waste water treatment tech
TRANSCRIPT
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Waste water Treatment Processes
Introduction
Sewage Treatment Processes:
A. Preliminary
B. Primary
C. Secondary
D. Tertiary
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Introduction
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Definitions:
Sewage:The content of sewer or drains
Sewage Treatment:
Removing of impurities so that the remaining waste water canbe safely returned to the river or sea and become part of thenatural water cycle again.
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Compositions:
Human waste
paper
Food
Grease
Mineral matter
and almost any things that can be carried by water
Introduction Contd
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4 2003 John Wiley and Sons Publishers
Fig 21.21 Diagram of sewage treatment processes.
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Disease-Causing Agents
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Sewage Treatment Processes
Preliminary
Primary
Secondary
Tertiary
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Solids like wood
paper, rags andplastic are removed
by screens
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Preliminary Treatment
Sewage Treatment Processes Contd
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The remaining solids that passed from thepreliminary treatment are removed
About 70% of solids settle out at this stage
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Primary Treatment
Sewage Treatment Processes Contd
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Secondary Treatment
Sewage Treatment Processes Contd
Biological treatment to reduce organic matter in the waste
stream
Aerobic bacteria is the main cause for this reduction
The chemical reaction:
Organic matter CO2 + H2OBacteria
O2
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This process can be
speeded up by blowing airinto tanks of sewage
These treatment units are
called Aeration Tanks.
Sewage Treatment Processes Contd
Secondary Treatment
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Bacteria Found in the Sewage
Aerobic
Require dissolved
oxygen for their
existence
Ex: Earobacter
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Facultative
Can grow with or
without oxygen
Ex: Salmonella
Anaerobic
Exist in the absence of
dissolved oxygen
Ex: Sulfate Reducer
Sewage Treatment Processes Contd
Secondary Treatment
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Several forms of tertiary treatment are available for
example:
1. Passing the effluent over grass plots
2. Retaining the effluent in lagoons
3. Filtering through sand beds
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Tertiary Treatment
Sewage Treatment Processes Contd
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Advantages Long history in the
industry - known
Easy to operate
Easy to construct
Disadvantages Requires large water
pumps
Operation smothers
the nitrifying biofilm Needs frequent
backwashing
Sand Filters
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Advantages Good air exchange
Simple to construct
Almost any material
will work
Disadvantages Uneven surface
wetting
May promote solids
retention & be hard toclean
Trickle Filters
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Advantages
Good air exchange Least maintenance of
all biofilters
Automatically
maintains a thin biofilm
Most efficient Biofilter
Disadvantages
No solids removal
Have to maintain
rotation
Needs space
Industrial RBC
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Advantages
Constant movementof beads promotes
thin biofilm
Large surface for
nitrification
Disadvantages
Hard to maintain constant
bead movement
Beads tend to stick together
Loss of Beads from the
filter
May promote growth of
heterotrophic bacteria
Fluidized Beds
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Filter Type MaintenanceCloggingPotential
OxygenLimited
Mechanical
Ability
Sand Filter high high yes goodUndergravel
Filter high high yes goodPlenum low medium yes noneTrickle Filter medium medium no noneRBC
low low no noneFluidized Bed med-high medium yes goodBead Filter high high yes good
Filter Comparison
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Activated sludge is a process for treating sewage and industrial
wastewaters using air and a biological floc composed of bacteriaand protozoans.
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oxidizing carbonaceous matter:biological matter.
oxidizing nitrogeneous matter: mainly ammonium and
nitrogen in biological materials.
removingphosphate.
driving off entrained gases carbon dioxide, ammonia,
nitrogen, etc.
generating a biological floc that is easy to settle.
generating a liquor that is low in dissolved or suspended
material.
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Activated sludge process
Activated sludge is abiochemicalprocess for treating sewage andindustrial wastewater that uses air (oroxygen) and microorganisms to
biologically oxidize organic pollutants, producing a waste sludge (or
floc) containing the oxidized material.
Any oxidizable material present in a natural waste will be oxidized bothbybiochemical (bacterial) or chemical processes. The result is that the
oxygen content of the water will be decreased.
Oxidizable material + bacteria + nutrient + O2
CO2
+ H2
O + oxidized
inorganics
S-- + 2 O2 SO4--
NO2- + O2 NO3
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In general, an activated sludge process includes:
An aeration tank where air (or oxygen) is injected and thoroughly
mixed into the wastewater. A settling tank (usually referred to as a "clarifier" or "settler") to
allow the waste sludge to settle. Part of the waste sludge is recycled to
the aeration tank and the remaining waste sludge is removed for further
treatment and ultimate disposal.
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Trickling filter system
A bed of filter medium upon which a
layer of microbial slime is promoted anddeveloped.
An enclosure or a container which
houses the bed of filter medium.
A system for distributing the flow of
wastewater over the filter medium.
A system for removing and disposing of
any sludge from the treated effluent.
The treatment of sewage or other
wastewater with trickling filters is
among the oldest and most well
characterized treatment technologies.