chemical treatment process ert 417/4 waste treatment in bioprocess industry sem 1 (2009/2010) by;...

CHEMICAL TREATMENTPROCESS

ERT 417/4 WASTE TREATMENT IN BIOPROCESS INDUSTRYSEM 1 (2009/2010)

By; Mrs Hafiza Binti Shukor


1) NEUTRALIZATION @ pH ADJUSTMENT

Neutralization – the removal of excess acidity or alkalinity with a chemical of opposite site composition.Chemical Stabilization is often required for highly treated wastewaters to control the aggressiveness with respect to corrosion.

Adapted from Eckenfelder,2000

Chemicals used most commonly for the control of pH (neutralization)



2)CHEMICAL COAGULATION & FLOCCULATION

Coagulation?

Employ of removal of waste materials in suspended @ colloidal form.

Is destabilization of colloids.(particles are essentially coated with a

chemicallysticky layer that allows them to

flocculate @ agglomerate and settle in a reasonable

period of time).


When coagulants such as Al2(SO4)3 are added to the water supply, they form solid precipitates (green)These precipitates catch other impurities (red) in the water, forming a solid mass containing the precipitate formed by coagulation and the trapped impurities. This mass will settle to the bottom by sedimentation, and the water (with the trapped impurities now removed) can be drained off of the top.


2)CHEMICAL COAGULATION & FLOCCULATION (continue………………)


(continue………………)

Colloids? Are presented by particle over a size range of

1nm to 0.1 nm (do not settle on standing & cannot removed by conventional physical treatment process)

Colloids in WW can be either: HYDROPHOBIC (eg. Clay)• No affinity for the liquid medium • Lack stability in the present of electrolytes and thus,

readily susceptible to coagulation.HYDROPHILLIC (eg. Protein)• Affinity for water• The absorbed water retards flocculation and

frequently required special treatment to achieve coagulation

Colloids posses electrical properties which create a REPELLING FORCE and PREVENT agglomeration and settling



Colloids?Are presented by particle over a size range

of 1nm to 0.1 nm (do not settle on standing & cannot removed by conventional physical treatment process)

Colloids in WW can be either:HYDROPHOBIC (eg. Clay) no affinity for the liquid medium and lack

stability in the present of electrolytes and thus, readily susceptible to coagulation.

HYDROPHILLIC (eg. Protein)Colloids posses electrical properties which

create a repelling FORCE and PREVENT agglomeration and settling


As a coagulant (+ve) dissolved, the cation serves to neutralize the negative charge of the colloids.This occur before visible floc formationRapid mixing which “COATS” the colloid is effective in the phase.Micro flocs are then formed which retain a positive charge in the acid range because of the ADSORPTION of H+.

This micro flocs serve to neutralize and coat the colloidal particles.Flocculation agglomerates the colloids with a hydrous oxide flocs.


MECHANISM OF COAGULATIONMECHANISM OF COAGULATION

Coagulation results from 2 basic mechanism:

PERIKINETIC @ ELECTROKINETIC COAGULATION

In which the repulsive force between the particles is reduced by ions @ colloids of apposite charge to level below the Van Der Waals attractive force

ORTHOKINETICS COAGULATIONSthe micelles aggregate & form clumps which agglomerate the colloidal particles.



Colloids?Are presented by particle over a size range

of 1nm to 0.1 nm (do not settle on standing & cannot removed by conventional physical treatment process)

Colloids in WW can be either:HYDROPHOBIC (eg. Clay) no affinity for the liquid medium and lack

stability in the present of electrolytes and thus, readily susceptible to coagulation.

HYDROPHILLIC (eg. Protein)Colloids posses electrical properties which

create a repelling FORCE and PREVENT agglomeration and settling


CHEMICAL COAGULANTSA coagulant has 3 key properties;TRIVALENT CATIONS

naturally occurring colloids are most commonly –ve charge

hence cation are required to achieve charge neutralization.

more effective than monovalent @divalent simple cation (Na+ or Ca2+)

NON TOXIC especially for the production of portable water

INSOLUBLE IN NEUTRAL pH RANGEincrease concentration of the coagulant in treated water is

undesirable.therefore, the coagulant is usually relatively insoluble at pH

value desired.




The 2 most commonly used metallic coagulants are aluminum (Al3+) and Ferric Ions (Fe3+)

a) ALUMINUM SULFATE (ALUM)

•The most popular coagulant in ww treatment application.•Commercial alum has an average molecular weight of 594, which approximately14 water of hydartion.•Alum reacts with;

AlkalinityAcidity

•The optimal pH range for alum is 5.5 to 6.5•The aluminum hydroxide is actually in the chemical form of Al203.xH2O and amphotheric•The floc charge is +ve (below pH 7.6) and –ve (above pH8.2).•Between this limit, the floc charges are mixed.




b) FERRIC SALTS

•Ferric salts have the disadvantages of being more difficult to handle.•A insoluble hydrous ferric oxide is produce over pH range of 3.0-13.0•The floc charge is positive in the acid range and negative in alkaline range with mixed charged over the pH range 6.5-8.0•Ferric cations can be supplied by adding either ferric sulfate (Fe2 (SO4)3.H2O) or ferric chloride (FeCl3.7H2O)•The reaction of ferric chloride in the presence of alkalinity is, FeCl3.7H2O + 3HCO3- -------Fe(OH)3 (s) +3CO2 +3 Cl- +7H2O•And without alkalinity, FeCl3 + 3H2O ---------Fe(OH)3 (s) + 3H+ + Cl-


•If the alkalinity is insufficient, the addition of ferric chloride results in the release of 3 moles of H+ for every mol of ferric chloride to lower the pH of the solution•Ferric salts generally have wider pH range for effective coagulation than aluminum (eg; pH range from 4 to 9)c) OTHER COAGULANTS

•Lime (Ca(OH)2) is not a true coagulant.•Lime sludge can frequently be thickened, dewatered and calcined to convert calcium carbonate to lime for reuse.


d) COAGULANT AIDS

•The addition of some chemicals will enhance coagulation by promoting the growth of large settling sludge.•Activated silica is a short chain polymer that serves to bind together particles of microfine aluminum hydrate.•At high dosage, silica will inhibit floc formation because of its electronegative properties. The usual dosage is 5-10mg/L.•Polyelectrolytes are high molecular weight polymers which contain adsorbable groups and form ridges between particles or charged flocs.•Large flocs (0.3-1.0mm) are created when small dosages of polyelectrolyte (1mg/L) are added in conjunction with alum or FeCl3•Polyelectrolyten is uneffected by pH an can serve as a coagulant itself by reducing the effective charge of the colloid.


•There are 3 types of polyelectrolyte;

CATIONICWhich adsorbed on a negative colloid or floc particles

ANIONICWhich replaces the anionic group on a colloidal particle and permit hydrogen bonding between the colloid and polymer

NON ANIONICWhich adsorbs and flocculates by hydrogen bonding between the solid surfaces and the polar groups in the polymer


COAGULANT EQUIPMENT

2 basic types of equipment adaptable to coagulant and flocculant of industrial WW.

2) AN UPFLOW SOLID CONTACT UNITKnown as a Sludge Blanket Unit combines MIXING, FLOCCULATION and SETTLING in a single unit.The influent raw water and chemical are added in the centre cone. As the water flow upward, the solid settle to form a sludge blanket that can provide further oppurtinity to drive the precipitation to completionMain advantage – reduce size

1) CONVENTIONAL SYSTEMUses rapid mixed-tank followed by a flocculation tank


AN UPFLOW SOLID CONTACT UNIT


3)ION EXCHANGEObjectives;

Used for the removal of undesirable anion and cationsCation are exchanged for hydrogen or sodium (H+ or Na+) Anions are exchanged for hydroxyl ionsION EXCHANGE RESINSResins – consist of an organic or inorganic network structure with attached functional groups

- made by POLYMERIZATION of organic compounds into porous 3D structure

-increase crosslinking between organic chains gives smaller pore sizes.

-the functional ionic group usually introduced by reacting the polymeric metric with a chemical compound containing the desired group.


Resins – their exchange capacity is determined by the number of functional groups perunit mass of resin.

- cationic resin ----if they exchange +ve ions (acidic functional group)

---- eg. sulfonic-anionic resin ------if they exchange –ve ions

(basic functional group)---- eg. Amine

- the strength of the acidic @ basic character depends on the degree of ionization of the fuctional group


ION EXCHANGE REACTIONSThe reaction depends upon chemical equilibria situations in which one ion will selectively replace another on the ionized exchange site.Cation exchange on the sodium cycle can be given as Na2.R + Ca2+ ----------------Ca.R + 2Na+

(R=resin)

When all the exchange sites have been replaced with calcium, the resin can be regenerated by passing a concentrated solution of sodium ions through the bed. This reverses equilibrium,

2Na+ + Ca.R ---------------- Na2.R + Ca2+

Similar reactions occur for ‘CATION EXCHANGE” on hydrogen cycleCa2+ + H2.R --------------Ca.R + 2H+


Regeneration with 2-10% H2SO4

Ca.R + 2H+ ----------------H2R + Ca+

(R=resin)

Anion exchange replaces anion with hydroxyl ions SO4

2- + R.(OH)2 ---------------- R.SO4 + 2OH-

Regeneration with 5-10% NaoH R.SO4+ 2OH- ---------------- R.(OH)2+ SO4

2-

The capacity of Ion Exchange Bed usually expressed as equivalents perliter of bed volume.Resin Utilization is defined as the ratio of the quantity of ions removed during treatment to the total quantity of ions that could be removed at 10% efficiency.The regeneration efficiency is the quantity of ions removed from the resin compared to the quantity of ions present in the volume of regenerate used.


ION EXCHANGE OPERATION UNITIt involves a sequence of operating steps.The ww is passed through te resin until the available exchange sites are filled and the contaminants appear in the effluent.This stage is defined as the breakthrough and the treatment is stopped and the bed is washed to remove dirt and to regrade the resin.The bed is then regenerated and rinsed with water to wash out residual regenerant.

Effluent conc.

Volume of waste treated

No regeneration

Regenerationbreakthrough


Example : Ion Exchange

An industrial ww ion exchange unit has a resin volume of 0.1m3 and need to process 1600 L/day of ww. The influent contains 340mg/L of hardness as CaCO3 and it is desirable to soften it to achieve a total hardness of 100mg/L as CaCO3. What should the bypass flowrate be?

Ans: 470.6L/day


4)ADSORPTIONObjectives:

•Process of collecting soluble substances that are in solution on a suitable interface.

Chemical adsorption results from molecular condensation in the capillaries of the solid.

In general, substance of higher molecular weight are more easily adsorbed.


Is polishing process for water that has receive Normal Biological Treatment. Carbon is used to removed a portion of the remaining dissolved organic matter.The overall rate of adsorption is controlled by ‘the rate of diffusion’ of solute molecules within the square of the particle diameter--------------increase with increasing temperature,

concentration of solute -------------decreases with increasing MW of solute.

ACTIVATED CARBON IN WASTEWATER TREATMENT


Produced by 1st making a char from materials such as coconut and wall nut hulls, wood and coal.The ‘char’ – produced by heating the materials to a red heat to drive off the hydrocarbon but with insufficient supply of air to sustain the combustion.

- Char particle is then activated by exposure to an oxidizing gas at high temperature (the gas develops a porous structure in the char and thus creates a large internal surface area)After certain amount of time for contact, the AC is allowed to settleable bottom of the tank.A coagulant such as polyelectrolyte may be needed to aid the removal of the carbon particle.Carbon regeneration is done once the adsorption capacity has been reached.

ACTIVATED CARBON


before

Figure 2; sketch of activated carbon before and after activation

after

Activated (making pore)


2 size classification of AC are; GRANULAR AC (GAC)• diameter >0.1mm• a fixed column is often used• the water is applied to the top of the column• regeneration in a furnace by oxidizing the organic matter

POWDERED AC (PAC)• diameter <200mesh• is added to the effluent from biological treatment process or directly to the various biological treatment processes or in physical-chemical treatment processes.• methodology for regeneration is not well defined.


Freundlich and Langmuir isotherm are most commonly used to describe the adsorption characteristics of the AC in WW treatment.

ANALYSIS OF THE ADSORPTION PROCESS

A) Freundlich Isotherm

nefCkm

x 1

The constant in Freundlich isotherm can be determined by plotting (x/m) vs C and making the equation as;

Amount of adsorbate per unit wt. of AC

Equilibrium concentration of adsorbate in solution after adsorption

Empirical constant

ef Cn

km

xlog

1loglog


B) Langmuir Isotherm

Langmuir isotherm assumes that;A fixed number of accessible sites are available on the AC, all of which have the same energy.Adsorption is reversible. Equilibrium is reached when the rate of adsorption is the same as the rate of desorption from the surface.The constant in the Langmuir isotherm can be determined by plotting C/(x/m) vs Ce

ee

bC

abC

m

x

1Amount of adsorbate per unit wt. of adsorbent (AC)

Equilibrium concentration of adsorbate in solution after adsorption

Empirical constant

ee Caabm

xC

11/


BREAKTHROUGH ADSORPTION CAPACITY

The fixed breakthrough adsorption capacity, (x/m)b of the GAC is some % of the theoretical adsorption capacity found from the isotherm.The (x/m)b of a single column is approximately 25-50% of the theoretical capacity (x/m)o.Once (x/m)b is known, the time to breakthrough can be calculated by solving the equation for tb.

c

bbi

c

b

m

tCCQ

m

x

m

x

2

Mass of organic material adsorbed in GAC column at breakthrough(g)

Mass of carbon in the column

Flow rate

Influent organic concentration (mg/L)

breakthrough organic concentration (mg/L)

Time to breakthrough (d)

Equation 1


Equation 1 was developed assuming that Ci is constant and that the effluent concentration increase linearly with time from 0 to Cb

Rearranging equation 1, tb can be calculated;

2b

i

cb

bC

CQ

mmx

t


Example : Adsorption (a)

Determine the Freundlich and Langmuir isotherm coefficients for the following GAC adsorption test data. The liquid volume used in the batch adsorption test was 1L.

Mass of GAC in solution, m (g)

Equilibrium conc of adsorbate, Ce

(mg/L)

0.000 3.37

0.001 3.27

0.010 2.77

0.100 1.86

0.500 1.33


Example : Adsorption (b)

Determine the breakthrough time for the GAC filter column when operated at a filtration rate of 0.203 m3/m2.min. Assume that the surface area of the filter column is 0.929 m2, the depth of filter is 1.524m. The influent TOC concentration is 3.25mg/L and the breakthrough TOC conc has been set at 0.75mg/L. The density of the GAC to be used in the filter column is 604kg/m3. Given that,

56.30015.0 eCm

x


5)CHEMICAL OXIDATION

Chlorination Chlorine has been applied for a wide variety of objectives other than disinfection including;

a) Pre chlorination for hydrogen sulfide controlb) Activated sludge bulking controlc) Odor control

The principle chlorine compounds used are chlorine (Cl2), chlorine dioxide (ClO2), calcium hypochlorite (Ca(OCl)2) and sodium hypochlorite (NaOCl).

Objectives; Reduction of BOD and COD The oxidation of ammonia and non- biodegradable organic compound,


Chlorine, Cl2Supplied as a liquefied gas under high pressure in containers.The size of vessel depends on the analysis of the rate chlorine usage, cost of chlorine, and facility requirement.Chlorine gas is toxic and corrosive.

Chlorine dioxide, ClO2Liquid chlorine is vaporized and metered through std evaporators and chlorinators and then converted into a chlorine solution using an injector.A contact time of about 1min is adequate.To increase the reaction rate, a slight excess of chlorine is recommended.

Calcium hypochlorite, Ca(OCl)2Granule or pellets are readily soluble in water and under proper storage conditions are relatively stable.Because of its tendency to crystallize, calcium hypochlorite may clog metering pumps, piping and valves.


Sodium hypochlorite, NaOClCan be either puchased in bulk lots of 12-15% of available chlorine or manufactured on site.The solution decomposes more readily at high concentration and is affected by exposure to light and heat.The handling of sodium hypochlorite requires special design considerations because of its corrosiveness and the presence of chlorine fumes.

Chlorine mixing and ContactThe contact time may be in the range of 15-45minThe appropriate chlorine residual should be determined from actual plant studies.The design of any chlorine contact system should provide for the injection and mixing of chlorine.The contact chamber should be designed so that at least 80-90% of the ww is retained in the basin for a specified contact time


THE END

chemical treatment process ert 417/4 waste treatment in bioprocess industry sem 1 (2009/2010) by;...

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