Lecture Notes: Water Treatment Process

Introduction

• Healthy lakes and rivers naturally clean themselves like cats.
  • Utilize soil and organisms to filter out contaminants.
  • Provide clean water for irrigation, drinking, and ecosystems.
• Pollution from humans (sewage, storm water) overwhelms natural systems.

Water Management Systems

• Used in urban areas of developed countries to treat water waste.
• Water from homes, businesses, and storm water travels through sewer pipes to water treatment plants.

Primary Sewage Treatment

• Also known as Physical Sewage Treatment.
• Large objects are physically removed to prevent pipe clogging.
• Process:
  • Series of screens filter out large objects (sticks, rocks, rags, plastic, hair).
  • Grit (sand, gravel, coffee grounds, food waste) is removed by slowing down water flow in narrow tanks.
  • Collected grit forms sludge, which is treated.

Secondary or Biological Treatment

• Water is aerated to increase population of aerobic bacteria.
• Bacteria break down organic waste to carbon dioxide and sludge.
• Activated sludge is sometimes added to boost bacteria growth.
• Described as caretaking microbial pets.
• Sludge is recycled or processed (dried/buried or turned into biosolids for agriculture).

Disinfection Stage

• Removes disease-causing bacteria and viruses not addressed by prior treatments.
• Methods:
  • Ultraviolet light prevents bacteria multiplication.
  • Chlorine or ozone treatments kill bacteria and viruses.
  • Chlorination is highly effective (kills >99% harmful bacteria).

Tertiary or Advanced Treatment

• Applied when water is released into drinking, agricultural, or recreational water sources.
• Techniques are expensive and not widely used.
• Methods:
  • Biological treatments for nitrogen/phosphorus removal.
  • Physical/chemical separation (filtration, carbon absorption, distillation, reverse osmosis).

Conclusion

• Cleaned water is released into the environment (oceans, rivers) or reused (e.g., Rubik's bath).