Parameters influencing calcium phosphate precipitation in granular sludge sequencing batch reactor

Parameters influencing calcium phosphate precipitation in Calcium phosphate precipitation inside microbial granules cultivated in a granular sequenced batch reactor (GSBR) has been demonstrated to contribute to phosphorus removal during wastewater treatment. Whereas hydroxyapatite (HAP) is proven to accumulate in the granule, the main calcium phosphate precursors that form prior to HAP are here investigated. A separate batch reactor was used to distinguish reactions involving biological phosphate removal from physicochemical reactions involving phosphateprecipitation in order to establish the kinetics and stoichiometry of calcium phosphate formation. Experiments and simulations with PHREEQC and AQUASIM software support the assumption that amorphous calciumphosphate (ACP) is the intermediary in HAP crystallization. The results provide the kinetic rate constants and thermodynamic constants of ACP. The formation of bioliths inside biological aggregates as well as the main parameters that drive their formations are discussed here. Finally, the influence of pH and calcium and phosphate concentrations in the influent was also assessed, in order to determine the contribution of precipitation in the different operating conditions

Biologically induced phosphorus precipitation in aerobic granular sludge process

Aerobic granular sludge is a promising process for nutrient removal in wastewater treatment. In this work, for the first time, biologically induced precipitation of phosphorus as hydroxyl-apatite (Ca5(PO4)3(OH)) in the core of granules is demonstrated by direct spectral and optical analysis: Raman spectroscopy, Energy dispersive X-ray (EDX) coupled with Scanning Electron Microscopy (SEM), and X-ray diffraction analysis are performed simultaneously on aerobic granules cultivated in a batch airlift reactor for 500 days. Results reveal the presence of mineral clusters in the core of granules, concentrating all the calcium and considerable amounts of phosphorus. Hydroxyapatite appears as the major mineral, whereas other minor minerals could be transiently produced but not appreciably accumulated. Biologically induced precipitation was responsible for 45% of the overall P removal in the operating conditions tested, with pH varying from 7.8 to 8.8. Major factors influencing this phenomenon (pH, anaerobic phosphate release, nitrification denitrification) need to be investigated as it is an interesting way to immobilize phosphorus in a stable and valuable product

Location and chemical composition of microbially induced phosphorus precipitates in anaerobic and aerobic granular sludge

This work focuses on combined scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDX) applied to granular sludge used for biological treatment of high-strength wastewater effluents. Mineral precipitation is shown to occur in the core of microbial granules under different operating conditions. Three dairy wastewater effluents, from three different upflow anaerobic sludge blanket (UASB) reactors and two aerobic granular sequenced batch reactors (GSBR) were evaluated. The relationship between the solid phase precipitation and the chemical composition of the wastewater was investigated with PHREEQC software (calculation of saturation indexes). Results showed that pH, Ca:P ratios and biological reactions played a major role in controlling the biomineralization phenomena. Thermodynamics calculations can be used to foresee the nature of bio-precipitates, but the location of the mineral concretions will need further investigation as it is certainly due to local microbial activity

Stability and performance of two GSBR operated in alternating anoxic/aerobic or anaerobic/aerobic conditions for nutrient removal

Two granular sludge sequencing batch reactors (GSBR) with alternating anoxic/aerobic (R1) and anaerobic/aerobic (R2) conditions were operated with a 4-carbon-source synthetic influent. The physical properties of the granular sludge were very good (SVI≈20 mL g−1) and high solid concentrations (up to 35 g L−1) were obtained in the bioreactor operated with a pre-anoxic phase with additional nitrate (R1). In contrast, performance and granule settleability were lower in R2 due to the development of filamentous heterotrophic bacteria on the surface of granules. These disturbances were linked to the fact that a fraction of COD remained during the aerobic phase, which was not stored during the anaerobic period. To stabilize a GSBR with a mixture of organic carbon sources, it is thus necessary to maximize the amount of substrate used during the non-aerated, anaerobic or anoxic, phase. Comparable phosphate removal efficiency was observed in both systems; enhanced biological P removal being greater in anaerobic/aerobic conditions, while the contribution of precipitation (Ca–P) was more significant in anoxic/aerobic conditions

Analyse et modélisation du traitement de l'azote dans un procédé de granulation aérobie hydride

Dans ce travail, le traitement des nutriments et plus particulièrement celui de l azote en procédé de granulation aérobie a été étudié. L approche expérimentale a dans un premier temps eu pour objet de comparer la stabilité des caractéristiques physiques et microbiologiques d agrégats développés dans deux réacteurs fonctionnant en alternances de phases anaérobie / aérobie ou anoxie / aérobie. L opération d un procédé de granulation aérobie en alternance de phases anoxie / aérobie a favorisé la stabilisation des performances de traitement de l azote et notamment celle de la nitrification. Le développement d une boue hybride comprenant une fraction de flocs et de granules a été observé. Dans le but d évaluer comment le caractère hybride de la boue obtenue en conditions anoxie/aérobie oriente les performances et vitesses de transformation de l azote, une caractérisation ex-situ des limitations au transfert d oxygène au sein des flocs, granules et boue hybride a été réalisée par respirométrie. En complément, la localisation des espèces nitrifiantes par la technique d hybridation fluorescente in situ (FISH) a été réalisée. Les résultats obtenus indiquent que la présence de flocs au sein d une boue granulaire permet d augmenter la vitesse de la nitrification, en particulier pour de faibles concentrations en oxygène dissous. D autre part, il est ici mis en évidence la nécessité de contrôler simultanément le ratio floc/granules et la taille des granules en vue de l optimisation du traitement de l azote.Enfin un outil mathématique permettant de décrire les phénomènes réactionnels ayant lieu au sein d une biomasse hybride a été développé. Celui-ci a été employé dans le but d optimiser le fonctionnement du procédé hybride par l évaluation de l effet des propriétés physiques de la biomasse, et plus particulièrement de la proportion de granules en présence, pouvant conduire à une élimination efficace de l azote et à l augmentation de la robustesse du procédé vis-à-vis de diminutions ponctuelles de l oxygène dissousIn this work, the treatment of nutrients, especially that of nitrogen in aerobic granulation process was studied.The experimental approach has initially been intended to compare the stability and the physical and microbiological characteristics of aggregates developed in two reactors operating in alternating anaerobic / aerobic or anoxic / aerobic conditions. The presence of a pre-anoxic phase promoted the stabilization of nitrogen removal performances and especially those of nitrification. The development of a hybrid sludge process containing a fraction of flocs and granules was observed.In order to evaluate and quantify the influence of the simultaneous presence of flocs and granules in the nitrifying activity of the hybrid sludge developed in the alternating anoxic / aerobic conditions, the nitrification rate and oxygen limitation of flocs, granules and hybrid sludge was assessed using respirometric assays at different dissolved oxygen concentrations. The spatial distribution of nitrifying bacteria was investigated using fluorescence in situ hybridization (FISH). Results indicated that the presence of flocs with granules could increase the rate of nitrification to transitory reductions of aeration. On the other hand, the optimization of nitrogen removal requires the simultaneous control of the floc to granule ratio and granule size.Finally, a mathematical model to describe the reaction phenomena taking place in the hybrid biomass was developed. It was used in order to optimize the operation of the hybrid process through the evaluation of the effect of physical properties of biomass, specifically the ratio of granules and flocs in the reactor that can lead to efficient removal of nitrogen and increase the robustness of the processTOULOUSE-INSA-Bib. electronique (315559905) / SudocSudocFranceF

Improvement of the treatment of salted liquid waste by integrated electrodialysis upstream biological treatment

As far as the reduction of the environmental impact of production processes is concerned, the management ofliquid wastes of high salinity remains a key point. In this paper, the possibility to use electrodialysis for the improvement of the management of such problematic liquid wastes is investigated. The ED experiments are carried out to investigate the influence of the operating parameters on the ED performances, i.e. on the variation of the organic loss factor versus the demineralisation factor. It is demonstrated that the demineralisation can be accompanied by a change in the mineral composition, i.e. an increase of the sulphate to chloride ratio. A concentration limit is pointed out. Then, the influence of the salt composition on the biological degradation is investigate

Attempts, Successes, and Failures of Distance Learning in the Time of COVID-19

Over 1.7 billion students around the world have had their education disrupted by the spread of the Coronavirus disease worldwide. Schools and universities have not faced this level of disruption since World War II. The COVID-19 pandemic presented a colossal challenge for teachers to urgently and massively adapt all their classes to distance learning in order to maintain educational continuity with the same quality. Even if some teachers and certain classes were ready to face the situation, a large majority had to adapt their teaching and learning in a very short time without training, with insufficient bandwidth, and with little preparation. This unexpected and rapid transition to online learning has led to a multiplication of teachers’ strategies for distance learning in lectures, tutorials, project groups, lab works, and assessments. The purpose of this paper is to present the feedback from students and teachers who participated in the lockdown semester of two different groups of a 5-year program in Chemistry, Environment and Chemical Engineering (100 students) at INSA Toulouse (France). The analysis has highlighted some great successes and some failures in the solutions proposed. Consequently, some guidelines can be given to help us all to learn the lessons of such a singular experience in order to face the unexpected future with more knowledge and more successful distance learning. Teachers have shown very strong resilience during this crisis, at the cost of significant personal commitment. They admit that they have learned more about distance education in two months than in the last 10 years

Une production de méthane à partir de dioxyde de carbone et d’électricité renouvelable

Une production de méthane à partir de dioxyde de carbone et d’électricité renouvelabl

Intéraction entre l'élimination des polluants azotés et la formation des franules aérobies en réacteur biologique séquencé

Le procédé à boues granulaires aérobie constitue une technologie prometteuse pour le traitement des pollutions azotées mais son application industrielle nécessite de comprendre certains verrous scientifiques de façon à optimiser les conditions de fonctionnement notamment en minimisant les besoins énergétiques. La structure spécifique des granules aérobies génère naturellement des limitations au transfert des polluants et une organisation spatiale beaucoup plus hétérogène que dans les flocs. Les bactéries autotrophes et hétérotrophes sont alors en interaction ou en compétition. Ainsi l objectif de ce travail est, au travers de deux études expérimentales, de mieux comprendre les interactions entre la croissance/respiration en anoxie/aérobie et la structuration des boues granulaires ainsi que leurs performances pour l élimination de l azote. Dans la première expérience, deux réacteurs SBR sont étudiés parallèlement en maintenant une concentration en oxygène de 1,8+-0,8 mg L-1. Un seul des deux réacteurs reçoit une charge en nitrate (50-200 mg N L-1). Dans le réacteur alimenté en nitrate les agrégats présentent des propriétés très proches de celles des granules aérobies alors que le système de référence purement aérobie présente des propriétés de décantation plus comparables à celles des biomasses floculées. L observation des cinétiques et des bilans azote montre que la dénitrification a lieu à l intérieur des agrégats dans des zones internes où l oxygène est très probablement limitant du fait des fortes activités spécifiques des agrégats microbiens et de la densification de ces agrégats. Un modèle mathématique développé sous AQUASIM® permet de décrire les gradients de concentrations dans les granules (1 dimension) et l évolution des espèces au cours du temps dans le réacteur. Ce modèle intégrant les phénomènes de respiration/croissance/stockage des espèces hétérotrophes en aérobie et en anoxie a permis de décrire l effet des nitrates sur la croissance hétérotrophe. Non seulement le profil de biomasse active montre une croissance plus en profondeur mais ceci génère également plus de stockage de composés de réserve. Enfin le modèle traduit le fait que la croissance plus en profondeur (générée par la présence de nitrates) constitue un moyen de mieux protéger la biomasse active du détachement par érosion. Dans la deuxième expérience, deux réacteurs identiques de type air-lift sont opérés avec des stratégies d aération différentes : dans le premier un débit d air relativement modéré (SAV=0,6 cm s-1) et une alternance anoxie/aérobie sont imposés (un complément en nitrate est maintenu pour éviter l anaérobie), alors que dans le deuxième réacteur le débit d air est élevé (SAV= 2,83 cm s-1) et les conditions principalement aérobies. Les résultats démontrent que l alternance entre des conditions d excès anoxie et de famine aérobie permettent de favoriser le développement des granules aérobies (la taille des granules est entre 500-1000 Bm) et la stabilisation des performances (nitrification en particulier). La caractérisation physique (taille et cohésion) des agrégats biologiques montre que les granules sont des agrégats microbiens dont la densité est plus élevée que celle des flocs et dont la cohésion est suffisante pour que leur taille ne soit pas calibrée par l échelle de la turbulence ; la formation des granules est caractérisée par plusieurs étapes : une phase de densification, une phase de croissance avec érosion (distribution bimodale), puis une phase de croissance et de maturation.Aerobic granular sludge process is a feasible technology for the treatment of nitrogen pollution, but some key points need to be further understood in order to optimize the operational conditions for its industrial application, especially considering the minimization of energy requirements. The special structure of aerobic granules generates naturally the pollutants transfer limit within granules. The spatial organization is much more heterogeneous than that in the flocs. The autotrophic bacteria and heterotrophic bacteria are interacting or competing. Thus the goal of this work is, in two experimental studies, to better understand the interactions between the growth / respiration under the anoxic/aerobic conditions and the structure of granular sludge as well as their performance for nitrogen removal. In the first experiment, two parallel SBR reactors are installed maintaining a dissolved oxygen concentration of 1.8+-0.8 mg L-1. Nitrate (50-200 mg N L-1) was only added in the influent of one reactor, in which the aggregates properties were comparable to aerobic granules, while the aggregates properties in the other reactor were more traditional (floc-like). The kinetic observation and nitrogen measurement show that denitrification occurs within the aggregates where the DO is probably limited because of high specific biological activities and the density of biological aggregates. A developing mathematical model by the software tool AQUASIM® allows describing the concentration gradients of substrates in the granules (1 dimension) and the evolution of biological species in the reactor. This model including the phenomena of respiration / growth / storage of heterotrophic species in aerobic and anoxic conditions helps to describe the effect of nitrate on the heterotrophic growth. Not only the profile of active biomass shows a growth in more depth but also generates more storage compounds. Finally, this model reveals that heterotrophic growth in more depth (generated by the presence of nitrate) protect well the active biomass to avoid the detachment by erosion. In the second experiment, two airlift reactors worked on the different aeration strategies: a relatively moderate air flow rate (SAV = 0.6 cm s-1) and alternating anoxic / aerobic conditions are applied in the first reactor (additional nitrate is maintained to avoid anaerobic condition), whereas a high air flow rate (SAV = 2.83 cm s-1) and strictly aerobic conditions maintain in the second reactor. The results show that the alternating anoxic feast / aerobic famine conditions encourage the formation of aerobic granules (the size is between 500-1000 Bm) and the stabilization of nitrification performance. The aggregates strength test shows that the density of aerobic granules is higher than the flocs. The size of aerobic granules is not calibrated by the Kolmogorov micro-scale. The formation of granules is characterized by several stages: a stage of densification, an expansion phase with particles erosion (bimodal distribution), then a growth phase and a maturationTOULOUSE-INSA (315552106) / SudocSudocFranceF

Caractérisation des substances polymériques extracellulaires de boues granulaires aérobies (propriétés chimiques et implication dans la cohésion du granule)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF