In this thesis, the influence of polymer dosage in mechanical dewatering and electro-dewatering and the relationship of sludge characteristics with sludge dewaterability was investigated. Moreover, a preliminary economic assessment was carried out. Thickened unconditioned (TU) sludge samples were collected from eight different WWTPs located in Milan, Italy. Thickened conditioned (TC) sludge samples at selected dosages of 4 and 8 g/kgDS were prepared in the laboratory by means of jar test. Initially, characterisation of TU and TC samples in terms of dry solids (DS), volatile solids (VS), total suspended solids (TSS), volatile suspended solids (VSS), pH, conductivity, zeta potential (ZP), capillary suction time (CST) and specific resistance to filtration (SRF) was carried out. Then, multiple centrifugation (mCFG), mechanical dewatering (MD) and electro-dewatering (EDW) tests were carried out on TU and TC samples from the eight WWTPs. The final cake DS content after mCFG, MD and EDW ranged 10.3-15.1%, 12.8-20.8% and 29-45.3% respectively. As expected, it was observed that addition of polymer had a positive effect over dewatering. In EDW, polymer dosage did not directly contribute to the final DS content: the addition of polyelectrolyte enhanced the water removal during compression phase but showed no observable effect when electric field was applied. Relationship between different sludge characteristics like VS, conductivity, ZP, DS after centrifugation and dewaterability was established with a preliminary statistical evaluation. It was found that sludge characteristics does not affect the performance of MD and EDW in a similar way. Certainly, CST and SRF was found to be good indicators of filterability but cannot be used as an indicator for estimating sludge dewaterability. However, CST and SRF were confirmed to be excellent tools for assessing the conditioning process. Remarkably, EDW was able to produce sludge cakes with DS up to 45%, which is significantly higher than conventional mechanical dewatering process (CMD). In some cases, EDW allowed to achieve savings due to reduction in the cost of disposal in comparison to CMD that is adopted in the WWTPs.
In questa tesi, sono state studiate l'influenza del dosaggio di polimero nella disidratazione meccanica e nella disidratazione elettro-assistita e la relazione tra le caratteristiche dei fanghi e la loro disidratabilità. Inoltre, è stata effettuata una valutazione economica preliminare. Sono stati raccolti campioni di fango ispessito non condizionato (TU) da otto diversi impianti di depurazione situati a Milano, Italia. Campioni di fango ispessito condizionato (TC) a dosaggi selezionati di 4 e 8 g/kgSS sono stati preparati in laboratorio mediante jar test. Inizialmente, è stata effettuata la caratterizzazione dei campioni TU e TC in termini di sostanza secca (SS), solidi volatili (SV), solidi sospesi totali (SST), solidi sospesi volatili (SSV), pH, conducibilità, potenziale zeta (PZ), tempo di suzione capillare (CST) e resistenza specifica alla filtrazione (SRF). Successivamente, sono stati condotti test di centrifugazione multipla (mCFG), disidratazione meccanica (MD) e disidratazione elettro-assistita (EDW) su campioni TU e TC dagli otto impianti. Il contenuto finale di SS dopo mCFG, MD ed EDW era rispettivamente del 10,3-15,1%, del 12,8-20,8% e del 29-45,3%. Come previsto, è stato osservato che l'aggiunta del polimero ha un effetto positivo sulla disidratazione. Nell’EDW, il dosaggio dei polimeri non ha contribuito direttamente al contenuto finale di SS: l'aggiunta di polielettrolita ha migliorato la rimozione dell'acqua durante la fase di compressione ma non ha mostrato alcun effetto osservabile quando è stato applicato il campo elettrico. Mediante una valutazione statistica preliminare, è stata stabilita la relazione tra le diverse caratteristiche dei fanghi come SV, conducibilità, PZ, SS dopo centrifugazione e disidratabilità. È stato riscontrato che le caratteristiche dei fanghi non influiscono in modo simile sulle prestazioni di MD e EDW. Sicuramente, CST e SRF sono risultati buoni indicatori di filtrabilità ma non possono essere usati come indicatore per la stima della disidratabilità dei fanghi. Tuttavia, CST e SRF si sono dimostrati strumenti eccellenti per la valutazione del processo di condizionamento. Sorprendentemente, l’EDW è stata in grado di produrre pannelli di fango con SS fino al 45%, che è significativamente superiore al processo di disidratazione meccanica convenzionale (CMD). In alcuni casi, l’EDW ha permesso di ottenere risparmi grazie alla riduzione dei costi di smaltimento rispetto alla CMD adottata negli impianti
Influence of the sludge characteristics on sludge dewatering and electro-dewatering
KUMAR, KAMALNATH
2019/2020
Abstract
In this thesis, the influence of polymer dosage in mechanical dewatering and electro-dewatering and the relationship of sludge characteristics with sludge dewaterability was investigated. Moreover, a preliminary economic assessment was carried out. Thickened unconditioned (TU) sludge samples were collected from eight different WWTPs located in Milan, Italy. Thickened conditioned (TC) sludge samples at selected dosages of 4 and 8 g/kgDS were prepared in the laboratory by means of jar test. Initially, characterisation of TU and TC samples in terms of dry solids (DS), volatile solids (VS), total suspended solids (TSS), volatile suspended solids (VSS), pH, conductivity, zeta potential (ZP), capillary suction time (CST) and specific resistance to filtration (SRF) was carried out. Then, multiple centrifugation (mCFG), mechanical dewatering (MD) and electro-dewatering (EDW) tests were carried out on TU and TC samples from the eight WWTPs. The final cake DS content after mCFG, MD and EDW ranged 10.3-15.1%, 12.8-20.8% and 29-45.3% respectively. As expected, it was observed that addition of polymer had a positive effect over dewatering. In EDW, polymer dosage did not directly contribute to the final DS content: the addition of polyelectrolyte enhanced the water removal during compression phase but showed no observable effect when electric field was applied. Relationship between different sludge characteristics like VS, conductivity, ZP, DS after centrifugation and dewaterability was established with a preliminary statistical evaluation. It was found that sludge characteristics does not affect the performance of MD and EDW in a similar way. Certainly, CST and SRF was found to be good indicators of filterability but cannot be used as an indicator for estimating sludge dewaterability. However, CST and SRF were confirmed to be excellent tools for assessing the conditioning process. Remarkably, EDW was able to produce sludge cakes with DS up to 45%, which is significantly higher than conventional mechanical dewatering process (CMD). In some cases, EDW allowed to achieve savings due to reduction in the cost of disposal in comparison to CMD that is adopted in the WWTPs.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/154581