Electroflocculation Coagulation Process for Treatment of Heavy Metals Containing Wastewaters Prof' Y

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Electroflocculation Coagulation Process for
Treatment of Heavy Metals Containing
WastewatersProf. Yung-Tse Hung, Ph.D., P.E.,
DEE, F-ASCE, ProfessorDepartment of Civil and
Environmental EngineeringCleveland State
UniversityCleveland, Ohio 44115-2214
USAVisiting ProfessorSchool of Civil and
Environmental EngineeringNanyang Technological
UniversitySingapore 639798
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OUTLINES

• Overview
• Objectives
• Literature Review
• Theory
• Experimental Setup, Math Model
• Mathematical Model
• Results Cd, Zn, Cd and Zn Removal
• Conclusions

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• Overview
• USEPA new Effluent Guidelines became effective in
  December 2000.
• Applicable to Metal Product Machinery (MPM)
  industries.
• 200 different types of industries affected by new
  standard.
• Typical operations include
• Acid treatment, Adhesive bonding, Anodizing,
  Chemical conversion coating, Abrasive blasting,
  Corrosion preventive coating, Electroplating,
  heat treatment, Solvent degreasing, and Dip
  coating and sputtering.
• MPM industry regulation include
• New facilities
• Existing facilities

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EU DRINKING WATER DIRECTIVE STANDARDS FOR
HEAVY METALS

• Heavy Metal  1980 Directive/   1998
  Directive/        
• 1988 Regulations (a)
  2000 Regulations (b)
• mg/L
  mg/L
• Arsenic (As)    0.05    
  0.01      
• Mercury (Hg)    0.001    
  0.001      
• Chromium (Cr)    0.05
  0.05  
• Lead (Pb)  0.05    
  0.01      
• Nickel (Ni) 0.05      
  0.02      
• Selenium (Se)    0.01      
  0.01      
• Antimony  (Sb)   0.01      
  0.005
• The limit shown will apply in 2013. There is an
  interim limit of 0.025 mg/L
• In effect to 31 December 2003
• In effect from 01 January 2004

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OSHA regulates heavy metals in the work place
through Permissible Exposure Levels (PELs) for
airborne chemicals

• Metal/Compound PEL
• Permissible Exposure Level ( mg/m3)
• Lead, 0.005
• Metallic Cr, 1.0
• Insoluble Cr soluble Cr3 salts 0.5
• Cr6 chromates, chromic acid, 0.1 (This is the
  highest acceptable level)
• Nickel, nickel compounds, 1.0
• Cadmium, 0.2

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• Objectives
• To determine the optimal operational parameters
  of the ECF reactor
• To determine the cadmium, zinc, and organic load
  removal efficiencies of the ECF reactor at
  different applied current levels
• To observe the influence that organic load
  concentrations may have upon the heavy metal
  removal efficiency
• To develop a theoretical mathematical model that
  describes the kinetics in the ECF reactor

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• To develop an empirical mathematical model that
  correlates the independent variables affecting
  the heavy metal removal rates
• To make predictions of output concentrations
  using the developed models
• To present a cost estimate for scaled-up ECF
  reactor.

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• Literature review
• Electroflotation Performance Studies
• Ketkar, Mallikarjunan, and Venkatachalam, 1991
• Alexandrova, Nedialkova, and Nishkov, 1994
• Hosny, 1996
• Llerena, Ho, and Piron, 1996
• Poon, 1997
• Venkatachalam, and Setty, 1997
• Kolesnikov, and Varaxin, 1998

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• Electrode Materials
• Kamenev, Bibikova, Simonova, and Rusin, 1983
• Ho and Chan, 1986
• Mraz and Kryza, 1993
• Mraz and Kryza, 1994
• Zubareva, 1997
• Poon, 1997
• Romanov, 1998

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• Separating oil from oil-water emulsion by
  electroflotation technique
• by Ashraf Y. Hosny, 1996
• Studied oil removal by continuous flow
  electroflotation reactor.
• (8 x 9 x 30 cm) plexiglass electroflotation cell.
• Volume 1.5 to 2.5 liters.
• Stainless steel cathode and lead anode
• Oil droplet distribution
• (1 ?m 38, 2 ?m 25, 3 ?m 20, 4 ?m 10
  and 5 ?m 7)
• pH range was 4.5
• Flocculant (Nalco 7720) 4 to 32 mg/l

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• 3.5 wt salt to simulate seawater
• Presence of salt decreases the size of oil
  droplets.
• Flow rate from 10 to 50 ml/min
• Maximum oil removal efficiency 92
• Optimal operating conditions
• 1.2 amp, 40 min, 3.5 salt conc., 16 mg/L
  flocculant conc.
• Linear Regression
• oil removal -22.3 9.18x10-3 (C) 1.09
  (t) 27.13 (I)
• valid for C (500 2000 mg/l), I (0.3
  -1.2 amp), t (10 -40 min)

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• Electroflotation for groundwater
  decontamination
• by Calvin P.C.Poon, 1997
• Removal of Ni, Zn, Pb, Cu, CN by
  electroflotation.
• Studied relation between depth (D), power input
  (P), HDT
• (40 x 15 x 30 cm) plexiglass electroflotation
  cell.
• Volume 5.25 to 10.67 liters
• Stainless steel cathode and platinum-clad
  columbium anode
• pH range 7.86 to 10.58
• 3.0 wt rock salt to simulate seawater
• Batch and continuous studies (4.8 75 min HDT)
• Samples taken at three depths (10.3, 15.45, 20.6
  cm)

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• Optimal conditions
• treatment effectiveness increased with depth
• 75 min detention time
• Effluent Conditions
• 0.02 - 0.08 mg/l Cu
• 0.02 - 0.16 mg/l CN
• 0.04 - 0.52 mg/l Zn
• 0.10 - 0.34 mg/l Pb

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• Multiple Linear Regression
• Cu removal 7669 - 226 (P) 593 (D)
• r2 0.896
• CN removal 30108 - 829 (P) 2138 (D)
• r2 0.726
• Zn removal 2422 - 55 (P) 243 (D)
• r2 0.91
• Pb removal 10375 - 300 (P) 368 (D)
• r2 0.819

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• Theoretical Background
• Electrolytic reactions
• 3.2(a) 2 e- 2 H2O ?
  H2 (g) 2 OH-
• (0.83 volts)
• 3.2(b) 2 H2O ?
  O2 (g) 4 H 4e-
• (1.23 volts)
• Product of reduction at the cathode
• 3.3 NaCl ? Na Cl-
• 3.4 Na e- ? Na
  (2.71 volts)
• 3.5 2 H2O 2 e- ? H2 2 OH-
  (1.23 volts)

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• Product of oxidation at the anode
• 3.6 2 Cl- ? Cl2 2e-
  (1.36 volts)
• 3.7 2 H2O ? O2 4H 4e-
  (1.23 volts)
• Hypo-chlorite formation
• 3.8 Cl2 (g) 2 OH- (aq) ? Cl- (aq)
  OCl- (aq) H2O (l)
• Overall product in the electrolysis of aqueous
  NaCl solutions
• 3.9 2 NaCl(aq) 2 H2O(l) ? 2 Na (aq) 2 OH-
  (aq) H2 (g) Cl2 (g)

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• Chemistry of Cadmium and Zinc
• Cadmium Reactions
• 3.11 CdCl2? Cd2
  2 Cl-
• 3.12 Cd2 H2O ? Cd(OH)
  H-
• 3.13 Cd(OH) OH- ? Cd(OH)2
• 3.14 Cd(OH) 2Cl- ? CdCl2
  2Cl-
• 3.15 Cd(OH) 2Cl- ? CdCl(OH)

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• Zinc Reactions
• 3.16 ZnCl2 ? Zn2 2Cl-
• 3.17 Zn2 H2O ? Zn(OH) H-
• 3.18 Zn(OH) OH- ? Zn(OH) 2

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• Primary reaction products involving the iron
  metal
• 3.20(a) Fe(s) ? Fe2 2 e- ? Fe3 e-
  
• 3.20(b) 4 Fe(s) 3 O2 (g) ? 2 Fe2O3
• 3.20(c) 2 Fe2 Cl2 (g) ? FeCl2
• 3.20(d) Fe2 2 OH- ? Fe(OH) 2
• 3.20(e) Fe3 3 OH- ? Fe(OH)3

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Chemistry of Iron Corrosion MechanismFig. 3.2
Two Major Pathways Involving Production and
Depletion of Fe2
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Fig. 3.3 Electrode Corrosion and Dilution
Mechanisms
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Experimental Setup
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Experimental Procedures

• (A) Preparation of synthetic wastewater
• cadmium chloride, CdCl2
• zinc chloride, ZnCl2
• pH adjustment by addition of lime, Ca(OH) 2
• adjustment by NaCl to facilitate conductivity
• evaporated milk (D-lactose) as organic load.
• (B) Experimental Conditions
• treatment time 5, 10, 15, 30, 45 min
• pH range 8.0, 9.5, and 10.5
• applied current 1, 3, and 6 amp
• NaCl 0.2 2.0

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• TOC 0, 100, 500, 1000 mg/l.
• (C) Measured initial final pH, temperature,
  conductivity, and turbidity.
• Initial and final samples prepared for TOC
  and AA analysis.
• Data gathered and analyzed
• (D) Instrument
• 3100 Perkins Elmer Atomic Adsorption unit
• 5050A Shimadzu TOC analyzer with ASI 5000A
  autosampler
• Orion, Inc. Model 116 Quickchek portable pH meter
• YSI, Inc. Model 30/40 FT conductivity,
  temperature and salinity meter.
• Hach Model 2100A turbidity meter.

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Mathematical Model and Manipulation

• Primary processes responsible for the cadmium
  removal efficiency
• cadmium hydrolysis
• coagulation-flotation.

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Figure 4.1 Generalized schematic of the
electrocoagulation/flotation process
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• Mathematical expression of the process may be
  written as
• Koverall Khydrolysis Kcoag-flot
• Previous studies showed first order behavior
  (i.e., Kolesnikov, Kokarev, Shalyt, Varaksin, and
  Kodintsev (1989).
• Kolesnikov (1989)
• kinetic study of cadmium hydroxide
  electroflotation
• rectangular (50 x 40mm) 0.5 liters
  electroflotation reactor
• steel screen as the cathode
• titanium sheet with a metal oxide coating served
  as the anode
• experiments at pH 9.5
• cadmium hydroxide initial concentration of 0.2
  g/L
• current density varied between 50 to 150 A/m2

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• Model based on observations of plotted data (i.e.
  Reff vs applied current)
• Determination rate constant from plotted
  experimental data
• Adjusted rate constant as a function of applied
  current.
• Representative Equations for Model Development
• Based on the concepts of kinetics for
  conservative substances
• Operating conditions (constant volume,
  temperature, and pressure)
• Generalized Mass balance equation
• Min Mout dM/dt (Accumulated Mass)

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• Substance A as cadmium ion (Cd2) the total net
  mass going out is zero for a batch reactor, the
  previous equation may be rewritten as
• Min dM/dt
• Generalized mass equation for batch reactor
• N NA NA,o X
• Mass balance equation with the rate expression
• dNA/dt rAV
• Rearranging in terms of concentration values and
  dividing both sides by the total volume (V), the
  resultant expression is shown below
• (-1/V)(dNA/dt) -d(NA/V)/dt
• -dCA/dt -rA
  

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• Rate expression of cadmium ion removal can be
  written as
• -rA -KCA
• If equation 4.10 is substituted in 4.9, the
  following expression may be written
• -dCA /dt -K CA
  
• Integrating the last equation between the initial
  and final concentrations and treatment time
• ln CA/CAo
  -K t.
• Mathematical manipulations lead to
• CA CAoe
  - Kt

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• Initial solution procedure based on showing how
  last equation fit the gathered experimental data
• CA CAoe
  - Kt
• Plot ln CA/CAo versus treatment time
• Linear regression with slope calculation
• Linear regression evidences a first order
  behavior for the entire process.
• A linear correlation representative of an
  experimentally determined rate constant, K for
  applied current values.
• Relationships for applied current and pH were not
  determined due to the fact that these variables
  changed during experimentation.

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CHAPTER 6Determinations of Optimal Operational
Parameters of Electrocoagulation/Flotation (ECF)
Batch ReactorFig. 6-7

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Fig 6-13
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Fig. 6-19
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Fig. 6-23
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Fig. 6-24
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Fig. 6-25
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Fig. 6-29
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Fig. 6-30 (Combine Fig. 6-13, 6-25)
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Fig. 6-31 (Combine Fig. 6-19, 6-24)
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Fig. 6-33
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Fig. 6-35
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Summary of Results

• Chapter 6
• Cadmium removal efficiency ranged between 90 to
  99 for treatment times of 30 and 45 minutes,
  respectively at all applied current levels
• Cadmium concentrations of 30 mg/l were reduced to
  0.03 mg/l under the influence of lime and to 0.01
  mg/l under the influence of alum.
• Optimal operational parameters were obtained
• pH 9.5
• current (I) 3 amp
• Time (t) 30 min
• A directed relationship was observed between the
  final wastewater temperature and the applied
  current.

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CHAPTER 7Determining the Effects of Organic
Loadings upon the Cadmium Removal EfficiencyFig.
7-5
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Fig. 7-10
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Fig. 7-15
47
Fig. 7-20
48
Fig. 7-21
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Fig. 7-22
50
Fig. 7-23
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Fig. 7-24
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Fig. 7-25
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Fig. 7-26
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Fig. 7-27
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Fig. 7-28
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Fig. 7-29
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Fig. 7-30
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Fig. 7-31
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Fig. 7-32
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Fig. 7-33
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Fig. 7-34
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Fig. 7-38
63
Fig. 7-40
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• Chapter 7
• The ECF reactor was able to simultaneously remove
  cadmium metal and organic matter.
• Cadmium removal efficiency ranged between 68.02
  and 99.47 for treatment times between 15 and 30
  min, respectively for all applied current levels.
  
• Cadmium concentrations of 30 mg/l were reduced to
  0.0 mg/l under the influence of organic loads and
  lime as the coagulant, and to 0.08 mg/l under
  influence of alum.
• Organic load removal efficiencies ranged between
  44.05 to 48.29 for treatment times of 15 and 30
  min for all applied current levels with the
  addition of lime as the coagulant.
• Organic loads were reduced by a factor of 50
  with the addition of lime as the coagulant, and
  by 30.37 under the influence of alum. The
  organic material caused a detrimental effect on
  the bubble formation in the ECF reactor.
• Considerable higher volumes of sludge were
  collected for studies conducted under the
  influence of organic loads.

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CHAPTER 8Determination of Zinc Removal
Efficiency with and without Effects of Organic
LoadsFig. 8-22
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Fig. 8-27
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Fig. 8-28
68
Fig. 8-29
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Fig. 8-30
70
Fig. 8-31
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Fig. 8-38
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Fig. 8-39
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Fig. 8-40
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Fig. 8-41
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Fig. 8-42
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Fig. 8-43
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Fig. 8-44
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Fig. 8-45
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Fig. 8-46
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Fig. 8-48
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• Chapter 8
• Zinc removal efficiencies ranged from 99.01 to
  99.0 for treatment times between 15 and 30
  minutes, respectively for all applied current
  levels.
• Initial zinc concentrations from 30 mg/l to 0.04
  mg/l under the influence of lime as the
  coagulant and to 0.01 mg/l under the influence
  of alum as the coagulant.
• Zinc removal efficiencies ranged between 99.01 to
  99.0 for treatment times of 15 and 30 minutes,
  respectively for all applied current levels.
• TOC removal efficiencies ranged around 56.99 for
  applied current values of 3 amperes.
• It was found a direct relationship between the
  organic load removal efficiency and the initial
  organic load concentration.

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CHAPTER 9DETERMINATION OF COMBINED REMOVAL
EFFICIENCIES FOR ZINC AND CADMIUM METAL USING
ELECTROCOAGULATION/FLOTATION TECHNOLOGY
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Fig. 9-2
84
Fig. 9-3
85
Fig. 9-4
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• Chapter 9
• Heavy metal removal efficiencies ranged between
  90.84 to 92.11 for cadmium and 97.74 to 98.30
  for zinc.
• Organic load removal efficiencies ranged between
  4 to 9 and 47.7 to 48 after 5 and 30 minutes of
  treatment time, respectively for all applied
  current levels.
• Organic loads had some negative effect upon the
  heavy metal removal efficiencies.

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CHAPTER 10Determination of Heavy Metal Removal
Efficiencies for ECF BatchReactor Using
Steady-State Theoretical and Empirical
ModelsFig. 10-3
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Fig. 10-4
89
Fig. 10-5
90
Fig. 10-10
91
Fig. 10-11
92
Fig. 10-17
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Fig. 10-20
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• Chapter 10
• Theoretical Model
• A theoretical model was developed based on the
  concepts of first order chemical kinetics.
• At low treatment times (i.e., 5, and 10 minutes)
  the model predicted lower final concentrations
  when compared to actual concentrations.
• Empirical Model
• A completely empirical model was developed using
  an SPSS computer package.
• Empirical mathematical relation is shown below
• Y() 55.079 5.101 (I) 0.08567 (C)
  1.741 (T) - 4.688 (A)
• valid for I (1- 3 amp) C
  (10-30 mg/l) T (5-45 min) A(8,9.5,10.5)
• where,
• Y predicted heavy metal removal
  efficiency, percentage ()
• I measured applied current, amperes
• C initial measured heavy metal
  concentration, (mg/l)
• T treatment time, minutes
• A acidity of solution, as measured in pH
  units.

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• Applied current and treatment time appeared to be
  the strongest variables influencing the predicted
  removal efficiencies.
• The empirical model tend to under and
  overestimate the values for removal efficiency
  when compared to the measured concentrations.
• The model predicted values over 100 percent after
  30 and 45 minutes of treatment time and at high
  applied current levels.
• The great variability between the calculated and
  predicted values may be attributed to the
  variation in the instrument readings