Water Purification: Consumer and Wastewater Treatment Processes

Drinking Water Purification

Raw Water Treatment

1. Screening: Raw water passes through gratings, filters, and screens to remove coarse solids.
2. Aeration: Oxidation of undesirable organic species improves taste and odor.
3. Coagulation: Colloidal particles are coagulated and flocculated.
4. Sedimentation: Solids are allowed to settle and are removed.
5. Filtration: Removal of any remaining coagulated solids.
6. Disinfection: Control of bacteria.
7. Softening: Using lime and soda methods.
8. Demineralization: By distillation or ion exchange resins.

Wastewater Treatment

Primary Treatment

1. Screening/Roughing: Removal of large objects and solids through sieves.
2. Grit Removal
3. Skimming
4. Sedimentation: Takes place in tanks or chambers where suspended solids settle. This removes approximately 35% of BOD and 60% of solids.

Secondary Treatment

1. Activated Sludge: Wastewater is aerated, promoting aerobic bacteria growth which degrades organic matter.
2. Biological Filtration: Wastewater trickles through a bed of stones with bacteria that degrade biodegradable organic substances.

Sludge Treatment

1. Concentration: Thickening and floating.
2. Stabilization and Digestion: Oxidation of biodegradable organic matter.
3. Dehydration and Drying
4. Disposal: To landfill or as hazardous waste.

Tertiary Treatment

Improves purification by removing remaining contaminants.

Chemical Reactions

Combustion Reaction

Chemical reaction between an oxidizing material and oxygen, releasing energy in a flame.

Explosion Reaction

Oxidation-reduction process recombining internal elements of the explosive molecule.

Electrolysis

Using electrical energy to drive a chemical process in an electrochemical cell in the opposite direction to that which is spontaneous.

Metals

• Ag (Silver): Difficult to oxidize, high potency.
• Al (Aluminum): Passive, easily oxidized to form a protective aluminum oxide layer.
• Zn (Zinc): Rusts easily due to low potential, passivated by forming a protective layer.
• Cr (Chromium): Low potential, easily oxidized.