Coagulation & flocculation in wastewater treatment

Coagulation & flocculation in wastewater treatment

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  Wastewater Treatment; Coagulation& Flocculation Md. Jamilur Rahman Tasnina Karim Maliha Tabassum 1/23/2018 1
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  outline • Introduction • CoagulationMechanism • Flocculation Mechanism 1/23/2018 2
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  Introduction Why need coagulationflocculation in wastewater treatment? • Removal of colloidal substances from water • Potable water requirements (health, aesthetics, economic) • Colloids • Size of colloids - light waves • Brownian motion • Stability of colloids 1/23/2018 3
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  Coagulation • Definition Destabilisation ofcolloid particles by the addition of chemicals. • Applications Industrial waste containing colloidal and suspended solids Source: Bioremediation of Turbid Surface Water Using Seed Extract from Moringa Oleifera Lam, (Drumstick) Tree. In: Current Protocols in Microbiology 1/23/2018 4
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  Coagulation (cont.) 1/23/2018 5
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  Coagulant • Metal coagulants aluminum-basedcoagulants, Ferro-based coagulants magnesium chloride (MgCl2) • Organic polymer coagulants Polyacrylamide, Chitosan, Moringa olifeira Alginates (brown seaweed extracts) Source: Bioremediation of Turbid Surface Water Using Seed Extract from Moringa Oleifera Lam, (Drumstick) Tree. In: Current Protocols in Microbiology 1/23/2018 6
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  Coagulant (Cont.) Other Coagulants •Lime • Sodium Aluminate • Aluminum Chloride • Chromic Chloride • Titanium Tetrachloride Source: Coagulation and Flocculation in Water Treatment J(Hans) van Leeuwen 1/23/2018 7
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  Coagulant agent Alum Magnesiumchloride Polyacrylamide Moringa oleifera1/23/2018 8
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  Chemical Formula PRIMARY COAGULANT oAluminum sulfate (Alum) Al2(SO4)3 o Ferrous sulfate FeSO4 o Ferric sulfate Fe2(SO4)3 o Ferric chloride FeCl3 Source: Coagulation and Flocculation in Water Treatment J(Hans) van Leeuwen 1/23/2018 9
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  ALUM • Alum canbe bought in liquid form with a concentration of 8.3%, or in dry form with a concentration of 17%. • It reacts with the water and results in positively charged ions. Source: COAGULATION IN WASTEWATER TREATMENT BY GARRET P. WESTERHOFF 1/23/2018 10
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  Advantages & Disadvantagesof Alum ADVANTAGES • It readily dissolves with water, • It does not cause the unsightly reddish brown staining of floors, walls and equipment like ferric-sulphate Source: COAGULATION IN WASTEWATER TREATMENT BY GARRET P. WESTERHOFF DISADVANTAGES • It is effective only at certain pH range • good flocculation may not be possible with alum in some waters 1/23/2018 11
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  Ferric sulfate • Ferricsulfate and chlorinated copperas exhibit a dual range of effective pH, one from 4 to 6 and the other from 8 to 10. • Copperas has appreciable solubility below pH 8.5 and its use is normally limited to the pH range of 8.5 to 10.5 Source: COAGULATION IN WASTEWATER TREATMENT BY GARRET P. WESTERHOFF 1/23/2018 12
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  Advantages of Ferroussulphate • Ferric hydroxide is formed at low pH values, so that coagulation is possible with ferric sulphate at pH values as low as 4.0 • Ferric hydroxide is insoluble over a wide range of pH values than aluminum hydroxide except for the zone of 7.0 to 8.5 • The floc formed with ferric coagulants is heavier than alum floc • The ferric hydroxide floc does not dissolve at high pH values • Ferric coagulants may be used in color removal at the high pH values required for the removal of iron and manganese and in softening of water. Source: CHEMICAL CLARIFICATION – COAGULATION METHODS by Michigan Department of Environmental Quality Operator Training and Certification Unit 1/23/2018 13
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  Coagulant Aids • Acceleratesthe process of coagulation and flocculation by producing quick forming, dense and rapid-settling flocs • Coagulant aids when added increase the density to slow-settling flocs and toughness to the flocs so that they will not break up during the mixing and settling processes. Source: lecture- HAZARDOUS WASTE TREATMENT TECHNOLOGIES 1/23/2018 14
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  Common Coagulant Aid •Activated silica • Polymer • Polyelectrolytes • Calcium carbonate Source: wastewater management lecture 12- Coagulation and Flocculation 1/23/2018 15
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  Effects of Coagulation •Improved primary treatment for raw sewage • Effluent polishing • Phosphate removal Source: lecture- HAZARDOUS WASTE TREATMENT TECHNOLOGIES Raw waste Floc Formation Settle floc 1/23/2018 16
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  Flocculation Forming aggregate offlocs to form larger settle able particle. The process can be described as follows; • Mutual collision of small floc resulting in bigger size. • Usually slow speed or gentle mixing is used so as not to break the large flocs due to shear. • Polymer or large molecular wt. compound is added to enhance floc build up. Most of them are proprietary chemicals Source: WHO (1996): Coagulation Flocculation and Clarification. In: Fact Sheet on Environmental Sanitation. ABU HASSAN, M.A, LI, T.P.; NOOR, Z.Z. (2009) 1/23/2018 17
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  Flocculation Mechanism 1/23/2018 18
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  Flocculation Mechanism (Cont.) 1/23/201819
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  Effects of Flocculation Thebenefits of flocculation are: • To improve settling of particles in sedimentation tank • To increase removal of suspended solids and BOD • To improve performance of settling tanks Source: Coagulation and Flocculation of Wastewater in Textile Industry using Chitosan. In: Journal of Chemical and Natural Resources Engineering 4, 43-53. APOSTOL, G.; KOUACHI, R.; CONSTANTINESCU, I. (2011) 1/23/2018 20
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  Differences • Coagulation: isa chemical technique which is directed towards the destabilization of the charged colloidal particles. • Flocculation: is the slow mixing technique which promotes the agglomeration of the stabilized particles. Source: Coagulation and Flocculation of Wastewater in Textile Industry using Chitosan. In: Journal of Chemical and Natural Resources Engineering 4, 43-53. APOSTOL, G.; KOUACHI, R.; CONSTANTINESCU, I. (2011) 1/23/2018 21