Lecture.chemical Process in Waste Water Treatment

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Chemical Unit Process

Gyeongsang National University Gyeongsang National University Enviromental Engineering Lab Enviromental Engineering Lab Ngoc Thuan Le

Ngoc Thuan Le

**

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The principal chemical unit processes used for wastewater The principal chemical unit processes used for wastewater treatmenttreatment a

a.. BaBasisic dec defifinnititiiononss b.

b. ChChememicical al prprececipipititatatioionn c.

c. CheChemicmical pal precrecipiipitatitation foon for phor phosphsphoruorus rems removaovall d.

d. ChChememicical al oxoxididatatioionn e.

e. ChChememicical al neneututraralilizazatitionon

Overview

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• For the complete secondary treatment of untreated wastewater, including

For the complete secondary treatment of untreated wastewater, including

the removal of either nitrogen or phosphorus or both.

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• To remove phosphorus by

To remove phosphorus by chemical precipitation

chemical precipitation

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• To be used in conjunction with

To be used in conjunction with biological treatment.

biological treatment.

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• For the removal of heavy

For the removal of heavy metals and specific organic compounds

metals and specific organic compounds

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• For advance treatment of wastewater, the disinfection of wastewater.

For advance treatment of wastewater, the disinfection of wastewater.

Application of chemical unit processes

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• Coagulant

Coagulant

is the chemical that is added to destabilize the colloidal

particles in wastewater.

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• A Flocculent

A

Flocculent

is a chemical, usually positive charge typically organic,

added to enhance the flocculation process.

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• Microflocculation

Microflocculation

(perikinetic flocculation), aggregation is brought about

by the random thermal motion of

by the random thermal motion of fluid molecules.

fluid molecules.

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• Macroflocculation

Macroflocculation

(orthokinetic flocculation), aggregation is brought

about by inducing velocity gradients and

about by inducing velocity gradients and mixing in the fluid containing

mixing in the fluid containing

Fundamental of chemical coagulation

Basic Definition

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• The size of colloidal particles: about 0.01-1µm, a net negative surface

The size of colloidal particles: about 0.01-1µm, a net negative surface

charge

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• The number of colloidal particles in untreated wastewater is from

The number of colloidal particles in untreated wastewater is from 10

10

66

_to

10

1122

_/ml.

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• Particles solvent interactions:

Particles solvent interactions:



_{Hydrophobic or “water-hating”}



_{Hydrophilic or “water-loving”}



_{Association colloids}

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• Ionization

Ionization

Nature particles in the wastewater

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Polyelectrolytes may be devided into two categories:Polyelectrolytes may be devided into two categories:



 _Natural_Natural_{: include polymers of biological origin such as cellulose derivatives}_{: include polymers of biological origin such as cellulose derivatives}

and alginates and alginates



 _Synthesis_Synthesis_{: simple monomers that are polymerized into high molecular}_{: simple monomers that are polymerized into high molecular}

weight substances. weight substances.

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The action of polyelectrolytes:The action of polyelectrolytes:



 Charge neutralizationCharge neutralization: the cationic polyelectrolytes are used for this purpose: the cationic polyelectrolytes are used for this purpose



 _{Polymer bridge formation}_{Polymer bridge formation}_{: polymers that are anionic and nonionic, a bridge}_{: polymers that are anionic and nonionic, a bridge}

is formed when two or more particles

is formed when two or more particles become absorbed along the length of become absorbed along the length of polymers

polymers

Particle destabilization and aggregation with polyelectrolytes

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Formation of hydrolysis productsFormation of hydrolysis products: in the past, it was thought that free Al: in the past, it was thought that free Al++33 _{and Fe}_{and Fe}++33

were responsible for particles aggregation, now their

were responsible for particles aggregation, now their hydrolysis products arehydrolysis products are responsible.

responsible.

Particle destabilization and removal with hydrolyzed metal ions

Me Me H H₂₂OO H H₂₂OO H H₂₂OO OH OH₂₂ OH OH₂₂ OH OH₂₂ 3+ 3+ Me Me H H₂₂OO H H₂₂OO H H₂₂OO OH OH OH OH₂₂ OH OH₂₂ 2+ 2+ + + HH++ Me: Cr, Al, Fe Me: Cr, Al, Fe In acid: Al(OH) In acid: Al(OH)_3(s)_3(s) + + 6H6H₃₃OO++ (aq)

(aq) AlAl33++ (aq)(aq) + + 6H6H22OO

In base: Al(OH)

In base: Al(OH)_3(s)_3(s) + + OHOH --(aq)

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In the past, chemical precipitation was used to enhance the degree of TSS andIn the past, chemical precipitation was used to enhance the degree of TSS and BOD removal

BOD removal

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In current practice, chemical precipitation is used for:In current practice, chemical precipitation is used for:



 _{Primary settling facilities}_{Primary settling facilities} 

 _{In the independent physical-chemical treatment of wastewater}_{In the independent physical-chemical treatment of wastewater} 

 _{Removal of}_{Removal of phosphorus}_phosphorus 

 _{Removal of heavy metals}_{Removal of heavy metals}

Chemical precipitation for improved plant performance

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Inorganic chemicals used most commonly for coagulation and

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With chemical precipitation, it is possible to removeWith chemical precipitation, it is possible to remove

  _{80-90% TSS}_{80-90% TSS}   _{50-80% BOD}_{50-80% BOD}   _{80-90% bacteria}_{80-90% bacteria}

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Dependent factorsDependent factors



 _{Quantity of chemical used}_{Quantity of chemical used} 

 _{Mixing time}_{Mixing time} 

 _{Loading rates}_{Loading rates} 

 _Operator_Operator

Enhance removal of suspended solids in

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Phosphorus precipitation with calciumPhosphorus precipitation with calcium



 Using as form of lime, CUsing as form of lime, Ca(OH)a(OH)₂₂



 _{pH of the wastewater increases beyond about 10}_{pH of the wastewater increases beyond about 10}

Chemical precipitation for phosphorus removal

10Ca

10Ca22++ _{+ 6PO}_{+ 6PO} 4

433-- + 2OH+ 2OH-- CaCa1100(PO(PO44))66(OH)(OH)22

Hydroxylapatite Hydroxylapatite

Dosage of lime depend on Dosage of lime depend on



 _{Amount of phosphate present}_{Amount of phosphate present} 

 _{The alkalinity of wastewater}_{The alkalinity of wastewater}

The quantity of lime required is typically about 1.4 to 1.5 times The quantity of lime required is typically about 1.4 to 1.5 times

the total alkalinity expressed as CaCO the total alkalinity expressed as CaCO₃₃

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Phosphate precipitation with aluminum and ironPhosphate precipitation with aluminum and iron

Al Al33++ ₊_{+ H}_H n nPOPO4433--nn AlPOAlPO44 + + nHnH Fe Fe33++ ₊_{+ H}_H n nPOPO44 3 3--nn _FePO_FePO 4 4 + + nHnH

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There are many competing reactions because of the effects of alkalinity, pH,There are many competing reactions because of the effects of alkalinity, pH, trace elements, and ligands in wastewater

trace elements, and ligands in wastewater

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Phosphorus reduction, Phosphorus reduction,

% %

Mole ratio, Al: P Mole ratio, Al: P R

Raannggee TTyyppiiccaall

7 755 11..2255::11--11..55::11 11..44::11 8 855 11..66::11--11..99::11 11..77::11 9 955 22..11::11--22..66::11 22..33::11 Developed in part from US. EPA (1976)

Developed in part from US. EPA (1976)

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Typical alum dosage requirements for various levels of phosphorus removalTypical alum dosage requirements for various levels of phosphorus removal

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Theoretically, the minimum solubility of AlPOTheoretically, the minimum solubility of AlPO₄₄ occurs at pH 6.3, FePOoccurs at pH 6.3, FePO₄₄ occursoccurs at pH 5.3. In practice, good p

at pH 5.3. In practice, good phosphorus rhosphorus removal emoval anywhere in the range of anywhere in the range of pHpH 6.5 to 7.0

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Factors effecting the choice of chemical for phosphorus removalFactors effecting the choice of chemical for phosphorus removal

a.

a. InInflflueuent pnt phohospsphohorurus les levevell b

b.. WaWaststewewateater sr sususpependnded ed sosolidlidss cc.. AAllkkaalliinniittyy

d.

d. CheChemicamical cl cost ost (in(inclucludinding g tratranspnsportortatioation)n) e.

e. ReReliliababililitity of cy of chehemimicacal sul supppplyly f.

f. SlSlududge ge hahandndliling ng fafacicililititieses g.

g. UlUltitimamate dte disispoposasal mel meththododss h.

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Phosphorus removal using metal salts and polymersPhosphorus removal using metal salts and polymers

a.

a. Iron Iron and aand aluminuluminum salts m salts can bcan be adde added at ed at a vara variety oiety of diff differenferent poit points innts in the treatment processes

the treatment processes b.

b. PolyPolyphosphosphates phates and and organorganic phic phosphosphorus orus are leare less easss easily reily removed moved thanthan orthophosphorus

orthophosphorus c.

c. AdAddinding alg alumiuminum num or or iroiron sn salts alts aftafter ser secoecondandary ry tretreatmeatment (nt (whewherere organic phosphorus and polyphosphate are transformed into

organic phosphorus and polyphosphate are transformed into orthophosph

orthophosphorus) results in orus) results in the best removal.the best removal. d.

d. PoPolylymemers rs mamay y be be adaddededd (1)

(1) to the mixing zoto the mixing zone of a highly mixne of a highly mixed or interned or internally recircally recirculatedulated clarifier,

clarifier, (2)

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Phosphorus removal using limePhosphorus removal using lime

a.

a. Lime tLime treareatmentment can be ut can be used tsed to preo precipicipitate a ptate a portortion oion of the pf the phoshosphophorusrus (about 65-80%)

(about 65-80%) b

b.. PrPrododucuct ot of pf precrecipipitaitatiotion: n: [C[Caa₅₅(PO(PO₄₄))₃₃(OH)].(OH)]. c.

c. pH is apH is aboubout 11 fot 11 for higr high lime sh lime systystemsems, abou, about 8.5t 8.5-9.-9.5 for l5 for low limow limee systems

systems 5Ca

5Ca22++ _{+ 3PO}_{+ 3PO} 4

433-- + + OHOH-- CaCa55(PO(PO44))33(OH)(OH)

Hydroxylapatite Hydroxylapatite

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Advantages and disadvantages of chemical addition in various section of a treatment Advantages and disadvantages of chemical addition in various section of a treatment

plant for phosphorus removal plant for phosphorus removal

L

Leevveel l oof f ttrreeaattmmeenntt AdAdvvaannttaaggeess AAiissaaddvvaannttaaggeess P

Prriimmaarryy aapppplliiccaabblle e tto o mmoosst t ppllaanntt, , iinnccrreeaassee BOD and TSS removal, lowest degree BOD and TSS removal, lowest degree of metal leakage, lime recovery

of metal leakage, lime recovery demonstrated

demonstrated

Least efficient use of metal, polymer may be Least efficient use of metal, polymer may be required for flocculation, sludge more difficult required for flocculation, sludge more difficult to dewater than primary sludge

to dewater than primary sludge

S

Seeccoonnddaarryy lloowweer r ccoosstt, , lloowweer r cchheemmiiccaal l ddoossaaggee than primary, improved stability of than primary, improved stability of activated sludge, polymer not required activated sludge, polymer not required

overdose of metal cause low pH toxicity, with overdose of metal cause low pH toxicity, with low alkalinity wastewaters, a pH control low alkalinity wastewaters, a pH control system may be necessary, canot use lime system may be necessary, canot use lime because of excess pH, inert solids added to because of excess pH, inert solids added to activated sludge mixer liquor, reducing the activated sludge mixer liquor, reducing the percentage of volatile solids

percentage of volatile solids Adva

Advanced pnced precrecipitaipitationtion lowelowest phost phosphosphorus efrus effluefluent, mont, mostst efficient metal use, lime recovery efficient metal use, lime recovery demonstrated

demonstrated

Highest capital cost, highest metal leakage Highest capital cost, highest metal leakage

advanced single and two advanced single and two stage filtration

stage filtration

lower cost can be combineed wieth the lower cost can be combineed wieth the removal of residual TSS

removal of residual TSS

Length of filter run may be reduced with Length of filter run may be reduced with single-stage filtration additional expense with single-stage filtration additional expense with two stage filtration process

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Most of metal of interest in wastewater can be precipitated as hydroxides andMost of metal of interest in wastewater can be precipitated as hydroxides and sulfides

sulfides

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Dependent factors:Dependent factors:



 _Solubility_Solubility 

 _pH_pH

Chemical precipitation for removal of heavy metals and

dissolved organic substances

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Oxidizing agents:Oxidizing agents: 

 ozone (Oozone (O₃₃),), 

 hydrogen peroxide (Hhydrogen peroxide (H₂₂OO₂₂),), 

 permanganate (MnO permanganate (MnO₄₄),), 

 chloride dioxide (ClOchloride dioxide (ClO₂₂),), 

 chlorine (Clchlorine (Cl₂₂) or (HClO) and) or (HClO) and 

 oxygen (Ooxygen (O₂₂))

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For reduction of:For reduction of:   _BOD,_BOD,   _COD,_COD,   _ammonia,_ammonia, 

 _{nonbiodegradable organic compounds.}_{nonbiodegradable organic compounds.}

Chemical oxidation

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Oxidation-reduction reactionOxidation-reduction reaction

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 Take place between oxidizing agent and reducing agent.Take place between oxidizing agent and reducing agent. Cu Cu22++ ₊_{+ Zn}_Zn _Cu_{Cu +}_{+ Zn}_Zn22++ Zn Zn - - 2e 2e ZnZn22++ _(oxidation)_(oxidation) Cu Cu22++ _-_{- 2e}_2e _Cu_{Cu (reduction)}_(reduction) 

 Oxidation-reduction reactions often require the presence of one or Oxidation-reduction reactions often require the presence of one or moremore catalysts to increase the rate of reaction.

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Typical applications of chemical oxidation in wastewater collection, treatment and disposal. Typical applications of chemical oxidation in wastewater collection, treatment and disposal.

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Chemical oxidation of BOD and CODChemical oxidation of BOD and COD

Organic Organic molecule molecule (e.g., BOD) (e.g., BOD) Intermediate Intermediate oxygenated oxygenated molecules molecules Simple end Simple end products (e.g., products (e.g., CO CO₂₂, H, H₂₂O…)O…) Cl, O3, Cl, O3, H2O2 H2O2 Cl, O3, Cl, O3, H2O2 H2O2

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Chemical oxidation of nonbiodegradable organic compoundsChemical oxidation of nonbiodegradable organic compounds

For treatment of remaining after biological treatment: low molecular weight For treatment of remaining after biological treatment: low molecular weight

polar organic compounds and complex

polar organic compounds and complex organic compounds build around theorganic compounds build around the benzene ring structure

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Scaling controlScaling control



 _{Acidifying to reduce pH and alkalinity}_{Acidifying to reduce pH and alkalinity} 

 Reducing calcium concentration by ion exchange or lime softeningReducing calcium concentration by ion exchange or lime softening



 _{Adding a scale inhibitor chemical (antiscalant) to increase the apparent}_{Adding a scale inhibitor chemical (antiscalant) to increase the apparent}

solubility of CaCO

solubility of CaCO₃₃ in the concentrate streamin the concentrate stream



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Chemical storage, feeding, piping, and control systems.

Chemical feeders Chemical feeders

Dry feeders

Dry feeders LLiiqquuiid d ffeeeeddeerrss GGaas s ffeeeeddeerrss

gravimetric

gravimetric volumetricvolumetric

Belt Belt Loss in weight Loss in weight Self-powered Self-powered Belt Belt Revolving plate Revolving plate Rotary Rotary Screw Screw Shaker Shaker vibratory vibratory Slurry solution

Slurry solution AmmoniaAmmonia Chlorine Chlorine Oxygen Oxygen Ozone Ozone sulfur dioxide sulfur dioxide

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Schematic of typical dry Schematic of typical dry chemical-feed system. chemical-feed system.

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Conveyor belt

Conveyor belt RotaryRotary

Screw

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C

Chheemmiiccaall AApppplliiccaattiioonn RReeccoommmmeennttddeedd mixing times, s mixing times, s Alum, Al

Alum, Al33++_{, Ferric chloride, Fe}_{, Ferric chloride, Fe}33++ _C_Coa_oagu_gula_lati_tion_{on of}_{of ccol}_ollloi_oida_dal_{l pa}_parrti_ticl_cleess _<1_<1

Alum, Al

Alum, Al33++_{, Ferric chloride, Fe}_{, Ferric chloride, Fe}33++ _S_Sw_weeeep_{p ffllo}_oc_{c p}_prreecciip_piittaattiio_on_n ₁_1--1₁₀₀

Lime Ca(OH)

Lime Ca(OH)₂₂ CChheemmiiccaal l pprreecciippiittaattiioonn 1100--3300 Chlorine, Cl

Chlorine, Cl₂₂ CChheemmiiccaal l ddiissiinnffeeccttiioonn <<11 Chloramine, NH

Chloramine, NH₂₂CCll CChheemmiiccaal l ddiissiinnffeeccttiioonn 55--1100 C

Caattiioonniic c ppoollyymmeerrs s DDeessttaabbiilliizzaattiioon n oof f ccoollllooiiddaal l ppaarrttiicclleess <<11 A

Anniioonniic c ppoollyymmeerrss paarrttiicclle p e bbrriiddggiinngg 11--1100 P

Poollyymmeerrss, , aanniioonniicc FFiilltteer r aaiiddss 11--1100

Typical mixing times for various chemicals used in wastewater treatment facilities Typical mixing times for various chemicals used in wastewater treatment facilities

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Thank you for your attention!