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Performance evaluation of hybrid electrocoagulation process parameters for the treatment of distillery industrial effluent
Accepted Manuscript Title: Performance evaluation of hybrid electrocoagulation process parameters for the treatment of distillery industrial effluent Author: P. Asaithambi Baharak Sajjadi Abdul Raman Abdul Aziz Wan Mohd Ashri Bin Wan Daud PII: DOI: Reference:
S0957-5820(16)30222-1 http://dx.doi.org/doi:10.1016/j.psep.2016.09.023 PSEP 885
To appear in:
Process Safety and Environment Protection
Received date: Revised date: Accepted date:
21-3-2016 26-8-2016 28-9-2016
Please cite this article as: P., Asaithambi, Sajjadi, Baharak, Abdul Aziz, Abdul Raman, Wan Daud, Wan Mohd Ashri Bin, Performance evaluation of hybrid electrocoagulation process parameters for the treatment of distillery industrial effluent.Process Safety and Environment Protection http://dx.doi.org/10.1016/j.psep.2016.09.023 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Performance evaluation of hybrid electrocoagulation process parameters for the treatment of distillery industrial effluent P. Asaithambi*, Baharak.Sajjadi, Abdul Raman Abdul Aziz*, Wan Mohd Ashri Bin Wan Daud Department of Chemical Engineering, Faculty of Engineering, University of Malaya, Malaysia – 50603. *Corresponding author: Tel.: +60 3 7967 7687; Fax: +60 3 79675319 Email address: [email protected](P. Asaithambi) [email protected](A. R. Abdul Aziz)
1
Graphical Abstract
DC power supply V
UV Lamb
100 Color removal COD removal Removal Efficincy, (%)
80
60
__ __ ___ __ __ __ __ __ __ __ ____ __ __ _ __ _____ _ _ _ _ _ _ __ _ _ __ __ ___ _ _ _ _ _ __ _ _ ___ __ __ _ _ _ __ ___ _______ __ __ __ __ __ __ __ _________ _ ____ ___ __ __ __ __ __ __ __________________________ ___ ___ _ __ __ ___ _ __ _ __
40
20
0 EC
EC+UV EC+UV+H2O2 EC+H2O2 Hybrid Electrocoagulation Process
Hybrid H2O2/UV/EC
2
+
A
-
H2O2
Research highlights
Hybrid electrocoagulation processes for removal of pollutants were investigated
Various electrocoagulation process were compared in terms of electrical energy consumption and color, COD removal
Effects of operating parameters in peroxi –electrocoagulation were studied
The direct- and alternating-current electrocoagulation processes were investigated
Abstract A hybrid electrocoagulation process using iron electrode was developed for removal of organic pollutants from distillery industrial effluent.
Combinations of electrocoagulation process with
different advanced oxidation processes such as electrocoagulation, photo–electrocoagulation, peroxi– 3
electrocoagulation and peroxi–photo–electrocoagulation processes investigated and compared in terms of color removal, Chemical Oxygen Demand (COD) removal and electrical energy consumption. An overall COD removal efficiency of 85% with 1.20kWh/m3 of energy consumption, current density of 0.13 A/dm2, initial COD concentration of 2500 ppm, initial pH of 7, H2O2 concentration of 234 mg/L, stirring speed of 100 rpm and reaction time of 240 min was observed in the peroxi–electrocoagulation process. The effects of different operating parameters such as initial pH of the effluent (3 to 11), current density (0.03 to 0.23 A/dm2) and concentration of H2O2 (58.5 to 585 mg/L) on color removal, COD removal and electrical energy consumption were studied. The directand alternating-current electrocoagulation processes were also studied. Keywords:
Distillery
effluent;
peroxi-photo-electrocoagulation;
alternating
current
electrocoagulation; COD removal; electrical energy consumption.
1.
Introduction
Electrocoagulation is an inexpensive process for treatment of various industrial effluents (Al-Shannag et al. 2013; Al-Shannag et al. 2015; Al-Shannag et al. 2014; Arun Kumar Sharma and Chopra 2015; Al-Shannag et al. 2012; Berrin Zeliha et al. 2014; Tianlong Zheng et al. 2015) to eliminate a wide 4
range of pollutants from the wastewater. Metallic electrodes like Iron, Aluminum are usually used as an anode which offers the anodic oxidation and in situ generation of active adsorbent of metallic hydroxides for the removal of the pollutants. In the cathodic reaction, hydrogen gas evolved which causing flotation of the adsorbants (Modirshahla et al. 2007; Sebastian Seculaa et al. 2011; Akbal et al. 2011). Many studies on removal of wastewater to ensure good-quality effluent have been done before its discharge into aquatic environment. Gomes et al. applied electrocoagulation for the treatment of wastewater containing high chemical oxygen demand and dissolved metal impurities. In recent years, new advanced oxidation processes induced by electrochemistry have been studied as an alternative approach for wastewater treatment (Sergi et al. 2012; Asha Keerthi et al. 2014). A combination of electrochemical processes with advanced oxidation processes is an interesting solution. In such a synergetic way, removal efficiency is maximized with minimal operating costs. The Electrochemical Advanced Oxidation Processes (EAOPs) provide several advantages for the prevention and remediation of pollution problems because the electron is a clean reagent. Other advantages of EAOPs include economic friendly requirement, versatility, amenability to automation, high energy efficiency, easy handling, simple equipment set up and also can be operated in room temperature and pressure. EAOPs are characterized by production of hydroxyl radicals and due to their nonselective characteristic, which is able to oxidize and mineralize most organic and inorganic pollutants to produce H2O, CO2 and inorganic ion (Sire´s et al. 2007). Hydroxyl radicals can be generated by a variety of chemical, electrochemical, photo assisted electrochemical methods, photo catalysis, Fenton’s methods, ozone-based methods, sonochemical methods and radiolytic methods. Depending on the types of AOPs, ultraviolet (UV) of λ reaching 200–300 nm could be used to produce •OH radicals. 5
The process of distillery industry results in release of huge amount waste and wastewater which have highly colored contains high organic and inorganic substances, COD, Biochemical Oxygen Demand (BOD), Total Organic Carbon (TOC), slightly acidic pH, etc. The distillery effluents need comprehensive treatment to meet the prescribed standard for disposal into natural water bodies. Many processes are used to remove pollutants from distillery effluents such as electro oxidation (Piyaareetham et al. 2006), electrocoagualtion (Krishna et al. 2010), bio–electrochemical methods (Mohanakrishna et al. 2007), ultrasound and enzyme-assisted biodegradation (Sangave et al. 2006), ozonation with aerobic oxidation (Sangave et al. 2007), anaerobic fluidized bed reactor (Fernández et al. 2008), nanofiltration (RaiUmesh et al. 2008), activated carbons (Satyawali et al. 2007) and coagulation (Liang et al. 2009). A comparison of various processes and electrocoagulation process for the removal pollutant from distillery wastewater was given in Table. 1 and table. 2. Alternatively, hybrid electrocoagulation can be an efficient and effective technique for treatment of distillery industrial effluent with low energy consumption, high quality effluent and low sludge formation can be made as desirable process for the treatment. In this study, hybrid electrocoagulation processes were investigated for the treatment of distillery industrial
effluent.
Performance
of
electrocoagulation,
peroxi–electrocoagulation,
photo–
electrocoagulation and peroxi–photo–electrocoagulation process using iron plate electrodes was compared in terms of electrical energy consumption, colour and COD removal. Effects of pH, current density and concentration of H2O2 on colour removal, COD removal and electrical energy consumption were studied for the treatment effluent in the peroxi – electrocoagulation process. The direct- and alternating-current electrocoagulation processes were also investigated. Influence of pulse duty cycle on alternating - current electrocoagulation process was studied. 1.1. Mechanisms of various electrocoagulation processes 6
1.1.1 Electrocoagulation The commonly accepted mechanism of removal of pollutants by electrocoagulation process with iron electrodes can be written as (Ayhan et al. 2009). Anodic reaction: Fe( s ) Fe(2aq ) 2e
Eo = -0.44 V vs SHE
(1)
Eo = 0.83 V vs SHE
(2)
Cathodic reaction:
2H 2O(l ) 2e H 2 ( g ) 2OH(aq) Overall reaction: Fe 2H 2O Fe(OH ) 2( s ) H 2( g )
(3)
If oxygen is present, dissolved Fe2+ is oxidized to insoluble Fe(OH)3 4Fe(2aq ) 10 H 2 O( l ) O2 ( g ) 4 Fe(OH ) 3( S ) 8H ( aq)
(4)
The Fe(OH)n(s) remains in the aqueous stream as a gelatinous suspension, which can remove the pollutants from the wastewater by either complexation or electrostatic attraction followed by coagulation. 1.1.2 Peroxi – electrocoagulation In an electrocoagulation system, H2O2 is added into the electrocoagulation system and a sacrificial Fe anode is used as the Fe2+ source.
Fe 2 H 2O2 Fe 3 OH OH
(5)
This reaction is propagated from ferrous ion regeneration mainly by reduction of the produced ferric species with hydrogen peroxide.
Fe 3 H 2O2 Fe 2 HO2 H
(6)
7
Ferrous ions are consumed more rapidly than they are produced. In addition, ferrous ions can be rapidly destroyed by hydroxyl radicals with the rate constant in the range of 3.2–4.3 X 108M-1 s-1 (Sun and Pignatello 1993; Farhadi et al. 2012). Fe 2 OH Fe 3 OH
(7)
Therefore, more ferrous ion dosage is needed to maintain hydroxyl radicals production in a moderate amount. This results in a large amount of ferric hydroxide sludge during neutralization stage of Fenton process, which requires additional separation process and disposal. 1.1.3 Peroxi – photo – electrocoagulation The performance of the electrocoagulation and peroxi–electrocoagulation process can be improved by using UV radiation, which is known as photo–electrocoagulation and peroxi-photo-electrocoagulation process (Farhadi et al. 2012). This process is improved due to higher production rate of •OH from the photoreduction of Fe(OH)2+ and photodecomposition of complexes from Fe3+ reactions as shown in equation (8) & (9). Fe(OH ) 2 hv Fe 2 OH
(8)
R(CO2 ) Fe 3 hv R( CO2 ) Fe 2 R CO2
(9)
2.
Material and Methods
2.1. Material The effluents were collected from distillery industries in nearby Malaysia. The main characteristics of the effluent are given in Table. 3. The chemicals used in the experiments were hydrogen peroxide (50% w/w) as the oxidizing reagent, sulphuric acid and sodium hydroxide to adjust the pH value. The other chemicals such as (NH4)2Fe(SO4)2.6H2O, K2Cr2O7 were of analytical grade and purchased from Merck Company. Only double distilled water was used to prepare the entire solution. 2.2.
Experimental Methods 8
The electrocoagulation process consisted of rector made-up of acrylic sheet with a capacity of 2.5 L (10 cm x 15 cm x 16 cm) and the working volume of the effluent was 2.0 L as shown in Fig. 1. The pH of the effluent was adjusted to the desired value using 0.1N H2SO4 or 0.1N NaOH solutions. Iron (grade MS 104) plates of 1 mm thickness were used as the anode and cathode. The electrode dimensions were 10 cm x 15 cm x 0.1 cm and the mode of electrode connection was bipolar. The distance between the anode and cathode was 3 cm in the electrochemical cell. In addition, two extra iron plates were inserted between anode and cathode to improve and produce more coagulant precursors which could enhance pollutant removal. The total effective electrode surface area was 100 cm2 and a gap of 5 cm was maintained between the electrodes and the bottom of the electrochemical cell to facilitate stirring. Magnetic stirrer was used in the reactor to maintain uniform concentration. The electrodes were cleaned with 15% HCl followed by distilled water prior to each experiment. The electrodes were connected to a direct-current power supply with galvanostatic operation for controlling the current density. An alternating pulse current electrocoagulation (0- 5A, 0 – 270 V, 50 Hz; AMETEK Model: EC 1000S) was carried out to investigate the alternating-current electrocoagulation process. For the photo–electrocoagulation process, a 16 W low-pressure mercury lamp was placed above the electrocoagulation cell. The distance between the UV lamp and treating solution was maintained at 10 cm. The peroxi–electrocoagulation and peroxi–photo– electrocoagulation process was carried out in the same system by only adding H2O2. All the experiments were carried out at a controlled temperature of 351°C. During the experiments, the samples were collected from the electrochemical reactor at regular time intervals and centrifuged (12,500 rpm, 20 min). Then, the colour and COD removal were measured. The COD tests were measured by a dichromatic closed reflux method according to the Standard Methods [APHA]. The colour was measured at the wavelength 9
corresponding to the maximum absorbance λmax (300 nm) using an UV/Vis spectrophotometer (Jasco, V-570). The percentage color removal was calculated by the following using equation Colour removal efficiency (%) =
([ ABS i ] [ ABS t ]) 100 ABS i
(10)
Where ABSi and ABSt are absorbance of samples at initial and different reaction time t for corresponding wavelength max. The percentage COD removal was calculated using equation COD removal efficiency (%) =
([CODi ] [CODt ]) 100 CODi
(11)
Where [CODi]is the initial COD value (mg/L) and [CODt]is the COD value at any reaction time, t (mg/L). The total electrical energy consumption of peroxi–photo–electrocoagulation process can be calculated by the following equation. The total electrical energy consumption = EEC + EUV
(12)
Electrical energy consumption for the electrocoagulation process (EEC). EEC = VIt / VR
(13)
Where, V is the cell voltage (V), I is the applied current (A), t is the electrolysis time (hour), VR is the volume of the effluent (L). Electrical energy consumption for the photo system (EUV).
EUV =
Pel * t *1000 C V * 60 * log i C f
(14)
10
Where, Pel is the electrical power input (kW), t is the irradiation time (min), V is the volume of effluent used (L), Ci and Cf is the initial and final effluent concentration (ppm) 3.
Results and discussion
3.1 Comparison of various electrocoagulation processes Various hybrid electrocoagulation processes were carried out based on the operating conditions such as current density of 0.13 A/dm2, COD concentration of 2500 ppm with initial pH of 5. The electrocoagulation system had an anode and cathode with an inter electrode distance of 3 cm and the electrodes were connected in a bipolar manner. The COD removal efficiency and electrical energy consumption of various hybrid processes are shown in Fig. 2. The COD removal percentage by electrocoagulation,
photo–electrocoagulation,
peroxi-electrocoagulation
and
peroxi-photo-
electrocoagulation processes was found to be 72%, 78%, 85% and 82% respectively after 4 hours of reaction. Addition of UV source showed positive effects on the electrocoagulation process due to increased availability of photo active sites. The economical aspect of a hybrid process is always associated with electrical energy consumption. The minimum electrical energy consumption of 1.2kWhr/m3 was required for the removal of 85% COD in the peroxi–electrocoagulation process. The remaining hybrid processes had higher electrical energy consumption compared to the peroxi– electrocoagulation process. 3.2 Peroxi –electrocoagulation process 3.2.1 Effect of current density The effect of current density on color and COD removal for wastewater with initial COD concentration of 2500 ppm and addition of H2O2 at initial pH of 5 was studied. The color and COD removal efficiency and electrical energy consumption are shown in Fig. 3. The experimental results show that the color and COD removal efficiency increased from 31 to 100% and from 25 to 97% with 11
increasing current density from 0.03 to 0.23 A/dm2. The percentage of color and COD removal efficiency increased sharply with current density up to 0.13 A/dm2. Further increase of current density did not significantly improve removal of COD. However, electrical energy consumption increased linearly with current density. It is well known that current density determines the production of coagulant and size of bubbles. Therefore, it is recommended that the peroxielectrocoagulation process to be operated at limited current density in order to avoid excessive oxygen evaluation and eliminate adheres effect. 3.2.2 Effect of H2O2 concentration It is important to optimize the amount of H2O2 used in the peroxi-electrocoagulation process due to cost and adherent effects caused by excessive H2O2. The effects of H2O2 concentration on color and COD removal efficiency are demonstrated in Fig. 4. The results showed that maximum COD removal of 97% at optimum H2O2 concentration of 234 mg/L was achieved after electrolysis duration of 4 hr. The COD removal occurred due to both electrocoagulation and Fenton processes. When the dosage of H2O2 concentration increased from 58.5 to 234 mg/L, the COD removal efficiency increased from 76 to 97%. However, further increase of H2O2 from 234 to 585 mg/L reduced COD removal efficiency to 73%. The experimental results showed that most of organic pollutants in an effluent could be oxidized by hydroxyl radicals. Also the hydroxyl radical was generated by H2O2, which could enhance the oxidation ability of treatment along with increment of concentration of H2O2. The decrease trend indicated that the over – abundant H2O2 could also consumed hydroxyl radical and become the elimination reagent hydroxyl radical (Farhadi et al. 2012). 3.2.3 Effect of initial pH The influence of initial pH of the solutions was studied with initial COD concentration of 2500 ppm and current density of 0.13 A/dm2 by adding 234 mg/L of H2O2. Fig. 5 shows the color and COD 12
removal at different initial pH. It was found that the optimal pH value was 5. Formation of Fe(OH) 3(s) did not only reduce the dissolved Fe3+ concentrations, but also inhibited Fe2+ regeneration by partially coating the electrode surface (Qiang et al. 2003). In acidic conditions, Fe3+ can be hydrated and species such as Fe(OH)2+, Fe(OH)2+ and Fe2(OH)24+ are present in the electrocoagulation system. Ionic species such as Fe(OH)6- and Fe(OH)4- can be found in an alkaline medium. In a homogeneous Fe3+ solution in an acidic medium, the main equilibrium hydrolysis reactions are as follows (Stumm et al. 1996).
Fe 3 H 2O FeOH 2 H
(15)
Fe 3 2H 2O FeOH 2 2H
(16)
2Fe 3 2H 2O Fe2 (OH ) 42 2H
(17)
Fe(OH)n(s) formed during the electrocoagulation process remains in the aqueous stream as a gelatinous suspension at 3 < pH < 11, which can remove the pollutants from wastewater either by complexation or by electrostatic attraction, followed by coagulation. Complexation, accompanied by Fenton oxidation may occur in the electro-Fenton process at pH 5. Effects of initial pH on electrical energy consumption were determined and the results are shown in Fig. 5 It was found that the electrical energy consumption increased from 1.16 to 1.47kWh/m3 with increasing initial pH from 3 to 7. However, the electrical energy consumption was found to reduce from 1.47 to 0.90kWh/m3 with increasing initial pH from 7 to 11. This might be due to the decrease in the conductivity of the electrolyte when pH changed from acidic to neutral condition and the increase in the conductivity of the electrolyte when pH changed from neutral to alkali condition in the peroxi – electrocoagulation process. 3.3 Comparison of direct current and alternating pulse electrocoagulation process 13
Direct-current electrocoagulation processes produces sludge and possibly, an impermeable oxide layer on the cathode, which is accompanied by deterioration of the anode due to oxidation. The passivation and mass transport control between the anode and cathode reduce the efficiency of the direct
current
electrocoagulation
process
was
declines.
Therefore,
alternating-current
electrocoagulation process has been proposed in order to overcome these difficulties (Keshmirizadeh et al.2011; Ren et al. 2011; Vasudevan et al. 2011; Eyvaz et al. 2009). An alternating-current electrocoagulation process can prevent the passivation of electrode material, reduce sludge, reduce electrical energy consumption and increase pollutant removal efficiency with minimum electrical energy consumption. In this process, anode and cathode are periodically interchanged and operating for 15 min until electrocoagulation is complete. The experimental conditions such as current density (0.13 A/dm2), effluent concentration (2500 ppm), effluent pH (7) and electrode distance (3cm) were studied. The direct-and alternating-current electrocoagulation processes were carried out and the results are shown in Fig. 6. The results showed that the COD removal was higher with lower electrical energy consumption in the case of alternating current electrocoagulation compared to direct-current electrocoagulation. The formation of impermeable layer and sludge are very low compared to the direct-current electrocoagulation process. Effect of pulse duty cycle is a very important parameter in an alternating-current electrocoagulation process. Fig. 7 shows that color and COD removal percentage increased from 80 to 95% and from 76 to 87% with increased pulse duty cycle from 0.2 to 0.5. The color and COD removal efficiency decreased from 95 to 81% and from 87 to 75%, respectively with further increase of pulse duty cycle from 0.5 to 0.8. Electrical energy consumption for different pulse duty cycles was also studied, as shown in Fig. 7. The results indicated that electrical energy consumption decreased from 1.32 to 1.31 kWh/m3 with increased pulse duty cycle from 0.2 to 0.5. Hence, by increasing the pulse duty cycle from 0.50 to 0.80, the electrical 14
energy consumption also increased from 1.31 to1.32 kWh/m3. At low and high pulse duty cycle, the removal efficiency of alternating-current electrocoagulation was similar to that of electrocoagulation. The experimental results showed that the pulse duty cycle should be operated between 0.40 to 0.60. Ren et al. (2011) investigated the pulse electro-coagulation technology for removal of refractory berberine hydrochloride from wastewater, the energy-relevant costs of pulse electrocoagulation and electro-coagulation were compared and it showed that pulse electrocoagulation saved 90% of energy compared to electrocoagulation. Cost estimation Cost estimation is very important economical parameters in hybrid electrocoagulation process like all other electrochemical and advanced oxidation process. The operating cost includes cost of electrodes, electrical energy, chemical consumed, as well as labor, maintenance, cost of sludge disposal and other fixed costs. Thus, the operating cost can be calculated using the following equation (Bayramoglu et al.2007; Bayramoglu et al.2004 ). Operating cost = aEEC + bELC + cCC
(18)
Where, EEC = electrical energy consumed – kWh/m3, ELC = electrode consumed– kg/m3 and CC = chemical consumed – kg/m3 (Sridhar et al. 2011). Under optimum condition such as COD concentration: 2500 ppm; current density: 0.13 A/dm2; initial pH: 7; H2O2 concentration: 234 mg/L; stirring speed: 100 rpm; reaction time: 240 min, the electrical energy, electrode and chemical consumptions were found to be 5.40 kWh/m3, 0.25 kg/m3 and 1.25 kg/m3, respectively. The operating cost was calculated under optimum condition using the equation (18) and it was found to be 1.25 US $/m3. 3.4 Conclusion
15
The performance of electrocoagulation, peroxi–electrocoagulation, photo–electrocoagulation and peroxi-photo-electrocoagulation processes for color removal, COD removal and energy consumption from the distillery industry effluent was investigated. The most efficient and effective decolorization and degradation were observed in the peroxi– electrocoagulation process compared to the other electrochemical advanced oxidation processes. The percentage colour and COD removal showed that the 100 and 86% in were achieved in the peroxi – electrocoagulation process with the minimum electrical energy consumption of 1.2kWhr/m3. Direct- and alternating-current electrocoagulation process were designed and applied for color and COD removal from distillery effluent with minimal energy consumption. Alternating-current electrocoagulation process was found to be more efficient than the direct-current electrocoagulation process. Acknowledgement The authors are grateful to the University of Malaya High Impact Research Grant (HIR-MOHED000037-16001) from the Ministry of Higher Education Malaysia which financially supported this work.
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List of tables Table.1. Comparison of some removal efficiencies technologies from distillery wastewater
Table.2. Electrocoagulation techniques for the treatment of distillery wastewater 20
Table.3. Characteristics of distillery wastewater
List Figures Fig.1. The schematic experimental setup for the peroxi – photo – electrocoagulation processes to the treatment of distillery effluent.
Fig.2. Comparison of various electrocoagulation process in terms of percentage COD removal and electrical energy consumption (conditions: COD concentration: 2500 ppm, current density: 0.13 A/dm2, initial pH: 7, H2O2concentration:234 mg/L, stirring speed: 100 rpm, reaction time: 240 min)
Fig.3. Influence of current density on percentage color removal, COD removal and electrical energy consumption (peroxi – electrocoagulation process; condition: COD concentration: 2500 ppm, initial pH: 7, H2O2 concentration: 234 mg/L, distance between anode and cathode: 3 cm, stirring speed: 100 rpm, reaction time: 240min)
Fig.4. Effect of hydrogen peroxide on percentage color removal, COD removal and electrical energy consumption (peroxi – electrocoagulation process; condition: COD concentration 2500 ppm, current density: 0.13 A/dm2, initial pH: 7, distance between anode and cathode: 3 cm, stirring speed: 100 rpm, reaction time: 240min)
Fig.5. Effect of initial pH on (a) percentage color, COD removal and electrical energy consumption (peroxi – electrocoagulation process; condition: COD concentration 2500 ppm, current density: 0.13 21
A/dm2, H2O2 concentration: 234 mg/L, distance between anode and cathode: 3 cm, stirring speed: 100 rpm, reaction time: 240min)
Fig.6. Performance of direct and alternating current electrocoagulation for thepercentage COD removal. (condition: COD concentration: 2500 ppm, current density: 0.13 A/dm2, initial pH: 7, distance between anode and cathode: 3 cm, stirring speed: 100 rpm, reaction time: 240 min)
Fig.7. Effect of pulse duty cycle on percentage color, COD removal and electrical energy consumption. (condition: COD concentration: 2500 ppm, current density: 0.13 A/dm2, initial pH: 7, distance between anode and cathode: 3 cm, stirring speed: 100 rpm, reaction time: 240 min)
Method
Removal efficiency
Optimum conditions
Literature
Electro oxidation
Color - 92.24%, COD 89.62%, BOD - 83.80%, TDS - 38.00%, TS 67.77%
current intensity - 9 A, initial pH - 1, anode - titanium sponge and NaCl - 1.0 M
Piya-areetham et al. 2006
Bio – electrochemical
COD – 72.84%, Color – 31.67%, TDS – 23.96%
MFC - open-air cathode, fedbatch mode under acidophilic pH-
Mohanakrishna et al.2007
22
6, Current: 2.12 – 2.48 mA Ultrasound and enzyme assisted biodegradation
COD – 62.5%, rate constant – 0.0310 h-1
Time - 36 hour,
Sangave et al. 2006
Ozonation with aerobic oxidation
COD – 79%, color – 34.9%
Ozone flow rate = 46.1 mls-1, ozone concentration - 1.9 x 10-2 g l-1, effluent pH -7.4 -7.6, impeller speed = 700 rpm
Sangave et al.2007
Anaerobic fluidized reactor
COD – 80%
organic loading rate - 2 to 5 g COD/l d, the fluidization level 20% and 40%, and the particle diameter of the natural zeolite0.2 to 0.8
Fernández et al. 2008
Nanofiltration
Color – 98-99.5%, COD – 96-99.5%, TDS – 8595%
pH - 4.0–7.0, Temperature 27⁰C, pressure - 1-5 bar, flow rate - 250 L/h
RaiUmesh Kumar et al. 2008
Activated carbons
Color – 80%
Commercially activated carbon
Coagulation
Color -96%, COD -86%
pH-8, Ferric salt - 3.5 g/L,
bed
Satyawali et al. 2007 Liang et al. 2009
Table. 1.
Types of electrode
Removal Efficiency (%)
Operating time
Optimum conditions
23
Literature
Fe
COD = 46.6%, Color = 80.3%, Turbidity=92.3%
90 min
pH=7, current density=300A/dm2,
Al
COD = 48.5%, Color = 97.2.3%, Turbidity=98.6%
120 min
pH=5.2, current density=300A/dm2,
Al-Shannag et al. 2015
Fe
COD =50.5%, color =95.2%
120 min
current density = 44.65 A/m2; initial pH (pH0)=8; inter-electrode distance= 2 cm
Modirshahla et al. 2007
Al
COD=81.3%
2hour
current density = 0.187A/cm2; pH=3; inter-electrode distance = 2 cm
Sebastian Secula et al. 2011
Fe
Color = 95%
4 hour
Current density = 31mA/cm2, dilution = 17.5%,
Akbal et al. 2011
Fe
Color=100, COD=62%
4hour
initial COD concentration: 2500 ppm, current density=3 Adm−2, initial pH= 6,
Sergi GarciaSegura et al .2012
Table.2.
24
Al-Shannag et al. 2015
Parameters
Range
pH
4.1- 4.3
COD
80,000 - 90,000 mg/L
BOD
7,000 - 8,000 mg/L
TSS
15.44 g/L
TDS
5550-5750 mg/L
Colour
dark brown
odour
burnt sugar
Table.3.
25
Mains
8
220/230 V AC / 30Hz
Volt
7
3
+
Amp
6
2
4 1
5
Fig. 1.
26
1. 2. 3. 4. 5. 6. 7. 8.
Electrocoagulation cell Anode (Iron) Cathode (Iron) Bipolar electrodes Magnetic Stirrer DC power supply UV Lamp Power Card
-
1.5 1.45
COD removal, (%)
80
1.4 60 COD removal 40
1.35
Electrical energy consumption 1.3
20
1.25
0
1.2
EC
EC+UV EC+UV+H2O2 EC+H2O2 Vrious process
Fig. 2.
27
Electrical energy consumption, (kWh/m3 )
100
2.5
80
2
60
1.5
40
1 Colour removal, (%) COD removal, (%) Electrical Energy Consumption
20
0 0
0.5
0 0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 Current density, (A/dm2 ) Fig. 3.
28
Electrical Energy consumption, (kWh/m3 )
Removal Efficiency, (%)
100
100
Removal, (%)
80
60
Colour emoval, (%) COD removal, (%)
40
20
0
0
100
200 300 400 500 Concentration of H2 O2, (mg/L)
Fig. 4.
29
600
100
1.6
1.2 60
COD removal (%)
0.8 colour removal (%)
40 Electrical energy consumption
0.4 20
0
0 1
3
5
7 Effluent pH Fig. 5
30
9
11
13
Electrical Energy Consumption, (kWh/m3 )
Removal Efficiency, (%)
80
100
COD removal, (%)
80
Alternating Current Direct Current
60
40
20
0 0
30
60
90
120 150 Time, (min)
Fig. 6.
31
180
210
240
80
1.315
60
1.31
40
1.305
20
1.3
Colour removal, (%) COD removal, (%) Electrical energy consumption
0
1.295 0
0.2
0.4
0.6
Pulse duty cycle
Fig. 7.
32
0.8
1
Electrical energy consumption (kWhr/m3)
1.32
Removal Efficincy, (%)
100
S0957-5820(16)30222-1 http://dx.doi.org/doi:10.1016/j.psep.2016.09.023 PSEP 885
To appear in:
Process Safety and Environment Protection
Received date: Revised date: Accepted date:
21-3-2016 26-8-2016 28-9-2016
Please cite this article as: P., Asaithambi, Sajjadi, Baharak, Abdul Aziz, Abdul Raman, Wan Daud, Wan Mohd Ashri Bin, Performance evaluation of hybrid electrocoagulation process parameters for the treatment of distillery industrial effluent.Process Safety and Environment Protection http://dx.doi.org/10.1016/j.psep.2016.09.023 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Performance evaluation of hybrid electrocoagulation process parameters for the treatment of distillery industrial effluent P. Asaithambi*, Baharak.Sajjadi, Abdul Raman Abdul Aziz*, Wan Mohd Ashri Bin Wan Daud Department of Chemical Engineering, Faculty of Engineering, University of Malaya, Malaysia – 50603. *Corresponding author: Tel.: +60 3 7967 7687; Fax: +60 3 79675319 Email address: [email protected](P. Asaithambi) [email protected](A. R. Abdul Aziz)
1
Graphical Abstract
DC power supply V
UV Lamb
100 Color removal COD removal Removal Efficincy, (%)
80
60
__ __ ___ __ __ __ __ __ __ __ ____ __ __ _ __ _____ _ _ _ _ _ _ __ _ _ __ __ ___ _ _ _ _ _ __ _ _ ___ __ __ _ _ _ __ ___ _______ __ __ __ __ __ __ __ _________ _ ____ ___ __ __ __ __ __ __ __________________________ ___ ___ _ __ __ ___ _ __ _ __
40
20
0 EC
EC+UV EC+UV+H2O2 EC+H2O2 Hybrid Electrocoagulation Process
Hybrid H2O2/UV/EC
2
+
A
-
H2O2
Research highlights
Hybrid electrocoagulation processes for removal of pollutants were investigated
Various electrocoagulation process were compared in terms of electrical energy consumption and color, COD removal
Effects of operating parameters in peroxi –electrocoagulation were studied
The direct- and alternating-current electrocoagulation processes were investigated
Abstract A hybrid electrocoagulation process using iron electrode was developed for removal of organic pollutants from distillery industrial effluent.
Combinations of electrocoagulation process with
different advanced oxidation processes such as electrocoagulation, photo–electrocoagulation, peroxi– 3
electrocoagulation and peroxi–photo–electrocoagulation processes investigated and compared in terms of color removal, Chemical Oxygen Demand (COD) removal and electrical energy consumption. An overall COD removal efficiency of 85% with 1.20kWh/m3 of energy consumption, current density of 0.13 A/dm2, initial COD concentration of 2500 ppm, initial pH of 7, H2O2 concentration of 234 mg/L, stirring speed of 100 rpm and reaction time of 240 min was observed in the peroxi–electrocoagulation process. The effects of different operating parameters such as initial pH of the effluent (3 to 11), current density (0.03 to 0.23 A/dm2) and concentration of H2O2 (58.5 to 585 mg/L) on color removal, COD removal and electrical energy consumption were studied. The directand alternating-current electrocoagulation processes were also studied. Keywords:
Distillery
effluent;
peroxi-photo-electrocoagulation;
alternating
current
electrocoagulation; COD removal; electrical energy consumption.
1.
Introduction
Electrocoagulation is an inexpensive process for treatment of various industrial effluents (Al-Shannag et al. 2013; Al-Shannag et al. 2015; Al-Shannag et al. 2014; Arun Kumar Sharma and Chopra 2015; Al-Shannag et al. 2012; Berrin Zeliha et al. 2014; Tianlong Zheng et al. 2015) to eliminate a wide 4
range of pollutants from the wastewater. Metallic electrodes like Iron, Aluminum are usually used as an anode which offers the anodic oxidation and in situ generation of active adsorbent of metallic hydroxides for the removal of the pollutants. In the cathodic reaction, hydrogen gas evolved which causing flotation of the adsorbants (Modirshahla et al. 2007; Sebastian Seculaa et al. 2011; Akbal et al. 2011). Many studies on removal of wastewater to ensure good-quality effluent have been done before its discharge into aquatic environment. Gomes et al. applied electrocoagulation for the treatment of wastewater containing high chemical oxygen demand and dissolved metal impurities. In recent years, new advanced oxidation processes induced by electrochemistry have been studied as an alternative approach for wastewater treatment (Sergi et al. 2012; Asha Keerthi et al. 2014). A combination of electrochemical processes with advanced oxidation processes is an interesting solution. In such a synergetic way, removal efficiency is maximized with minimal operating costs. The Electrochemical Advanced Oxidation Processes (EAOPs) provide several advantages for the prevention and remediation of pollution problems because the electron is a clean reagent. Other advantages of EAOPs include economic friendly requirement, versatility, amenability to automation, high energy efficiency, easy handling, simple equipment set up and also can be operated in room temperature and pressure. EAOPs are characterized by production of hydroxyl radicals and due to their nonselective characteristic, which is able to oxidize and mineralize most organic and inorganic pollutants to produce H2O, CO2 and inorganic ion (Sire´s et al. 2007). Hydroxyl radicals can be generated by a variety of chemical, electrochemical, photo assisted electrochemical methods, photo catalysis, Fenton’s methods, ozone-based methods, sonochemical methods and radiolytic methods. Depending on the types of AOPs, ultraviolet (UV) of λ reaching 200–300 nm could be used to produce •OH radicals. 5
The process of distillery industry results in release of huge amount waste and wastewater which have highly colored contains high organic and inorganic substances, COD, Biochemical Oxygen Demand (BOD), Total Organic Carbon (TOC), slightly acidic pH, etc. The distillery effluents need comprehensive treatment to meet the prescribed standard for disposal into natural water bodies. Many processes are used to remove pollutants from distillery effluents such as electro oxidation (Piyaareetham et al. 2006), electrocoagualtion (Krishna et al. 2010), bio–electrochemical methods (Mohanakrishna et al. 2007), ultrasound and enzyme-assisted biodegradation (Sangave et al. 2006), ozonation with aerobic oxidation (Sangave et al. 2007), anaerobic fluidized bed reactor (Fernández et al. 2008), nanofiltration (RaiUmesh et al. 2008), activated carbons (Satyawali et al. 2007) and coagulation (Liang et al. 2009). A comparison of various processes and electrocoagulation process for the removal pollutant from distillery wastewater was given in Table. 1 and table. 2. Alternatively, hybrid electrocoagulation can be an efficient and effective technique for treatment of distillery industrial effluent with low energy consumption, high quality effluent and low sludge formation can be made as desirable process for the treatment. In this study, hybrid electrocoagulation processes were investigated for the treatment of distillery industrial
effluent.
Performance
of
electrocoagulation,
peroxi–electrocoagulation,
photo–
electrocoagulation and peroxi–photo–electrocoagulation process using iron plate electrodes was compared in terms of electrical energy consumption, colour and COD removal. Effects of pH, current density and concentration of H2O2 on colour removal, COD removal and electrical energy consumption were studied for the treatment effluent in the peroxi – electrocoagulation process. The direct- and alternating-current electrocoagulation processes were also investigated. Influence of pulse duty cycle on alternating - current electrocoagulation process was studied. 1.1. Mechanisms of various electrocoagulation processes 6
1.1.1 Electrocoagulation The commonly accepted mechanism of removal of pollutants by electrocoagulation process with iron electrodes can be written as (Ayhan et al. 2009). Anodic reaction: Fe( s ) Fe(2aq ) 2e
Eo = -0.44 V vs SHE
(1)
Eo = 0.83 V vs SHE
(2)
Cathodic reaction:
2H 2O(l ) 2e H 2 ( g ) 2OH(aq) Overall reaction: Fe 2H 2O Fe(OH ) 2( s ) H 2( g )
(3)
If oxygen is present, dissolved Fe2+ is oxidized to insoluble Fe(OH)3 4Fe(2aq ) 10 H 2 O( l ) O2 ( g ) 4 Fe(OH ) 3( S ) 8H ( aq)
(4)
The Fe(OH)n(s) remains in the aqueous stream as a gelatinous suspension, which can remove the pollutants from the wastewater by either complexation or electrostatic attraction followed by coagulation. 1.1.2 Peroxi – electrocoagulation In an electrocoagulation system, H2O2 is added into the electrocoagulation system and a sacrificial Fe anode is used as the Fe2+ source.
Fe 2 H 2O2 Fe 3 OH OH
(5)
This reaction is propagated from ferrous ion regeneration mainly by reduction of the produced ferric species with hydrogen peroxide.
Fe 3 H 2O2 Fe 2 HO2 H
(6)
7
Ferrous ions are consumed more rapidly than they are produced. In addition, ferrous ions can be rapidly destroyed by hydroxyl radicals with the rate constant in the range of 3.2–4.3 X 108M-1 s-1 (Sun and Pignatello 1993; Farhadi et al. 2012). Fe 2 OH Fe 3 OH
(7)
Therefore, more ferrous ion dosage is needed to maintain hydroxyl radicals production in a moderate amount. This results in a large amount of ferric hydroxide sludge during neutralization stage of Fenton process, which requires additional separation process and disposal. 1.1.3 Peroxi – photo – electrocoagulation The performance of the electrocoagulation and peroxi–electrocoagulation process can be improved by using UV radiation, which is known as photo–electrocoagulation and peroxi-photo-electrocoagulation process (Farhadi et al. 2012). This process is improved due to higher production rate of •OH from the photoreduction of Fe(OH)2+ and photodecomposition of complexes from Fe3+ reactions as shown in equation (8) & (9). Fe(OH ) 2 hv Fe 2 OH
(8)
R(CO2 ) Fe 3 hv R( CO2 ) Fe 2 R CO2
(9)
2.
Material and Methods
2.1. Material The effluents were collected from distillery industries in nearby Malaysia. The main characteristics of the effluent are given in Table. 3. The chemicals used in the experiments were hydrogen peroxide (50% w/w) as the oxidizing reagent, sulphuric acid and sodium hydroxide to adjust the pH value. The other chemicals such as (NH4)2Fe(SO4)2.6H2O, K2Cr2O7 were of analytical grade and purchased from Merck Company. Only double distilled water was used to prepare the entire solution. 2.2.
Experimental Methods 8
The electrocoagulation process consisted of rector made-up of acrylic sheet with a capacity of 2.5 L (10 cm x 15 cm x 16 cm) and the working volume of the effluent was 2.0 L as shown in Fig. 1. The pH of the effluent was adjusted to the desired value using 0.1N H2SO4 or 0.1N NaOH solutions. Iron (grade MS 104) plates of 1 mm thickness were used as the anode and cathode. The electrode dimensions were 10 cm x 15 cm x 0.1 cm and the mode of electrode connection was bipolar. The distance between the anode and cathode was 3 cm in the electrochemical cell. In addition, two extra iron plates were inserted between anode and cathode to improve and produce more coagulant precursors which could enhance pollutant removal. The total effective electrode surface area was 100 cm2 and a gap of 5 cm was maintained between the electrodes and the bottom of the electrochemical cell to facilitate stirring. Magnetic stirrer was used in the reactor to maintain uniform concentration. The electrodes were cleaned with 15% HCl followed by distilled water prior to each experiment. The electrodes were connected to a direct-current power supply with galvanostatic operation for controlling the current density. An alternating pulse current electrocoagulation (0- 5A, 0 – 270 V, 50 Hz; AMETEK Model: EC 1000S) was carried out to investigate the alternating-current electrocoagulation process. For the photo–electrocoagulation process, a 16 W low-pressure mercury lamp was placed above the electrocoagulation cell. The distance between the UV lamp and treating solution was maintained at 10 cm. The peroxi–electrocoagulation and peroxi–photo– electrocoagulation process was carried out in the same system by only adding H2O2. All the experiments were carried out at a controlled temperature of 351°C. During the experiments, the samples were collected from the electrochemical reactor at regular time intervals and centrifuged (12,500 rpm, 20 min). Then, the colour and COD removal were measured. The COD tests were measured by a dichromatic closed reflux method according to the Standard Methods [APHA]. The colour was measured at the wavelength 9
corresponding to the maximum absorbance λmax (300 nm) using an UV/Vis spectrophotometer (Jasco, V-570). The percentage color removal was calculated by the following using equation Colour removal efficiency (%) =
([ ABS i ] [ ABS t ]) 100 ABS i
(10)
Where ABSi and ABSt are absorbance of samples at initial and different reaction time t for corresponding wavelength max. The percentage COD removal was calculated using equation COD removal efficiency (%) =
([CODi ] [CODt ]) 100 CODi
(11)
Where [CODi]is the initial COD value (mg/L) and [CODt]is the COD value at any reaction time, t (mg/L). The total electrical energy consumption of peroxi–photo–electrocoagulation process can be calculated by the following equation. The total electrical energy consumption = EEC + EUV
(12)
Electrical energy consumption for the electrocoagulation process (EEC). EEC = VIt / VR
(13)
Where, V is the cell voltage (V), I is the applied current (A), t is the electrolysis time (hour), VR is the volume of the effluent (L). Electrical energy consumption for the photo system (EUV).
EUV =
Pel * t *1000 C V * 60 * log i C f
(14)
10
Where, Pel is the electrical power input (kW), t is the irradiation time (min), V is the volume of effluent used (L), Ci and Cf is the initial and final effluent concentration (ppm) 3.
Results and discussion
3.1 Comparison of various electrocoagulation processes Various hybrid electrocoagulation processes were carried out based on the operating conditions such as current density of 0.13 A/dm2, COD concentration of 2500 ppm with initial pH of 5. The electrocoagulation system had an anode and cathode with an inter electrode distance of 3 cm and the electrodes were connected in a bipolar manner. The COD removal efficiency and electrical energy consumption of various hybrid processes are shown in Fig. 2. The COD removal percentage by electrocoagulation,
photo–electrocoagulation,
peroxi-electrocoagulation
and
peroxi-photo-
electrocoagulation processes was found to be 72%, 78%, 85% and 82% respectively after 4 hours of reaction. Addition of UV source showed positive effects on the electrocoagulation process due to increased availability of photo active sites. The economical aspect of a hybrid process is always associated with electrical energy consumption. The minimum electrical energy consumption of 1.2kWhr/m3 was required for the removal of 85% COD in the peroxi–electrocoagulation process. The remaining hybrid processes had higher electrical energy consumption compared to the peroxi– electrocoagulation process. 3.2 Peroxi –electrocoagulation process 3.2.1 Effect of current density The effect of current density on color and COD removal for wastewater with initial COD concentration of 2500 ppm and addition of H2O2 at initial pH of 5 was studied. The color and COD removal efficiency and electrical energy consumption are shown in Fig. 3. The experimental results show that the color and COD removal efficiency increased from 31 to 100% and from 25 to 97% with 11
increasing current density from 0.03 to 0.23 A/dm2. The percentage of color and COD removal efficiency increased sharply with current density up to 0.13 A/dm2. Further increase of current density did not significantly improve removal of COD. However, electrical energy consumption increased linearly with current density. It is well known that current density determines the production of coagulant and size of bubbles. Therefore, it is recommended that the peroxielectrocoagulation process to be operated at limited current density in order to avoid excessive oxygen evaluation and eliminate adheres effect. 3.2.2 Effect of H2O2 concentration It is important to optimize the amount of H2O2 used in the peroxi-electrocoagulation process due to cost and adherent effects caused by excessive H2O2. The effects of H2O2 concentration on color and COD removal efficiency are demonstrated in Fig. 4. The results showed that maximum COD removal of 97% at optimum H2O2 concentration of 234 mg/L was achieved after electrolysis duration of 4 hr. The COD removal occurred due to both electrocoagulation and Fenton processes. When the dosage of H2O2 concentration increased from 58.5 to 234 mg/L, the COD removal efficiency increased from 76 to 97%. However, further increase of H2O2 from 234 to 585 mg/L reduced COD removal efficiency to 73%. The experimental results showed that most of organic pollutants in an effluent could be oxidized by hydroxyl radicals. Also the hydroxyl radical was generated by H2O2, which could enhance the oxidation ability of treatment along with increment of concentration of H2O2. The decrease trend indicated that the over – abundant H2O2 could also consumed hydroxyl radical and become the elimination reagent hydroxyl radical (Farhadi et al. 2012). 3.2.3 Effect of initial pH The influence of initial pH of the solutions was studied with initial COD concentration of 2500 ppm and current density of 0.13 A/dm2 by adding 234 mg/L of H2O2. Fig. 5 shows the color and COD 12
removal at different initial pH. It was found that the optimal pH value was 5. Formation of Fe(OH) 3(s) did not only reduce the dissolved Fe3+ concentrations, but also inhibited Fe2+ regeneration by partially coating the electrode surface (Qiang et al. 2003). In acidic conditions, Fe3+ can be hydrated and species such as Fe(OH)2+, Fe(OH)2+ and Fe2(OH)24+ are present in the electrocoagulation system. Ionic species such as Fe(OH)6- and Fe(OH)4- can be found in an alkaline medium. In a homogeneous Fe3+ solution in an acidic medium, the main equilibrium hydrolysis reactions are as follows (Stumm et al. 1996).
Fe 3 H 2O FeOH 2 H
(15)
Fe 3 2H 2O FeOH 2 2H
(16)
2Fe 3 2H 2O Fe2 (OH ) 42 2H
(17)
Fe(OH)n(s) formed during the electrocoagulation process remains in the aqueous stream as a gelatinous suspension at 3 < pH < 11, which can remove the pollutants from wastewater either by complexation or by electrostatic attraction, followed by coagulation. Complexation, accompanied by Fenton oxidation may occur in the electro-Fenton process at pH 5. Effects of initial pH on electrical energy consumption were determined and the results are shown in Fig. 5 It was found that the electrical energy consumption increased from 1.16 to 1.47kWh/m3 with increasing initial pH from 3 to 7. However, the electrical energy consumption was found to reduce from 1.47 to 0.90kWh/m3 with increasing initial pH from 7 to 11. This might be due to the decrease in the conductivity of the electrolyte when pH changed from acidic to neutral condition and the increase in the conductivity of the electrolyte when pH changed from neutral to alkali condition in the peroxi – electrocoagulation process. 3.3 Comparison of direct current and alternating pulse electrocoagulation process 13
Direct-current electrocoagulation processes produces sludge and possibly, an impermeable oxide layer on the cathode, which is accompanied by deterioration of the anode due to oxidation. The passivation and mass transport control between the anode and cathode reduce the efficiency of the direct
current
electrocoagulation
process
was
declines.
Therefore,
alternating-current
electrocoagulation process has been proposed in order to overcome these difficulties (Keshmirizadeh et al.2011; Ren et al. 2011; Vasudevan et al. 2011; Eyvaz et al. 2009). An alternating-current electrocoagulation process can prevent the passivation of electrode material, reduce sludge, reduce electrical energy consumption and increase pollutant removal efficiency with minimum electrical energy consumption. In this process, anode and cathode are periodically interchanged and operating for 15 min until electrocoagulation is complete. The experimental conditions such as current density (0.13 A/dm2), effluent concentration (2500 ppm), effluent pH (7) and electrode distance (3cm) were studied. The direct-and alternating-current electrocoagulation processes were carried out and the results are shown in Fig. 6. The results showed that the COD removal was higher with lower electrical energy consumption in the case of alternating current electrocoagulation compared to direct-current electrocoagulation. The formation of impermeable layer and sludge are very low compared to the direct-current electrocoagulation process. Effect of pulse duty cycle is a very important parameter in an alternating-current electrocoagulation process. Fig. 7 shows that color and COD removal percentage increased from 80 to 95% and from 76 to 87% with increased pulse duty cycle from 0.2 to 0.5. The color and COD removal efficiency decreased from 95 to 81% and from 87 to 75%, respectively with further increase of pulse duty cycle from 0.5 to 0.8. Electrical energy consumption for different pulse duty cycles was also studied, as shown in Fig. 7. The results indicated that electrical energy consumption decreased from 1.32 to 1.31 kWh/m3 with increased pulse duty cycle from 0.2 to 0.5. Hence, by increasing the pulse duty cycle from 0.50 to 0.80, the electrical 14
energy consumption also increased from 1.31 to1.32 kWh/m3. At low and high pulse duty cycle, the removal efficiency of alternating-current electrocoagulation was similar to that of electrocoagulation. The experimental results showed that the pulse duty cycle should be operated between 0.40 to 0.60. Ren et al. (2011) investigated the pulse electro-coagulation technology for removal of refractory berberine hydrochloride from wastewater, the energy-relevant costs of pulse electrocoagulation and electro-coagulation were compared and it showed that pulse electrocoagulation saved 90% of energy compared to electrocoagulation. Cost estimation Cost estimation is very important economical parameters in hybrid electrocoagulation process like all other electrochemical and advanced oxidation process. The operating cost includes cost of electrodes, electrical energy, chemical consumed, as well as labor, maintenance, cost of sludge disposal and other fixed costs. Thus, the operating cost can be calculated using the following equation (Bayramoglu et al.2007; Bayramoglu et al.2004 ). Operating cost = aEEC + bELC + cCC
(18)
Where, EEC = electrical energy consumed – kWh/m3, ELC = electrode consumed– kg/m3 and CC = chemical consumed – kg/m3 (Sridhar et al. 2011). Under optimum condition such as COD concentration: 2500 ppm; current density: 0.13 A/dm2; initial pH: 7; H2O2 concentration: 234 mg/L; stirring speed: 100 rpm; reaction time: 240 min, the electrical energy, electrode and chemical consumptions were found to be 5.40 kWh/m3, 0.25 kg/m3 and 1.25 kg/m3, respectively. The operating cost was calculated under optimum condition using the equation (18) and it was found to be 1.25 US $/m3. 3.4 Conclusion
15
The performance of electrocoagulation, peroxi–electrocoagulation, photo–electrocoagulation and peroxi-photo-electrocoagulation processes for color removal, COD removal and energy consumption from the distillery industry effluent was investigated. The most efficient and effective decolorization and degradation were observed in the peroxi– electrocoagulation process compared to the other electrochemical advanced oxidation processes. The percentage colour and COD removal showed that the 100 and 86% in were achieved in the peroxi – electrocoagulation process with the minimum electrical energy consumption of 1.2kWhr/m3. Direct- and alternating-current electrocoagulation process were designed and applied for color and COD removal from distillery effluent with minimal energy consumption. Alternating-current electrocoagulation process was found to be more efficient than the direct-current electrocoagulation process. Acknowledgement The authors are grateful to the University of Malaya High Impact Research Grant (HIR-MOHED000037-16001) from the Ministry of Higher Education Malaysia which financially supported this work.
References Akbal, F., Camci, S., 2011. Copper chromium and nickel removal from metal plating wastewater by electrocoagulation. Desalination, 269, 214-222. Al-Shannag, M., Al-Qodah, Z., Alananbeh, K., Bouqellah, N., Assirey, E., 2014. COD reduction of baker's yeast wastewater using batch electrocoagulation. Environ. Eng. Manage. J, 13, 31533160.
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Al-Shannag, M., Bani-Melhem, K., Al-Anber, Z., Al-Qodah, Z., 2013. Enhancement of COD-nutrients removals and filterability of secondary clarifier municipal wastewater influent using electrocoagulation technique. Sep. Sci. Technol, 48 (4), 673-680. Al-Shannag, M., Lafi, W., Bani-Melhem, K., Gharagheer, F., Dhaimat, O., 2012. Reduction of COD and TSS from paper industries wastewater using electro-coagulation and chemical coagulation. Sep. Sci. Technol, 47 (5), 700-708. Al-Shannag, M., Zakaria Al-Qodah., Bani-Melhem, K., Qtaishat, M. R., Alkasrawi, M., 2015. Heavy metal ions removal from metal plating wastewater using electrocoagulation: Kinetic study and process performance. Chem. Eng. J, 216, 749-756. Arun Kumar Sharma., Chopra, A. K., 2015. Removal of nitrate and sulphate from biologically treated municipal wastewater by electrocoagulation. Appl Water Sci. 10.1007/s13201-0150320-0 Asha Keerthi, A., Muthukrishnaraj, A., Balasubramanian, N., 2014. Improvement of biodegradability index through electrocoagulation and advanced oxidation process. Int J Ind Chem, 5, 4. Ayhan, SengilI., Kulac, Sedat., Ozacar, Mahmut., 2009.Treatment of tannery liming drum wastewater by electrocoagulation. J. Hazard. Mater, 167, 940–946. Bayramoglu, M., Eyvaz, M., Kobya, M., 2007. Treatment of the textile wastewater by electrocoagulation: economic evaluation. Chem. Eng. J. 128, 155–161. Bayramoglu, M., Kobya, M., Can, O.T., Sozbir, M., 2004. Operating cost analysis of electrocoagulation of textile dye wastewater. Sep. Purif. Technol. 37, 117–125. Berrin Zeliha, Can., Recep Boncukcuoglu., Alper Erdem Yilmaz., Baybars Ali Fil., 2014. Effect of some operational parameters on the arsenic removal by electrocoagulation using iron electrodes. Journal of Environmental Health Science and Engineering. 12:95 17
Eyvaz, M., Kirlaroglu, M., Aktas, T. S., Yukse, E., 2009. The effects of alternating current electrocoagulation on dye removal from aqueous solutions. Chem. Eng. J, 153,16–22. Farhadi, S., Aminzadeh, B., Torabian, A., Khatibikamal, V., Fard M. A., 2012. Comparison of COD removal from pharmaceutical wastewater by electrocoagulation, photo-electrocoagulation, peroxi-electrocoagulation and peroxi-photo-electrocoagulation processes. J. Hazard. Mater, 219-220,35-42. Fernández, N., Montalvo, S., Borja, R., Guerrero, L., Sánchez, E., Cortés, I., Colmenarejo, M.F., TraviesoL, RaposoF., 2008. Performance evaluation of an anaerobic fluidized bed reactor with natural zeolite as support material when treating high-strength distillery wastewater. Renewable energy, 33, 2458 -2466. Keshmirizadeh, E., Yousefi, S., Kazem Rofouei, M., 2011. An investigation on the new operational parameter effective in Cr(VI) removal efficiency: A study on electrocoagulation by alternating pulse current. J. Hazard. Mater, 190,119–124. Krishna, B. M., Usha, N. Murthy., Manoj, B., Kumar, Lokesh K. S., 2010. Electrochemical pretreatment of distillery wastewater using aluminum electrode . J. Appl. Electrochem, 40, 663-67. Liang, Z., Wang, Y., Zhou, Y., H. Liu., 2009. Coagulation removal of melanoidins from biologically treated molasses wastewater using ferric chloride. Chem. Eng. J, 52, 88–94. Modirshahla, N., Behnajady, A., Kooshaiian, S., 2007. Investigation of the effect of different electrode connections on the removal efficiency of Tartrazine from aqueous solutions by electrocoagulation. Dyes and Pigm, 74, 249-257.
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Mohanakrishna, G., Venkata Mohan, S., Sarma, P.N., 2007. Bio-electrochemical treatment of distillery wastewater in microbial fuel cell facilitating decolorization and desalination along with power generation. J. Hazard. Mater , 177, 487–494. Piya-areetham, P., Shenchunthichai, K., Hunsom, M., 2006. Application of electrooxidation process for treating concentrated wastewater from distillery industry with voluminous electrode. water Res, 40, 2857 – 2864. Qiang, Z., Chang, J.H., C.P. Huang., 2003. Electrochemical regeneration of Fe2+ in Fenton oxidation processes. Water Res, 37, 1308–1319. RaiUmesh, Kumar., Muthukrishnan, M., Guha, B.K., 2008. Tertiary treatment of distillery wastewater by nanofiltration. Desalination, 230, 70–78. Ren, M., Song, Y., Xiao, S., Zeng, P., Peng, J., 2011. Treatment of berberine hydrochloride wastewater by using pulse electro-coagulation process with Fe electrode, Chem. Eng. J, 169, 84–90. Sangave, P. C., Gogate Parag, R., Pandit, A. B., 2007. Combination of ozonation with conventional aerobic oxidation for distillery wastewater treatment.Chemosphere, 68, 32 -41. Sangave, P. C., Pandits, A. B., 2006. Ultrasound and enzyme assisted biodegradation of distillery wastewater. J. Environ. Manage, 80(1),36 – 46. Satyawali, Y., Balakrishnan, M., 2007. Removal of color from biomethanated distillery spentwash by treatment with activated carbons. Bioresou.Technol, 98, 2629–2635. Sebastian Seculaa, M., Creţescub, I., Petrescu, S., 2011. An experimental study of indigo carmine removal aqueous solution by electrocoagulation. Desaliantion, 277, 227-235. Sergi, Garcia-Segura., Abdellatif, El-Ghenymy., Francesc, Centellas., Rosa M. Rodríguez., Conchita Arias., José A. Garrido., Pere L. Cabot., EnricBrillas., 2012. Comparative degradation of the 19
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List of tables Table.1. Comparison of some removal efficiencies technologies from distillery wastewater
Table.2. Electrocoagulation techniques for the treatment of distillery wastewater 20
Table.3. Characteristics of distillery wastewater
List Figures Fig.1. The schematic experimental setup for the peroxi – photo – electrocoagulation processes to the treatment of distillery effluent.
Fig.2. Comparison of various electrocoagulation process in terms of percentage COD removal and electrical energy consumption (conditions: COD concentration: 2500 ppm, current density: 0.13 A/dm2, initial pH: 7, H2O2concentration:234 mg/L, stirring speed: 100 rpm, reaction time: 240 min)
Fig.3. Influence of current density on percentage color removal, COD removal and electrical energy consumption (peroxi – electrocoagulation process; condition: COD concentration: 2500 ppm, initial pH: 7, H2O2 concentration: 234 mg/L, distance between anode and cathode: 3 cm, stirring speed: 100 rpm, reaction time: 240min)
Fig.4. Effect of hydrogen peroxide on percentage color removal, COD removal and electrical energy consumption (peroxi – electrocoagulation process; condition: COD concentration 2500 ppm, current density: 0.13 A/dm2, initial pH: 7, distance between anode and cathode: 3 cm, stirring speed: 100 rpm, reaction time: 240min)
Fig.5. Effect of initial pH on (a) percentage color, COD removal and electrical energy consumption (peroxi – electrocoagulation process; condition: COD concentration 2500 ppm, current density: 0.13 21
A/dm2, H2O2 concentration: 234 mg/L, distance between anode and cathode: 3 cm, stirring speed: 100 rpm, reaction time: 240min)
Fig.6. Performance of direct and alternating current electrocoagulation for thepercentage COD removal. (condition: COD concentration: 2500 ppm, current density: 0.13 A/dm2, initial pH: 7, distance between anode and cathode: 3 cm, stirring speed: 100 rpm, reaction time: 240 min)
Fig.7. Effect of pulse duty cycle on percentage color, COD removal and electrical energy consumption. (condition: COD concentration: 2500 ppm, current density: 0.13 A/dm2, initial pH: 7, distance between anode and cathode: 3 cm, stirring speed: 100 rpm, reaction time: 240 min)
Method
Removal efficiency
Optimum conditions
Literature
Electro oxidation
Color - 92.24%, COD 89.62%, BOD - 83.80%, TDS - 38.00%, TS 67.77%
current intensity - 9 A, initial pH - 1, anode - titanium sponge and NaCl - 1.0 M
Piya-areetham et al. 2006
Bio – electrochemical
COD – 72.84%, Color – 31.67%, TDS – 23.96%
MFC - open-air cathode, fedbatch mode under acidophilic pH-
Mohanakrishna et al.2007
22
6, Current: 2.12 – 2.48 mA Ultrasound and enzyme assisted biodegradation
COD – 62.5%, rate constant – 0.0310 h-1
Time - 36 hour,
Sangave et al. 2006
Ozonation with aerobic oxidation
COD – 79%, color – 34.9%
Ozone flow rate = 46.1 mls-1, ozone concentration - 1.9 x 10-2 g l-1, effluent pH -7.4 -7.6, impeller speed = 700 rpm
Sangave et al.2007
Anaerobic fluidized reactor
COD – 80%
organic loading rate - 2 to 5 g COD/l d, the fluidization level 20% and 40%, and the particle diameter of the natural zeolite0.2 to 0.8
Fernández et al. 2008
Nanofiltration
Color – 98-99.5%, COD – 96-99.5%, TDS – 8595%
pH - 4.0–7.0, Temperature 27⁰C, pressure - 1-5 bar, flow rate - 250 L/h
RaiUmesh Kumar et al. 2008
Activated carbons
Color – 80%
Commercially activated carbon
Coagulation
Color -96%, COD -86%
pH-8, Ferric salt - 3.5 g/L,
bed
Satyawali et al. 2007 Liang et al. 2009
Table. 1.
Types of electrode
Removal Efficiency (%)
Operating time
Optimum conditions
23
Literature
Fe
COD = 46.6%, Color = 80.3%, Turbidity=92.3%
90 min
pH=7, current density=300A/dm2,
Al
COD = 48.5%, Color = 97.2.3%, Turbidity=98.6%
120 min
pH=5.2, current density=300A/dm2,
Al-Shannag et al. 2015
Fe
COD =50.5%, color =95.2%
120 min
current density = 44.65 A/m2; initial pH (pH0)=8; inter-electrode distance= 2 cm
Modirshahla et al. 2007
Al
COD=81.3%
2hour
current density = 0.187A/cm2; pH=3; inter-electrode distance = 2 cm
Sebastian Secula et al. 2011
Fe
Color = 95%
4 hour
Current density = 31mA/cm2, dilution = 17.5%,
Akbal et al. 2011
Fe
Color=100, COD=62%
4hour
initial COD concentration: 2500 ppm, current density=3 Adm−2, initial pH= 6,
Sergi GarciaSegura et al .2012
Table.2.
24
Al-Shannag et al. 2015
Parameters
Range
pH
4.1- 4.3
COD
80,000 - 90,000 mg/L
BOD
7,000 - 8,000 mg/L
TSS
15.44 g/L
TDS
5550-5750 mg/L
Colour
dark brown
odour
burnt sugar
Table.3.
25
Mains
8
220/230 V AC / 30Hz
Volt
7
3
+
Amp
6
2
4 1
5
Fig. 1.
26
1. 2. 3. 4. 5. 6. 7. 8.
Electrocoagulation cell Anode (Iron) Cathode (Iron) Bipolar electrodes Magnetic Stirrer DC power supply UV Lamp Power Card
-
1.5 1.45
COD removal, (%)
80
1.4 60 COD removal 40
1.35
Electrical energy consumption 1.3
20
1.25
0
1.2
EC
EC+UV EC+UV+H2O2 EC+H2O2 Vrious process
Fig. 2.
27
Electrical energy consumption, (kWh/m3 )
100
2.5
80
2
60
1.5
40
1 Colour removal, (%) COD removal, (%) Electrical Energy Consumption
20
0 0
0.5
0 0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 Current density, (A/dm2 ) Fig. 3.
28
Electrical Energy consumption, (kWh/m3 )
Removal Efficiency, (%)
100
100
Removal, (%)
80
60
Colour emoval, (%) COD removal, (%)
40
20
0
0
100
200 300 400 500 Concentration of H2 O2, (mg/L)
Fig. 4.
29
600
100
1.6
1.2 60
COD removal (%)
0.8 colour removal (%)
40 Electrical energy consumption
0.4 20
0
0 1
3
5
7 Effluent pH Fig. 5
30
9
11
13
Electrical Energy Consumption, (kWh/m3 )
Removal Efficiency, (%)
80
100
COD removal, (%)
80
Alternating Current Direct Current
60
40
20
0 0
30
60
90
120 150 Time, (min)
Fig. 6.
31
180
210
240
80
1.315
60
1.31
40
1.305
20
1.3
Colour removal, (%) COD removal, (%) Electrical energy consumption
0
1.295 0
0.2
0.4
0.6
Pulse duty cycle
Fig. 7.
32
0.8
1
Electrical energy consumption (kWhr/m3)
1.32
Removal Efficincy, (%)
100