Mass transport in aquifers:

1. Presentation On
Mass transport in aquifers: Advection, Dispersion,
Diffusion, Sorption, Retardation, Biodegradation
Course Name: Hydrology & Hydrogeology
Course code: ESE-2101
Presented to:
Professor Dr. Ashraf Ali Seddique
Chairman
Dept. of Environmental Science & Engineering
Jatiya Kabi Kazi Nazrul Islam University.
Presented by:
Md. Maksudul Amin Talukder
ID No: 20103402
Session : 2019-20
Department of Environmental Science & Engineering.
Jatiya Kabi Kazi Nazrul Islam University.

2. Transportation: The movement of material across the Earth's surface by water, wind, ice or
gravity.
Mass Transport: Mass transfer is the net movement of
mass from one location, usually meaning stream, phase,
fraction or component, to another.
Mass moves and distributes by:
 Physical process (Advection,
Dispersion).
 Chemical process (Reactions,
Diffusion).
 Biological process(Re-
distributions of mass
forms,Diffusion).

3. Advection: Mass transport due simply to the flow of
water in which the mass is dissolved. Transport of pollutants
in a river by bulk water flow downstream is an example of
advection. This movement can be viewed as the advection of
fluid across a coordinate surface.
Dispersion: It is a process of mixing that causes a zone
of mixing to develop between a fluid of one composition that
is adjacent to or being displaced by a fluid with a different
composition.
Diffusion: Diffusion is the movement of particles from an
area of higher concentration to one of lower concentration. It
is powered by the motion of particles which creates collisions
Types
of Mass
Transpor
t Process

4. Advection
 It’s the main process.
 Mass carried forward with groundwater
flow.
 Mass transport rate depends on the local
concentration and the specific discharge
(volume flux; Darcy velocity).
 Significant interest is generally placed
on distribution of subsurface flow paths
and travel times along these paths (see
textbook for analytical treatment of flow
paths –streamlines – and travel times).
Direction and rate of transport = direction
and rate of groundwater flow

5. Advection
a) Advection alone
b) Advection + Dispersion

6. Diffusion
Diffusion is the movement of a
solute or a gas from an area of
high concentration to an area
of low concentration through
air or water.
It occurs across a
concentration gradient.
Molecular diffusion: Mixing
caused by random molecular
motions due to thermal
kinetic energy of the solute.
Coefficient is larger in gases
than in liquids, in liquids than
solids.

7. Dispersion
 Dispersion is an irreversible phenomenon by
which a miscible liquid ( the tracer) that is
introduced toa flow system spreads gradually to
occupy an increasing portion of the flow region.
 Causes a zone of mixing to develop between a
fluid of one composition that is adjacent to or
being displaced by a fluid with a different
composition.
 Hydrodynamic dispersion is caused by velocity
variations within each pore channel and from
one channel to another.
Dispersion spreads mass beyond the
region it normally would occupy due to
advection alone.

8. Dispersion occurs due to two process:
1.Diffusion: Mass transport by concentration gradient.
2.Molecular Dispersion: Mixing due to local differences around some mean velocity of flow
1.
Diffusion
2.
Molecular Disperation

9. Sorption
 Precipitation of surface coating that
is compositionally different from that
of the underlying host grain.
 Incorporation of ions into crystal
structure of the mineral by processes
of diffusion or dissolution and
reprecipitation(also called
absorption).
 Accumulation of a substance
between a solid surface and the
solution.

10. Sorption
It also includes absorption. Forces involved in Absorption:
Physical Forces( distance and valance)
1. Van der Waals ( Weak electrostatic forces between nonpolar molecules due to
temporary dipole moment).
i. Electrostatic complexes (ion exchange).
Chemical Forces (Electron configuration;
breaking/making bonds)
1. Inner sphere complexation ( ligand exchange , covalent/ionic bonding).
2. Chromatography

11. Biodegradation
 Process by which substances are
broken down by the environmental
effects and by the living organisms.
 Biodegradation is the disintegration of
materials by Fungi, bacteria, or other
biological means.
 Organic material can be degraded by
aerobically or an anaerobically.
 Biodegradable matter is generally
organic material that provides
nutrition for microorganisms.

13. Importance of Biodegradation
Biodegradation is nature's way of recycling wastes, or breaking
down organic matter into nutrients that can be used by other
organisms. "Degradation" means decay, and the "bio-" prefix
means that the decay is carried out by a huge assortment of
bacteria, fungi, insects, worms, and other organisms that eat dead
material and recycle it into new forms.
In nature, there is no waste because everything gets recycled. The
waste products from one organism become the food for others,
providing nutrients and energy while breaking down the waste
organic matter.
By harnessing these natural forces of biodegradation, people can
reduce wastes and clean up some types of environmental
contaminants.