| Author | Chang, Jing Song |
| Call Number | AIT Diss. no. EV-89-02 |
| Subject(s) | Filters and filtration--Mathematical models
|
| Note | A doctoral dissertation submitted in partial fulfilment of the
requirements for the degree of Doctor of Engineering |
| Publisher | Asian Institute of Technology |
| Abstract | Most of the mathematical models in deep bed filtration have been
developed for predicting clean bed filter efficiency and efficiency
during ripening period of filtration. Most of them do not take into
account the size distribution of particles in suspension and pores of
granular medium. The effect of chemistry of liquid on transient behaviour
of filtration has not been studied in detail. In this research therefore,
the above aspects have been included in the mathematical models and the
models were tested with experimental results.
The O'MELIA-ALI model for ripening stage of filtration has been
modified to describe the entire cycle of filtration. Two mathematical
models developed based on two different concepts to describe the entire
cycle of filtration were tested with experimental results. The first
model was based on the detachment of deposited particles. The degree of
detachment was assumed proportional to the hydraulic gradient and the
number of particles already retained on the filter grain. The second
model was based on the concept that there exists a maximum limit of
particle deposition on the filter grain. It was found that the first model
can simulate better than second model can. This may be an experimental
proof for the concept of detachment which is now agreed by most of the
researchers. The ultimate specific deposit was estimated experimentally
for a wide range of filtration velocities to give a qualitative
justification on the applicability range of the proposed models.
A mathematical model was proposed incorporating one of the important
parameters, the size distribution of particles in suspension, which is
the case in real situation. The improvement of removal efficiency of
finer particles in the presence of coarser particles in suspension is
explained based on the assumption that some of the retained coarser
particles in addition to retained finer particles act as "particle
collectors" in the removal of finer particles. The concept of detachment
of retained particles due to hydraulic gradient is also incorporated to
describe the decrease in removal efficiency during the filter
breakthrough period. The four coefficients appearing in this
mathematical model were determined for different operating conditions
using experimental results obtained from filtration of suspension of
uniform pollen grains. Although these model coefficients were different
for different operating conditions, a uniform trend was observed in the
variation with operating conditions. These model coefficients calculated
for suspensions with single size particles were then used to predict the
removal efficiencies when particles of different sizes are in mixture in
suspension. Some data collected from Antwerp Water Works, Belgium, were
used to verify the assumption made in the mode l formulation.
Another important parameter of filtration, the pore size
distribution has not been taken into account in the existing mathematical
models. In this study, the effect of pore size distribution has been
studied theoretically. For this, the O'MELIA - ALI model which falls in
the category of external flow model was modified to the internal flow
model and this modified model was then incorporated with the model
developed using Effective Medium Approximation (EMA) approach to
investigate the effect of pore size distribution in deep bed filtration.
Six different pore size distributions were assumed and the filter
performances were simulated for these cases to get the preliminary idea
on the effect of pore size distribution in deep bed filtration.
The removal efficiency of particles in deep bed filtration depends
both on transport and attachment mechanisms of particles. The particle
attachment mechanisms depend mainly on chemical characteristics of
aqueous phase, suspended particles and filter media. In this study, the
effect of ionic strength on the particle removal efficiency during
ripening period was studied experimentally. The removal efficiencies
were related to ionic strength and zeta potential. The clean filter bed
efficiency and removal efficiency during the ripening period on different
ionic strength were quantitatively related to the two model coefficients
appearing in O'MELIA - ALI model. These model coefficients represent the
clean bed filter efficiency and ripening stage filter efficiency
respectively. An observed uniform trend in the variation of these
coefficients with ionic strength of suspension showed the importance of
quantitative incorporation of chemical effects in filtration mathematical
models. |
| Year | 1989 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Vigneswaran, S.; |
| Examination Committee(s) | I, Fude;Chongrak Polprasert;Gupta, Ashim Das;Huynh, Ngoc Phien;Ives, K.J.; |
| Scholarship Donor(s) | Japanese Government; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1989 |