Microbes in Waste Treatment

Wastewater Treatment Overview - Bugs at Work

Wastewater (domestic, industrial) contains pollutants: organic matter (↑BOD), nutrients (N, P), pathogens. Treatment aims: ↓BOD/COD, pathogen removal.

• BOD (Biochemical Oxygen Demand): $O_2$ microbes use to decompose organics. High BOD = high pollution.
• COD (Chemical Oxygen Demand): $O_2$ for chemical oxidation of all pollutants. Typically, COD ≥ BOD.

Treatment Stages: 📌 People Prefer Sanitized Toilets.

• Preliminary: Removes large solids, grit.
• Primary: Physical sedimentation.
• Secondary (Biological): Microbes actively degrade dissolved organic matter.

  ⭐ Bulk of organic matter removal occurs here (e.g., activated sludge, trickling filters), reducing BOD by 85-95%.

• Tertiary: Polishing (e.g., nutrient removal), disinfection.

Aerobic Microbial Processes - Oxygen Powerhouse

• Activated Sludge Process (ASP):
  • Suspended microbial growth; bioflocculation is key.
  • Flocs: Formed by Zooglea ramigera, Pseudomonas, nitrifying bacteria (Nitrosomonas, Nitrobacter).
  • Sludge Volume Index (SVI): Measures settleability. Normal 50-150 mL/g. SVI > 150 mL/g indicates bulking (e.g., filamentous Nocardia, Sphaerotilus).
• Trickling Filters:
  • Attached microbial growth (biofilm) on media (e.g., stones, plastic).
  • Biofilm layers: Outer aerobic, inner anoxic/anaerobic.
• Nitrification ($NH_4^+ \xrightarrow{Nitrosomonas} NO_2^- \xrightarrow{Nitrobacter} NO_3^-$): Key aerobic, oxygen-dependent.
  • $2NH_4^+ + 3O_2 \xrightarrow{Nitrosomonas} 2NO_2^- + 4H^+ + 2H_2O$
  • $2NO_2^- + O_2 \xrightarrow{Nitrobacter} 2NO_3^-$

⭐ Zooglea ramigera plays a key role in forming the gelatinous matrix of flocs in activated sludge.

Anaerobic Digestion & Sludge - Methane Makers

Anaerobic digestion: Microbial process for sludge stabilization & biogas ($CH_4, CO_2$) production. 📌 HAAM.

• Four Stages:
  • Hydrolysis: Complex organics (polysaccharides, proteins, lipids) $\rightarrow$ simple monomers.
  • Acidogenesis: Monomers $\rightarrow$ VFAs (e.g., butyric, propionic acid), alcohols.

    ⭐ Methanogens are strictly anaerobic Archaea, highly sensitive to oxygen and pH changes.

  • Acetogenesis: VFAs $\rightarrow$ acetate, $H_2, CO_2$.
  • Methanogenesis: Acetate ($CH_3COOH \rightarrow CH_4 + CO_2$), $H_2/CO_2 \rightarrow CH_4$. Key microbes: Methanobacterium, Methanosarcina.
• Key Factors:
  • Temperature: Mesophilic (30‑38°C optimal), Thermophilic (50‑58°C).
  • pH: 6.5‑7.5 (critical for methanogens).
  • C/N ratio: Balanced for microbial activity.

Solid Waste & Pathogen Control - Clean Finish

• Composting: Aerobic decomposition of solid organic waste.
  • Phases: Mesophilic → Thermophilic (>55°C pathogen kill; Bacillus stearothermophilus, Aspergillus fumigatus) → Cooling → Maturation.

  ⭐ The thermophilic stage (>55-65°C) in composting is essential for effective pathogen inactivation and rapid decomposition.

• Wastewater Pathogen Reduction:
  • Disinfection Methods:
    • Chlorination: Oxidizes. Residual effect; forms Disinfection Byproducts (DBPs).
    • UV Irradiation: Damages DNA. No residuals; turbidity affects efficacy.
    • Ozonation: Strong oxidant. Effective; high cost, no residual.
• Indicator Organisms (Fecal Contamination):
  • e.g., E. coli, fecal coliforms, enterococci.
  • Ideal criteria: Present with pathogens, similar survival, easily detected, non-pathogenic.
• Biomedical Waste Sterilization:
  • Autoclaving: 121°C, 15 psi, 15-20 min.

High‑Yield Points - ⚡ Biggest Takeaways

• Activated sludge process relies on aerobic bacteria like Zooglea for floc formation.
• Anaerobic digestion uses methanogens (e.g., Methanobacterium) to produce methane (biogas).
• Trickling filters utilize aerobic microbial biofilms on inert media for wastewater treatment.
• Oxidation ponds depend on algal-bacterial symbiosis for organic matter degradation.
• E. coli serves as a key indicator of fecal contamination in treated water.
• Sludge bulking is often caused by filamentous bacteria like Sphaerotilus natans.
• Bioremediation employs microbes for degrading environmental pollutants and contaminants.