BCE 3403 - Environmental Engineering

1. BCE 3403 - Environmental Engineering Water Treatment MdmNurSyazwanibinti Noor Rodi

2. Water resources • Water resources are sources of water that are useful or potentially useful to humans. • Uses of water include agricultural, industrial, household, recreational and environmentalactivities. • Fresh water is a renewable resource, yet the world's supply of clean, fresh water is steadily decreasing. • Water demand already exceeds supply in many parts of the world, and as world population continues .to rise at an unprecedented rate, many more areas are expected to experience this imbalance in the near future

3. Water resources Sources of fresh water ; • Surface water – includes rivers, lakes, and reservoirs. • Sub-surface water – pumped from wells that are drilled into aquifers • Desalination – artificial process by which saline water is converted to fresh water • Frozen water – make use of icebergs

4. Water resources

5. Surface water vs groundwater • Surface water • variable composition • low mineral content • high turbidity • colored • D.O. present • low hardness • taste and odor Groundwater • constant composition • high mineral content • low turbidity • low color • low or no D.O. • high hardness • high Fe, Mn

6. Water Treatment Water treatment describes those processes used to make watermore acceptable for a desired end-use. The purpose; • remove existing contaminants in the water, • of reduce the concentration of such contaminants • returning water that has been used back into the natural environment without adverse ecological impact.

7. Water Treatment

8. Water Treatment The processes involved in treating water may include; 1) Preliminary treatment • consists of the removal of substances that may interfere with the downstream processes or be detrimental to the plant equipment. • physical; screening process

9. Water Treatment 2) Secondary Treatment • usually consists steps to remove the dissolved and colloidal organic material not removed by the preliminary treatment. • chemical process such as coagulation.

10. Water Treatment • Cont.. • The waste enters sedimentation basin which remove suspended and floating materials –settling basin

11. Water Treatment 3) Tertiary treatment • The final treatment step for the water is disinfection to destroy pathogenic (disease-producing) organisms. • E.g. disinfection using chlorine

12. Homework – Water Treatment Process Based on the figure above, explain the purpose of each process ( no. 2 – no. 7)

13. Waste treatment Process - An Overview

14. 1. Screening • The first step in purifying surface water is to remove large debris such as sticks, leaves, trash and other large particles which may interfere with subsequent purification steps.

15. 2. Aeration • process of providing oxygen to the water. • Exposure to oxygen in the air will oxidizes some of the compounds, creating atomic sulfur which can be filtered from the water.

16. 2. Aeration • Aeration Chemistry; • Oxidation of reduced metals 4Fe2+ + O2 + 10H2O  4Fe(OH3)(s) + 8H+ 2Mn2+ + O2 + 2H2O  2MnO2(s) + 4H+ • Stripping of dissolved gases H2S(aq)  H2S(g)

17. 3. Coagulation • Coagulation and flocculation occur in successive steps intended to overcome the forces stabilizing the suspended particle, allowing particle collision and growth of floc. • First step is to destabilizes the particle’s charges. • Coagulants with charges opposite those of the suspended solids are added to the water.

18. 3. Coagulation High energy rapid-mix is used to properly disperse the coagulant. Proper contact timing in the rapid-mix is typically 1 – 3 minutes.

19. 4. Flocculation • Following the first step of coagulation, a second process called flocculation occurs. • A gentle mixing stage, increases the particle size from submicroscopic microfloc to visible suspended particle. • High molecular weight polymers may be added during this step to help strengthen the floc, add weight and increase settling rate.

20. 4. Flocculation

21. 4. Flocculation • Design contact times for flocculation range from 15 – 20 minutes to an hour or more. • Factors influencing coagulation & flocculation; turbidity, pH and color. • Once the floc reached it optimum size and strength, the water is ready for sedimentation.