Phosphore | EPFL Graph Search

Le phosphore est l'élément chimique de numéro atomique 15, de symbole P. C'est un membre du groupe des pnictogènes. Le corps simple phosphore se présente sous plusieurs formes de couleurs différentes : blanc-jaune, rouge et violet-noir. Très pur, le phosphore « blanc » est transparent ; plus généralement il est blanc ambré, légèrement malléable avec une faible odeur d'ail. Les formes rouge et noire peuvent se présenter en poudre ou cristallisées. Le nom dérive du mot grec φώσφορος, qui signifie « porteur de lumière » et évoque la planète Vénus, l'étoile du berger. Cette origine a été attribuée au fait que le phosphore blanc émet de la lumière visible dans l'obscurité quand il est exposé à l'air, par chimiluminescence. En raison du fait qu'il est indispensable à la vie et d'une consommation mondiale qui pourrait dépasser les ressources disponibles avant une centaine d'années, l'ONU et divers scientifiques le classent comme matière première minérale critique, qu'il faudrait apprendr

Co-culture of microalgae and bacteria for wastewater treatment

Thierry Mounir

To address the problem of insucient wastewater treatment and eutrophication of lakes and rivers, the symbiotic association of microalgae and bacteria has shown great potential and numerous advantages. First, co-cultures can exhibit ecient treatment of domestic wastewater, with the combination of high nutrients (nitrogen and phosphorus) removal abilities of the microalgae and ecient degradation of organic matter by bacteria. Second, the symbiosis between microalgae and bacteria exchanging CO2 and O2 makes aeration not necessary, thus signicantly reducing the operating costs of the wastewater treatment plant. Third, recovered biomass of algae could be used as highpro t products like biofuels and food source. Fourth, the xation of the atmospheric CO2 by the microalgae through photosynthesis would contribute to greenhouse gas reduction in the atmosphere. Finally, the decayed microalgal biomass could serve as organic carbon source for denitrication by bacteria. However, this technology is not well-known yet, and further research on the in uence of the operating parameters have to be conducted. Furthermore, its main drawback is the harvesting of the microalgae. Due to their small size, microalgae demonstrate a low settling rate of 3.6 x 10􀀀3 m/h. A solution is to enhance aggregation of the biomass through occulation, followed by granulation to reach fully-developed microalgal-bacterial consortia. These granules exhibit high treatment performances and high settleability. The rst objective of this project was to identify the optimal microalgae:bacteria ratio for COD and nutrients removal. The second objective was to form fully-developed granules, starting from a co-culture, and assess the in uence of dierent agitation speeds on the granulation. The photobioreactor with a microalgae:bacteria ratio of 75:25 expressed the most promising results in COD removal eciency (95% after 8 days), nitrogen removal eciency (94% after 9 days), phosphorus removal eciency (93% after 7 days), and biomass productivity (144 mg/L/d). In this photobioreactor, nitrogen was removed by a combination of assimilation into microalgal biomass and nitrication/denitrication by the bacteria. The COD was removed by degradation by bacteria and mixotrophic microalgae that used the organic matter as carbon source. Finally, phosphorus was removed by assimilation into microalgal biomass. Although obvious aggregation between microalgae and bacteria could be observed, no fully-developed granules were formed after 89 batches of 24 hours. Because of low COD and nitrogen removals, no starvation period was experienced by the co-cultures. Therefore, extracellular polymeric substances were not released in sucient amounts to enhance the granulation. Furthermore, excessive stirring (200 rpm) may have lead to microalgal cells damage, thus promoting bacterial growth over microalgal growth. On the other hand, slower agitation speeds (80 and 120 rpm) seemed to enhance microalgal growth. Overall, the agitation speed appeared to have an indirect impact on the treatment performances and the settleability of the co-cultures, by signicantly in uencing the microalgal and bacterial growths.

2020

Transition of the Swiss Phosphorus System towards a Circular EconomyPart 2: Socio-Technical Scenarios

Claudia Rebeca Binder Signer, Jonas Ramon Mehr

A transition towards a circular economy of phosphorus (P) in Switzerland is a multi-faceted challenge as P use is subject to a variety of influencing factors comprising policy interventions, consumption trends, or technological innovations on different spatial scales. Therefore, scenarios for P use that take into account both the social and the technical dimension of change are needed for investigating possible pathways of a transition towards more sustainable P futures. Drawing on the multi-level perspective of transition theory, we develop scenarios on the landscape level, i.e., a balanced and healthy human diet, on the regime level, i.e., P recovery from sewage sludge (ash) and meat and bone meal, and on the niche level, i.e., urine separation. Based on the P system of the year 2015, we assess the quantitative implications of the scenarios for the Swiss P system. While scenario 1 mainly affects the agricultural system by reducing the overall P throughput, scenario 2 significantly changes P use in waste management, because P losses to landfills and cement plants decrease and the production of secondary P increases. Scenario 3 shows little quantitative impact on the national P system. From a qualitative transition perspective, however, urine separation entails fundamental socio-technical shifts in the wastewater system, whereas P recovery from sewage sludge (ash) represents an incremental system adaptation. The combination of flow- and transition-oriented research provides more general insights into how a circular economy of P can be reached. Furthermore, the analysis of P recycling scenarios reveals that transition processes in Switzerland are embedded in a global resource economy. Thus, a sole focus on concepts of national P self-sufficiency and the reduction of Switzerland's P import dependency tend to fall short when analysing the economisation of secondary P materials in the face of transnational resource flows and markets.

2018

Transition of the Swiss Phosphorus System towards a Circular Economy — Part 1: Current State and Historical Developments

Claudia Rebeca Binder Signer, Jonas Ramon Mehr

Current phosphorus (P) use in European countries is highly dependent on mineral P imports and not sustainably managed. In order to identify and implement measures for sustainable P management, a comprehensive understanding of national P flows and stocks and their temporal dynamics is essential. We conduct a substance flow analysis (SFA) of the Swiss P system of the year 2015, and study the dynamics of the national P system by looking into its development since 1989. Furthermore, we investigate how political-legislative interventions affected the P system during this period. The results show that between 1989 and 2015, the P efficiency in Swiss agriculture increased from 59% to 94%, mainly due to a considerable reduction of fertilization in the agricultural subsystem. At the same time, Switzerland's P import dependency decreased from 33% to 24% between 1989 and 2002 because of a reduction of mineral fertilizer import and use. Between 2002 and 2015, the import dependency stagnated because further improvements in P use efficiency in agriculture were outweighed by a decrease of P recycling and an increase of P losses in the waste management system. By embedding these temporal dynamics in their political-legislative context, we found that top-down interventions such as incentives for a balanced nutrient budget in agriculture, restrictions of the use of animal by-products in the agri-food system or the ban of direct sewage sludge recycling in agriculture significantly affected and shaped the national P system. Our analysis provides profound quantitative and qualitative insights into past and present P management in Switzerland and is followed by part 2 of the paper, where we analyze possible future pathways of P management.

2018

Co-culture of microalgae and bacteria for wastewater treatment

Thierry Mounir

2020

Transition of the Swiss Phosphorus System towards a Circular EconomyPart 2: Socio-Technical Scenarios

Claudia Rebeca Binder Signer, Jonas Ramon Mehr

2018