A bench-scale, two-dimensional multi-compartmentalized fluidized reactor was designed and studies of hydrodynamic behavior of fluidization of struvite pellets were performed. Also size growth distribution tests were analyzed qualitatively. The study validated a previously-proposed theory, concerning the relationship between dynamic pressure drop and upflow velocity as well the experimental protocol to determine the minimum fluidization velocity. Findings indicated that the mixture of two-sized particles would behave rather independently of each other, before the bed expansion. It was suggested that bed height measurement could be another promising method to pinpoint minimum fluidization velocity as there is a sharp bed surface "waking episode" during the process of a packed bed being gradually fluidized. Bed expansion equations for the prediction of void fraction as a function of superficial upflow velocity or vice versa, have been established for 4 groups of monosize particles, as well as two mixtures of two-sized particles. The equation constants did not agree well with previously established ones. The two layers of segregated mixture bed had congruent linear relationships between the logarithmic void fraction and logarithmic upflow velocity. It was found that a mixture does not always go through segregation, but only when the size difference is large enough. Size growth distribution tests were performed under different hydrodynamic configurations as well as seeding conditions. Conclusions can be made that a bed with uniformly- distributed particle void fractions and higher mixing energy input (upflow velocity), normally has better performance of struvite growth in size.

A bench-scale, two-dimensional multi-compartmentalized fluidized reactor was designed and studies of hydrodynamic behavior of fluidization of struvite pellets were performed. Also size growth distribution tests were analyzed qualitatively. The study validated a previously-proposed theory, concerning the relationship between dynamic pressure drop and upflow velocity as well the experimental protocol to determine the minimum fluidization velocity. Findings indicated that the mixture of two-sized particles would behave rather independently of each other, before the bed expansion. It was suggested that bed height measurement could be another promising method to pinpoint minimum fluidization velocity as there is a sharp bed surface "waking episode" during the process of a packed bed being gradually fluidized. Bed expansion equations for the prediction of void fraction as a function of superficial upflow velocity or vice versa, have been established for 4 groups of monosize particles, as well as two mixtures of two-sized particles. The equation constants did not agree well with previously established ones. The two layers of segregated mixture bed had congruent linear relationships between the logarithmic void fraction and logarithmic upflow velocity. It was found that a mixture does not always go through segregation, but only when the size difference is large enough. Size growth distribution tests were performed under different hydrodynamic configurations as well as seeding conditions. Conclusions can be made that a bed with uniformly- distributed particle void fractions and higher mixing energy input (upflow velocity), normally has better performance of struvite growth in size.

Declining phosphate reserves and stricter regulations regarding wastewater discharge have increased the need for phosphorus removal and recovery. Crystallization is a promising option since P would not only be removed from the waste stream, but could also be recovered as struvite, a potential fertilizer. The purpose of this research was to achieve effective P removal and recovery through struvite precipitation from agricultural wastewater with minimal chemical input. It was found that raw swine manure had the potential for P removal and recovery through struvite precipitation by raising the pH through aeration without any Mg2+ amendment. This led to the development of a side-stream continuous 12 L reactor design with a novel combination of fluidized seedbed and aeration for pH increase. Synthetic feed was used to optimize the operational parameters of the reactor system. It was found that for a 100 ml/min influent rate, an aeration and recycle rate combination of 4.5 – 7 LPM and 700 ml/min was sufficient for increasing and maintaining the reactor pH from 6.7 to between 7.6 and 8.0. Significant P removal was achieved in six h runs without a seedbed (91 – 92%), while neither the struvite nor sand seedbeds improved P removal (91 – 96%). Struvite was recovered in all runs, with additional Ca2+ precipitation in the seedbed runs. Long-term runs showed that operation of the reactor was possible for an extended period of time, up to 46 h without any major adjustment. The average P removal was 85 – 88%, and precipitate collected after 24 h was found to be mainly struvite, while the final precipitate also contained calcite. This study has demonstrated the technical feasibility of an aerated crystallization reactor system for struvite removal and recovery from synthetic swine wastewater. By avoiding chemical amendments this reactor system has eliminated a significant portion of the operational costs found in comparable systems. The major obstacle for achieving system stability and consistency was scaling.

The over application of manure phosphorus (P) to farmlands can lead to P build up in the soil and eventual runoff to surface waters causing eutrophication. Reducing P in manure by precipitation of struvite enables P capture and reuse as a fertilizer in the agricultural supply stream. Struvite precipitation is dictated by levels of soluble P which can be highly variable according to manure treatment and management. This research studied P forms in liquid pig manure, ways of increasing P-PO4 levels in manure from strategic storage conditions, novel struvite reactors, and the effectiveness of struvite as a fertilizer. Studies that monitored soluble nutrients during manure storage revealed that P-PO4 concentration was sensitive to pH and time. Anaerobic fermentation of manure increased P-PO4 by 2.5 fold with 12 days of storage, provided the buffering by alkalinity was low. Two different struvite reactors were operated, a batch-type system for processing lagoon supernatant and an upflow air sparged reactor that used supernatant from a rotary press solids separator. They achieved 75% and 31% total P removal, respectively. The upflow reactor operated without chemical addition at pH 6.8 to produce high purity struvite free of calcium phosphates. Costs of both reactors were comparable ($0.0139 and $0.0167/kg live pig wt) and similar to other pilot struvite reactors. Manure derived struvite was compared with pure struvite and commercial fertilizer for agronomic value in canola production. Results of a greenhouse pot experiment showed no significant difference between the two struvites despite impurities in the manure precipitate.

Declining phosphate reserves and stricter regulations regarding wastewater discharge have increased the need for phosphorus removal and recovery. Crystallization is a promising option since P would not only be removed from the waste stream, but could also be recovered as struvite, a potential fertilizer. The purpose of this research was to achieve effective P removal and recovery through struvite precipitation from agricultural wastewater with minimal chemical input. It was found that raw swine manure had the potential for P removal and recovery through struvite precipitation by raising the pH through aeration without any Mg2+ amendment. This led to the development of a side-stream continuous 12 L reactor design with a novel combination of fluidized seedbed and aeration for pH increase. Synthetic feed was used to optimize the operational parameters of the reactor system. It was found that for a 100 ml/min influent rate, an aeration and recycle rate combination of 4.5 – 7 LPM and 700 ml/min was sufficient for increasing and maintaining the reactor pH from 6.7 to between 7.6 and 8.0. Significant P removal was achieved in six h runs without a seedbed (91 – 92%), while neither the struvite nor sand seedbeds improved P removal (91 – 96%). Struvite was recovered in all runs, with additional Ca2+ precipitation in the seedbed runs. Long-term runs showed that operation of the reactor was possible for an extended period of time, up to 46 h without any major adjustment. The average P removal was 85 – 88%, and precipitate collected after 24 h was found to be mainly struvite, while the final precipitate also contained calcite. This study has demonstrated the technical feasibility of an aerated crystallization reactor system for struvite removal and recovery from synthetic swine wastewater. By avoiding chemical amendments this reactor system has eliminated a significant portion of the operational costs found in comparable systems. The major obstacle for achieving system stability and consistency was scaling.

The over application of manure phosphorus (P) to farmlands can lead to P build up in the soil and eventual runoff to surface waters causing eutrophication. Reducing P in manure by precipitation of struvite enables P capture and reuse as a fertilizer in the agricultural supply stream. Struvite precipitation is dictated by levels of soluble P which can be highly variable according to manure treatment and management. This research studied P forms in liquid pig manure, ways of increasing P-PO4 levels in manure from strategic storage conditions, novel struvite reactors, and the effectiveness of struvite as a fertilizer. Studies that monitored soluble nutrients during manure storage revealed that P-PO4 concentration was sensitive to pH and time. Anaerobic fermentation of manure increased P-PO4 by 2.5 fold with 12 days of storage, provided the buffering by alkalinity was low. Two different struvite reactors were operated, a batch-type system for processing lagoon supernatant and an upflow air sparged reactor that used supernatant from a rotary press solids separator. They achieved 75% and 31% total P removal, respectively. The upflow reactor operated without chemical addition at pH 6.8 to produce high purity struvite free of calcium phosphates. Costs of both reactors were comparable ($0.0139 and $0.0167/kg live pig wt) and similar to other pilot struvite reactors. Manure derived struvite was compared with pure struvite and commercial fertilizer for agronomic value in canola production. Results of a greenhouse pot experiment showed no significant difference between the two struvites despite impurities in the manure precipitate.

A bench-scale, two-dimensional multi-compartmentalized fluidized reactor was designed and studies of hydrodynamic behavior of fluidization of struvite pellets were performed. Also size growth distribution tests were analyzed qualitatively. The study validated a previously-proposed theory, concerning the relationship between dynamic pressure drop and upflow velocity as well the experimental protocol to determine the minimum fluidization velocity. Findings indicated that the mixture of two-sized particles would behave rather independently of each other, before the bed expansion. It was suggested that bed height measurement could be another promising method to pinpoint minimum fluidization velocity as there is a sharp bed surface "waking episode" during the process of a packed bed being gradually fluidized. Bed expansion equations for the prediction of void fraction as a function of superficial upflow velocity or vice versa, have been established for 4 groups of monosize particles, as well as two mixtures of two-sized particles. The equation constants did not agree well with previously established ones. The two layers of segregated mixture bed had congruent linear relationships between the logarithmic void fraction and logarithmic upflow velocity. It was found that a mixture does not always go through segregation, but only when the size difference is large enough. Size growth distribution tests were performed under different hydrodynamic configurations as well as seeding conditions. Conclusions can be made that a bed with uniformly- distributed particle void fractions and higher mixing energy input (upflow velocity), normally has better performance of struvite growth in size. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The application of struvite (magnesium ammonium phosphate,!MgNH&PO& ∙ 6H+O) precipitation and its recycling use for the purpose of ammonia removal from both synthetic solutions and landfill leachate were investigated in this study. The results demonstrated that chemical precipitation by struvite formation is efficient for ammonia removal from aqueous solutions. In addition, by recycling the thermal residue of struvite, continuously removing ammonia can technically be achieved. In the struvite precipitation, ammonia removal significantly depended on the pH and chemical molar ratios of NH& ,:!Mg+,:!PO& ./. For synthetic solution (TAN=1,000 mg/L), remarkable TAN removal efficiency of over 98% has been reported when the molar ratio of NH& ,:!Mg+,:!PO& ./ equals 1.0:1.2:1.2, 1.0:1.3:1.3, 1.0:1.3:1.4 and 1.0:1.5:1.5 at optimum pH 9. The optimum combinations of reagents applied in landfill leachate (TAN=1,878 mg/L) were!NH& ,:!Mg+,:!PO& ./ =1.0:1.3:1.3, 1.0:1.4:1.3, 1.0:1.5:1.4 and 1.0:1.5:1.5 at optimum pH 9.5, all of which displayed excellent TAN removal efficiencies of over 99%. Response surface method (RSM) helped to analyze the data and optimize the results. The struvite pyrolysate provided best performance of removing ammonia in both simulated wastewater and landfill leachate at a dosage of 60 g/L, when struvite was previously heated at 105 􀀁 by oven for 2.5 h. In the recycling phase, the struvite pyrolysate resulting from NaOH-mediated pyrolysis was more effective at continuously treating ammonia synthetic solution than was direct heating, with an initial mode of 87.4% at the beginning to 75.1% in the fifth round and direct heating of struvite from 80.9% in the first cycle and 60.6% in the final cycle. The struvite pyrolysate formed by NaOH-mediated pyrolysis performed with greater ability to continuously eliminate ammonia from landfill leachate (97.2% removal at the beginning and 72.3% in the fifth round), than did directly heated struvite (98.4% in the first cycle and 81.3% in the final cycle). Additionally, microwave irradiation could also dissociate struvite, which subsequently demonstrated moderate TAN removal in recycling phases.

O φωσφόρος είναι ένα χημικό στοιχείο με πολλές λειτουργικότητες. Μία από τις βασικές χρήσεις του είναι ότι αποτελεί αναντικατάστατο λίπασμα ενώ επιπλέον είναι βασικό συστατικό του γενετικού υλικού, των κυτταρικών μεμβρανών, των οστών και των δοντιών, απαραίτητο στοιχείο της διατροφής ανθρώπων και ζώων κλπ. Η παρουσία υψηλών συγκεντρώσεων φωσφόρου στα υδάτινα οικοσυστήματα είναι ιδιαιτέρως βλαβερή καθώς αποτελεί την κύρια αιτία του ευτροφισμού. Αυξημένες ποσότητες φωσφόρου υπάρχουν στα αστικά υγρά απόβλητα, γεγονός που καθιστά αναγκαία την επεξεργασία τους για την απομάκρυνση του, πριν την τελική διάθεση τους στους υδάτινους αποδέκτες. Δεδομένου του ότι, ο φώσφορος προέρχεται από ορυκτά αποθέματα, τα οποία δεν είναι ανεξάντλητα, είναι επιβεβλημένη η ανάκτησή του, η οποία αποτελεί συμβολή στην αειφορία. Μία από τις μεθόδους ανάκτησης του φωσφόρου η οποία κερδίζει όλο και περισσότερο ερευνητικό ενδιαφέρον τα τελευταία χρόνια, είναι η καταβύθιση του με την μορφή στρουβίτη. Ο στρουβίτης, (MgΝΗ4PO4.6H2O) είναι ένα λευκό κρυσταλλικό στερεό το οποίο μπορεί να χρησιμοποιηθεί ως βραδέως αποδεσμευόμενο λίπασμα, εμπλουτίζοντας τις καλλιέργειες με τρία από πιο βασικά θρεπτικά συστατικά. Στην παρούσα εργασία μελετήθηκε η καταβύθιση στρουβίτη από υπέρκορα διαλύματα, η σύσταση των οποίων, προσομοιώνει την αντίστοιχη των αστικών υδατικών λυμάτων ως προς την περιεκτικότητα σε φωσφόρο και αμμωνία, σε αντιδραστήρα συνεχούς λειτουργίας του 1L. Η κινητική της καταβύθισης μελετήθηκε σε συνθήκες σταθερού υπερκορεσμού, pH 9.00 στους 25οC. Τα πειράματα πραγματοποιήθηκαν σε διαλύματα υπέρκορα ως προς στρουβίτη, στα οποία η στοιχειομετρική αναλογία των πλεγματικών ιόντων, ήταν 1:1:1 και 1:1:3 ως προς οποιοδήποτε από τα τρία ιόντα. Επίσης, μελετήθηκε καταβύθιση του στρουβίτη σε υπέρκορα διαλύματα παρουσία Na¬2SO4 και με διαβίβαση αέρα μέσω των διαλυμάτων. Τα αποτελέσματα των πειραμάτων έδειξαν, ότι ο ρυθμός καταβύθισης του στρουβίτη στα υπέρκορα διαλύματά του, εξαρτάται κυρίως από τον αντίστοιχο υπερκορεσμό, ο οποίος αποτελεί και την κινούσα δύναμη. Η ανάλυση των αποτελεσμάτων έγινε με την βοήθεια της κλασσικής θεωρίας πυρηνογένεσης. Η εξάρτηση του χρόνου επαγωγής, ο οποίος μεσολαβούσε μεταξύ της παρασκευής των υπέρκορων διαλυμάτων και της ανίχνευσης των πρώτων υπερκρίσιμων πυρήνων, από τον υπερκορεσμό, έδωσε τιμές για την επιφανειακή ενέργεια της σχηματιζόμενης φάσης ίσης με 15mJ/m2, ενώ ο αριθμός των δομικών μονάδων οι οποίες συγκροτούν τον κρίσιμο πυρήνα, βρέθηκε ίσος με 9. Επίσης, ο ρυθμός, φάνηκε να επηρεάζεται σε μικρό βαθμό από την σχετική αναλογία των πλεγματικών ιόντων. Συγκεκριμένα, όταν η αναλογία των ιόντων Mg :NH3 :P ήταν 3:1:1 ή 1:1:3, οι ρυθμοί οι οποίοι μετρήθηκαν ήταν μεγαλύτεροι σε σύγκριση με τους αντίστοιχους σε διαλύματα με αναλογία 1:1:1. Σε όλες τις περιπτώσεις, το βραδύ στάδιο στον μηχανισμό της καταβύθισης ήταν η επιφανειακή διάχυση των δομικών μονάδων στους υπερκρίσιμους πυρήνες. Το αποτέλεσμα αυτό είναι σε συμφωνία με τα αντίστοιχα σε διαφορετικές τιμές pH, και υποδηλώνει και στην περίπτωση αυτή, τον καθοριστικό ρόλο της επιφάνειας στην οποία λαμβάνει χώρα η πυρηνογένεση. Η παρουσία άλλων ουσιών στο διάλυμα, όπως το Na¬2SO4, είχε ως αποτέλεσμα την αύξηση του ρυθμού αυθόρμητης καταβύθισης του στρουβίτη στα υπέρκορα διαλύματά του. Η διαβίβαση αέρα μέσα από τα υπέρκορα διαλύματα, είχε ως αποτέλεσμα την επιτάχυνση του ρυθμού καταβύθισης σε βαθμό ανάλογο με τον αντίστοιχο παρουσία Na¬2SO4. / Phosphorus is a multifunctional chemical element. One of it’s significant uses is that it consists a non substituted fertilizer, moreover it is one of the basic components of DNA, of cell membranes, bones, teeth, an essential element in human and animal nutrition etc. Increased phosphorous concentration in water systems can be particularly damaging since it is the main cause of eutrophication. Increased amounts of phosphorous have been demonstrated in municipal wastewaters, so processing is required in order to remove phosphorous before final disposal to aquatic systems. Taking into consideration that phosphorus comes from mineral deposits that are not infinite, recovery is demanded, offering a contribution to sustainability. One of the recovery methods that is attracting more and more researcher’s interest over the past years is phosphorous precipitation as struvite. Struvite (MgΝΗ4PO4.6H2O) is a white mineral that can be used as a slow-release fertilizer, enriching agricultures with three of the basic nutrients. In the present study was investigated struvite precipitation in supersaturated solutions, with composition similar to that of municipal wastewaters in phosphorous and ammonia, in 1L continuously operated reactor. The kinetics of spontaneous precipitation was studied at constant solution supersaturation, pH 9.00 and 25οC. The experiments were carried out in supersaturated solutions with stoichiometric molar ratio of the ions 1:1:1 and 1:1:3 for any of the three ions. Struvite precipitation in supersaturated solutions was also studied in the presence of Na¬2SO4 and transmission of air in the solutions. The results showed that the rate of struvite precipitation in supersaturated solutions mainly depends on the supersaturation in respect to the precipitating solid, which is the driving force. Results analysis was performed in accordance to the classical nucleation theory. The dependence of the induction time, the period of time between the achievement of supersaturation and the formation of the first critical nucleus, from supersaturation, lead to surface energy for the newly formed phase 15mJ/m2, and the number of molecules in a critical nucleus was calculated p=9. The rate of struvite precipitation proved to have a minor dependence on the ratio of the ions. More specifically, when stoichiometric molar ratio of the ions Mg :NH3 :P was 3:1:1 or 1:1:3, the calculated rates were a bit higher compared to the ratios in supersaturated solutions with stoichiometric molar ratio 1:1:1. In all the cases the slow step in the mechanism of precipitation was surface diffusion of the solute molecules on the critical nuclei surface. The results are in accordance with those under different pH values and suggest the importance of the surface where nuclei formation takes place. The presence of other substances in the solution, such as Na¬2SO4, resulted in an increased rate of struvite spontaneous precipitation in supersaturated solutions. The transmission of air through the supersaturated solutions also increased the rate of precipitation in a way similar to that under the presence of Na2SO4.

Widespread arsenic contamination with adverse effects to human health is a global problem. Most previous studies on arsenic contamination in natural environments and those associated with mining and agricultural activities focused largely on arsenic-rich minerals such as arsenates, arsenites, sulfarsenides, and sulfides. Rock-forming minerals generally contain only minor or trace amounts of arsenic but, owing to their sheer abundances, are potentially important (and sometimes dominant) sources of this metalloid and can play significant roles in the attenuation and sequestration of arsenic in various environments. However, there remains a significant gap in my knowledge about the uptake and speciation of arsenic in rock-forming minerals. This thesis research is intended to bridge this gap by investigating the uptake and speciation of arsenic in selected rock-forming sulfate and phosphate minerals (i.e., gypsum, struvite and newberyite). Gypsum (CaSO4•2H2O) is a major by-product of mining and milling processes of borate, phosphate and uranium deposits worldwide and, therefore, potentially plays an important role in the stability and bioavailability of heavy metalloids, including As, in tailings and surrounding areas. Gypsum containing 1,900 and 185 ppm As, synthesized with Na2HAsO4•7H2O and NaAsO2 in the starting materials, respectively, has been investigated by synchrotron X-ray absorption spectroscopy (XAS), single-crystal electron paramagnetic resonance spectroscopy (EPR), and pulsed electron nuclear double resonance spectroscopy (ENDOR). Quantitative analyses of As K edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra show that arsenic occurs in both +3 and +5 oxidation states and the As3+/As5+ value varies from 0.35 to 0.79. Single-crystal EPR spectra of gamma-ray-irradiated gypsum reveal two types of arsenic-associated oxyradicals: [AsO3]2− and an [AsO2]2−. The [AsO3]2− center is characterized by principal 75As hyperfine coupling constants of A1 = 1952.0(2) MHz, A2 = 1492.6(2) MHz and A3 = 1488.7(2) MHz, with the unique A axis along the S-O1 bond direction, and contains complex 1H superhyperfine structures that have been determined by pulsed ENDOR. These results suggest that the [AsO3]2− center formed from electron trapping on the central As5+ ion of a substitutional (AsO4)3− group after removal of an O1 atom. The [AsO2]2− center is characterized by its unique A(75As) axis approximately perpendicular to the O1-S-O2 plane and the A2 axis along the S-O2 bond direction, consistent with electron trapping on the central As3+ ion of a substitutional (AsO3)3− group after removal of an O2 atom. These results confirm lattice-bound As5+ and As3+ in gypsum and point to potential application of this mineral for immobilization and removal of arsenic pollution. EPR spectra show that another sulfate boussingaultite is also sequestering both As5+ and As3+ at its S site. Synthesis experiments at pH from 2 to 14 also show that arsenic uptake in gypsum is pH dependent. Struvite and newberyite, common biominerals and increasingly important green fertilizers recovered from wastewater treatment plants, are capable of sequestering a wide range of heavy metals and metalloids, including arsenic. Inductively coupled plasma mass spectrometric (ICPMS) analyses show that struvite formed under ambient conditions contains up to 547±15 ppm As and that the uptake of As is controlled by pH. Synchrotron As K-edge XANES spectra measured at 20 K show that As5+ is the predominant oxidation state in struvite, irrespective of Na2HAsO4•7H2O or NaAsO2 as the source for As. Modeling of As K-edge EXAFS data suggest that local structural distortion associated with the substitution of As5+ for P5+ in struvite reaches up to 3.75 Å. Single-crystal electron paramagnetic resonance (EPR) spectra of gamma-ray-irradiated struvite disclose five [AsO3]2- radicals and one [AsO4]2- radical. These arsenic-centered oxyradicals are all readily attributed to form from diamagnetic [AsO4]3- precursors during irradiation, providing further support for exclusive incorporation and local structural expansion beyond the first shell of As5+ at the P site in struvite. Arsenic doped newberyite (MgHPO4•3H2O) obtained from the gel diffusion method has investigated by synchrotron XAS at the As K-edge (11,867 eV) at 8 K and single-crystal EPR spectroscopy at room temperature. XANES data show that As5+ is dominant and EXAFS analysis reveals a local environment typical of the arsenate species as well. Single-crystal EPR spectra of gamma-ray-irradiated newberyite contain two arsenic-associated oxyradicals: [AsO3]2− and [AsO2]2− derived from As5+ and As3+, respectively, at the P site in the newberyite structure. Elevated concentrations of arsenic have also been observed in natural newberyite from guano deposits and reflect the accumulation of this metalloid in the food chain. Therefore, struvite and newberyite can both sequester significant amounts of arsenic, and their direct use as fertilizers (irrespective of origins from guano deposits or wastewaters) is a potential source of arsenic contamination. On the other hand, the capacities of struvite and newberyite for accommodating significant amounts of arsenic in crystal lattices coupled with their simple chemistry and crystallization under ambient conditions make them attractive materials for immobilization and removal of arsenic contamination in aqueous environments.