MASS TRANSPORT IN AQUIFERS ADVECTION,DISPERSION, DIFFUSION,SORPTION AND BIODEGRADATION

1. Presented by:
Md. Eftekharul Alam Emon
Roll: 19103413 Session: 2018-19
Department of Environmental Science and
Engineering
Presentation on
“MASS TRANSPORT IN
AQUIFERS:
ADVECTION,DISPERSION,
DIFFUSION,SORPTION
AND BIODEGRADATION”

2. Introduction
 Mass Transport: Mass transfer is the net movement of mass from one
location, usually meaning stream, phase, fraction or component, to
another.
❑ Delivery/distribution problems
 Dissolved mass: Ions+ molecules
 Natural or contaminated: Source
Mass moves and distributes by:
 Physical process (Advection, Dispersion)
 Chemical process (Reactions, Diffusion)
 Biological process(Redistributions of mass forms,Diffusion)

3. 1
Advection
• Mass transport due simply to the flow of water in which the
mass is dissolved
2
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
3
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

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. Mass spreading by Advection in a shallow unconfined aquifer

7. 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

8. 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

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

10. 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

11. Sorption

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

13. 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

14. Micro
organisms
Environmental
condition
Biodegradation
Compounds
to degrade
Factors affecting biodegradation
➢Presence of Oxygen and
nutrient
➢Abiotic factors- Temperature,
pH, salinity
➢Presence of light and water
➢Predation
➢Synergism

15. 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

16. THE END