53,772 research outputs found
Aerated blast furnace slag filters for enhanced nitrogen and phosphorus removal from small wastewater treatment plants
Rock filters (RF) are a promising alternative technology for natural
wastewater treatment for upgrading WSP effluent. However, the application
of RF in the removal of eutrophic nutrients, nitrogen and phosphorus, is very
limited. Accordingly, the overall objective of this study was to develop a lowcost
RF system for the purpose of enhanced nutrient removal from WSP
effluents, which would be able to produce effluents which comply with the
requirements of the EU Urban Waste Water Treatment Directive (UWWTD)
(911271lEEC) and suitable for small communities. Therefore, a combination
system comprising a primary facultative pond and an aerated rock filter
(ARF) system-either vertically or horizontally loaded-was investigated at
the University of Leeds' experimental station at Esholt Wastewater
Treatment Works, Bradford, UK.
Blast furnace slag (BFS) and limestone were selected for use in the ARF
system owing to their high potential for P removal and their low cost. This
study involved three major qperiments: (1) a comparison of aerated
vertical-flow and horizontal-flow limestone filters for nitrogen removal; (2) a
comparison of aerated limestone + blast furnace slag (BFS) filter and
aerated BFS filters for nitrogen and phosphorus removal; and (3) a
comparison of vertical-flow and horizontal-flow BFS filters for nitrogen and
phosphorus removal.
The vertical upward-flow ARF system was found to be superior to the
horizontal-flow ARF system in terms of nitrogen removal, mostly thiough
bacterial nitrification processes in both the aerated limestone and BFS filter
studies. The BFS filter medium (whieh is low-cost) showed a much higher
potential in removing phosphortls from pond effluent than the limestone
medium. As a result, the combination of a vertical upward-flow ARF system
and an economical and effective P-removal filter medium, such as BFS,
was found to be an ideal optionfor the total nutrient removal of both nitrogen
and phosphorus from wastewater.
In parallel with these experiments, studies on the aerated BFS filter effective
life and major in-filter phosphorus removal pathways were carried out. From
the standard batch experiments of Pmax adsorption capacity of BFS, as well
as six-month data collection of daily average P-removal, it was found that
the effective life of the aerated BFS filter was 6.5 years. Scanning electron
microscopy and X-ray diffraction spectrometric analyses on the surface of
BFS, particulates and sediment samples revealed that the apparent
mechanisms of P-removal in the filter are adsorption on the amorphous
oxide phase of the BFS surface and precipitation within the filter
Pore-scale modeling of fluid-particles interaction and emerging poromechanical effects
A micro-hydromechanical model for granular materials is presented. It
combines the discrete element method (DEM) for the modeling of the solid phase
and a pore-scale finite volume (PFV) formulation for the flow of an
incompressible pore fluid. The coupling equations are derived and contrasted
against the equations of conventional poroelasticity. An analogy is found
between the DEM-PFV coupling and Biot's theory in the limit case of
incompressible phases. The simulation of an oedometer test validates the
coupling scheme and demonstrates the ability of the model to capture strong
poromechanical effects. A detailed analysis of microscale strain and stress
confirms the analogy with poroelasticity. An immersed deposition problem is
finally simulated and shows the potential of the method to handle phase
transitions.Comment: accepted in Int. Journal for Numerical and Analytical Methods in
Geomechanic
Comparison of macro- and microscopic solutions of the Riemann problem I. Supercritical shock tube and expansion into vacuum
The Riemann problem is a fundamental concept in the development of numerical methods for the macroscopic flow equations. It allows the resolution of discontinuities in the solution, such as shock waves, and provides a powerful tool for the construction of numerical flux functions. A natural extension of the Riemann problem involves two phases, a liquid and a vapour phase which undergo phase change at the material boundary. For this problem, we aim at a comparison with the macroscopic solution from molecular dynamics simulations. In this work, as a first step, the macroscopic solution of two important Riemann problem scenarios, the supercritical shock tube and the expansion into vacuum, were compared to microscopic solutions produced by molecular dynamics simulations. High fidelity equations of state were used to accurately approximate the material behaviour of the model fluid. The results of both scenarios compare almost perfect with each other. During the vacuum expansion, the fluid obtained a state of non-equilibrium, where the microscopic and macroscopic solutions start to diverge. A limiting case was shown, where liquid droplets appeared in the expansion fan, which was approximated by the macroscopic solution, assuming an undercooled vapour.DFG, 84292822, TRR 75: Tropfendynamische Prozesse unter extremen Umgebungsbedingunge
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