Environmental Engineering II chapter five

Presentation on Environmental Engineering II

1. By Prof. Dr. Ganesh Chandra Saha Department of Civil Engineering DIU, Dhaka Lecture-02 Presentation on Environmental Engineering II

2. Presentation Contents Title Subtitle Water treatment Sedimentation Coagulation Filtration Disinfection Chemical Precipitation Ion Exchange Reverse Osmosis

3. CAUSES OF WATER POLLUTION DOMESTIC WASTE SEWAGE SYSTEM SOLID WASTE INDUSTRIAL WASTE OIL INDUSTRY ACID RAIN The principal sources of water pollution resulting from exploration and production operations are:

4. Definition Destabilisation of colloid particles by the addition of chemicals (coagulant) Applications Industrial waste containing colloidal and suspended solids (e.g. pulp and paper, textile)

5. Metal coagulants : aluminium -based coagulants, Fero -based coagulants magnesium chloride (MgCl 2 ) Organic polymer coagulants : Polyacrylamide, Chitosan, Moringa olifeira Alginates (brown seaweed extracts)

6. Coagulant agent

7. Coagulant - Reaction Some of the coagulants used include: Aluminium sulphate Ferric chloride Ferric sulphate Lime (not true coagulant) Polymer as coagulant aid eg cationic, anionic, non-ionic. PAC – new types Al 2 (SO 4 ) 3 .18H 2 0+ 3Ca(HCO 3 ) 2AI(OH) 3 + 3CaSO 4 + 6C0 2 + 18H 2 AI(OH) 3 or Al 2 O 3 ( form as floc is the key element causing destabilisation of charge).

8. Flocculation is a process of forming aggregate of flocs to form larger settleable 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.

9. Flocculation mechanism

10. Flocculation mechanism

11. Flocculation mechanism

12. Flocculation The benefits of flocculation are: To improve settling of particles in sedimentaion tank To increase removal of suspended solids and BOD To improve performance of settling tanks

13. Differences Coagulation: is a chemical technique which is directed towards the destabilisation of the charged colloidal particals . Flocculation: is the slow mixing technique which promotes the agglomeration of the stabilised particles.

14. 6/10/2024 Water filtration 32

15. 6/10/2024 Water filtration 33

16. 6/10/2024 Water filtration 34

17. 6/10/2024 Water filtration 35

18. 6/10/2024 Water filtration 36 Filtration Mechanisms Important to understand the mechanisms Settling, adsorption and diffusion Not much screening

19. 6/10/2024 Water filtration 37

20. 6/10/2024 Water filtration 38 A B C

21. 6/10/2024 Water filtration 39

22. 6/10/2024 Water filtration 40

23. 6/10/2024 Water filtration 41 Filter operation

24. 6/10/2024 Water filtration 42 Slow Sand Filter Underdrain

25. 6/10/2024 Disinfection 43 Disinfection:

26. Disinfection a reduction in the number of viable organisms Can be achieved by: Low-temperature steam Boiling water Chemical disinfectants

27. Low-temperature steam

28. Chemical disinfectants Destroys microorganisms by chemical or physicochemical means Different organisms vary in their sensitivity Gram-positive - highly sensitive Gram-negative - relatively resistant Clostridial & mycobacterial species - very resistant Slow viruses - highly resistant Disinfectants are suitable for heat-sensitive items Less effective than heat Chemicals used include: Clear soluble phenolics Hypochlorites Alcohols Quaternary ammonium compounds

29. Sterilisation Removal of viable microorganisms including spores and viruses Can be achieved by: Autoclaves Hot air ovens Ethylene oxide Low-temperature steam and formaldehyde Sporicidal chemicals Irradiation Gas plasma

30. CHEMICAL PRECIPITATION (Applications) Removal of metals from waste stream e.g. plating and polishing operations, mining, steel manufacturing, electronics manufacturing include arsenic, barium, chromium, cadmium, lead, mercury, silver Treatment of “hard” water – removal of Mg 2+ and Ca 2+ Phosphorus removal Making pigments Removing salts from water in water treatment

31. ION EXCHANGE Definition Ion exchange is basically a reversible chemical process wherein an ion from solution is exchanged for a similarly charged ion attached to an immobile solid particle. Removal of undesirable anions and cations from solution through the use of ion exchange resin Applications Water softening Removal of non-metal inorganic Removal or recovery of metal

32. ION EXCHANGE (Basic Principles) Cation Resin Cr 3+ , CN - H + , CN - Anion Resin H + , OH - Clean water

33. Types of Osmosis There are two types of Osmosis processes as shown in Fig 1.1 Direct Osmosis (DO): DO uses low pressure. The solvent passes through the membrane driven by the difference in solute concentrations on the two sides. Equilibrium is reached when sufficient water has moved to equalize the solute concentration on both sides of the membrane. Reverse osmosis (RO): RO uses a high-pressure which is larger than OP on the high concentration side. So, the carrier is preferentially permeated, while the retentate contains the rejected solute (contaminant). Thus, the membrane divides the water from the contaminants. The main aim is to purify water and not dilute the contaminants. EQUILIBRIUM p Osmotic Pressure The solvent flux is stopped . Pure solvent Solution Membrane OSMOSIS Solvent passes the membrane to the solution side. From low solute concentration to high concentration. D P > p REVERSE OSMOSIS The flux is reversed when a P greater than p is applied. From high solute concentration to low concentration

34. Permeate Feed Reject In Reverse Osmosis a pump is used to raise the pressure and the feed is distributed among a number, n , of modules. The reject is collected and taken for further treatment, disposal or sale. The permeate is recovered and constitute the clean stream. Reverse Osmosis can be used in a legion of applications. Some of them are: seawater desalting, treatment of cheese whey, metal finishing solutions, bleach and dye plant effluent and waste water from sewage treatment works. Reverse Osmosis Performance ultrafiltration evaporation Reverse osmosis evaporation Bleach plant effluent Sugars 5%(w/v) Water for reuse Sugars 20%(w/v) Sugars 60%(w/v) Lignosulfonates 30% (w/v) Lignosulfonates 60% (w/v) Reverse Osmosis for pulped paper industry waste treatment. REVERSE OSMOSIS

35. REVERSE OSMOSIS MEMBRANE AND MODULES HOLLOW FIBER FLAT SHEET TUBULAR According to Geometric Shape , membranes can be classified in Hollow Fiber module Spiral wound module Plate and Frame module Tubular module

36. Water Supply and Sanitation by M Feroze Ahmed Chapter-18 ,19 (Water Treatment and Specific groundwater treatment processes ) Suggested Reading

37. THANK YOU