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Back up Of hw

• Topic No4
• J.H.Patel
• 2012

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Topic No4 Volume and Strength Reduction ,
Equalization and Proportioning(10Lecture 15 marks)
4.1Removal Of Suspended solids, - Sedimentation,
, floatation and screening 4.2 Removal of Organic
Solids by -Lagooning,, activated sludge
treatment, aeration, trickling filtration, wet
combustion, anaerobic digestion, well injection,
foam phase separation, Pure Oxygen treatment
etc. 4.3 Removal of inorganic dissolved solids
by- evaporation, dialysis, ion exchange and
reverse Osmosis 4.4 treatment and disposal of
Sludge solids- Aerobic , Anaerobic digestion,
vacuum filtration, drying beds, drying and
incineration, sanitary land fills-
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Physical Treatment Methods
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As per syllabus 4.1Removal Of Suspended solids,
- Sedimentation, , floatation and screening
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screening
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Screening
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floatation
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Oils and grease removal
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Floatation and sedimentation
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The API separator is a gravity separation device
designed by using Stokes Law to define the rise
velocity of oil droplets based on their density
and size. The design is based on the specific
gravity difference between the oil and the
wastewater because that difference is much
smaller than the specific gravity difference
between the suspended solids and water. The
suspended solids settles to the bottom of the
separator as a sediment layer, the oil rises to
top of the separator and the cleansed wastewater
is the middle layer between the oil layer and the
solids
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Parallel plate separators are similar to API
separators but they include tilted parallel plate
assemblies (also known as parallel packs). The
parallel plates provide more surface for
suspended oil droplets to coalesce into larger
globules. Such separators still depend upon the
specific gravity between the suspended oil and
the water. However, the parallel plates enhance
the degree of oil-water separation. The result is
that a parallel plate separator requires
significantly less space than a conventional API
separator to achieve the same degree of
separation
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Flotation Dissolved Air Flotation
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SEDIMENTATION OR GRAVITY SETTLEMENT
A VERY SIMPLE PROCESS IN WHICH WATER IS ALLOWED
TO REMAIN IN CALM OR QUISCENT CONDITION. ALL
IMPURITIES HEAVIER specific gravity more than 1
WILL SETTLE AT BOTTOM. ALL IMPURITIES OF TYPE 1
WILL SETTLE LIKE THIS
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•                                                 
                                                    
                                                    
                        
• Discrete Particle Settling

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Zone Inlet Outlet Sludge Settling
Function Even horizontal and vertical distribution of flow Point discharge from even flow Trap and remove settled solids Allow particles to settle
Device(s) Baffles and weirs Baffles and weirs Scrappers Gravitational forces
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Types of BasinsThree common types of
sedimentation basins are shown below
Rectangular basins are the simplest design,
allowing water to flow horizontally through a
long tank.  This type of basin is usually found
in large-scale water treatment plants. 
Rectangular basins have a variety of advantages -
predictability, cost-effectiveness, and low
maintenance.  In addition, rectangular basins are
the least likely to short-circuit, especially if
the length is at least twice the width.  A
disadvantage of rectangular basins is the large
amount of land area required.
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Double-deck rectangular basins are essentially
two rectangular sedimentation basins stacked one
atop the other.  This type of basin conserves
land area, but has higher operation and
maintenance costs than a one-level rectangular
basin.   
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Square or circular sedimentation basins with
horizontal flow are often known as clarifiers. 
This type of basin is likely to have
short-circuiting problems. 
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A fourth type of sedimentation basin is more
complex.  Solids-contact clarifiers, also known
as upflow solids-contact clarifiers or upflow
sludge-blanket clarifiers combine coagulation,
flocculation, and sedimentation within a single
basin.  Solids-contact clarifiers are often found
in packaged plants and in cold climates where
sedimentation must occur indoors.  This type of
clarifier is also often used in softening
operations. 
                                                            
                                                            
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Rectangular Clarifier (Inlet End)
                                                
                                                  
                                                  
                                                  
                 Rectangular Clarifier
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Rectangular Clarifier (Outlet End)
                                                  
                                                  
                                                  
                                                  
                              Circular Clarifier
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Circular Clarifier                              
                                                  
                                                  
                                                  
                                   
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Advantages Disadvantages Comments
Simple, low cost technology to reduce settable solids and perhaps some microbes for water Only settable solids, such as sands, silts and larger microbes settle efficiently clays and smaller microbes do not settle only moderate to low microbe reductions Can be applied to large and small volumes of water using commonly available water collection and storage vessels settled material must be removed and vessels cleaned regularly
Removal of settable solids can reduce turbidities and make the water more amenable to other treatment methods to reduce microbes In some waters solids are not efficiently removed by settling and alternative methods of removing solids are required Reduced levels of solids (turbidity) improves penetration of UV radiation (from sunlight), decreases oxidant (e.g., chlorine) demand, decreases solids-associated pathogens
Recommended as a simple pre-treatment of household water prior to application of other treatments to reduce microbes Unreliable method to reduce pathogens solids are not efficiently removed by settling from some waters can be labor-intensive Pre-treatment to remove solids (turbidity) is recommended for turbid waters prior to solar or chemical disinfection
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Sedimentation Tube Settlers
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4.2 Removal of Organic Solids by -Lagooning,,
activated sludge treatment, aeration, trickling
filtration, wet combustion, anaerobic digestion,
well injection, foam phase separation, Pure
Oxygen treatment etc. Removal of Organic Solids
by -Lagooning,, activated sludge treatment,
aeration, trickling filtration, wet combustion,
anaerobic digestion, well injection, foam phase
separation, Pure Oxygen treatment etc.
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Lgooning
Symbiosis of algae-bacteria in lagoon
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Topic of syllabus trickling filtration activated
sludge treatment, aeration,, Slime Growth
Processes (Trickling Filter, ) In the slime
growth process, pH, concentration of food and
oxygen are the big control factors.  In
microbiology, with the yeast organisms greater
concentration of food restricted, the growth,
enzyme saturation, space and waste build-up were
the controlling factors of concentration.
Increasing Recirculation decreases concentration
of food, but allows excessive cooling in cold
weather.  Increasing recirculation increases the
amount of oxygen in the water and can help in the
removal of B.O.D.
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Trickling Filter
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• Tank is filled with solid media
• Rocks
• Plastic packing material
• Bacteria grow on surface of media
• Wastewater is trickled over media, at top of tank
  
• As water trickles through media, bacteria degrade
  BOD
• Bacteria eventually die, fall off of media
  surface
• Filter is open to atmosphere, air flows naturally
  through media
• Treated water leaves bottom of tank, flows into
  secondary clarifier
• Bacterial cells settle, removed from clarifier as
  sludge
• Some water is recycled to the filter, to maintain
  moist conditions

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Trickling Filter System                        
                                                  
                                              
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Trickling Filter Process                       
                                                  
                      
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Bacteria Removal                               
      
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As bacteria grow they become too heavy to cling
to the media and are swept away by the water to
be thrown out as sludge, leaving room on the
media for new bacteria growth.
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Trickling Filter                                
                                           
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Normally there are two modes of TF system
popular single-stage and two- (or separate-)
stage. Single-stage Carbon oxidation and
nitrification take place in a single TF unit.
Two- (separate-) stage Reduction of organic
material occurs in the first treatment stage, and
nitrification occurs in the second stage.
Although numerous types and combinations of
treatment units exist, in general, a single-stage
TF has to remove organic material in the upper
portion of the unit and provide nitrifying
bacteria for nitrification in the lower part.
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RECOMMENDED DESIGN CRITERIA FOR TRICKLING
FILTERS A.    General ConsiderationsB.    Design
BasisC.    Hydraulic Considerations D.   
MediaE.    Underdrainage SystemF.    Special
Design Considerations
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A.    General Considerations Trickling filters
may be used where the treatment of wastewater is
amenable to aerobic biological treatment
processes. Trickling filters shall be preceded by
primary clarifiers equipped with scum and grease
collecting devices, or other suitable
pretreatment facilities. If fine screening is
provided the screen size shall have from 0.03 to
0.06 inch openings. Bar screens and/or
communitors are not suitable as the sole means of
primary treatment. Filters shall be designed to
provide for reduction in carbonaceous and/or
nitrogenous oxygen demand in accordance with the
Secondary Treatment requirements Water Quality
Standards, or to effectively reduce organic
loading on the downstream treatment processes.
Information as well as all functional design
calculations used in sizing trickling filter
facilities shall be included in an engineer's
report with the facilities plan, plans and
specifications and/or be submitted separately for
review and approval. This report shall include
the following
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• Influent wastewater characteristics
• Temperature range of applied wastewater
• Pretreatment processes
• Type of filter, i.e., single stage or multi-
  stage
• Hydraulic and organic loadings applied to the
  filter
• Hydraulic factors involving proper distribution
  computations
• Recirculation rate and piping system
• Filter beds-volume, area and depth
• Media-type, specific weight, void space
• Underdrainage and ventilation systems
• Equations utilized for treatment efficiency
  computations and
• Degree of treatment anticipated.

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• D.    Media
• The media may be crushed rock, slag, redwood, or
  specially manufactured artificial material. The
  media should be durable, resistant to spalling or
  flaking and be insoluble in the wastewater being
  treated. The material should be free of fine
  particles, grease and oil and also should be
  properly screened and/or washed to remove dust
  and dirt before placement. Slag media shall be
  free from iron.
• If rock media is used, the top 18 inches shall
  have a loss by the 20-cycle, sodium sulfate
  soundness test of not more than 10 percent. The
  balance of the media shall pass a 10-cycle test
  using the same criteria. All tests shall be
  conducted as prescribed by ASCE Manual of
  Engineering Practice, No. 13. Manufactured media
  shall be resistant to ultraviolet degradation,
  disintegration, erosion, aging, all common acids
  and alkalies, organic compounds, and fungus and
  biological attack. Such media shall be capable of
  supporting a person's weight or a suitable access
  walkway shall be provided to allow for
  distributor maintenance.

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• . 3.Rock and/or slag filter media for standard-
  rate filters shall be at least 5 feet but not
  more than 10 feet in depth above the underdrains.
  The filter media for high-rate filters shall be
  at least 3 feet but not more than 7 feet in depth
  above the underdrains. Manufactured filter media
  should be at least 10 feet deep to provide
  adequate contact time with the wastewater.
  Manufactured filter media depths shall not exceed
  30 feet except where special construction is
  justified by extensive pilot studies or
  additional proven engineering data. The
  suitability of the manufactured media may be
  evaluated on the basis of full scale experience
  with other plants treating similar wastes and
  loadings or through actual use of a pilot plant
  on site. Super-rate trickling filters must have
  manufactured media.
• 4.Rock, slag and similar media shall not contain
  more than 5 percent by weight of pieces whose
  longest dimension is three times the least
  dimension. They shall be free from thin,
  elongated and flat pieces, dust, clay, sand or
  fine material and shall conform to the following
  size and grading when mechanically graded over
  vibrating screen with square openings.

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Passing 4-1/2 inch screen - 100 by
weight Retained on 3 inch screen - 95-100 by
weight Passing 2 inch screen - 0-2 by
weight Passing 1 inch screen - 0-1 by weight If
hand picked field stone are used, the dimensions
shall be from 2 1/2 to 5 inches in diameter.
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4.Material delivered to the filter site shall be
stored on wood-planked or other approved clean,
hard- surfaced areas. All material shall be
rehandled at the filter site and no material
shall be dumped directly into the filter. Crushed
rock, slag and similar media shall be washed and
rescreened or forked at the filter site to remove
all fines. Such material shall be placed by hand
to a depth of 12 inches above the tile
underdrains. The remainder of material may be
placed by means of belt conveyors or equally
effective methods approved by the engineer. All
material shall be carefully placed so as not to
damage the underdrains. Manufactured media shall
be handled and placed as approved by the
engineer. Trucks, tractors, and other heavy
equipment shall not be driven over the filter
during or after construction. 5.The required
volumes of rock or slag media filters shall be
based upon pilot testing with the particular
wastewater or any of the various empirical design
equations that have been verified through actual
full scale experience. Such calculations must be
submitted if pilot testing is not utilized. Pilot
testing is recommended to verify performance
predictions based upon the various design
equations, particularly when significant amounts
of industrial wastes are present.
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• .    Underdrainage System
• Subfloor The floor of the filter shall be able to
  support the underdrainage system, the filter
  media, and the water load. A minimum gradient of
  1 percent shall be provided for the subfloor
  which slopes to a collection channel.
• Filter Block Precast filter blocks, made of
  vitrified clay or concrete should be used. The
  underdrainage system shall cover the entire floor
  of the filter. Inlet openings of the filter
  blocks into the underdrains shall have an
  unsubmerged gross combined area equal to at least
  20 percent of the surface area of the filter.
  Underdrains shall have a minimum slope of 1
  percent to a collection channel. Redwood timbers
  resting on concrete sleepers may be used in the
  place of filter blocks, when stacked redwood
  media is used.
• Collection Channel The collection channels
  (central or peripheral) shall provide capacity to
  carry the flow from the underdrains and permit
  free passage of air to the underdrains for
  ventilation. Channels should be sloped to provide
  a minimum flow velocity of 2 feet per second. The
  water level in the collection channel should be
  below the bottom of the filter blocks during peak
  flow conditions. Drains, channels and pipe shall
  be designed to have 50 percent of their
  cross-sectional area unsubmerged at peak hourly
  flows.

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5.Ventilation All trickling filters shall be
provided with ventilation openings to the
underdrains. Ventilation openings will be
provided with dampers or other adjustable devices
to permit adjustment of the ventilation rates.
Natural draft ventilation openings shall have a
minimum gross area of 4 square feet per 1,000
square feet of filter area. Forced ventilation
providing a mimimum air flow of 1 cubic foot per
minute per square foot (1 cfm/ft2) shall be
provided for covered filters and deep
manufactured media filters. 6.Flushing
Provision shall be made for flushing the
underdrains such as, adjustable ventilation
ports. In small filters, use of a peripheral head
channel with vertical vents is acceptable for
flushing purposes. Inspection facilities shall be
provided.
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• .    Special Design Considerations
• Flooding Appropriate valves, sluice gates, walls
  and other structures shall be provided to permit
  flooding of filters comprised of rock or slag
  media.
• Climatic Protection
• The surrounding wall shall extend at least 4 feet
  above the media of all uncovered filters to
  maximize the containment of windblown spray and
  reduce heat losses.
• Other protection such as covers, wind screens or
  windbreaks shall be provided to maintain
  operation and treatment efficiencies when
  climatic conditions are expected to result in
  icing problems.
•    

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• .3    Maintenance
• All distribution devices, underdrains, channels
  and pipes shall be installed so that they may be
  properly maintained, flushed or drained. Access
  shall be provided around the periphery of the
  underdrain system to allow flushing of the
  underdrains.
• Suitable and safe access shall be provided to the
  top of the structure for inspection and
  maintenance.
• Treatment operators should be supplied with a
  complete set of operational instructions,
  including maintenance schedules, tools and spare
  parts as may be necessary.
•     4.    Structure
• The walls, floor and underdrain system should be
  constructed of concrete, concrete blocks,
  vitrified clay or other approved material for
  containment of wastewater.
• The wall structure shall be designed such that a
  cover, dome or other means may be easily
  installed over the trickling filter at a later
  date.
• Enclosed structures shall be well lighted and
  ventilated.
• Electrical equipment and controls shall meet the
  requirements of the National Electrical Code.

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• Activated Sludge Principles
• Wastewater is aerated in a tank
• Bacteria are encouraged to grow by providing
• Oxygen
• Food (BOD)
• Correct temperature
• Time

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• As bacteria consume BOD, they grow and multiply
• Treated wastewater flows into secondary
  clarifier
• Bacterial cells settle, removed from clarifier
  as sludge
• Part of sludge is recycled back to activated
  sludge tank, to maintain bacteria population
• Remainder of sludge is wasted

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The activated sludge process is the biological
process by which non-settleable substances
occurring in dissolved and colloidal forms are
converted into settleable sludge which is removed
from the liquid carrier (water). At a plant the
activated sludge is settled out along with the
suspended solids present in the wastewater. The
activated sludge process provides one of the
highest degrees of treatment obtainable within
the limits of practical economy and present
knowledge of the art and science of waste
treatment.
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The process depends upon groups of
microorganisms, mainly bacteria, along with
protozoan, fungi and rotifers, being maintained
in contact with the organic matter in the waste
in an aerobic (oxygen containing) environment.
Many forms of organic matter carried in the
wastewater serve as a food supply for these
microorganisms. The mass of microorganisms
present in the system is referred to as
biological solids or mixed liquor suspended
solids (MLSS). In practice, MLSS represents all
suspended matter in the activated sludge system
including inert matter, non-biological organic
matter, as well as active microorganisms. The
basic reactions involve the breakdown of the
organic matter (represented by 5 day Biochemical
Oxygen Demand - BOD5) and the formation of cell
mass (activated sludge) and by-products (carbon
dioxide and water).
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The basic purpose of the activated sludge system
is to establish and maintain a viable population
of microorganisms by supplying food (BOD5) and
the proper environment. In the proper environment
the microorganisms convert the soluble and
colloidal material present in the wastewater into
new cells (activated sludge) and end products
(CO2 and water). During their life cycle, the
microorganisms undergo a continuously changing
cycle of growth and decline. Figure in next slide
shows an ideal growth curve for microorganisms
growing in a batch activated sludge system. A
batch system is one in which a specific volume is
placed under aeration in a container with no
inlet or outlet therefore there is no flow
through the system. A batch system is contrasted
to a continuous system in which new liquid is
continuously added to the system and an equal
volume is withdrawn.
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Schematic of activated sludge unit
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ACTIVATED SLUDGE AERATION TANK
                                                
                          
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Activated Sludge MicroorganismsRoutine
microscopic analysis of biological treatment
systems provides information that is unavailable
through other means. The microscope reveals that
bubbling tankful of dark liquid is an amazing
habitat teaming with life. By examining the
tiniest creatures that inhabit every drop, much
can be learned about the treatment environment.
You may be unimpressed by the shear numbers of
protozoa and metazoa organisms present, typically
4-40 million per gallon. But, the complexity of
the single-celled Euplotes patella, with its
specialized feeding and locomotion bristles,
water cavities, gullet, food pockets, and dual
nuclei, will surely grab your interest. There
are many who have a great desire to learn about
microorganisms and their roles. This web site is
Engitech's attempt to share the wealth of current
information, get your feedback, and gather more
information. Please comment or question at will.
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Aerobic Organisms Under a microscope at 400
power                                       
                                                  
 
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Rotifers are the larger microorganisms in old
sludge, a few are in the right age sludge, and
none are in the young sludge.     
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Anaerobic Organisms Under a microscope at 400
power    All are a single cell type
                      Good Settleability 
The good settleability comes from the sticky
enzymes that help hold them together. 
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The floc graphic shows where, in relationship to
the biomass, the treatment organisms can be
found. Bacteria will be part of the floc or
present as free cells around the floc. Swimming
and gliding ciliates work the open water
engulfing bacteria or other prey. Stalked
ciliates attach to the biomass and vortex
suspended bacteria into their gullets, while
crawlers break bacteria loose from the floc
surface. Predators feed mostly on stalked and
swimming ciliates. The omnivores, such as most
rotifers, eat whatever is readily available,
while the worms feed on the floc or prey on
larger organisms.
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Microorganisms are directly affected by their
treatment environment. Changes in food, dissolved
oxygen, temperature, pH, total dissolved solids,
sludge age, presence of toxins, and other factors
create a dynamic environment for the treatment
organisms. Food (organic loading) regulates
microorganism numbers, diversity, and species
when other factors are not limiting. The relative
abundance and occurrence of organisms at
different loadings can reveal why some organisms
are present in large numbers while others are
absent.
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•  Wastewater is aerated in a tank
•   Bacteria are encouraged to grow by providing
• Oxygen
• Food (BOD)
• Correct temperature
• Time

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As bacteria consume BOD, they grow and multiply
  Treated wastewater flows into secondary
clarifier   Bacterial cells settle, removed
from clarifier as sludge   Part of sludge is
recycled back to activated sludge tank, to
maintain bacteria population   Remainder of
sludge is wasted
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Typical aeration tank with compressed air
aeration
                                                
       Aeration Methods
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• Mechanical aerators
• Turbines
• Surface aerators
•                                                
  
•  
•  

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Secondary Sedimentation                         
                                                  
                                                  
                                                
  
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4.3 Removal of inorganic dissolved solids by-
evaporation, dialysis, ion exchange and reverse
Osmosis
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Removal Of Solids
By evaporation
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Evaporation is the process by which molecules in
a liquid state (e.g. water) spontaneously become
gaseous (e.g. water vapor). It is the opposite of
condensation. Generally, evaporation can be seen
by the gradual disappearance of a liquid when
exposed to a significant volume of gas
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forms of matter-- solid, liquid, gas and plasma.
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1. Natural evaporators evaporation is caused by
   natural phenomena, such as solar energy or
   diffusion.
2. Direct contact evaporators evaporation is
   caused when the heating sourceis in contact with
   the liquid.
3. Indirect evaporators evaporation that conducts
   heat through physical barriers to the liquid.

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Natural evaporators Evaporation ponds are
artificial ponds with very large surface areas
that are designed to efficiently evaporate water
by sunlight and exposure to the ambient
temperatures. Evaporation ponds are used to
prevent pesticides, hazardous waste and salts
from any waste wastewater from contaminating the
water bodies they would flow into.
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• Evaporation is a proven technology for reducing
  aqueous wastes. By using active evaporation or
  heating to evaporate excess water, hazardous
  waste rinse water disposal or wastewater
  treatment can be minimized.

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Combustion vaporization Fuel droplets vaporize as
they receive heat by mixing with the hot gases in
the combustion chamber. Heat (energy) can also be
received by radiation from any hot refractory
wall of the combustion chamber.
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Electric Powered Wastewater Evaporators
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Pulse Drying Systems
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The burner is aerodynamically designed to produce
a pulsating air flow within the burner system
along with the heat valve. It is fossil fueled
and produces both pressure waves and heat from
one fuel source.
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• A single detonation cycle causes the pressure to
  rise in the pulse burner, shutting off the fuel
  flow and air supply momentarily and then exiting
  through the exhaust to the drying cone section.
  These pressure waves shear the bond that the
  water has with the solids and atomizes the water
  while the heat evaporates the water in less than
  one second. The evaporation rate is improved by
  increasing the heat and mass transfer rates so
  less tiem is required for drying.
• High moisture/low solids raw materials can be fed
  into the drying cone without the need for high
  pressure nozzles or rotary disks

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What is Forced Evaporation? Forced evaporation is
heating wastewater with a heat source, causing it
to boil and vaporize. The vapor is vented to the
atmosphere or recaptured through a
condenser/chiller. A volume reduction of up to
95 can be achieved, leaving only the residual
solids or sludge to disposed of. Evaporation
rates range from 12 litres per hour to over
460litres per hour depending on the size of the
evaporator, type of heat source and humidity
levels.
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• Components of Forced Evaporators
• There are four main components to most forced
  evaporation systems a heat source, a wastewater
  reservoir, a steam vapor evacuation system, and a
  control system.
• Heat source options include natural gas, liquid
  propane, electric or steam heat.
• The wastewater holding reservoir is usually
  insulated, and constructed of mild or stainless
  steel. Holding capacities range from 50
  gallons(200L) to over 500 gallons(2000L0.
• The steam evacuation system is a blower or inline
  draft-inducing fan. It is critical for maximum
  evaporation rates to remove the vapor quickly and
  efficiently.
• The control system operates the evaporator. This
  system controls the level of the liquids, the
  temperature, and provides a series of safety
  controls to prevent to high of temperature or
  over-flow conditions.

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• Types of Forced Evaporators
• The five most popular wastewater evaporation
  systems are listed below. There are other systems
  available but not presented in this paper.
• Under Floor Heating-This design transfers the
  heat from an insulated heat chamber through out
  the entire floor. The heat source options include
  natural gas, liquid propane, or electric heat.
• Immersion Tube-This type of design uses a heated
  tube under the solution as a heat exchanger. The
  heat source is usually natural gas, liquid
  propane or steam.
• Submerged Combustion-Submerged combustion is
  similar to an immersion tube. The difference is
  the small holes in the top of the heat bubble,
  allowing bubbles of hot gases to come in contact
  with the solution. The heat sources are usually
  natural gas or liquid propane.
• Direct Injection-Evaporation is achieved by
  spraying wastewater directly into a natural gas
  or liquid propane flame.
• Thermal Oxidation-This is also known as an
  incinerator. The thermal oxidizer burns the
  wastewater more than evaporating it. Operating
  temperatures are as high as 1400 degrees
  Fahrenheit.

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Removal Of Solids by
ion exchange
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In the ion-exchange method, used in many
households, hard water is effectively softened as
it is passed through a bed or tank of zeolite.
Zeolite is a complex of sodium aluminum silicate.
In this process sodium ions replace objectionable
calcium and magnesium ions, and the water is
thereby softened Na2 Zeolite(s) Ca2(ag)
?-CaZeolite(s) 2Na (aq)
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 Principle ions in solution are preferentially
exchanged over ions on solid medium. Solid media
Synthetic resins Cationic Anionic Natural
zeolites (only cationic)
130
Ion Exchange Process                           
                            
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Zeolites Aluminum silicate minerals Ca and Mg
captured, Na released Regenerated with salt
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The zeolite is regenerated by back-flushing with
concentrate sodium chloride solution, reversing
the foregoing reaction. The sodium ions that are
present in water softened either by chemical
precipitation or by the zeolite process are not
objectionable to most users of soft water.
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Synthetic Resins Made of synthetic organic
chemicals Ca and Mg captured, H or OH- released
Regenerated with an acid or base
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Softening Theory    Hardness removal Ca2
2Na R Û Ca R 2Na Mg2 2Na R Û Mg R
2Na Where R represents the cation exchange resin
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Regeneration (strong NaCl brine required) Ca R
2Na Û Ca2 2Na R Mg R 2Na Û Mg2 2Na
R  Wash (required after regeneration to rinse
off excess brine)
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In demineralization both cations and anions are
removed by a two-stage ion exchange system.
Special synthetic organic resins are used in the
ion-exchange beds. In the first stage metal
cations are replaced by hydrogen ions. In the
second stage anions are replaced by hydroxide
ions. The hydrogen and hydroxide ions react, and
essentially pure, mineral free water is produced.
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Demineralization Theory    Cation exchange Mz
zH R Û M Rz zH Where M represents the
cationic species removed from solution    Anion
exchange Ax- xR OH Û Rx M xOH-
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•  Regeneration
• Use strong mineral acid for cation exchange resin
  (H2SO4 or HCl)
• Use caustic soda( NaOH) solution to regenerate
  anion exchange resin

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 Selectivity coefficient For any exchange
reaction, such as M1 R M2 Û M2 R M1 A
corresponding selectivity, K, coefficient is
found
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The greater the selectivity oefficient, the
greater the preference for the ion exchanger K
increases with Ionic valence . Inverse of
hydrated ionic radius Degree of polarization
Inversely with degree of complexation in
solution
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Ion Exchange Selectivity (continued) Ions with
higher valence are typically preferred by the ion
exchange resin. For example a typical cationic
resin has the following preference Th4 gt Al3 gt
Ca2 gt Na Similarly, an anionic resin typically
has the following preference PO43- gt SO42- gt
Cl- Exceptions are also possible as in
the following case SO42- gt I- gt NO3- gt CrO42- gt
Br
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• Cationic Preference Series
• Ba2 gt Pb2 gt Sr2 gt Ca2 gt Ni2 gt Cd2 gt Cu2 gt
  Co2 gt Zn2 gt Mg2
• Ag gt Cs gt K gt NH4 gt H
• Anionic Preference Series
• SO42- gt I- gt NO3- gt HCrO4- gt Br- gt Cl- gt OH-

143
Ion-exchange
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• Mechanisms
• Movement of the ions from bulk of solution
• Diffusion of the ions through the laminar film
• Diffusion of the ions through the pores
• Ion exchange
• Diffusion of the exchanged ions outward
• Diffusion of the exchanged ions through laminar
  layer
• Movement of exchanged ion into bulk of solution
• Mechanisms 2 or 3 tend to control exchange rate

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Ion Exchange Batch Operation The wastewater is
placed in an agitated tank and added with the ion
exchange resins. After equilibrium has been
reached the resin is filtered and the water is
discharged. The resin in not typically regenerated
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Moving-Bed Ion Exchange Operation The resin and
the wastewater are moving countercurrently in the
column. The process is continuous. This means
that not only is the wastewater continuously fed
and removed from the column but also that fresh
resin is added and spent resin is removed. The
spent resin is then regenerated and fed back to
the column
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Fixed-Bed Ion Exchange Columns "Cocurrent"
Column "Countercurrent" Column Mixed Bed
Column Remark in any kind of fixed-bed operation
with a single phase passing through a column
(e.g., a wastewater over a bed of activated
carbon or ion exchange resins) the terms
cocurrent and countercurrent lose their meaning.
However, in ion exchange operations these terms
are used to indicate the direction of the
regenerating solution with respect to that of the
wastewater
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Cocurrent Fixed-Bed Ion Exchange Column The
term "cocurrent" indicates that the direction of
the flow of the regenerating solution (at the end
of a cycle) is the same as that of the incoming
wastewater (during normal operation) Cocurrent
operation, although not the most efficient, is
the most common because of its simple design and
operation Regeneration is conducted with 1 - 5
N acid or base solutions Typical column height
0.6 - 1.5 m Wastewater flow rate 8 - 40 bed
volumes/hr
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Countercurrent Fixed-Bed Ion Exchange Column In
these columns the regenerating solution enters
the column in a direction opposite to that of the
wastewater. This improves the efficiency of the
regeneration process resulting in smaller amounts
of spent regenerating solution utilized. This
approach also allows the more concentrated regener
ating solution to contact the "cleaner" part of
the resin first Special care must be pay to
preventing fluidization of the resin during
regeneration
150
Design of Fixed-Bed Ion Exchange Processes
Fixed-bed ion exchange columns have
many similarities in common with
fixed-bed adsorbers For example in fixed-bed
ion exchange columns an "exchange zone" similar
to the adsorption zone is formed and travels
through the column until the breakpoint is reached
Design of Fixed-Bed Ion Exchange Processes
(continued) As a result the design of such
processes can be carried out using an approach
similar to that described to design adsorption
fixed-bed columns More complex models also
exist to account for the fact that ion exchange
is also associated with charge transport and
electroneutrality
151
Two-Stage Ion Exchange Operation
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Characteristics of Ion Exchange Columns for
Wastewater Treatment Ion exchanger particle
diameter 0.4 - 0.8 mm Bed height 0.6 - 2.5 m (2 -
8 ft) Height-to-diameter ratio 2 to 1 Bed
expansion 25 - 50 Hydraulic loading 1.4 - 6.8
L/m2 s (2 - 10 gpm/ft2)
155
Examples of Ion Exchange Processes in Industrial
Wastewater Treatment Recovery of chromic acid
from plating rinsewaters Recovery of metals
from acid copper-plating and nickel-plating
rinsewaters Recovery of metals from mixed
rinsewaters Removal of chromates from cooling
water circuits Recovery, purification and
re-use of spent acids from metal pickling and
etching processes Removal of radioactive
components from the wastewaters of nuclear power
plants
156
Organic ion exchange resins find extensive use
for the removal of toxic heavy metals such as
lead, mercury, and chromium from a variety of
industrial processes. They are finding increasing
use for waste minimization and management.
However, the commercially available resins are
only partially effective or unusable in many
situations, and new materials are required. (i)
the removal of trace or low levels of cations
from hot organic solvents, (ii) separation and
recovery of Cr3 from tannery waste, and (iii)
recovery of precious metals from hostile
environments such as nuclear waste streams. There
exists a large array of inorganic compounds which
possess ion exchange properties. We will utilize
natural and synthetic micas, layered titanium and
zirconium phosphates, both as gels and crystals,
compounds with tunnel structures of the
pharmocosiderite type and redox exchangers units
157
AS many solvents must be cooled and diluted with
water in order to remove ions such as Cu2, Ni2,
and Cr3. These ions need to be removed in order
to reuse the solvents and minimize waste disposal
of these toxic solutions. The inorganic
exchangers chosen are stable in hot organics,
have high exchange capacities, and can be used
without cooling or diluting the solvents. . Each
year thousands of tons of valuable chromium
hydroxide are discarded because the currently
available organic resins are not selective enough
to separate Cr3 from Al3, Fe3 in the tanning
solutions. Highly selective inorganic exchangers
will be chosen and separations carried out on
simulated tannery solutions.
158
The use of ion exchange is therefore limited to
situations where polishing step was required
to remove an inorganic constituent that could not
be reduced to satisfactory levels by preceding
treatment processes. One example for this is the
use of anion exchanges for the removal of anionic
nickel cyanide complex and chromate ions from
waste solutions.
159

• Removal of, solids by
• Membrane Processes
• Reverse Osmosis
• dialysis
• Electrodialysis

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Reverse Osmosis Water is forced through a porous
membrane Minerals can't pass through Product
water is very pure Reject water has high mineral
concentration
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