This thesis deals with the feasibility of including a mixed microalgal community in a real wastewater treatment sequence with the double aim of removing nitrogen and producing biomass to feed the anaerobic digesters. In particular, this thesis focuses on identification of relevant waste streams from agricultural and municipal activities (like effluents, centrates, digestates, and a mixture of them) as a substrate for microalgal culture. Chapter 2 contains a critical review, this manuscript summarizes the current approaches to microalgal biomass production using waste streams, including wastewater, waste or CO2-enriched gas (flue gas and biogas), waste organics (i.e., crude glycerol) and waste heat, as well as the primary common operational challenges and corresponding mitigation strategies involved in culturing approaches. The core of experimentation is described in Chapters 3-7 using wastewater from urban or agriculture activity as a substrate for microalgal culture. In particular, Chapter 3 shows the results of experimentation using municipal centrate to produce biomass to feed the anaerobic digesters removing at the same ammonia nitrogen. The novelty of the study consists in the use of raw centrate from urban wastewater treatment plant as a substrate to grow microalgae, while the majority of literature data were obtained on pre-treated (diluted and/or supplemented and/or furtherly clarified) centrate samples, in the use of a continuously fed PhotoBio Reactor (PBR) operated under natural, uncorrected environmental conditions. This work demonstrates that microalgae (Chlorella sp and Scenedesmus sp) are able to easily grow on the centrate. The average specific growth rate in indoor and outdoor batch tests is satisfactory and comparable with literature data, ranging between 0.14-0.16 d-1. During the continuous test the average biomass production is 50 mgTSS L-1 d-1 and the difference between N-NH4 concentration in the influent and in the effluent demonstrates an important removal. Also BMP tests showed good results: the production of biomethane from algal biomass is slower than from sludge, but its final value is slightly higher than that from waste sludge (208 mLCH4 gVS-1 vs. 190 mLCH4 gVS-1). Wastewaters from agricultural activities are the subject of Chapter 4, chemical and physical analyses showed that the liquid fractions of swine manure and the first effluent could be suitable for algal treatment, while the other samples had unacceptable levels of both solid content and turbidity which would seriously limit light penetration. The papers in Chapter 4 and Chapter 5 report the results obtained in lab-scale tests using the agro wastes which had been shown to be more suitable. In Chapter 5 a new approach is proposed using Activated Carbon (AC) from wood as a pre-treatment to facilitate microalgal growth, without addition of tap water for dilution. The optimal optical density values were obtained with 40 g L-1 of AC dosage and 10 minutes adsorption time, corresponding to 88% of turbidity reduction. Then semi-continuous microalgae culturing were tested using adsorbed and not adsorbed liquid centrate (3 replicates). The encouraging lab scale results presented in Chapter 4 and Chapter 5 justify further pilot-scale experimentation, using agrowastes as the nutrient source for microalgae, presented in Chapter 6. The pilot scale (PBR) was installed at a piggery farm in Northern Italy. During the culturing period, microalgal density remained quite constant, around the average value of 0.55 gTSS/L, and the efficiency of Total Nitrogen and of N-NH4+ removal were both very high (on average 80 and 87%, respectively). The search for the best biomass harvesting technique is the main objective of Chapter 7. In this point, microalgal biomass is processed by three solid/liquid separation processes: gravity settling; centrifugation tests, flocculation tests. The main conclusions are reported in Chapter 8.

Questa tesi è volta a valutare l’integrazione delle microalghe in impianti di depurazione con il duplice scopo di rimuovere azoto e produrre biomassa da convogliare ai digestori anaerobici. In particolare, questa tesi si concentra sulla identificazione dei acque reflue di tipo agricolo e civile (come effluenti, centrati, digestato, e una miscele di loro) più idonee ad essere usate come substrato per la cultura microalghe. Il capitolo 2 contiene un resoconto che tratta degli attuali approcci per la produzione di biomassa microalgale utilizzando diversi tipi di rifiuti. Il cuore della mia sperimentazione è descritta nei capitoli 3-7; in particolare, il capitolo 3 mostra i risultati di test nei quali il centrato di origine civile è stato usato come substrato per la produzione di biomassa algale. La novità dello studio consiste: (i) nell’uso di centrato tal quale come substrato di crescita, mentre la maggior parte dei dati di letteratura sono stati ottenuti su refluo pretrattato, (ii) nell'uso di un fotobioreattore alimentato in continuo e (iii) nello svolgimento delle prove in condizioni ambientali naturali. Questo lavoro ha dimostrato che le microalghe (Chlorella sp e Scenedesmus sp) sono in grado di crescere facilmente sul centrato e il loro tasso medio di crescita specifico, che varia tra 0,14-0,16 d-1 è comparabile con i dati di letteratura. Anche i test di produzione di biometano (BMP) hanno mostrato buoni risultati: il BMP ottenuto dalla biomassa microalgale è più lento rispetto ai fanghi, ma il suo valore finale è leggermente superiore (208 mLCH4 gVS-1 vs 190 mLCH4 gVS-1). Nel capitolo 4 sono stati studiati diversi reflui agricoli, che potenzialmente potrebbero essere usati come substrato di crescita per le microalghe. Le analisi chimiche e fisiche hanno dimostrato che le frazioni liquide di letame suino potrebbe essere utilizzato a tale scopo. Nel capitolo 5 viene proposto un pre-trattamento con carboni attivi (AC) del centrato di origine suina per facilitare la crescita microalghe. Sono stati testati diversi dosaggi di carbone attivo e il dosaggio di 40 g L-1 e 10 minuti di tempo di adsorbimento sembra essere il più promettente. Nello specifico la riduzione della torbidità del refluo è stata pari all’88%. Gli incoraggianti risultati in scala di laboratorio presentati nel Capitolo 4 e 5 giustificano le successive sperimentazioni su scala pilota, utilizzando reflui di origine agricola come fonte di nutrienti per microalghe. Nel capitolo 6 viene presentato il lavoro in scala pilota, un fotobioreattore è stato installato presso una azienda agricola nel Nord Italia. Durante la sperimentazione, la densità microalghe è rimasta abbastanza costante, intorno al valore medio di 0,55 gTS/l, mentre le efficienze di rimozione dell’azoto totale e di N-NH4+ erano entrambe molto alte (in media 80 e 87%, rispettivamente). L'obiettivo principale del capitolo 7 è volto a trovare la migliore tecnica di separazione della biomassa algale dal substrato di crescita. In questa sezione sono stati testati tre processi di separazione liquido/solido della biomassa microalgale: (i) sedimentazione per gravità; (ii) centrifugazione, (iii) flocculazione. Le principali conclusioni sono riportate nel capitolo 8: l'integrazione delle microalghe negli schemi di trattamento delle acque reflue offre una strategia economicamente fattibile e ambientalmente sostenibile; la crescita microalgale è fortemente influenzata dalle condizioni ambientali; il pretrattamento del digestato, combinato con i processi di strippaggio e adsorbimento con carbone attivo potrebbe migliorare notevolmente l'efficacia della coltivazione delle microalghe; le microalghe potrebbero essere co-digerite con fanghi di scarto senza effetti negativi sul consorzio anaerobico, nonostante le biomassa microalgale abbia alcuni punti critici come la parete cellulare resistente che limita la sua bioconversione.

(2017). Growth of microalgal biomass on supernatant from biosolid dewatering. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2017).

Growth of microalgal biomass on supernatant from biosolid dewatering

MARAZZI, FRANCESCA ALICE
2017

Abstract

This thesis deals with the feasibility of including a mixed microalgal community in a real wastewater treatment sequence with the double aim of removing nitrogen and producing biomass to feed the anaerobic digesters. In particular, this thesis focuses on identification of relevant waste streams from agricultural and municipal activities (like effluents, centrates, digestates, and a mixture of them) as a substrate for microalgal culture. Chapter 2 contains a critical review, this manuscript summarizes the current approaches to microalgal biomass production using waste streams, including wastewater, waste or CO2-enriched gas (flue gas and biogas), waste organics (i.e., crude glycerol) and waste heat, as well as the primary common operational challenges and corresponding mitigation strategies involved in culturing approaches. The core of experimentation is described in Chapters 3-7 using wastewater from urban or agriculture activity as a substrate for microalgal culture. In particular, Chapter 3 shows the results of experimentation using municipal centrate to produce biomass to feed the anaerobic digesters removing at the same ammonia nitrogen. The novelty of the study consists in the use of raw centrate from urban wastewater treatment plant as a substrate to grow microalgae, while the majority of literature data were obtained on pre-treated (diluted and/or supplemented and/or furtherly clarified) centrate samples, in the use of a continuously fed PhotoBio Reactor (PBR) operated under natural, uncorrected environmental conditions. This work demonstrates that microalgae (Chlorella sp and Scenedesmus sp) are able to easily grow on the centrate. The average specific growth rate in indoor and outdoor batch tests is satisfactory and comparable with literature data, ranging between 0.14-0.16 d-1. During the continuous test the average biomass production is 50 mgTSS L-1 d-1 and the difference between N-NH4 concentration in the influent and in the effluent demonstrates an important removal. Also BMP tests showed good results: the production of biomethane from algal biomass is slower than from sludge, but its final value is slightly higher than that from waste sludge (208 mLCH4 gVS-1 vs. 190 mLCH4 gVS-1). Wastewaters from agricultural activities are the subject of Chapter 4, chemical and physical analyses showed that the liquid fractions of swine manure and the first effluent could be suitable for algal treatment, while the other samples had unacceptable levels of both solid content and turbidity which would seriously limit light penetration. The papers in Chapter 4 and Chapter 5 report the results obtained in lab-scale tests using the agro wastes which had been shown to be more suitable. In Chapter 5 a new approach is proposed using Activated Carbon (AC) from wood as a pre-treatment to facilitate microalgal growth, without addition of tap water for dilution. The optimal optical density values were obtained with 40 g L-1 of AC dosage and 10 minutes adsorption time, corresponding to 88% of turbidity reduction. Then semi-continuous microalgae culturing were tested using adsorbed and not adsorbed liquid centrate (3 replicates). The encouraging lab scale results presented in Chapter 4 and Chapter 5 justify further pilot-scale experimentation, using agrowastes as the nutrient source for microalgae, presented in Chapter 6. The pilot scale (PBR) was installed at a piggery farm in Northern Italy. During the culturing period, microalgal density remained quite constant, around the average value of 0.55 gTSS/L, and the efficiency of Total Nitrogen and of N-NH4+ removal were both very high (on average 80 and 87%, respectively). The search for the best biomass harvesting technique is the main objective of Chapter 7. In this point, microalgal biomass is processed by three solid/liquid separation processes: gravity settling; centrifugation tests, flocculation tests. The main conclusions are reported in Chapter 8.
MEZZANOTTE, VALERIA FEDERICA MARIA
microalgae,; wastewater,; biofuel,; nitrogen; removal
microalgae,; wastewater,; biofuel,; nitrogen; removal
BIO/07 - ECOLOGIA
English
10-apr-2017
SCIENZE - 80R
29
2015/2016
open
(2017). Growth of microalgal biomass on supernatant from biosolid dewatering. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2017).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/158195
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