour adsorption on the biomass. Other runs will be performed with an anoxic/anaerobic phase followed by an aerated phase to study the colour degradation and to obtain the nitrification and denitrification removal rates (results here not presented)
Applicazione di reattori SBR e SBBR al trattamento di acque di falda contaminate
No full textLo scopo di questa ricerca è stato lo studio dell’applicazione del reattore sequenziale discontinuo (Sequencing Batch Reactor, SBR) al trattamento di acque di falda contaminate da fenolo e clorofenolo (2-CP). In particolare, l’SBR è stato impiegato sia nella configurazione tradizionale a biomassa sospesa che in quella, di più recente introduzione, a biomassa adesa (Sequencing Batch Biofilm Reactor, SBBR). In entrambi i casi, sono state valutate sia le efficienze di depurazione che le cinetiche di biodegradazione, per diverse condizioni di alimentazione (solo 2-CP o 2-CP miscelato con fenolo).
I risultati ottenuti hanno evidenziato la validità di questo tipo di tecnologia sia a biomassa sospesa che adesa, per la decontaminazione di falde contenenti composti clorofenolici. In condizioni di regime, raggiunte peraltro in tempi piuttosto brevi, le concentrazioni effluenti sono risultate molto inferiori ai limiti di legge; inoltre, la rimozione completa dei contaminanti è sempre avvenuta in tempi inferiori alla durata del ciclo. La presenza del ricircolo dell’effluente nell’SBBR durante la fase di reazione, determinando una crescita uniforme del biofilm lungo l’altezza del reattore, ha consentito di migliorare le prestazioni e la stabilità del processo. Infine, l’adsorbimento dei composti sul materiale di riempimento e/o sul biofilm ha fornito un importante contribuito alla rimozione dei contaminanti
Trattamenti di ozonolisi per la riduzione della produzione dei fanghi
No full textNegli ultimi 20 anni, sono stati fatti numerosi progressi nell’ambito della depurazione delle acque reflue, ed in particolare nella gestione dei fanghi biologici. Tuttavia, attualmente i costi per il trattamento dei fanghi rappresentano ancora una voce economica particolarmente rilevante nell’ambito della gestione delle acque reflue, raggiungendo in taluni casi il 50%, e talvolta anche il 60%, dei costi totali di trattamento delle acque. Relativamente allo smaltimento finale dei fanghi, le soluzioni attualmente praticate (principalmente confinamento in discarica controllata, ma anche incenerimento in impianti di termodistruzione per rifiuti o cementifici, ed impiego in agricoltura) devono rispettare limiti molto restrittivi imposti dalla normativa vigente in materia, o richiedono costi elevati. Pertanto, la gestione dei fanghi di depurazione può essere considerata a ragione un problema tutt’altro che risolto. Un utile contributo alla risoluzione di tale problema è dato sicuramente dallo studio di tecnologie di trattamento alternative che risultano più efficienti e meno costose, ma al contempo anche dall’applicazione di quelle strategie che consentono la riduzione della produzione di fango, ed in particolare di quello biologico, alcune delle quali già utilizzate con successo in applicazioni impiantistiche reali. Nell’articolo viene riportata una sintetica descrizione dei meccanismi alla base del funzionamento dell’ozonizzazione nella riduzione dei fanghi biologici, ed illustrate alcune esperienze condotte sul tema, evidenziando i principali parametri di interesse ed i risultati ottenuti.
Allo stato attuale delle conoscenze, stante il fatto accertato che attraverso l’ozonizzazione è possibile conseguire la riduzione dei fanghi biologici, rimane la necessità di definire le condizioni ottimali del processo al fine di massimizzare il risultato conseguito, a fronte di costi complessivi contenuti. In particolare, è indispensabile effettuare ulteriori studi e ricerche soprattutto alla scala reale, per valutare l’applicabilità di tale tecnologia nel caso di alimentazione con refluo reale (e non come fatto spesso sino ad ora con refluo sintetico), e di diversa provenienza (civile ed industriale) e quindi composizione, per determinare gli effetti del trattamento di ossidazione sia ai fini della riduzione della produzione di fango biologico che delle prestazioni più generali dell’impianto di depurazione, nonché dei relativi costi di investimento ed operativi. E’, inoltre, necessario comprendere meglio le variazioni indotte sulle caratteristiche del fango durante il processo di ozonizzazione, per definire i meccanismi che sono alla base del processo di riduzione.
L’obiettivo finale dovrebbe essere quello di individuare una serie di parametri chiave sulla base dei quali valutare le potenzialità tecnico-economiche dell’ozonizzazione in relazione alle caratteristiche specifiche dell’impianto nel quale si intende adottare tale tecnologia, valutandone le prestazioni anche in confronto a tecnologie alternative di minimizzazione dei fanghi
The effect of operating variables on chelant-assisted remediation of contaminated dredged sediment
No full textThe paper shows the results from a number of lab-scale washing treatments using the four chelating agents EDTA, NTA, citric acid and [S,S]-EDDS aiming at the remediation of a real heavy metal-contaminated sediment. Investigation of the influence of chelant type and concentration as well as solution pH was the major focus of the work. The analysis of speciation of metals and chelating agents in solution was carried out through geochemical speciation modelling in order to identify the optimal conditions for the washing process as well as to evaluate the competition phenomena of metal-chelant complexes in solution. The major competing cations were found to be Ca above all and Mg under specific conditions. Among the investigated chelating agents, EDDS appeared to be less affected by competition by major cations while ensuring adequate heavy metal extraction efficiencies. For a 1:1 chelant/metal ratio, the following ranking was observed: EDDS > Cit > NTA > EDTA for As, EDDS > NTA congruent to EDTA >> Cit for Cu, EDDS congruent to EDTA congruent to NTA > Cit for Zn, EDTA > NTA > EDDS > Cit for Pb at pH 5 and EDTA congruent to EDDS congruent to NTA >> Cit for Pb at pH 8. For a 10:1 chelant/metal ratio geochemical modelling indicated that at the equilibrium the extracting solutions were dominated by the free form of the chelating agents, indicating the inability of such species to complex trace metals due the strong interactions existing between heavy metal ions and sediment constituents. (c) 2006 Elsevier Ltd. All rights reserved
Modelling lead adsorption on clays by models with and without electrostatic terms
No full textThe research describes the adsorption of heavy metals (lead) on clay minerals (kaolinite) as function of different experimental conditions, The lead adsorption was investigated as function of pH and ionic strength at several initial lead concentrations, The adsorption of proton and sodium (obtained by titration curves and negative surface charge measurements, respectively) was also investigated as function of pH, AU experimental variables were simultaneously accounted for by using the multivariate nonlinear regression of data, according to different models including or not including electrostatic interactions, The adsorption of lead, proton, and sodium on the clay was successfully described by a three-layer electrostatic model considering two discrete types of adsorption sites (with fixed and variable charge, respectively) and the additional effect of the heterogeneity of each site (in terms of continuous distribution of the affinity constants), Confident estimates were obtained for the site concentrations (adsorption maxima) and the heterogeneity parameters. The sites with fixed and variable charge were found to be 40 and 60% of the total, respectively. Both of them contribute to the lead adsorption in proportions which highly depend on the pH, The heterogeneity parameters of both sites have low values which underline the high influence of the continuous distribution of the affinity constants, The diffuse layer potential was also well estimated. It depends mainly on the ionic strength and it is quite different from the measured zeta potential (about one order of magnitude more negative). To consider simultaneously all experimental variables by a multivariate approach appeared to be very important for an accurate modeling, If only the lead adsorption was taken into account at a single ionic strength, the electrostatic effects could be neglected with no practical difference on the calculated behavior
Olive mill wastewater treatment by combined chemical-physical and membrane-SBR processes
No full textThe aim of the present research was the study of a combined treatment scheme of the Olive Mill Wastewaters (OMWs) made by chemical-physical and membrane-Sequencing Batch Reactor (M-SBR) processes for their proper disposal and possible reuse. As pre-treatments, the chemical precipitation with different reagents (lime, alum and iron chloride salts), the acid cracking (AC) with salt addition and the granular activated carbon (GAC) adsorption were selected. The best removal efficiencies in terms of COD, total polyphenols (TP), lipids and total suspended solids (TSS) were determined. A further pre-treatment was tested to be used as alternative to or in combination with chemical precipitation consisting of the physical separation trough an ultrafiltration (UF) membrane. Permeate quality indicated that membrane separation was able to achieve about 30% COD and 60% polyphenols removal efficiencies. Based on these results, lime precipitation was chosen as the feed of the following biological process that consisted of a lab-scale SBR later converted into a membrane-SBR, inserting the UF membrane inside the reactor. A comparison between the performances of the reactor fed with either diluted OMWs or with the chemically pre-treated OMW was carried out through periodical analysis on inlet and outlet samples and kinetic studies within typical operating cycles
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