simultaneous removal of hardness and fluoride by chemical and electrocoagulation

SIMULTANEOUS REMOVAL OF HARDNESS AND FLUORIDE FROM WATER BY CHEMICAL AND ELECTROCOAGULATION

By P. MAHAMMEDRAFI

MTECH – ENVIRONMENTAL ENGG

OVER VIEW 1.Introduction 2.Literature review 3.Materials and methodology 4.Results and discussions 5.Conclusions 6.Scope for future work

INTRODUCTIONWater quality:• It refers to the chemical, physical and biological characteristics

of water. • It is a measure of the condition of water relative to the

requirements of any human need or purpose.

Water quality parameters:Physical : Taste, colour, turbidity, temperature.Chemical: pH, acidity, alkalinity, hardness, fluoride, chlorides, sulphates,

DO, BOD, COD, heavy metals, nitrogen and phosphorous.

Biological : MPN test

Effects of poor water quality:Colour – aesthetically unobjectionableAcidity – corrosivenessAlkalinity – bitter taste, corrosion, deposition of scales in pipe networks.Dissolved solids- palatability decreases , carcinogenicChlorides - corrosion, taste salty, unsuitable for agricultural irrigation.Sulphates - noxious odours. Destruction of fabric of concrete sewer pipes.Hardness – encrustation in water supply structure & adverse effect on domestic usage.Fluoride – dental & skeletal fluorosisHeavy metals – toxic to humansNitrogen - poisonous to humans or aquatic organisms.Phosphorous – algae booms, death of fishDO – impact on aquatic lifeBOD – impact on aquatic lifeCOD - impact on aquatic lifeMPN – waterborne diseases

Occurrence of Hardness:Sources -• Water becomes hard by acquiring cations and anions like Ca2+ ,

Mg2+ and SO4-, Cl- .

Problems -• Water hardness poses a lot of problems for life and industry. • Formation of deposits in boiler and household facilities. • Surface of glassware, silverware, and plumbing fixtures.• Decrease of heat transfer in boiler, decrease of fluid rate, bursting of

water pipeline, formation of stains in dishes and clothes.• High concentrations of magnesium may induce a bitter taste. • Considering problems of water hardness, its removal is essential

(Kawamura, 2000). Limits:Desirable -300 ppmMax -600 ppm

Occurrence of Fluoride:Sources:• Geological and man made sources contribute to the occurrence of

fluoride.Occurrence of fluoride:• Fluoride related health hazards are a major environmental problem in

many regions of the world.• India is among the 25 nations around the globe, where health problem

occurs due to the consumption of fluoride-contaminated water. • In India, 17 states have been identified as epidemic for fluorosis.• Cuddapa,Krishna,Ananthapur,Kurnool,Prakasam,Chittoor,Guntur,Nellore.Health implications:• Excess of fluoride (>1.5 mg/L) in drinking water is harmful to the

human health.• Effects – dental fluorosis (1.5-4 mg/l) skeletal fluorosis (above 4 mg/l)• According to WHO (1996), max permissible limit =1.5 mg/l

Necessity and importance of simultaneous removal

• Most of the treatment processes are designed to remove a targeted parameter i.e. either hardness or fluoride.

• But in reality, when one parameter is targeted for removal, associated water quality parameters also get affected, often leading to their removal.

• Thus when water is treated for removal of fluorides, some associated hardness may also be removed and vice versa may also happen.

• Therefore the present study focuses on simultaneous removal of hardness and fluoride by a novel treatment process namely electrocoagulation.

• In view of the health and other implications of presence of fluorides and hardness, they are removed by treatment processes to the permissible limits before supplied for consumption.

Objective of the study:

To study simultaneous removal of Hardness and Fluoride by Electrocoagulation employing iron plate electrodes and compare with conventional chemical coagulation by alum.

Methods for treatment:Hardness 1.Ion exchange process2.Chemical precipitation3.Electro based methods4.Adsorption 5.Membrane filtration

Fluoride 1.Chemical methods2.Adsorption3.Ion exchange4.Electro based methods5. Membrane filtration

LITERATURE REVIEW

Review on Hardness removal :

SULEYMAN A. MUYIBI and LILIAN M. EVISON – investigations -the possible use of MO seed suspension for the softening of hardwater. Gamal O. El-Sayed – Investigated -using peanut hull as a low cost sorbent to remove calcium and magnesium

ions.Loewenthal et.al. – Lime soda process and the kinetics of magnesium precipitation were extensively studied.Agostinho et.al –water hardness removal for industrial use –application of electrolysis. (80%)M. Malakootian, N.Yousefi - investigated the efficiency of EC technique in removal of water hardness under different

conditions. Electro-Based Methods for Hardness Removal Number of studies have been done to soften water by electro-chemical methods.

(Malakootian and Yousefi, 2009).

The electro based techniques include electrodialyis, electrodeionization (EDI) (Younos and Tulou, 2005), electrocoagulation (EC) (Drouiche,2007) and capacitive deionization (CDI) (Seo, et al.,2010).

Review on Hardness removal ……….

Hardness Removal by Ion Exchange Ion exchange - the exchange of calcium and magnesium ions in water for sodium

ions (Manahan, 2000). Sulphonated waste plastics are used to produce resin for hardness removal

(Pentamwa, et al.,2011). Zeolites was used as an ion exchanger to soften hard water Gholikandi, et al., (2010).

Adsorption Adsorbent materials - hardness removal include

1.pumice stone (Sepehr, et al, 2013), 2.Moringa oleifera seed (Muyibi and Evison, 1994), 3.polyacrylic acid (Gilbert, 2010) and 4.peanut hull (Idris, et al., 2012) among others.

Study conducted by Sepehr, et al. (2013) found natural pumice stone removing about 80% Ca ions and 50% Mg ions.

Alkali modified pumice stone were found to remove 95% Ca ions and 78% Mg ions at optimum adsorption conditions.

Review on defluoridation

C.M.Vivek Vardhan and J.Karthikeyan(2011) Investigations - removal of Fluoride , employing processes of adsorption

and coagulation employing abundantly available and low-cost materials.Pali Shahjee, B.J.Godboley, A.M.Sudame (2013) Investigated efficiency of low cost adsorbent (Bleaching Powder) for the

removal of fluoride from aqueous solution. G. Alagumuthu, V. Veeraputhiran and R. Venkataraman (2010) Investigated the removal of fluoride from the water using cynodon dactylon

as adsorbent. Bhagyashree M Mamilwar, A.G.Bhole, A.M.Sudame (2012)

Investigated the adsorption of Fluoride using bark of babool as adsorbent.

Review on defluoridation ……… Mohammad Mehdi Mehrabani Ardekani, Roshanak Rezaei Kalantary,

Sahand Jorfi, Mohammad Nurisepehr (2013)

Compared the efficiency of Bagas, Modified Bagas and Chitosan for fluoride removal from water by adsorption.

Chitozan and bagas did not show good capability for fluoride removal. but modified bagas showed more than 90% removal at optimized

conditions.Nagendra Rao (2004) investigated removal of fluorides from water by adsorption onto

Gamma Alumina (GA).Bhakuni, T.A. (1970), ‘Studies on removal of fluoride from drinking water by different ion

exchange materials.

Review on defluoridation ……… Prabavathi - studied defluoridation techniques by using lignite rice husk and

rice husk powder as adsorbent. M. Srimurali and J. Karthikeyan - investigated the household applicability of

activated alumina for removal of fluoride.Srimurali, M., Pragathi, A., Karthikeyan, J. (1998). ‘A study on removal of fluorides from drinking water by adsorption onto low-

cost materials’D. J. Killedar and D. S. Bhargava. Fluoride Adsorption on Fish Bone Charcoal Through a Moving Media

Adsorption Column. ‘Nalgonda Technique’ was developed by NEERI, Nagpur, India (Bulusu, et. al.) Adsorption onto low-cost materials like lime stone (Xanxinwang, 2002), kaolinite, bentonite, charfines, lignits and nirmali seeds extract (Srimurali et al.,

1998), bone char (Killedar and Bhargava, 1988), Serpentine (Bulusu et al., 1979), and Sulfonated saw-dust carbon (Bhakuni, 1970) are of limited scope.

Electrocoagulation/flotation

• EC- the process of destabilizing suspended or dissolved contaminants.

• ECF process treats water/wastewater containing soluble or colloidal pollutants.

• ECF reactor contains two electrodes known as sacrificial electrodes. • In ECF process, DC is applied to the electrodes in a reactor

containing water. • The produced current breaks water molecules in to hydrogen and

oxygen gases as shown in equation 1: 2H2O ↔ 2H2 + O2 ……………………………………………….. (1) Anode: 2H2O → O2 +4H+ +4e− ………………………………… ... (2) Cathode: 2H2O + 2e−→ H2 +2OH-…………………………… …… (3)

• The produced current generates metal ions from sacrificial electrodes.

• These metal ions will react with hydroxyl ions and produce metal hydroxides as shown in equations.

• The following chemical reactions occurring in the electro coagulation process using iron electrodes:

Fe (s) ↔ Fe+3 aq + 3e- (anode) (4) 3H2O + 3e- ↔ 3/2 H2 g + 3OH- aq (cathode) (5) Fe+3 aq + 3OH- aq ↔ Fe(OH)3 (overall) (6)• Iron hydroxide flocs normally act as adsorbents.

Electrocoagulation/flotation…….

Chemical Coagulation

• Process of adding chemicals/coagulants to the treating water.

• Various coagulants -• Colloidal paricles- negatively charged.• A coagulant – positively charged.Flocculation (mixing): • Slow stirring to aggregate destabilized particles and

forming a rapid settling floc.

MATERIALS AND METHODOLOGYMaterials :• Iron plate electrode was made in required dimensions of

5 cm x 10 cm from raw material.• Sodium fluoride (NaF), Calcium chloride, Magnesium

chloride, Magnesium sulphate and Calcium sulphate were used as analytical grade.

Standard solutions :• Hard water solution: By dissolving 20g of CaCl2, 14g of

MgCl2 . 6H2O, 8g of MgSO4 and 8g of CaSO4 in 300ml mineral water.

• Working solution of hardness: required quantity of hard water solution was diluted with 1L Mineral water and so that required concentrations of hardness of 700, 1000, 1200 and 1300 mgL-1 by EDTA method.

MATERIALS AND METHODOLOGY ………Fluoride stock solution : By dissolving 221 mg anhydrous

sodium fluoride in 1000 mL distilled water. Working solution of fluoride : • 2 mgL-1 fluoride concentration was prepared by dilution of

200 ml of fluoride stock solution with 800 ml of mineral water.

Alum stock solution : By dissolving 10g in 1 litre of distilled water;

Each 1ml of this stock solution was equal to 10ppm.Analytical methods:• Hardness rate was determined by EDTA titrimetric method

(APHA / AWWA /WEF, 1999).• The Residual Fluoride concentration was determined by

SPADNS method using UV-VIS Spectrophotometer @570 nm.

Work methodology

Chemical coagulation • Coagulation experiments were conducted by standard jar

test procedures using a six place jar test apparatus.

• To a 500 mL sample of the test hard water/Fluoride solution taken in a beaker, coagulant dose in the range of 100, 200, 300, 400, 500, 600, 700, 800 mgL-1 was added and mixed for a typical rapid mixing time of 2 minutes at 120 rpm followed by slow mixing at 30rpm for 20 minutes.

• The contents were then sedimented for 2 hours and an aliquot of supernatant was withdrawn and analyzed for residual total hardness and fluoride concentration.

Jar test apparatus

Under settling

Work methodology …….Electrocoagulation method:• Electrocoagulation experiments were performed in a

monopolar batch reactor, with two iron plate electrodes. • Laboratory scale experimental setup was made - A

power source, two iron electrodes (5 ×10 cm) spaced at 1.0 cm and a glass beaker of capacity 1 L.

• Electrodes were connected as monopolar with the help of wood.

• Test solutions of desired concentrations of hardness and fluoride with pH adjusted to required values were poured into the reactor.

Electrocoagulation……..

• A DC power supply having a variable output of 0–32V (5, 10, and 15 V for this study) with maximum current of 1 ampere was used as direct current source.

• Desired electrical potential was applied and an aliquot of samples was withdrawn from the reactor at different time intervals of 30, 60, 120,180, 240 and 300 minutes, filtered through Whatman 42 filter paper.

EC SETUP

After 2hrs

RESULTS AND DISCUSSIONSFluoride removal by chemical coagulation:

3 4 5 6 7 8 9 10 110

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100

3 mgL-1

pH

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Figure 4.1 Fluoride removal at different pH values.

Fluoride removal by chemical coagulation …….

0 100 200 300 400 500 600 7000

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2 mgL-1

3 mgL-1

5 mgL-1

Alum dose, mgL-1

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Figure 4.2 Removal of Fluoride by chemical coagulation.

Hardness removal by Chemical coagulation

Fluoride removal by electrocoagulation

0 50 100 150 200 250 300 3500

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2 mgL-13 mgL-15 mgL-1

Contact time, minutes

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Figure 4.3 Removal of fluoride at 5V voltage and pH 6.

Fluoride removal by electrocoagulation……..

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Fluoride removal by electrocoagulation …….

Removal of hardness by Electrocoagulation

0 50 100 150 200 250 300 3500

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700 mgL-11000 mgL-11200 mgL-11300mgL-1


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Figure 4.8 Removal of hardness at voltage 5V and contact times (pH=6).

Removal of hardness by Electrocoagulation………….

0 50 100 150 200 250 300 3500

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700 mgL-1, 10V

1000 mgL-1, 10V

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Removal of hardness by Electrocoagulation……….

0 50 100 150 200 250 300 3500

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Simultaneous removal of fluoride and hardness by electrocoagulation

Effect of applied voltage :

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Fluoride = 2 mgL-1 , 5 vFluoride = 2 mgL-1 , 10 vFluoride = 2 mgL-1 , 15 vHardness = 700 mgL-1 , 5 vHardness = 700 mgL-1 , 10 vHardness = 700 mgL-1 , 15 v


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Figure 4.13 Removal of hardness and fluoride at different voltages and contact time (pH=8).

Simultaneous removal of fluoride and hardness by electrocoagulation ………..Effect of applied voltage :

0 50 100 150 200 250 300 3500

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Fluoride = 3 mgL-1, 5 vFluoride = 3 mgL-1, 10 vFluoride = 3 mgL-1, 15 vHardness = 700 mgL-1 5 vHardness = 700 mgL-1 10 vHardness = 700 mgL-1 15 v


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Simultaneous removal of fluoride and hardness by electrocoagulation ………..Effect of applied voltage :

0 50 100 150 200 250 300 3500

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Fluoride = 5 mgL-1, 5 vFluoride = 5 mgL-1, 10 vFluoride = 5 mgL-1, 15 vHardness = 700 mgL-1 5 vHardness = 700 mgL-1 10 vHardness = 700 mgL-1 15 v


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Simultaneous removal of fluoride and hardness by electrocoagulation ………..Effect of pH :

0 50 100 150 200 250 300 3500

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Fluorde = 2 ppm 6 pHFluorde = 2 ppm 7 pHFluorde = 2 ppm 8 pHHardness = 700 ppm 6 pHHardness = 700 ppm 7 pHHardness = 700 ppm 8 pH


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Figure 4.16 Simultaneous removal of hardness and fluoride at 15 V and at different pH.


0 50 100 150 200 250 300 3500

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Fluoride = 3 mgL-1, 6 pHFluoride = 3 mgL-1, 7 pHFluoride = 3 mgL-1, 8 pHHardness = 700 mgL-1 6 pHHardness = 700 mgL-1 7 pHHardness = 700 mgL-1 8 pH


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0 50 100 150 200 250 300 3500

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Fluoride = 5 mgL-1, 6 pHFluoride = 5 mgL-1, 7 pHFluoride = 5 mgL-1, 8 pHHardness = 700 mgL-1 6 pHHardness = 700 mgL-1 7 pHHardness = 700 mgL-1 8 pH


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Simultaneous removal of hardness and fluoride by chemical coagulation

0 100 200 300 400 500 600 700 800 9000

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5 mgL-11300 mgL-1

Alum dose, mgL-1

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Figure 4.19 Effect of hardness on Fluoride removal.

ConclusionsChemical coagulation:• Removal of fluoride 80 - 90% - found effective .• Alum coagulation was found ineffective to

remove hardness only (8 %).• Alum coagulation was found to be ineffective to

remove Hardness along with Fluoride. • Hardness was removed by 10 – 15% in association

with fluoride.• Fluoride removed by 65% in the presence of

hardness concentration (1300 mgL-1 ).

Conclusions ……. Electrocoagulation:• Individual removal of Hardness and fluoride hardness : 65 -78 % (700-1300 ppm) fluoride : 74 – 90% (2-5 ppm)• Simultaneous removal of Hardness and fluoride hardness : 65 – 79% (700-1300 ppm) fluoride : 74 – 92% (2 - 5 ppm)• Hardness and Fluoride removal are more effective at pH 6-8. • At low voltages (5, 10 and 15 V), the time needed to achieve

required efficiencies increased (30 - 360 minutes) and removal of hardness also increased.

• The removal of hardness was rapid during the initial 60 minutes for all concentrations and thereafter rate of removal decreased gradually.

• Whereas in the case of fluoride, removal of fluoride increased to a certain contact time and after which fluoride removal decreases.

Scope for future work

• Simultaneous removal of hardness and fluoride using iron electrodes at various currents are recommended.

• A continuous flow pilot study is recommended. • Sludge analysis was suggested by FTIR, XRD,XRF and

SEM techniques. • Analysis of residual iron concentration in the treated

water is suggested.

THAN Q

simultaneous removal of hardness and fluoride by chemical and electrocoagulation

Engineering