1,768 research outputs found
Greenhouse gas emissions from and storm impacts on wastewater treatment plants : process modelling and control
Cette thĂšse Ă©tudie l'interaction entre les stations dâĂ©puration (STEP) et le changement climatique: soit en premier lieu la production ainsi que les Ă©missions de gaz Ă effet de serre (GES), en particulier le protoxyde dâazote (N2O), gĂ©nĂ©rĂ© Ă la STEP et en second lieu lâeffet des pluies plus intenses dues aux changements climatiques sur la STEP. Des campagnes de mesure sur le terrain et la modĂ©lisation Ă Ă©chelle rĂ©elle ont Ă©tĂ© utilisĂ©es conjointement dans cette recherche. Une campagne de mesure d'une durĂ©e dâun mois a Ă©tĂ© rĂ©alisĂ©e dans une STEP traitant les eaux usĂ©es de 750,000 Ă©quivalents habitants, soit la STEP dâEindhoven aux Pays-Bas. Des capteurs en ligne ont Ă©tĂ© installĂ©s dans la zone d'aĂ©ration du biorĂ©acteur. Une usine virtuelle de grande Ă©chelle, soit la STEP dĂ©crit par le Benchmark Simulation Model No.2 (BSM2), ainsi quâune usine rĂ©elle de grande Ă©chelle, soit la STEP dâEindhoven aux Pays-Bas, Ă©taient incluses dans cette Ă©tude. Dans les deux cas, les modĂšles ont Ă©tĂ© modifiĂ©s afin de prendre en compte les GES, en particulier la production de N2O. Deux modĂšles de boues activĂ©es (ASM) ont Ă©tĂ© dĂ©veloppĂ©s, soit lâASMG1 et lâASMG2d. En plus de la conversion de N2O par les bactĂ©ries hĂ©tĂ©rotrophes, les deux modĂšles sont en mesure de simuler la production de N2O par la dĂ©nitrification catalysĂ©e par les bactĂ©ries oxydant l'ammoniac (AOB). Les modĂšles dĂ©crivent aussi l'effet de lâoxygĂšne dissous (OD) sur la cinĂ©tique de production de N2O par les AOB grĂące Ă une modification de la cinĂ©tique dâHaldane. Les rĂ©sultats montrent que les AOB produisent beaucoup de N2O tandis que les hĂ©tĂ©rotrophes en consomment considĂ©rablement. Les Ă©missions de N2O augmentent lorsque les concentrations de NH4+ sont Ă©levĂ©es et que les concentrations dâOD sont modĂ©rĂ©es (jusquâĂ 2.5 mg O2/l dans cette Ă©tude). Ces conditions peuvent avoir Ă©tĂ© crĂ©Ă©es par le contrĂŽle en cascade de NH4+-OD qui vise Ă rĂ©duire la consommation d'Ă©nergie en diminuant les concentrations d'OD lorsque la concentration de NH4+ est suffisamment faible. En outre, ce contrĂŽleur en cascade est une stratĂ©gie de rĂ©troaction Ă gain faible. C'est-Ă -dire, un retard significatif se produit entre la dĂ©tection d'une augmentation de NH4+ et l'accroissement de l'aĂ©ration. Toutes ces propriĂ©tĂ©s produisent des conditions favorables Ă la production de N2O par les bactĂ©ries AOB. DiffĂ©rents scĂ©narios alternatifs ainsi que des stratĂ©gies de contrĂŽle ont Ă©tĂ© comparĂ©s selon la qualitĂ© de l'effluent, le coĂ»t dâopĂ©ration et les Ă©missions de GES. Dans le cadre de BSM2, un bon Ă©quilibre entre la qualitĂ© de l'effluent, le coĂ»t dâopĂ©ration et les Ă©missions de GES a Ă©tĂ© obtenu avec Ă la mise en Ćuvre d'un contrĂŽleur rĂ©troactif pur de lâOD sur la premiĂšre zone d'aĂ©ration et dâun contrĂŽleur en cascade de NH4+-DO sur les deux zones d'aĂ©ration suivantes et en utilisant soit une stratĂ©gie d'alimentation Ă©tagĂ©e ou le contrĂŽle du recyclage des boues afin de gĂ©rer les pics de dĂ©bits. Mots-clĂ©s: Traitement des eaux usĂ©es par boues activĂ©es, contrĂŽle de procĂ©dĂ©, campagne de mesures en terrain, modĂ©lisation mathĂ©matique Ă Ă©chelle grandeur rĂ©elle, gaz Ă effet de serre, protoxyde dâazote, temps de pluie.This PhD thesis studied the interaction between wastewater treatment plants (WWTPs) and climate change, i.e. the production and emission of greenhouse gases (GHGs), especially nitrous oxide (N2O), from WWTPs and the effect of the climate change induced more intense rain events on WWTPs. Both field measurements and full-scale modelling were pursued in this research. A one-month measurement campaign was performed by installing on-line sensors at the aeration zone of the bioreactor of a 750,000 person equivalents WWTP, i.e. the Eindhoven WWTP in the Netherlands. The models of a full-scale virtual plant, i.e. the Benchmark Simulation Model No.2 (BSM2), and a full-scale real plant, i.e. the Eindhoven WWTP in the Netherlands, were extended with respect to GHG emissions, especially the pathways involving N2O. Two types of extended Activated Sludge Models (ASM) were developed, i.e. ASMG1 for COD/N removal and ASMG2d for COD/N/P removal. Besides heterotrophic N2O production, both proposed models include N2O production by nitrite denitrification by ammonia-oxidizing bacteria (AOB) and describe the DO effect on AOB N2O production by a modified Haldane kinetics term. Results showed that AOB are the major producer of N2O while the heterotrophs consume N2O considerably. The high N2O emissions occurred under high NH4+ and intermediate DO concentrations (up to 2.5 mg O2/l in this work). Such conditions can be created by NH4+-DO cascade control which aims at reducing energy consumption by lowering the DO concentrations when the NH4+ concentration is sufficiently low. Moreover, this cascade controller is a low-gain feedback control strategy, i.e. a significant delay will occur between the detection of a NH4+ increase and the increase in aeration. All these properties lead to conditions favourable to N2O production by AOB. Different alternative scenarios and control strategies were compared in terms of effluent quality, operational cost and GHG emissions. In the framework of BSM2, a good balance among effluent quality, operational cost and GHG emissions was realized by implementing a pure DO feedback controller in the first aeration zone and a NH4+-DO cascade controller in the following two aeration zones and using either step feed or sludge recycling control to deal with hydraulic shocks. Keywords: Activated sludge, wastewater treatment, process control, field measurements, full-scale mathematical modelling, greenhouse gases, nitrous oxide, wet weather conditions
Distributed OSN Crawling System based on Ajax Simulation
AbstractIn the age of Web2.0, lots of online social networks (OSNs) like Facebook, Twitter, WeiBo become the most popular information transform platform, which catch more and more attention from Information Retrieval (IR). However, traditional web crawling System get into trouble because of the complicated OSN web pages, the rapid message exploding and the heavy using of Asynchronous JavaScript and XML(AJAX). We design and implement a distributed system based on Message Oriented Middleware (MOM) and Ajax simulation, which crawls 70 millions of Twitter detail items in one month. The data Acquisition shows that the crawling with Ajax simulation is able to get items loaded by Ajax without limitations, the distributed system based on MOM and Ajax simulation is able to crawl massive OSN data completely, quickly, frequently and unrestrictedly
GPU-accelerated subgraph enumeration on partitioned graphs
Ministry of Education, Singapore under its Academic Research Funding Tier
Probing Higgs properties at the CEPC
In the Circular Electron Positron Collider (CEPC), a measurement of the Higgs
mixing through process is presented, with $5.6\
\mbox{ab}^{-1}e^{+} e^{-}240\ \mathrm{GeV}CP\hat{\alpha}_{A \tilde{Z}} -8.27\times
10^{-2}8.09 \times 10^{-2}\hat{\alpha}_{Z \tilde{Z}}-2.15 \times 10^{-2}2.02 \times 10^{-2}95\%CP$ properties at
the CEPC
- âŠ