m9 sewage effluent plasticplating
TRANSCRIPT
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SEWAGE TREATMENT BY
ELECTROLYTIC PROCESS
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The wastewater from domestic sourcesotherwise called sewage could be treated by
various methods based on
aerobic biological treatment processes,
anaerobic biological treatment processes and
electro-chemical treatment processes.
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ELECTROCOAGULATION AS A
WASTEWATER TREATMENT
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The most widely practiced method in India is
based on aerobic biological treatment of
sewage. In this article, the electro-chemicalprocess of sewage treatment has been briefly
discussed.
Electrolytic process is a technique involvingthe passage of electricity through wastewater
or effluent to be treated. The electric current
destabilizes the dissolved colloid particles andalters the charge on suspended particles
permitting their coagulation, flotation and
separation.
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Coagulation and flocculation are traditional
methods for the treatment of polluted water.
Electrocoagulation presents a robust novel
and innovative alternative in which a sacrificial
metal anode doses water electrochemically.
This has the major advantage of providing
active cations required for coagulation,
without increasing the salinity of the water.
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Electrocoagulation is a complex process with a
multitude of mechanisms operating
synergistically to remove pollutants from the
water
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A wide variety of opinions exist in the
literature for key mechanisms and reactor
configurations.
A lack of a systematic approach has resulted in
a myriad of designs for electrocoagulation
reactors without due consideration of the
complexity of the system.
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A systematic, holistic approach is required to
understand electrocoagulation and its
controlling parameters.
This will enable a priori prediction of the
treatment of various pollutant types.
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A current is passed through a metal electrode,
oxidising the metal (M) to its cation (M n+ )
Simultaneously, water is reduced to hydrogen
gas and the hydroxyl ion (OH-) .
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Electrocoagulation thus introduces metal
cations in situ, electrochemically, using
sacrificial anodes (usually aluminium or
iron).
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The cation hydrolyzes in water forming a
hydroxide with the dominant species
determined by solution pH.
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The Third Annual Australian Environmental
Engineering Research Event. 23-26 November
Castlemaine, Victoria 1999
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Highly charged cations destabilize any
colloidal particles by the formation of
polyvalent polyhydroxide complexes. These
complexes have high adsorption properties,forming aggregates with pollutants.
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Evolution of hydrogen gas aids in mixing and
hence flocculation. Once the floc is generated,
the electrolytic gas creates a flotation effect
removing the pollutants to the floc - foamlayer at the liquid surface.
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There are a variety of ways in which species can
interact in solution:
1. Migration to an oppositely charged
electrode (electrophoresis) and aggregation
due to charge neutralisation.
2. The cation or hydroxyl ion (OH-) forms a
precipitate with the pollutant.
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3. The metallic cation interacts with OH- to
form a hydroxide, which has high adsorption
properties thus bonding to the pollutant
(bridge coagulation).
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4. The hydroxides form larger lattice-like
structures and sweeps through the water
(sweep coagulation).
5. Oxidation of pollutants to less toxic species.
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6. Removal by electroflotation and adhesion
to bubbles.
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The inherent complexity of the process makes
it difficult to model and control. Adequate
scaleup parameters, a systematic approach to
the optimization and a priori prediction for the
performance ofthe electrocoagulation reactor
are yet to be established. The literature
reveals that previously each new system hasbeen considered separately on an individual
basis.
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There has been little or no attempt to provide
a holistic approach to electrocoagulation. In
order to understand the mechanisms behind
electrocoagulation, and thus control thesystem better, a holistic approach is required.
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Brief Description of Electrolytic
Process:
The wastewater is allowed to pass through the
bar screen chamber to remove the coarse
particles (such as plastic, wood pieces, leaves,
paper, etc) before entering in to theequalisation tank.
The equalisation tank helps in maintaining a
uniform flow to the Electro Cell. The size anddesign of the equalisation tank depends upon
the flow rate and type of the effluent.
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In general the size of the Equalisation tank
varies between 20 35% of the total flow. Theelectrolysed brine from the brine electrolyser
is also continuously injected at about 1% of
waste water flow to the equalisation tank.
The brine electrolyser gets mixed with the
effluent where it oxidizes the organics and
also works as an electrolyte in the Electrocell
for further degradation of organic
components.
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The suspended solids settle down at the
bottom of the equalisation tank and are
pumped out with the help of a sewage pump,
time-to-time.
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The pre-oxidized sewage from the equalization
tank is pumped to the Electro Cell where
electro-coagulation process helps in de-
stabilizing the colloidal and suspendedparticles.
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In the electrolytic process the coagulant is
generated by electrolytic oxidation of anode.
The charged ionic species are removed by
allowing it to react with an ion of oppositecharge.
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It is the use of sacrificial electrodes either of
aluminium or iron which releases positive ions
(Al 3+ or Fe 3+) to coagulate the suspended
particles by forming polyvalent poly-hydroxidecomplexes.
When an electric current is passed through a
metal electrode, dissolution of metal takesplace with simultaneous formation of hydroxyl
ions and hydrogen gas.
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Diagram: EQUALISATION TANK
Excess supernatant liquid from Slurry tank
For instance, if aluminum electrodes are used, aluminum
dissolves into the solution
reacting with the hydroxyl ions to form aluminum hydroxide.
The hydroxide coagulates the suspended solids purifying the
water.
The solids could be removed from the top of the treated tank
by flotation method and treated effluent be allowed to move
by gravity to the sand filter. The sludge could also be allowed
to settle and pumped for sand filtration.
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Electrolysis Process
Ions being acted upon
The treated wastewater from the Electro Cell
is allowed to flow by gravity to the activated
carbon filter. This gives the final treatment
and the treatedwastewater is pumped to the
treated water tank.
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Electrolysis sewage treatment
system The principle of theory supplies the electronic
energy through electrode cells to soil, wastewater
including electrolyte (seawater, NaCl),then it treats
the sewage, wastewater as the oxidation response byHOCl, O3 in the electrode response of oxidation,
reduction, solution which is made by exchange of
direct election between interface of cell and solution
and it's originated material
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After electrolysis treatment of NaCl,It purifies
and sterilizes as causes oxidation action to soil
and wastewater by the strong steriliting power
which is originated in surface of cells.
It treats as floats the suspended solid of
colloid side and the suspended solid material
of water by rising minute hydrogen gas whichis originated in processing of electrolysis
treatment
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Applied Area
Factory wastewater of organic chemical
Factory wastewater of inorganic chemical
Dyeing factory wastewater
Plating factory wastewater
Stock rising wastewater
Petrochemical wastewater
Sewage soil treatment
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INTRODUCTION
There are many industries, such as pulp and papermills, pharmaceutical, and electroplating industries,
which discharge wastewaters with certain pollutants
which would cause a serious impact to the
environment (Chiang et al., 1997). Many pollutants have certain substituints such as
halogen, sulfo-, azo- or nitro-groups. Particularly the
accumulation of such groups and specific
substitution patterns confer xenobiotic character to a
synthetic compound (Campbell, 1977; Knackmuss,
1996). As a consequence, many of these chemicals
tend to persist in the environment.
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Persistent chemicals present the problem of accumulation in
organisms near the top of food chains to a much higher level
generally than in the environment (Alexander, 1977;
Campbell, 1977; Melo and Azevedo, 1997; Tortora et al.,
2000). Consequently, the treatment of the industrial wastewaters
has always been conducted to minimize the threat to the
environment. Biological processes are the treatment systems
used most and they can usually remove readily biodegradableorganics (Chiang et al., 1997).
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However, if the main part of the organic compounds
present in a wastewater is persistent,
microorganisms are not able to degrade it and the
biological processes are not suitable. Depending on their quantity and their
ecotoxicological behavior, the recalcitrant organics
have to be removed by additional treatment (Gulyas,
1997; Chiang et al., 1997; Israilides et al., 1997;Panizza et al., 2000; Moraes et al., 2000; Janssen and
Koene, 2002).
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Electrochemical treatment is a powerful tool
for the purification of this kind of wastewater.
This technology has attracted a great deal of
attention because of the versatility, whichmakes the treatment of liquids, gases and
solids possible. Other characteristics include
energy efficiency, amenability to automationand environmental compatibility.
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In fact, the main reagent is the electron, which is a
"clean reagent" (Rajeshwar et al., 1994). The
electrochemical methods have been successfully
used for the treatment of wastewater fromslaughterhouse (Marconato et al., 1998), textile
wastewater (Naumczyk et al., 1996; Shen et al.,
2001; Xiong et al., 2001), tannery wastewater
(Vlyssides and Israilides, 1997; Szpyrkowics et al.,2001), domestic wastewater (Vlyssides et al., 2002),
and biorefractory organics (Saracco et al., 2001).
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After the electrochemical treatment of
wastewater containing persistent compound,
the biodegradation and toxicity can be
improved (Vlyssides and Israilides, 1997;Chiang et al., 1997; Israilides et al., 1997;
Angelis et al., 1998).
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The present study investigated the degradation of a simulated
wastewater containing the compound n-phenyl n
isopropyl p phenylenediamine (commercial name is
Flexzone 3P), using Ti/TiRuO2 electrodes.
The Ti/TiRuO2 electrodes are dimensionally stable anodes
(DSA) and they are suitable for electro oxidation of organic
compounds.
They show high corrosion resistance and physical/chemistrystability under high positive potentials (Pelegrino et al., 2002).
However, other kinds of electrodes have also been utilized for
electro oxidation of organic compounds such as the synthetic
boron-doped diamond (BDD) electrodes (Panizza et al., 2001). DSA electrodes have been chosen for these experiments due
their good features for treating wastewaters containing
organic compounds (Rgis and Bidoia, 2001a; Chung and Park,
2000).
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The commercial compound Flexzone 3P is an aromatic amine
used by a chemical industry of rubber antioxidant and
antiozonant (Rgis and Bidoia, 2001a) located in Rio Claro, So
Paulo State, Brazil.
The compound Flexzone 3P has been chosen because it is one
of the most important chemical compounds present in the
effluent from that Brazilian industry.
Many aromatic amines have been reported to be powerful
carcinogens and mutagens, and/or hemotoxicants (Chung et
al., 1997; Benigni and Passerini, 2002).
Consequently the treatment of the industrial wastewaters
containing these kinds of chemicals is very important to
minimize the threat to the environment.
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We studied the electrochemical treatment in order
to reduce the toxicity of the simulated wastewater
containing Flexzone 3P.
In particular, conductivity and pH were monitoredwith electrolysis duration. After electrolysis duration,
samples of wastewater were submitted to UV-visible
spectrophotometry analysis, gas chromatography,
toxicity assay and biodegradation test using therespirometric Bartha flask.
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ELECTROPLATING PLASTIC
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Electroplating is the deposition of metal ions
from solution onto an electrically chargedsurface.
The surface must therefore be conductive.
Plastic is not conductive, so directelectroplating of plastic is not practicable.
Instead, the process is performed in steps,
covering the plastic in an adhesive conductor,
like metallic paint, before performing genuine
electroplating.
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METHODS TO PLATE PLASTIC
There are two methods to plate plastic:
One is to roughen the surface to allow metal
to adhere. Then electroplate over that layer to
build up layers of metal. This process is called
electroless, auto-catalytic or chemical plating.
The second method is to apply conductive
paint to the plastic, then electroplate it.
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To begin the roughening method, first clean
the plastic part of all oil, grease and other
foreign matter.
This process can be made complicated if you
want to be thorough, with a long series of
applications of acids and bases. Rinse with
water several times after each step to clearaway the prior cleaning agent before the next
is applied.
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Drop the part in a chrome-sulfur bath. The
acid will pit, or etch, the surface, so that metal
can adhere. An alternative method of etching
is to sandblast the surface.
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Drop the part in a palladium chloride bath.
This will leave an initial layer of metal which
will allow electroplating the standard way.
Specifically, the part will then be electroplatedwith copper as yet another preparation layer,
then gold, chrome, nickel or whatever the
final metal layer is to be.
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Paint Approach
Purchase conductive paint. Inexpensive
conductive paint can be purchased from
Acheson Colloids or Cybershield.
Clean the surface, as above.
Apply the paint.
Electroplate with an initial copper layer, as
above. The rest of the electroplating is the
same as in the pitting approach.
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