Liquid digestate, the effluent of anaerobic digestion plants, can be treated with High Rate Algae-Bacterial Pond (HRABP) systems. On top of removing inorganic nitrogen and phosphorus, the algal biomass growing in these ponds can be used for bio-energetic applications. Since large volumes of water are necessary for diluting the digestate before its treatment, to reduce freshwater usage, water released from oil and gas extractions during drilling operations can be used instead. However, the high salinity of these so-called produced waters is deeply affecting the system's dynamics. To understand and represent quantitatively the process, a mathematical modelling of these systems can be developed. However, current models simulate chemical, physical and biological reactions considering dilution with freshwater, therefore not accounting on salinity, a distinctive characteristic that cannot be neglected for produced waters. This thesis aims to develop a new chemical model that simulates the equilibria of ions typically present in high saline wastewaters. The significant ionic concentration of these waters, which qualifies them as ‘salty’ or ‘hyper-salty’, required not to consider concentrations, but activities of ions, and to take into account the ionic strength, main driver for the ion paring phenomena. In this work, by using the PHREEQC software, the most significant ion pairing products were identified, adding further unknowns to the model. Subsequently, dedicated experiments and pH measurements were performed on solutions replicating the chemical environment of the biological reactor for which these modifications are intended. The experimental results and the simulated results obtained using PHREEQC were compared with those of the new chemical model developed in MATLAB. The implemented model showed good initial results in simulating pH values and ionic strength in saline solutions, also providing a prediction of ion pairing products concentration sufficient to formulate initial hypothesis on final solutions composition.
Il digestato liquido, effluente degli impianti di digestione anaerobica, può essere trattato con sistemi HRABP (High Rate Algae-Bacterial Pond). Oltre a rimuovere azoto inorganico e fosforo, la biomassa algale che cresce in queste vasche può essere utilizzata per successive applicazioni bioenergetiche. Poiché è necessario un grande volume di acqua per diluire il digestato in ingresso all'unità di trattamento, per ridurre l'uso di acqua dolce si può utilizzare in alternativa l'acqua rilasciata dall'estrazione di petrolio e gas durante le operazioni di perforazione. Tuttavia, l'elevata salinità di queste cosiddette acque di produzione influisce profondamente sulla dinamica del sistema. Per comprendere e rappresentare quantitativamente il processo, una modellazione matematica di questi sistemi deve essere sviluppata. Tuttavia, i modelli attuali simulano le reazioni chimiche, fisiche e biologiche considerando diluizione con acqua dolce, ignorando pertanto la salinità, caratteristica distintiva e che deve essere tenuta in considerazione per le acque di produzione. Questa tesi ambisce a sviluppare un nuovo modello chimico che simuli gli equilibri degli ioni tipicamente presenti nelle acque reflue altamente saline. La notevole concentrazione ionica di queste acque, che le qualifica come "salate" o "iper-salate", ha richiesto di non considerare le concentrazioni, ma le attività degli ioni, e di tenere conto della forza ionica, principale motore dei fenomeni di ion pairing. Utilizzando il software PHREEQC, sono stati identificati i prodotti di ion pairing più significativi, aggiungendo ulteriori incognite al modello. Successivamente, sono stati eseguiti esperimenti dedicati e misure di pH su soluzioni che riproducono l'ambiente chimico del reattore biologico per il quale queste modifiche sono destinate. I risultati sperimentali e i risultati simulati utilizzando PHREEQC sono stati confrontati con quelli del nuovo modello chimico sviluppato in MATLAB. Il modello implementato ha dimostrato buoni risultati iniziali nella simulazione dei valori di pH e forza ionica per soluzioni saline, nonché una previsione delle concentrazioni dei prodotti di ion pairing adeguata a formulare ipotesi iniziali sulla composizione finale delle soluzioni.
Enhanced chemical modelling of algae-bacteria systems for treating high salinity wastewaters
REALI, ANNALISA
2023/2024
Abstract
Liquid digestate, the effluent of anaerobic digestion plants, can be treated with High Rate Algae-Bacterial Pond (HRABP) systems. On top of removing inorganic nitrogen and phosphorus, the algal biomass growing in these ponds can be used for bio-energetic applications. Since large volumes of water are necessary for diluting the digestate before its treatment, to reduce freshwater usage, water released from oil and gas extractions during drilling operations can be used instead. However, the high salinity of these so-called produced waters is deeply affecting the system's dynamics. To understand and represent quantitatively the process, a mathematical modelling of these systems can be developed. However, current models simulate chemical, physical and biological reactions considering dilution with freshwater, therefore not accounting on salinity, a distinctive characteristic that cannot be neglected for produced waters. This thesis aims to develop a new chemical model that simulates the equilibria of ions typically present in high saline wastewaters. The significant ionic concentration of these waters, which qualifies them as ‘salty’ or ‘hyper-salty’, required not to consider concentrations, but activities of ions, and to take into account the ionic strength, main driver for the ion paring phenomena. In this work, by using the PHREEQC software, the most significant ion pairing products were identified, adding further unknowns to the model. Subsequently, dedicated experiments and pH measurements were performed on solutions replicating the chemical environment of the biological reactor for which these modifications are intended. The experimental results and the simulated results obtained using PHREEQC were compared with those of the new chemical model developed in MATLAB. The implemented model showed good initial results in simulating pH values and ionic strength in saline solutions, also providing a prediction of ion pairing products concentration sufficient to formulate initial hypothesis on final solutions composition.File | Dimensione | Formato | |
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2024_07_Reali_executive_summary.pdf
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2024_07_Reali_supplementary_material_executive_summary.pdf
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2024_07_Reali.pdf
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Descrizione: Testo della tesi
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https://hdl.handle.net/10589/223712