Water Purification by Electrocoagulation

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Christiana Pearson
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1 Water Purification by Electrocoagulation Dr. Sompong Hirunmasuwan Mr. Boonyarit Punpeng A Plus Team Co., Ltd.

2 Electrolysis of electrochemical cell e - Power supply e - Anion Oxidation Reduction M n+ Cation M n+ Anode Cathode

3 Suspended solids and colloids property Pollutant size, m molecule Virus 1 micron Colloid Bacteria Algae 1 mm Suspended solid Pollutant size (mm) Type of particle Sand Small sand Silt Bacteria Colloid Small colloid Settling velocity 6 m/s 0.48 m/min 13.3 m/d 48.5 m/yr 4.85 m/ 10 yr 1 m/206 yr

4 Destabilization of Colloid Stabilization of Colloid 1) Double layer compression 2) Change neutralization 3) Entrapment in a precipitate 4) Interparticle bridging

5 Suspeded solid (Rapid mixing) (slow mixing) Floc Colloid (Alum) Al 3+, Al(OH) 3 Polymer Chemical coagulation and flocculation

6 Coagulation and flocculation process Polymer NaOH phc Settling tank coagulant wastewater Equalization tank Rapid mixing tank Flocculation tank Sludge

7 ถ งตกตะกอน ถ งปฏ กรณ

8 Direc Electric Coagulation=Electrocoagulation : The coagulating ions are produced in situ and it involves three stages: + - M n+ Coagulation Flocculation 1) Formation of coagulants by electrolytic oxidation of sacrificial electrode 2) Destabilization of the contaminants, colloids, suspension and breaking emulsion 3) Aggregation of the destabilized phases to form flocs.

9 The electrochemical reactions of electrode : At anode : 1) Metal dissolution 1.1) Iron electrode Fe Fe e - Fe OH - Fe(OH) 2 4Fe 2+ +O 2 +2H 2 O 4Fe 3+ +4OH - Fe 3+ +3H 2 O Fe(OH) 3 +2H + 1.2) Aluminium electrode Al Al e - Al OH - Al(OH) 3 2) O 2 generation 2H 2 O O 2 +4H + + 2e - At cathode 1) Metal deposition M n+ + ne - M 2) H 2 generation 2H 2 O + 2e - H 2 + 2OH -

10 The electrochemical reactions of electrode :

11 The generation of oxygen and hydrogen : e - Power supply e - H 2 O H 2 O O 2 Mixing Adhesion flotation H 2

12 Main process involved in the electrocoagulation Floated sludge M n+ M n+ hydrated Precipitated (Pollutant) H 2 O H 2 OH - Settled sludge

13 Flow Directions Flow Cells Monopolar electrodes Bipolar electrodes

16 Advantages of Electrocoagulation (EC) to chemical coagulation 1) EC requires simple equipment and is easy to operate 2) Sludge formed by EC tends to readily settleable and easy to de-water, and low sludge production 3) Flocs formed by EC are similar to chemical floc, except that EC floc tends to be much larger 4) EC produces effluent with less total dissolved solids 5) EC has advantage of treating water with low turbidity 6) The gas bubbles produced can carry the pollutant to the top of solution where it can be easily concentrated 7) EC cells are controlled electrically, no moving parts, thus requiring less maintenance

17 Factors affecting electrocoagulation 1) Current density or charge loading Current density A/m 2 (6-24 V) Hydraulic retention time 3 20 min 2) Conductivity > 500 µs/cm 3) ph effect High efficiency near neutral ph Power consumption is higher at neutral ph but when conductivity is high, ph effect is not significant

1) Water treatment 2) Wastewater treatment : pretreatment for suspended solid, oil & grease and heavy metal removal Industrial wastewater Domestic wastewater 2) Existing wastewater treatment plant

18 1) Water treatment 2) Wastewater treatment : pretreatment for suspended solid, oil & grease and heavy metal removal Industrial wastewater Domestic wastewater 2) Existing wastewater treatment plant Increase the treatment capacity Application of Electrocoagulation Pretreatment to reduce organic loading Limiting area for expanding of wastewater treatment plant, EC requires much smaller area with same capacity Reduce the treatment operating cost

19 Water treatment: pilot testing unit

20 Wastewater treatment: batch testing unit Test results of Royal Orchid Sheraton Hotel & Towers After BOD mg/l Before After Efficiency %

21 Test results with Direct Electrical Coagulation System PP Hotel (Laundry wastewater) Before After Parameter Before After Efficiency COD (mg/l) % Phosphate (mg/l) % Batch test

22 Test results with Direct Electrical Coagulation System Petroleum authority of Thailand Exploration and Production Public Company Limited (Main Office Building) BOD mg/l Before After Efficiency % Before After Batch test

23 Domestic Wastewater : PPT Building

24 Wastewater Treatment Flow Diagram Influent Screen Equalization tank EC Sand filter Effluent Settling tank

25 Influent and Effluent Characteristic ค า BOD มก./ล ค า BOD น าเส ย ค า BOD น าท ง ก.ค.-07 ก.ย.-07 พ.ย.-07 ม.ค.-08 ม.ค.-08 พ.ค.-08 ก.ค.-08 ก.ย.-08 พ.ย.-08 ม.ค.-09 ม.ค.-09

26 Water recycle from Greywater : K-bank Building

27 Wastewater Treatment Flow Diagram Influent Screen EQ tank EC Sand filter Ozone Microfiltration Recycled water Effluent

28 Effluent characteristics

29 Domestic Wastewater : Wat Thammaguy

30 Wastewater treatment and water recycle

31 Batch test

32 Effluent characteristics

Test results with Direct Electrical Coagulation System Central Department store (Bangna) Before After Parameter Unit Standard Before After % Efficiency BOD mg/l <20 489 8.

34 Test results with Direct Electrical Coagulation System Central Department store (Bangna) Before After Parameter Unit Standard Before After % Efficiency BOD mg/l < % SS mg/l < % Oil & Grease mg/l < Nill 100% TKN mg/l < % Org-N mg/l % Sulfide mg/l < <0.10 >86% ph