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The purification of polluted water

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Jasmine Zhang

on 27 November 2013

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Transcript of The purification of polluted water

Electro-assisted methods for water purification
Advantages
very high electrochemical efficiency
reduces the possibility of volatilization and the discharge of unreacted waste.
The waste treatment can be terminated within seconds
Flotation
Flotation is used to separate solid or dispersed liquids from a liquid phase.
The separation is effected by introducing fine gas bubbles, usually air, into the system.
Adsorption
Adsorption is usually used to remove organic impurities, nondegradable organics, heavy metals from raw water.
The most commonly used adsorbent is activated carbon.
Adsorption is a physical phenomena by which molecules of the solid are attached on the surface of adsorbent materials.


Electro-assisted methods
Flotation
Absorption
Ion exchange
Membrane process

Introduction
What is water purification
The undesirable parts in polluted water
Requirements for drinking water
Methods used for water purification

Traditional methods of water purification
Coagulation
Rapid mixing
Flocculation
Sedimentation
Filtration
Disinfection

The purification of polluted water
Coagulation
Definition & purpose
Feature
Reagent
Methods
Qian Zhang(Jasmine), Siyuan Wu (Max), Xiaofang Zhai(Savannah)
Sedimentation
Principle & Purpose
Factors affect the efficiency of sedimentation
Four distinct types of sedimentation
Conventional sedimentation tanks
Flocculation
Definition & purpose
Principles & mechanisms of flocculation
Feature
Reagent
Two main modes of process operations
Three types of flocculators
Filtration
Disinfection
Definition
Destabilization and initial coalescing of colloidal partical specifically hydrophobic colloids.
Purpose
Form colloids
Feature
Quickly
Reagent Coagulant
Aluminum sulfate ( alum )
Ferric sulfate
Ferric chloride
Polymerized aluminum
Iron salt
Organic polymer
Undesirable parts in polluted water
Chemicals: heavy metal(Cd,Hg,Pd)
Biological contaminants: parasites, bacteria, algae, viruses, fungi
Suspended solid and gas:colloids,SO2,NH3
Principle
Electrochemistry deals with the charge transfer at the interface between an electrically conductive (or semi-conductive) material and an ionic conductor (e.g. liquids, melts or solid electrolytes) as well as with the reactions within the electrolytes and the resulting equilibrium.
Classification

Anodic oxidation: direct oxidation, indirect oxidation
Membrane-assisted methods
Electrochemically generated species for disinfection
Example of some reaction
Requirements for drinking water
Free from pathogenic organisms
Clear
Not saline
Free from offensive taste or smell
Free from compounds that may have adverse effects on human health.
Methods used for water purification
Physical processes: filtration (fast sand filter), sedimentation, distillation(boiling)
Biological processes: slow sand filter, biologically active carbon
Chemical processes: use some chemical compounds to disinfection and flocculation, pH adjustment
Electromagnetic radiation: ultraviolet light

Aluminum sulfate:
Ferric sulfate:
Direct oxidation
Water purification is the process of removing undesirable substances from polluted water
Method
STEP 1: Adjust pH value


STEP 2: Add coagulant


STEP 3: Rapid Mixing
Rapid mixing
Definition & Purpose
Principle
Influence factor of rapid mixing
Two kinds of mixing device

Definition &  Purpose
To disperse coagulant chemicals uniformly throughout the raw water as rapidly as possible in order to destabilize the colloidal particles present in the raw water
Indirect oxidation
The organic pollutants are destroyed by an electrontransfer agent (eg.silver ions )
How soon?
the contact between coagulant and colloidal particles occur before the hydrolysis reaction with alkalinity completed
Cause water agitated by using mixing devices.
Add the coagulant at the most turbulent zone.
Principle of operation
Two ways mainly effect the rapid mixing
Hydraulically
Mechanically
Two types of mixing device
Hydraulic mixer
Mechanical mixer
Advantages & Disadvantages
Hydraulically: economical
Mechanical: flexible
Application
anion exchange membrane
Hydraulically: developing area
Mechanical: used extensively
Cation exchange membrane
Electrochemically generated species for disinfection
Definition
The longer term process of forming larger particles from small particles formed by coagulation
Water treatment in Region of Waterloo
chloride and hypochlorite
Principles & mechanisms of flocculation
Aggregation result from random Brownian movement of fluid molecules.
Aggregation induced by velocity gradient in the fluid
Different settling, where flocculation is due to the different rates of settling of partial of different size.
Two main modes of process operations
Hydraulic flocculators: hydraulic energy provide the necessary velocity gradient (widely used in developing country)
Mechanical flocculators: the velocity gradient is created by mechanical power input
Three types of flocculator
Baffled channel flocculator
Gravel bed flocculator
Alabama-type floccultor
Ion exchange
process of exchanging certain cations and anions in the water.
Sedimentation is a solid-liquid process, making use of the gravitational settling principle.
Remove settable solids
Principle & Purpose
Factors affect the efficiency of sedimentation
Loading rate
Water quality
Particle/floc size and weight
Tank geometry
Four distinct types of sedimentation
Class-1:settling of dilute suspensions that have little or no tendency to flocculation
Class-2 settling of dilute suspensions with flocculation taking place during the settling process
Zone settling:particle settle as a mass and not as discrete particles. interparticle forces hold the particle in a fixed position,so that the settlement take place in a zone
Compression settling:settlement takes place over the resistance provided by the compacting mass resulting from particles that are in contact with each other
Conventional sedimentation tank
Schematic diagram of a rectangular sedimentation tank
Schematic diagram of a circular sedimentation tank
Definition & purpose
Two mainly types of filtration
Comparison between slow sand filtration and fast sand filtration
Operation which is used to separating of water and other undesirable substance by passing through some area.
After separating most floc, the water is filtered as the final step to remove remaining suspended particles and unsettled floc.
Definition & Purpose
Water purification progress
in Region of Waterloo
Two mainly types of filtration
Slow sand filtration
Fast sand filtration
Comparison between the two types
Definition & purpose
Principle
Main methods of disinfection
Definition & purpose
Removed pathogens, particularly viruses, and other microorganism that may cause disease.
Principle
It can be carried out both physical and chemical means, while chemical means has been used extensively.
Main methods of disinfection
Chlorination
Chloramine
Ozone
UV Radiation
Membrane process
New technologies of water treatment
Hybrid process
Water purification in waterloo
MF (or UF) is coupled with a chemical coagulant to improve the removal efficiency.
References
C. Binnie & M. Kimber, (2009). Basic water treatment (4th,ed.). London, UK: Thomas
Telford Limited.
C.G. Darwin (1987). Handbook of water purification(2nd ,ed.). Chichester, England:
Ellis Horwood Limited.
J.Grimm, D.Bessarabov & R.Sanderson (March,1998) Review of electro-assisted methods for water purification. Desalination 115 (1998)285-294.
S.Vigneswaran & C.Visvanathan (1995). Water treatment processes: simple options.
New York, US: CRC Press.
Region of waterloo.(2010). Retrieved from http://www.regionofwaterloo.ca/en/aboutTheEnvironment/QualityTreatment2.asp



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