5,161 research outputs found
Réduction et contrÎle du foisonnement filamenteux des boues activées par application d'un régime turbulent
Le foisonnement filamenteux des boues activĂ©es est un problĂšme important dans les stations d'Ă©puration du type Boues ActivĂ©es, car il peut entraĂźner des pertes de biomasse avec l'eau Ă©purĂ©e. Les techniques de lutte utilisĂ©es actuellement sont, soit des techniques dites « biologiques » (sĂ©lecteurs), soit des techniques chimiques (floculants, biocides). L'objectif de notre travail a Ă©tĂ© la mise au point d'un procĂ©dĂ© original basĂ© sur la crĂ©ation d'une zone de turbulence pour casser les rĂ©seaux filamenteux. La rĂ©duction et le contrĂŽle du bulking sont obtenus par passage (de durĂ©e limitĂ©e T1) de la biomasse dans un systĂšme venturi, Ă©quipĂ©e d'une prise d'air. L'efficacitĂ© du procĂ©dĂ© dĂ©pend principalement de la turbulence due Ă l'auto-aspiration d'air au niveau du rĂ©trĂ©cissement du venturi. Cette turbulence contribue d'une part au mĂ©canisme de « cisaillement » des filaments, et d'autre part Ă la qualitĂ© de l'effluent sortant. Une gestion adaptĂ©e (aĂ©ration sĂ©quentielle en procĂ©dĂ© Ă faible charge) permet d'obtenir, outre une amĂ©lioration de la dĂ©cantation, une amĂ©lioration de l'Ă©limination de l'azote. De plus, le contrĂŽle de la biomasse optimise l'Ă©limination de la pollution carbonĂ©e.The loss of biomass in a waste water plant as a result of sludge bulking is an important problem. Biological (ex.: selector configuration) or chemical (ex. : floculating reagents, biocides...) methods habe been used in order to control bulking. A new process based on the generation of turbulence to break the filaments is described. To reduce and control sludge bulking, the biomass is pumped through a venturi equipped with an air inlet. Figure 1 represents the pilot scheme. Two processes can be used : the emulsor with air is introduced on recycling of sludge or is placed in an independent loop. Here, it is the latter that has been used.We tried to reduce bulking by mechanical treatment. The hydrodynamic efficiency of the process depends mostly on the degree of turbulence generated by the waters speed and by the suction of air in the constricted part of the venturi.During the first trials on the plant, we defined the maximum turbulence allowed in order not to break the floc. We could not use a big aeration to prevent defloculation.The main factors to reduce bulking are :- the sequences of usage of the emulsor venturi (the periodicity of the treatment is T),- the speed of the water in the nozzle of the venturi (we can refer to the Reynolds Number Re = Ud/Ê; but this number canât really represent the turbulence created),- the duration of the emulsor's application. The emulsor venturi is used during a period T1 with a periodicity T (T>T1), with T1 : n X (VR/qv) where VR/qv is the contact time in the venturi and n is the frequence of recycling.During the period T, it is possible to use continuous aeration or to work with sequential aeration.a) continuous aeration|_________________________| TTime between two applications of the venturi|_______________| T1Venturi durationThe process is the same as the aeration of activated sludge. COD is reduced but only with low load, significant nitrification occurs. Figure 5 shows the efficiency of the continuous aeration process especially versus the sludge index parameter.b) sequential aerationAs we try to remove nitrogen, the sequential aeration is more useful than continuous aeration. A cycle is divided in two periods (T2, T3 with T = T2 + T3), and of course, the duration of the venturi use equal to T1.|_________________________| TTime between two applications of the venturi|_____________| T1Venturi duration|_________________| T2Aeration duration          |_____| T3Anoxic periodFigures 6 and 7 show the efficiency of the emulsor if we consider lB (sludge index) as the main parameter for the sequential operation (T2, T3) and it's also possible to obtain a good removal of nitrogen pollution.Our operations parameters were for these experiments :T = 8 or 12 hoursT1 between 20 min. and 1 hourT2 between 4 and 5 hoursThis process is now patiented and the first industrial applications are now defined
Decay resistance against Coriolus versicolor in Sessile oak ( Quercus petraea Liebl.): analysis of the between-tree variability and correlations with extractives, tree growth and other basic wood properties
Abstract : Weight loss due to fungus Coriolus versicolor has been measured on 614 samples according to the NF EN 113 norm. Up to eight samples were cut at breast height (two opposite radiiĂfour radial positions in heartwood) from 82 mature sessile oaks ( Quercus petraea Liebl.) originating from contrasting regions, silvicultural schedules and site qualities in France. The following points are addressed in the paper: (i) contribution to the total variability for weight loss of the effects "treeâ, "position in the treeâ, as well as their interaction; (ii) percentage of wood samples and trees in each of the five classes of natural durability defined by the norm NF EN 350-2; (iii) test of the effects of region, silvicultural schedule and site quality on weight loss and evaluating their contribution to the total variation; and (iv) correlations at tree level between weight loss and several traits related to tree growth and basic wood properties (density, swelling, grain angle, multiseriate wood rays characteristics, extractives content). The results are discussed with a view to aid the forest manager as well as the log/wood user to take advantage of the high level of between-tree variability observed as natural durability against C. versicolo
Asymptotics of Random Contractions
In this paper we discuss the asymptotic behaviour of random contractions
, where , with distribution function , is a positive random
variable independent of . Random contractions appear naturally in
insurance and finance. Our principal contribution is the derivation of the tail
asymptotics of assuming that is in the max-domain of attraction of an
extreme value distribution and the distribution function of satisfies a
regular variation property. We apply our result to derive the asymptotics of
the probability of ruin for a particular discrete-time risk model. Further we
quantify in our asymptotic setting the effect of the random scaling on the
Conditional Tail Expectations, risk aggregation, and derive the joint
asymptotic distribution of linear combinations of random contractions.Comment: 25 page
PDB8 TYPE-2 DIABETES AND BODY MASS INDEX (BMI):WHAT CAN WE LEARN FROM A LONGITUDINAL DATABASE STUDY?
Farrando, Jordi;Febles, Maria Dolors ;Henrich, Jordi;TarrasĂł, Olga ;Fuertes, J.C.;PĂ©rez, S
Thermal Diffusion of a Two Layer System
In this paper thermal conductivity and thermal diffusivity of a two layer
system is examined from the theoretical point of view. We use the one
dimensional heat diffusion equation with the appropriate solution in each layer
and boundary conditions at the interfaces to calculate the heat transport in
this bounded system. We also consider the heat flux at the surface of the samle
as boundary condition instead of using a fixed tempertaure. From this, we
obtain an expression for the efective thermal diffusivity of the composite
sample in terms of the thermal diffusivity of its constituent materials
whithout any approximations.Comment: 16 pages, 1 figure, RevTeX v. 3.0 macro packag
Laiduntarkkailu erÀillÀ tiloilla Suomessa kesÀllÀ 1926
vokKirjasto Aj-kThe control of pastures on some farms in Finland (Suomi) in 192
Laiduntarkastus erÀillÀ tiloilla Suomessa kesÀllÀ 1925
vokKirjasto Aj-kThe control of pasture on some farms in Finland (Suomi) in 192
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