💧 Wastewater and Drinking Water Treatment

🧫 Why It Matters

Wastewater treatment keeps our environment clean and prevents disease by removing organic matter, nitrogen, and phosphorus using both microbes and physical/chemical processes.

⚙️ Primary Treatment — “The Physical Cleanup”

• Goal: Remove large solids and materials.
• Process:
  1. Screens filter out trash (bottles, plastics, grit).
  2. The remaining water sits in large tanks → solids settle → sludge forms at the bottom.
  3. That sludge goes to anaerobic digesters, where microbes turn it into methane 🔥 for energy recovery.
  4. The remaining liquid (effluent) goes to secondary treatment.

🧪 Secondary Treatment — “Microbial Power!”

Here microbes do the heavy lifting by oxidizing organic matter under aerobic conditions.

Two main systems:

1. Activated Sludge Process
   • Aeration tanks mix wastewater with air and microbes.
   • Bacteria form flocs (biofilm-like clumps) full of Zoogloea ramigera and other organisms.
   • Flocs settle → some reused as inoculum, rest goes to digesters.
   • Result: BOD (biochemical oxygen demand) drops up to 95%! → Less food for microbes = cleaner water 🫧
2. Trickling Filter
   • Wastewater sprayed over rocks.
   • Microbes grow as biofilms on rocks → break down organic matter into CO₂, nitrate, sulfate, and phosphate.

💡 After secondary treatment, the water may be disinfected (chlorine or ozone) before release.

🌿 Tertiary Treatment — “Polishing the Water”

Removes leftover phosphorus and nitrogen to prevent eutrophication (algal blooms 🌱).

🧬 Enhanced Biological Phosphorus Removal (EBPR)

• Uses phosphorus-accumulating organisms (PAOs) such as:
  • Accumulibacter phosphatis (Betaproteobacteria)
  • Tetrasphaera (Actinobacteria)
• PAOs cycle between:
  • Anaerobic phase: use polyphosphate and glycogen → store carbon as PHA.
  • Aerobic phase: use stored PHA → rebuild polyphosphate inside cells.
• High-phosphorus sludge is then removed.

🧪 Nitrogen Removal

1. Classical nitrification–denitrification:
   • Ammonia → nitrite → nitrate (aerobic)
   • Nitrate → N₂ (anaerobic)
   • Needs organic carbon (often added as methanol).
2. Advanced nitritation–denitrification:
   • Stops oxidation early at nitrite (NO₂⁻) → saves oxygen and carbon costs.
   • Works by adjusting temperature, pH, and sludge retention time to suppress nitrite-oxidizing bacteria (NOB).
3. Aerobic Granular Sludge (Nereda® Process):
   • Microbes form dense granules (not loose flocs).
   • Outer layer = aerobic (nitrification, phosphate uptake).
   • Inner core = anoxic (denitrification).
   • Compact, energy-efficient, and effective!

🔁 Sludge Treatment — “Microbial Recycling”

All sludge goes to anaerobic digesters, large sealed tanks where:

• Bacteria and archaea ferment polymers → acids → methane + CO₂.
• Syntrophic cooperation is key!
• Methane can be used as bioenergy for the plant. ♻️ Sludge volume ↓, energy ↑.

Sometimes this process creates side streams rich in nitrogen (N) and phosphorus (P) → need more treatment.

🧬 The Anammox Revolution (Partial Nitritation–Anammox)

• Anammox = anaerobic ammonium oxidation
• Reaction: NH₄⁺ + NO₂⁻ → N₂ + H₂O + a bit of NO₃⁻
• Benefits:
  • No carbon addition needed
  • Lower energy use
  • Less sludge
  • Lower greenhouse gas output 🌍 → very eco-friendly!

⚠️ Contaminants of Emerging Concern

Modern life adds new pollutants: 💊 Pharmaceuticals 🧴 Cosmetics & fragrances 🌽 Pesticides ☀️ Sunscreens

Even at low concentrations, they can disrupt hormones (e.g., estrogens feminizing fish). Bioremediation here is tough — microbes often ignore these until easier organics are gone.

🚰 Drinking Water Purification

After wastewater treatment, drinking water needs its own purification process.

1️⃣ Sedimentation

• Removes sand, soil, and big particles.

2️⃣ Coagulation & Flocculation

• Add alum (aluminum sulfate) and polymers → small particles clump into flocs → settle.

3️⃣ Filtration

• Through sand, charcoal, and ion exchangers → removes fine solids, organics, and microbes.

4️⃣ Disinfection

• Chlorination: kills most microbes, improves taste, but not perfect for Cryptosporidium.
• UV Radiation: physically damages DNA, leaves no chemical residues.

🚿 Water Distribution Systems

After treatment, water travels through pipes to consumers. But inside the pipes:

• Chlorine levels drop with distance.
• Microbes form biofilms on walls.
• Some pathogens can survive or regrow.

💡 That’s why monitoring and maintaining residual chlorine (0.2–0.6 mg/L) is vital.

🧭 Summary Time!