Metode Fisik‐KimiaMetode Fisik Kimia

Materi Kuliah Pengolahan Limbah B3Yulinah TrihadiningrumYulinah Trihadiningrum

Pra‐pengolahanPra pengolahanHal penting dilakukan sebelum pengolahan limbah B3 adalahmereduksi volume limbah: • Dipilih proses produksi yang menghasilkan air limbah

seminimum mungkin.• Limbah diklasifikasi berdasarkan karakteristik dan kadar

kontaminan yang terkandung. Misal: limbah air pendingin, limbah kamar mandi harus dipisahkan dari limbah pabrikyang memerlukan pengolahan khusus.

• Volume air sedapat mungkin dikurangi dalam prosesproduksi.p

• Air limbah yang berkonsentrasi rendah atau air limbah yang telah diolah sedapat mungkin digunakan kembali untukmengurangi volume pembuangan.g g p g

Physico-chemical treatmentPhysico chemical treatment•aims to reduce the hazardous potential of wastes

ff li i i•may offer re‐use or recycling opportunities•often used in combination to optimise hazardous wastes treatment

Chemical processes use chemical reactions to transform hazardous wastes into less hazardous substanceshazardous wastes into less hazardous substances

Physical processes enable different waste components to b t d i l t d f i tbe separated or isolated, for re‐use or appropriate treatment or disposal

TRP Chapter 6.2  3

Physico-chemical treatmentf ilitifacilities

O it ff it t t tOn‐site vs off‐site treatment:

•Some physical processes can be done on‐site, egSome physical processes can be done on site, egsedimentation 

•Treatment may be integrated into manufacturing process

O i dOn‐site treatment reduces: •volumes needing transport•transport costs

TRP Chapter 6.2  4

•transport costs 

Physico-chemical treatment in central t t t f ilittreatment facility

•Off‐site treatment facility should provide:•Waste receiving station•Storage facilities for wastes awaiting treatmentTreatment areas for n mber and ariet of•Treatment areas for number and variety of processes used •Storage and disposal facilities for treatmentStorage and disposal facilities for treatment residues eg reaction products, filter cake and wastewater•Storage for treated wastes to be incinerated, where  appropriate L b i

TRP Chapter 6.2  5

•Laboratory services•Trained personnel

Treatment residueseat e t es dues

All physico‐chemical treatment processes generate residues which may:

•be hazardous wastes themselves

•be more concentrated than original waste

•be suitable for recycling

• require further treatment

• Sludge from physico‐chemical treatment after pressing need to be landfilled

TRP Chapter 6.2  6

pressing need to be landfilled

Source: Safe

Physical processesPhysical processes•Most are simple and low‐cost Ch i d d h i l f f d•Choice depends on physical form of waste and its characteristics

Options include:∙Separationp∙Sedimentation∙Flotation∙Drying∙EvaporationSludge dewatering Filter press

TRP Chapter 6.2  7

∙Sludge dewatering ∙Filtration

Source: Safe hazardous waste management systems 2002 ISWA

Filter press

SeparationSeparation

Examples of separation techniques:Examples of separation techniques:• Sieving and screening ‐ for dry materials of different particle size

• Distillation ‐ to separate liquids • Use of washing medium ‐ to extract contaminants from soils or solublecontaminants from soils or soluble components from solid wastes

TRP Chapter 6.2  8

Molecular separation

Molecular separation is often based upon membrane processes in which dissolved contaminants or solvent are pforced through a membrane. 

• The most widely used membrane process is reverse osmosis inThe most widely used membrane process is reverse osmosis in which water from wastewater is forced through a membrane that is selective to water yielding purified water product and leaving behind a concentrated liquor containing impurities.

• Other membrane processes include ultrafiltration and electrodial sis in hich ions in a sol tion s bjected to electrol siselectrodialysis in which ions in a solution subjected to electrolysis migrate selectively through alternate membranes that allow for the passage of cations and anions.

M i f i l d i ifi i f h

Membrane separationMain functions: volume reduction, recovery or purification of the liqiud phase, concentration or recovery of the contaminant or solute.

Pressure driven processes:Pressure driven processes:Reverse osmosis ‐ water separation from a feed stream containing inorganic ions . The recovered water is relatively high in purity ‐suitable for recycling.Nanofiltration separates ions or organic components from water by limiting the size of membrane pores. Typically used for removing g f p yp y gcontaminants with molecular weight 100‐500 from water.Ultrafiltration ‐ separates organic compounds from water according  to the size (MW) of the organic molecules Membranes areto the size (MW) of the organic molecules. Membranes are manufactured with the capability to remove contaminants with the MW between 100 ‐ 1, 000,000.Microfiltration ‐ separates with a micrometre sized membrane 

Types of membrane filtrationTypes of membrane filtration

Electric potential driven processesElectric potential driven processes

• Electrodialysis ‐ removes ionic componentsElectrodialysis removes ionic components from water. It produces moderate quality product water (i e several hundred mg/Lproduct water (i.e. several hundred mg/L salts).

Fundamentals of membrane separation

INLET CONCENTRATEINLET

PERMEATE

EATE

2. P

ERM

E

Reverse osmosisReverse osmosis treatment of landfill 

leachate

AdsorptionAdsorbents Application

Activated carbon Solvent recoveryElim ination of odoursG ases purification

Alum ina Drying of gases andAlum ina Drying of gases andliquids

Bauxite Treatm ent of petroleumf tifractionsDrying of gases andliquids

M olecular sieves Selective rem ovalof contam inantsfrom hydrocarbons

TRP Chapter 6.2  16

Silica gel Drying and purifying gases

Sedimentation

•Used to separate particles held in suspension in a liquid which is principally aqueous•Uses gravity•May require mechanical or manual stirring•May require mechanical or manual stirring•Suitable for a wide range of hazardous wastes

•metals in waste watermetals in waste water•neutralised acids and alkalis containing suspended metal hydroxides•metals that have been precipitated

•The resulting sludges may need further screening, d i d i

TRP Chapter 6.2  17

drying or dewatering •Separated liquid may need further treatment

Sedimentation - exampleSedimentation example

TRP Chapter 6.2  18Source: Davd S Newby 1991

FlotationFlotation

•Used for treating particles which are less dense•Used for treating particles which are less dense than water

•Is suitable for a range of waste types, egoil/water separation

•Efficiency can be improved by blowing air through the liquidthrough the liquidsize of air bubbles should be varied 

according to waste type

TRP Chapter 6.2  19

according to waste type

Drying and evaporationy g a d e apo at o

May be needed after sedimentation

Options include:Options include: •Sludge drying beds   C if l i•Centrifugal separation 

•Filtering and pressing

TRP Chapter 6.2  20

Drying and evaporation - exampley g p p

Belt filter ‐ a continuous filtering process widely used for

TRP Chapter 6.2  21

Belt filter  a continuous filtering process widely  used for dewatering sludges

Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

Chemical processesChemical processes•aims to change chemical properties of haz waste 

d i i i h h dand to minimize the hazard •use chemical(s)  •need details of waste composition and reactivity•need details of waste composition and reactivity •need qualified staff to:

•assess waste compositionp•monitor chemical reaction •check reaction results

Options include:∙Reduction and oxidationN li i

TRP Chapter 6.2  22

∙Neutralisation∙Precipitation

Reduction and oxidationeduct o a d o dat o

Some common oxidising and reducing reagents:

Oxidising reagents 

•Sodium or calcium hypochlorite

Reducing reagents

•Ferrous sulphate

•Hydrogen peroxide

•Chlorine

•Sodium sulphite

•Sulphuric acidChlorine

•Potassium permanganate

UV

Sulphuric acid

•Iron

Al i i•UV

•Ozone

•Aluminium

•Zinc

TRP Chapter 6.2  23

•Sodium borohydride

Oxidation in practiceOxidation in practice

N d t d i f l ti t b f• Needs expert design, careful operation to be safe

• Is cost effective

• Enables avoidance of harmful side reactions

• Commonly used for cyanides• Commonly used for cyanides

Easiest oxidising reagents: 

sodium or calcium hypochlorite

TRP Chapter 6.2  24

sodium or calcium hypochlorite

Reduction in practiceReduction in practice

Commonly used for chromates and chromic acids from chromium plating and tanning industries

Cr VI           reduced to Cr III           then removed by e o ed byprecipitation

Common reducing reagents:•ferrous sulphate•sodium sulphite/sulphuric acid

TRP Chapter 6.2  25

Other chemical processesOther chemical processes

Practical options can include:Practical options can include:

•Hydrolysis, eg for some pesticides

•Electrolysis, eg for silver recovery from 

photographic wastewaters

•Dechlorination, eg for solvents or residues from 

hl i d h d b fchlorinated hydrocarbon manufacture 

TRP Chapter 6.2  26

Combined physical & chemical p yprocesses

T lTwo common examples:∙Solvent extraction∙Coagulation and flocculationCoagulation and flocculation

TRP Chapter 6.2  27

Coagulation and flocculation

Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

Physico-chemical treatment

TRP Chapter 6.2  28Source: David  S Newby

NetralisasiNetralisasiNetralisasi dilakukan dengan penambahan asam (H2SO4) ataubasa pada limbah korosif, hingga mencapai kisaran pH akhir 6‐9.

Basa‐basa penetral komersial yang umum digunakan untukmenetralkan limbah B‐3 adalah:• quicklime atau CaO, berbentuk bongkahan atau hancuran;• dolomitic lime, CaO.MgO, berbentuk bongkahan atau

hancuran;;• hydrated lime, Ca(OH)2, berbentuk serbuk;• dolomitic hydrated lime, Ca(OH)2 + Mg(OH)2, berbentuk

serbuk;serbuk;• limestone, CaCO3, berbentuk granul, serbuk, hancuran;• dolomite, CaCO3.MgCO3, berbentuk hancuran, granul, serbuk.

PRECIPITATIONA precipitation reaction is a reaction in

PRECIPITATION

which soluble ions in separate solutions are mixed together to form an insolublecompound that settles out of solution as acompound that settles out of solution as a solid. That insoluble compound is called a precipitateprecipitate.

Precipitation of Metals from WastewaterMetals PrecipitationTransforms dissolved contaminants into an insoluble solidTransforms dissolved contaminants into an insoluble solid, facilitating the contaminant's subsequent removal from the liquid phase by sedimentation and / or filtration. 

Usually accomplished by:•pH Adjustmentp j•Chemical Coagulation•Flocculation•Separation•Separation

Hydroxide Precipitation

Most soluble heavy metals will precipitatewhen pH is raised to a given valuewhen pH is raised to a given value

H i i d b ddi i f h d idpH is raised by addition of hydroxide

Cu(NO3)2(aq)       +     2 NaOH(aq)                    Cu(OH)2(s) + 2 NaNO3(aq) 3( q)

Hydroxide Precipitation

Sodium Hydroxide (NaOH) Caustic Soda

Calcium Hydroxide, Ca(OH)2H d t d LiHydrated Lime

DolomiteCa(OH) Mg (OH)Ca(OH)2 Mg (OH)2

Process WaterChemicalTreatment

..            

Equalization Tank Treatment Tank

Treated Water Clarifier

Filter PressBack ToEqualization Tank 

Sludge Tank

Sludge Bin

Cu(NO3)2(aq) + 2 NaOH(aq) ‐‐> Cu(OH)2(s) + 2 NaNO3(aq)

Ni(NO3)2(aq) + 2 NaOH(aq) ‐‐> Ni(OH)2(s) + 2 NaNO3(aq) 

2 AgNO3(aq) + 2 NaOH(aq) ‐‐> Ag2O(s) + 2 NaNO3(aq) + H2O(l) 

Precipitation of Metals from Wastewater

The Solubility of Metals is Dependent on pH

Hydroxide Precipitation

Cadmium 

Minimum Solubility (Best Removal) Value for Some Metals 

pH 11.0Copper pH 8.1

Chromium pH 7.5Nickel pH 10.8Zinc 

pH 10.1

Hydroxide PrecipitationNeed to Determine Optimum pH for Waste

Metals Precipitate at Various pH LevelsMetals Precipitate at Various pH Levels Depending on:

The Metal Being Precipitated

The Chemistry of the Wastewater

Other Metals PresentOther Metals Present

Presence of ChelatesPresence of Chelates

Metal PrecipitationPrecipitation of more than one metal from the same solution:Adjust for Optimum pH for One Metal(With Lowest Discharge Permit Limit)

Adjust for Compromise pH

Operate in Stages

Adjust pH for Each Metal in Stages

D Off Sl d T fDraw Off Sludge, or TransferSupernatant Between Stages

Expected Effluent Quality (mg/L) for Total MetalsHydroxide Precipitation

Precip + Precip +Settling Settling + Filtration

Expected Effluent Quality (mg/L) for Total Metals

Settling Settling + Filtration

Cr 0.1 to 1.0 0.05 to 0.5C 0 2 t 1 5 0 05 t 0 5Cu 0.2 to 1.5 0.05 to 0.5Ni 0.5 to 2.5 0.25 to 1.5Cd 0.2 to 1.5 0.05 to 1.0Zn 0.2 to 1.5 0.05 to 1.0

NaOH

Mix Tank Clarifier Filter

Hydroxide Precipitation of Soluble Metals

Many Metals are Amphoteric

Double solubility curve

pH must be carefully t ll dcontrolled

Presence of chelating agentswill interfere with ability to precipitate metalsprecipitate metals 

Chelates

An agent that will form a compound with a heavy metal ion, with the intended purpose of keeping the metal in l tisolution.

Generally used in plating solutionsGenerally used in plating solutions

Abigproblem in hazardous wastewater treatmentgp

Commonly Used Chelating Agents:Commonly Used Chelating Agents:

•Ammonia NH•Ammonia, NH3

•Phosphate•Phosphate

•EDTA•EDTA

Cit t•Citrate

C id•Cyanide

Methods of removing the chelate problem

1.  Precipitate at high pH: pH > 10  (may also add CaCl2)

2.  Add a material which the chelate prefers over the metal to be precipitated (Ferrous Sulfate)

3.  Use a reducing agent to convert the heavy metal from the ion back to the metal (Sodium Borohydride)

4. Use precipitating chemicals  that removes the metal from the chelate:•Sulfide•Sodium Dimethyldithiocarbamate (DTC)

Sulfide Precipitation of  Soluble Metals

Extremely Low Metal Solubilities

Often Preferred for Wastewaters Containing Chelating Agents

Disadvantages:

• More negative environmental impacts

• More costly (About twice cost as for OH)

• May produce H S in lethal concentrations• May produce H2S in lethal concentrations

Sulfide Precipitation of  Soluble Metals

Cu(NO3)2(aq) + Na2S(aq) ‐‐> CuS(s) + 2 NaNO3(aq)

CdCl2(aq) + Na2S(aq) ‐‐> CdS(s) + 2 NaCl(aq) 

Ni(NO3)2(aq) + Na2S(aq) ‐‐> NiS(s) + 2 NaNO3(aq) 

Ca(OH)2 FeS

Mix Tank Clarifier FilterMix Tank

OH OH + S

Clarifier FilterMix Tank

Precip + Precip +Settling + Settling +Filtration Filtration

Cr 0.05 to 0.5 0.01 to 0.20Cu 0 05 to 0 5 0 01 to 0 25Cu 0.05 to 0.5 0.01 to 0.25Ni 0.25 to 1.5 0.05 to 0.50Cd 0.05 to 1.0 0.01 to 0.25Zn 0.05 to 1.0 0.01 to 0.25

Sodium Dimethyldithiocarbamate (DTC or SDDC)(DTC or SDDC)

Organic sulfur compound 

Not pH sensitive – any pH above 3

Controls chelated waste streams 

Not pH sensitive  any pH above 3  

Non amphotericNon amphoteric

Very toxicVery toxic 

Agricultural insecticide 

Industrial biocide 

Sodium polythiocarbonate (PTC)Thio‐RedThio Red 

Much less toxic than DTC 

50% less sludge than DTC, lime or iron chemistries; 

Requires lower dosing of flocculent chemistry for li id/ lid tiliquid/solid separation

Treated waters pass toxicity tests for NationalTreated waters pass toxicity tests for National Pollutant Discharge Elimination System (NPDES) dischargesdischarges 

Hydroxide Precipitation of Soluble Metals

Metals are AmphotericDouble Solubility CurvepH Must be Carefully Controlled

Presence of Chelating Agents will Interferewith Ability to Precipitate Metals 

Hydroxide Sludges May be Difficult to DewaterHydroxide Sludges May be Difficult to Dewater

Metal Finishing Sludge is Classified as a Hazardous Wasteby Federal & State Law (RCRA)

Batch Treatment

ll f d f ll lUsually Preferred for Small Flows

Either a Holding Tank and Reaction Tank,or Two Reaction Tanksor Two Reaction Tanks

Reaction Tanks Serve Also as Clarifiers

Allows for Maximum Control of Effluent Quality

Influent Wastewater

NaO

H

NaO

H

EffluentEffluent

SludgeSludge

Continuous (Flow-Through) Treatment

Usually Used For Larger Flows

Addition of OH controlled by pH Meter / ControllerAddition of OH controlled by pH Meter / Controller

NaOHpH

Storage Reactg

FlocculationClarifier

Review – Metal Precipitation

1 Sodium Hydroxide is hazardous to handle in that it is both _____________ and ______________.toxic corrosive

2.  List three options for precipitating two metals with different optimum pH.

a.

b.

Optimize for one metal

Find a compromise pHb.

c.

Find a compromise pH

Operate as a two‐stage system

3.  Metal hydroxides that resolubilize if the pH increases or decreases from the optimum precipitation value are said to bedecreases from the optimum precipitation value are said to be __________________.amphoteric

4. Ammonia, phosphates, and EDTA are _______________agents used in plating solutions. 

chelating

5.  Describe the problem that may occur when precipitating metals from wastewater where the materials described in #4 are present.

Chelates hold metals in solution, not allowing them to precipitate.

6.  List 3 ways a wastewater treatment plant operator may be able to overcome the problem in #5 that is caused by the materials to overcome the problem in #5 that is caused by the materialslisted in #4.

a. Precipitate at high pH

b.

c.

Add a metal to tie up chelate

Add a chemical that steals metal

7 Recirculation of may be beneficial in that it

from the chelate (Sulfide)

precipitated sludge7. Recirculation of _________________ may be beneficial in that it provides “seed” material for the precipitation process. 

precipitated sludge