Phosphorus (P) extraction from sewage sludge ash (SSA) by wet chemical leaching represents a feasible and sustainable solution to the concerns about P supply. However, related technologies are still economically unviable, requiring a reduction in operational costs to compete with primary P sources. This study aims at optimizing P recovery from SSA by wet acid leaching followed by alkaline precipitation, to pave the way for a future scale-up of this process from lab- to pilot-scale. Lab-scale and pilot-scale leaching and precipitation tests were conducted, based on the Design of Experiment approach. The obtained outcomes were analysed through advanced statistical techniques and were employed to develop an optimization tool for the P recovery process. Lab-scale tests exhibited the best trade-off between high P extraction and low metal co-extraction under specific leaching operating conditions (1 N, 10 mL/g, 0.5 h), regardless of the extractant used (H2SO4, HCl). Pilot-scale tests indicated the need to identify proper flocculants for each process configuration, highlighting the relevance of mixing during the leaching phase and the importance of a careful filter-press management. Moreover, these tests demonstrated the effectiveness of a magnesium-rich mining byproduct in increasing the pH and the nutrient content of the precipitate, although further investigation is required to optimize its dosage. From the process integrated assessment, leaching by HCl (0.8 N, 10 mL/g, 0.5 h) and precipitation by Ca(OH)2 emerged as the best trade-off solution, despite the significant acid consumption. To improve the economic sustainability of the process, it was highlighted the need to explore alternative cost-effective acid extractants and to evaluate recovery strategies for the management of acidic solid residues. Further research is needed to study the precipitation under different leaching operating conditions, to allow a more comprehensive assessment of the P recovery process.
L'estrazione chimica a umido del fosforo (P) dalle ceneri di fanghi di depurazione (CFD) rappresenta una soluzione pratica e sostenibile alle preoccupazioni sull'approvvigionamento di P. Tuttavia, le relative tecnologie non sono ancora economicamente vantaggiose, richiedendo la riduzione dei costi operativi per competere con le fonti primarie di P. Questo studio mira a ottimizzare il recupero di P dalle CFD mediante estrazione acida a umido seguita da precipitazione alcalina, per favorire lo scale-up del processo dalla scala di laboratorio a quella pilota. Sono stati condotti test di lisciviazione e di precipitazione a scala di laboratorio e pilota, tramite l'approccio del Disegno Sperimentale. I risultati ottenuti sono stati analizzati con tecniche statistiche avanzate e impiegati per sviluppare uno strumento di ottimizzazione del processo di recupero del P. I test di laboratorio hanno identificato il miglior compromesso tra un'elevata estrazione di P e una bassa co-estrazione di metalli sotto specifiche condizioni operative (1 N, 10 mL/g, 0,5 h), per qualsiasi estraente usato (H2SO4, HCl). I test pilota hanno sottolineato la necessità di trovare flocculanti adeguati ad ogni configurazione di processo, evidenziando l'importanza della miscelazione durante la lisciviazione e della corretta gestione della filtropressa. Inoltre, questi test hanno dimostrato l'efficacia di un sottoprodotto minerario ricco di magnesio nell'aumentare il pH ed il contenuto nutritivo del precipitato, sebbene siano richiesti ulteriori studi per ottimizzarne le dosi. Dalla valutazione integrata del processo, la lisciviazione con HCl (0.8 N, 10 mL/g, 0,5 h) e la precipitazione con Ca(OH)2 sono emerse come la migliore configurazione, nonostante un consumo d’acido elevato. Per migliorare la sostenibilità economica del processo, si è evidenziato il bisogno di cercare estraenti acidi alternativi ed economicamente vantaggiosi e di valutare soluzioni di recupero per la gestione dei residui solidi acidi. Ulteriori ricerche sono necessarie per studiare la precipitazione al variare delle condizioni di lisciviazione, al fine di permettere una valutazione più completa del processo di recupero del P.
Assessing the scale-up potential of wet chemical phosphorus recovery from sewage sludge ash: a step towards pilot-scale implementation
Esposito, Lorenzo
2022/2023
Abstract
Phosphorus (P) extraction from sewage sludge ash (SSA) by wet chemical leaching represents a feasible and sustainable solution to the concerns about P supply. However, related technologies are still economically unviable, requiring a reduction in operational costs to compete with primary P sources. This study aims at optimizing P recovery from SSA by wet acid leaching followed by alkaline precipitation, to pave the way for a future scale-up of this process from lab- to pilot-scale. Lab-scale and pilot-scale leaching and precipitation tests were conducted, based on the Design of Experiment approach. The obtained outcomes were analysed through advanced statistical techniques and were employed to develop an optimization tool for the P recovery process. Lab-scale tests exhibited the best trade-off between high P extraction and low metal co-extraction under specific leaching operating conditions (1 N, 10 mL/g, 0.5 h), regardless of the extractant used (H2SO4, HCl). Pilot-scale tests indicated the need to identify proper flocculants for each process configuration, highlighting the relevance of mixing during the leaching phase and the importance of a careful filter-press management. Moreover, these tests demonstrated the effectiveness of a magnesium-rich mining byproduct in increasing the pH and the nutrient content of the precipitate, although further investigation is required to optimize its dosage. From the process integrated assessment, leaching by HCl (0.8 N, 10 mL/g, 0.5 h) and precipitation by Ca(OH)2 emerged as the best trade-off solution, despite the significant acid consumption. To improve the economic sustainability of the process, it was highlighted the need to explore alternative cost-effective acid extractants and to evaluate recovery strategies for the management of acidic solid residues. Further research is needed to study the precipitation under different leaching operating conditions, to allow a more comprehensive assessment of the P recovery process.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/219508