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Coagulation & flocculation in wastewater treatment

The document discusses the processes of coagulation and flocculation in wastewater treatment, emphasizing their importance in removing colloidal substances to meet potable water requirements. It outlines different types of coagulants, their chemical properties, advantages, and disadvantages, as well as the flocculation mechanism that enhances particle aggregation. Additionally, it highlights the role of coagulant aids in improving the efficiency of these processes.

Environment◦
Wastewater Treatment; Coagulation & Flocculation Md. Jamilur Rahman Tasnina Karim Maliha Tabassum 1/23/2018 1
outline • Introduction • Coagulation Mechanism • Flocculation Mechanism 1/23/2018 2
Introduction Why need coagulation flocculation 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
Coagulation • Definition Destabilisation of colloid 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
Coagulation (cont.) 1/23/2018 5
Coagulant • Metal coagulants aluminum-based coagulants, 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
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
Coagulant agent Alum Magnesium chloride Polyacrylamide Moringa oleifera1/23/2018 8
Chemical Formula PRIMARY COAGULANT o Aluminum 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
ALUM • Alum can be 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
Advantages & Disadvantages of 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
Ferric sulfate • Ferric sulfate 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
Advantages of Ferrous sulphate • 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
Coagulant Aids • Accelerates the 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
Common Coagulant Aid • Activated silica • Polymer • Polyelectrolytes • Calcium carbonate Source: wastewater management lecture 12- Coagulation and Flocculation 1/23/2018 15
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
Flocculation Forming aggregate of flocs 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
Flocculation Mechanism 1/23/2018 18
Flocculation Mechanism (Cont.) 1/23/2018 19
Effects of Flocculation The benefits 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
Differences • Coagulation: is a 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