The objective of this work is to optimize high-power low-frequency sonication (US) pretreatment of sludge, and especially to investigate for the first time possible improvements by higher pressure and audible frequency. After a preliminary examination of regular process conditions (sludge conditioning, sludge type, prior alkalization, temperature control, etc), effects of US parameters (power -PUS, intensity -IUS, specific energy input -ES, frequency -FS, etc.) and of hydrostatic pressure (Ph) were specifically looked into, separately and in combination, first under cooling at constant temperature (28°C), then under the progressive temperature rise provoked by sonication. First, it was confirmed that specific energy input (ES) plays a key role in sludge US disintegration (i.e. solubilisation of organic matter) and that temperature rise during adiabatic-like sonication is beneficial through additional effects of thermal hydrolysis and cavitation. At a given ES value, low FS (12 kHz vs. 20 kHz) and high PUS enhance soluble chemical oxygen demand (SCOD) due to more violent cavitation, while hydrostatic pressure gives rise to an optimum value due to its opposite effects on cavitation threshold and intensity. One major result is that optimal pressure depends on IUS (P¬US) as well as temperature profile, but not on ES, FS, nor sludge type. Setting the other parameters at the most favorable conditions expected, i.e. 12 kHz, 360 W , 28 gTS/L, and adiabatic conditions, final optimization was achieved by searching for this pressure optimum and examining sequential procedure to avoid too high temperature dampening cavitation intensity and damaging the transducer. Such conditions with sequential mode and Ph of 3.25 bar being selected succeeded in achieving very high SCOD, but only marginally improved subsequent methanization yield.

High nitrogen discharge from the municipal wastewater is a major concern for the South Australian Government, primarily due to negative impacts on the marine environment. Therefore, under the South Australian Environmental Improvement Program, (SA EIP), all metropolitan wastewater treatment plants have been reconfigured to achieve enhanced nitrogen removal. Secondary treatment (denitrification process) at the metropolitan wastewater treatment plants must be optimised to meet the discharge guideline of 10 mg/L total nitrogen. However, secondary treatment at some plants is carbon limited (low C/N ratio), and external carbon supplementation is required to meet this discharge guideline. Molasses provides the current external carbon source at two plants. It is relatively inexpensive, but other carbon sources, particularly industrial waste streams, may be more attractive, due to the potentially lower material cost, as it is practically free, and environmentally friendly. Potato starch and sonicated return activated sludge (RAS) were considered. In this study, the bioavailability of the soluble carbon in potato starch and ultrasound treated RAS were assessed. The associated objective was to investigate the potential of both carbon sources as an external carbon donor for the denitrification zone of wastewater treatment plants to economically improve biological nitrogen removal. The economic analysis was performed using mainly United States dollars and the fixed capital investments and total capital costs were converted to Australian dollars. This was due to the United States dollars currency quotes obtained for the materials and unit operations required. SCOD from the three sources was quantified and preliminary results were presented. Molasses provided the highest SCOD release of 1.1285 x 10⁶ mg-SCOD/L, sonicated RAS produced 5.6 to 68.4 times the SCOD release of the untreated RAS (35.6 mg-SCOD/L) depending on the ultrasound intensity and treatment time, while the highest soluble carbon release obtained using potato starch was 809 mg-SCOD/L (using 20.9 g/100 mL potato starch concentration). Based on the experimental SCOD results, batch denitrification tests using the proposed carbon sources were carried out. The nitrogen removal efficiency at low dose (12.48 mg-SCOD/L) using molasses, potato starch and sonicated RAS were 77.54%, 57.24%, and 72.76% respectively, whilst at high dose (124.80 mg-SCOD/L) were 94.04%, 66.32%, and 92.10% correspondingly. In similar order of the proposed carbon sources, the nitrate removal rates for the first phase denitrification with low dose were 1.44, 1.16, and 1.18 mg-NO₃ − /h respectively, whilst the nitrate removal rate of the first phase denitrification with high dose improved to 2.01, 1.26, and 1.96 mg-NO₃ −/h correspondingly. From the denitrification test results, molasses proved to be the optimal carbon source in terms of nitrate removal. However sonicated RAS possesses similar denitrification performance and may be a suitable alternative. An economic analysis for sonicated RAS Option 2 confirmed it as the most viable substitute. The time to recover the initial investment (payback period) is approximately 6.5 years and the breakeven point is approximately 8 years. Both denitrification tests and economic analyses demonstrate that sonicated RAS may be a viable and attractive substitute for the molasses. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1337059 / Thesis (M.Eng.Sc.) - University of Adelaide, School of Chemical Engineering, 2008

High nitrogen discharge from the municipal wastewater is a major concern for the South Australian Government, primarily due to negative impacts on the marine environment. Therefore, under the South Australian Environmental Improvement Program, (SA EIP), all metropolitan wastewater treatment plants have been reconfigured to achieve enhanced nitrogen removal. Secondary treatment (denitrification process) at the metropolitan wastewater treatment plants must be optimised to meet the discharge guideline of 10 mg/L total nitrogen. However, secondary treatment at some plants is carbon limited (low C/N ratio), and external carbon supplementation is required to meet this discharge guideline. Molasses provides the current external carbon source at two plants. It is relatively inexpensive, but other carbon sources, particularly industrial waste streams, may be more attractive, due to the potentially lower material cost, as it is practically free, and environmentally friendly. Potato starch and sonicated return activated sludge (RAS) were considered. In this study, the bioavailability of the soluble carbon in potato starch and ultrasound treated RAS were assessed. The associated objective was to investigate the potential of both carbon sources as an external carbon donor for the denitrification zone of wastewater treatment plants to economically improve biological nitrogen removal. The economic analysis was performed using mainly United States dollars and the fixed capital investments and total capital costs were converted to Australian dollars. This was due to the United States dollars currency quotes obtained for the materials and unit operations required. SCOD from the three sources was quantified and preliminary results were presented. Molasses provided the highest SCOD release of 1.1285 x 10⁶ mg-SCOD/L, sonicated RAS produced 5.6 to 68.4 times the SCOD release of the untreated RAS (35.6 mg-SCOD/L) depending on the ultrasound intensity and treatment time, while the highest soluble carbon release obtained using potato starch was 809 mg-SCOD/L (using 20.9 g/100 mL potato starch concentration). Based on the experimental SCOD results, batch denitrification tests using the proposed carbon sources were carried out. The nitrogen removal efficiency at low dose (12.48 mg-SCOD/L) using molasses, potato starch and sonicated RAS were 77.54%, 57.24%, and 72.76% respectively, whilst at high dose (124.80 mg-SCOD/L) were 94.04%, 66.32%, and 92.10% correspondingly. In similar order of the proposed carbon sources, the nitrate removal rates for the first phase denitrification with low dose were 1.44, 1.16, and 1.18 mg-NO₃ − /h respectively, whilst the nitrate removal rate of the first phase denitrification with high dose improved to 2.01, 1.26, and 1.96 mg-NO₃ −/h correspondingly. From the denitrification test results, molasses proved to be the optimal carbon source in terms of nitrate removal. However sonicated RAS possesses similar denitrification performance and may be a suitable alternative. An economic analysis for sonicated RAS Option 2 confirmed it as the most viable substitute. The time to recover the initial investment (payback period) is approximately 6.5 years and the breakeven point is approximately 8 years. Both denitrification tests and economic analyses demonstrate that sonicated RAS may be a viable and attractive substitute for the molasses. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1337059 / Thesis (M.Eng.Sc.) - University of Adelaide, School of Chemical Engineering, 2008

L'objectif de ce travail est d'optimiser le prétraitement de boues par des ultrasons de puissance (US) à basses fréquences, et en particulier d‘étudier pour la première fois des améliorations possibles en modifiant la pression hydrostatique, et la fréquence jusqu’à l’audible. Après un examen préliminaire des conditions du procédé (conditionnement des boues, type de boues, alcalinisation préalable, contrôle de la température), les effets des paramètres ultrasonores (puissance, intensité, énergie spécifique, fréquence) et de la pression hydrostatique ont été spécifiquement étudiés, séparément et simultanément, d’abord à température constante (28°C), puis sans refroidissement. On a ainsi vérifié que l’énergie spécifique joue un rôle clé dans la désintégration des boues sous US (i.e. solubilisation de la matière organique) et que l'élévation de température pendant la sonication adiabatique est bénéfique grâce aux effets combinés d’hydrolyse thermique et de cavitation. Pour une énergie spécifique donnée, une faible fréquence (12 kHz contre 20 kHz) et une haute puissance améliorent la solubilisation de la matière organique grâce à une cavitation plus violente, tandis qu’on observe un optimum de pression hydrostatique en raison de ses effets opposés sur le seuil et l'intensité de la cavitation. Un résultat important est que la pression optimale dépend de l’intensité ultrasonore et du profil de température, mais pas de l’énergie spécifique, ni de la fréquence, ni du type de boues. Après avoir fixé les conditions les plus favorables (soit 12 kHz, 360 W, 28 gTS/L et conditions adiabatiques), l‘optimisation finale a fourni la pression de travail (3,25 bar) et les paramètres du mode séquentiel (US ON/OFF, permettant d‘éviter de hautes températures qui amortissement l‘intensité de la cavitation et peuvent endommager le transducteur). Ces conditions ont permis d‘atteindre un rendement d’extraction de la DCO très élevé, mais n’améliorent que faiblement le rendement ultérieur de méthanisation. / The objective of this work is to optimize high-power low-frequency sonication (US) pretreatment of sludge, and especially to investigate for the first time possible improvements by higher pressure and audible frequency. After a preliminary examination of regular process conditions (sludge conditioning, sludge type, prior alkalization, temperature control, etc.), effects of US parameters (power -PUS, intensity -IUS, specific energy input -ES, frequency -FS, etc.) and of hydrostatic pressure (Ph) were specifically looked into, separately and in combination, first under cooling at constant temperature (28°C), then under the progressive temperature rise provoked by sonication. First, it was confirmed that specific energy input (ES) plays a key role in sludge US disintegration (i.e. solubilisation of organic matter) and that temperature rise during adiabatic-like sonication is beneficial through additional effects of thermal hydrolysis and cavitation. At a given ES value, low FS (12 kHz vs. 20 kHz) and high PUS enhance soluble chemical oxygen demand (SCOD) due to more violent cavitation, while hydrostatic pressure gives rise to an optimum value due to its opposite effects on cavitation threshold and intensity. One major result is that optimal pressure depends on IUS (PUS) as well as temperature profile, but not on ES, FS, nor sludge type. Setting the other parameters at the most favorable conditions expected, i.e. 12 kHz, 360 W , 28 gTS/L, and adiabatic conditions, final optimization was achieved by searching for this pressure optimum and examining sequential procedure to avoid too high temperature dampening cavitation intensity and damaging the transducer. Such conditions with sequential mode and Ph of 3.25 bar being selected succeeded in achieving very high SCOD, but only marginally improved subsequent methanization yield.