Modeling, Optimization and Design of Fluidized Beds for Biological Denitrification

A mathematical model for fluidized bed denitrification has been derived, based on the fluidization theory and on zero order kinetics for biological nitrate reduction with nitrite as an intermediate product. Bed expansion, particle size, sludge concentration and nitrate and nitrite concentration can be calculated as a function of the height in the bed. Complete optimal conditions were not found using carrier materials of various specific gravities and with sizes above a radius of 0.2 mm, which was arbitrarily chosen as the smallest carrier particle. However, for each size and type of carrier material an optimal thickness of the biomass layer has been calculated for a standard type of wastewater at constant flow rate. For the kinetic and other constants used in this study, graphs are presented which can be used in the design of fluidized beds for denitrification.</jats:p

Seismic Risk Assessment For Geothermal Projects: With The Creation Of A Physical Screening Model

Geothermal energy can be a great solution for the downscaling fossil fuel society, but it can potentially lead to seismic hazards. A doublet system, with a cold water injection well and a hot water production well, alters the stress situation in the subsurface, which can result in (micro)fracturing and fault reactivation. Even in water filled reservoirs, aquifers, with relatively good permeabilities, the acting in-situ stress on already existing fault can be changed such that there can be a seismic hazard. The three dominant phenomena that influence the fault reactivation and are triggered by geothermal water injection and production are the direct pore pressure change, poro-elastic stress change and thermo-elastic stress change. To predict and subsequently diminish or limit the seismic hazards in geothermal operations, Seismic Risk Analysis (SRA) are to be completed before such operations can take place in an often seismic risky location, like densely populated areas. In the current (Dutch) geothermal environment mainly three SRA’s are used; “Methodiek voor risicoanalyse ontrent geinduceerde beving door gaswinning” by the Staatstoezicht op de Mijnen (SodM), “Defining the Framework for Seismic Hazard Assessment in Geothermal Projects V0.1” by Q-con/IF-technology [6] and an Excel-model created by TNO/Geomech. By investigating and reviewing these three SRA’s in this thesis their shortcoming and limitations are exposed, for example their lack of physical foundation and explanatory results. From the foundation of the currently excising SRA’s a new alternative SRA, which corresponds in some steps with the older SRA’s, is created in this thesis. In order to successfully finish the new SRA one of the three steps should be completed, starting with SRA Step 1. In this first step of the new SRA a new Physical Screening Model (PSM) is created. When completing the SRA an indication of what type of seismic monitoring there should be done during production. This PSM is a fairly quick and simple in its use but provides sufficient informative data to investigate the seismic hazard for most geothermal operations in the Netherlands. In four different steps in the PSM, the potential reactivation of faults over the whole reservoir during production will be evaluated. With the spatio-temporal evolution of ΔP, Δσporo, ΔT (PSM Step 1) this model can predict fault reactivation at any place and time inside the reservoir, while it can also look at which parameter dominated this reactivation. In this thesis the physical background and results of the PSM will be explained step by step. Eventually there are three final results from the PSM; a Mohr plot that predicts if certain faults (at certain locations) are stable or not and the maximum Moment magnitude (Mw) in combinations with the Peak Ground Velocity (PGV), which predict the severity of a possible event. Sensitivity analyses and case studies done with the PSM in this thesis show the influence of dominating parameters, like permeability and injection rate, and what results can be expected when using this model.Applied Earth Science

De hydrogenering van alkylnaftalenen over palladium

Applied Science

PIV experiments on the flow induced by a sphere sedimenting towards a solid wall

The motion induced by gravity of solid spheres in a vessel filled with fluid has been investigated experimentally at Reynolds numbers in the range from 1-74 and Stokes numbers ranging from 0.2-17. Trajectories of the spheres have been measured with a focus on start-up behavior, and on impact with a horizontal wad. Two models have been investigated. The first describes the accelerating motion of the sphere. The second model predicts the distance from the wall at which the sphere starts decelerating. The fiow in the vicinity of the sphere was measured by means of PIV. The time scales and fiow structures strongly depend on the Reynolds nmnber. Measurements performed are in good agreement with simulations performed at the Kramers Laboratorium.Kramers Laboratorium voor Fysische TechnologieApplied Science

Fluidization and Sedimentation of Carrier Material in a Pilot-Scale Airlift Internal-Loop Reactor

Balsalt (ρ=2760 kg.m−3, d=0.245 mm) was used as the solid carrier in a pilot-scale airlift internal-loop reactor for wastewater treatment (AILRW), which was filled with tap water in this study, to investigate the regimes of fluidization and sedimentation. Solid sediment was observed even when the liquid velocity in the riser was much higher than the terminal settling velocity of the particles. Circulation cannot be maintained if the superficial liquid velocity in the downcomer ud. is below a definite value (blocking velocity ub) . In a dimensionless model, ub is related to the bulk volume of carrier solids added (Vt), the available space at the bottom (Va) and the gap size at the bottom (a0) according to ub2/(a0.g) = 0.04(Vt/Va) −0.036.</jats:p

Feasibility of simultaneous nitrification and denitrification in a pilot-scale airlift-loop reactor

Airlift-loop reactors have become competitive in treating municipal wastewater. Many studies have verified that high COD conversion efficiencies can be reached. When simultaneous nitrification and denitrification could be realised to the same degree as is possible in low loaded conventional activated sludge processes, their application would be more interesting. In theory nitrification and denitrification are simultaneously possible in an airlift-loop reactor. Based on qualitative assumptions, the biofilm around a particle in an airlift-loop reactor hypothetically can contain an aerobic layer for carbonaceous oxidation and nitrification and an anoxic layer for denitrification. The aim of the research described in this report is to test this hypothesis by a pilot-scale experiment treating municipal wastewater. The experimental results demonstrate that the hypothesis is correct. During about 30 days it was possible to remove 70- 80% of the nitrogen at a hydraulic retention time of 1.5 h. For unfiltered effluent samples, which included the sludge production as suspended solids, COD removal was about 70% compared to the unfiltered influent. Further research is needed to establish the relation between the thickness of the biofilm and the concentration of dissolved oxygen in relation to nitrification and denitrification and overall reactor performance.Water ManagementCivil Engineering and Geoscience