🌍 Overview

This lecture focused on wastewater treatment, microbial community composition, and resource recovery — showing how environmental biotechnology transforms waste into valuable resources.

💧 1. Importance of Wastewater Treatment

• Global relevance: 10–20% of all freshwater becomes wastewater.
• Problem: Only a small fraction is treated; untreated wastewater causes eutrophication and disease.
• Goal: Protect the environment and recover valuable resources.
• Modern view: “Waste is a resource.”
  • From clean water focus → to biorefinery approach (energy, biogas, nutrients).
• Denmark as leader: Many Danish wastewater plants are net energy producers due to biogas recovery.
  • Example: Billund Biorefinery integrates waste from agriculture, industry, and treatment plants to produce biogas and potentially bioplastics and phosphorus recovery.

🧪 2. Composition and Measurement

• Raw material: Wastewater containing:
  • Organic matter (BOD/COD)
  • Suspended solids
  • Nitrogen (N)
  • Phosphorus (P)
• Measured in Person Equivalent (PE): amount produced per person per year.
• Regulations: EU and Danish laws set limits for effluent concentrations of organic matter, nitrogen, and phosphorus.

🧫 3. The Activated Sludge Process

• Invented over 100 years ago by Ardern & Lockett (UK).
• Principle: Aerate sludge → bacteria form flocs that degrade organic pollutants.
• System design:
  1. Aeration tank: bacteria grow in flocs.
  2. Clarifier: flocs settle; part of biomass is returned to maintain concentration.
  3. Digester: leftover sludge converted to biogas (methane).
  4. Output: clean water + renewable energy + fertilizer (biosolids).

🔬 Microbial communities:

• Bacteria form flocs (~100 µm) containing various shapes and species.
• Many bacteria cannot be cultured on lab media — thus modern sequencing is essential to study them.

🧱 4. Process Variants

a) Carrier-based systems (MBBR)

• Use plastic carriers to increase surface area and biofilm density.
• Benefits:
  • Better biomass retention and settling.
  • Formation of aerobic outer and anoxic inner layers in biofilm → supports multiple metabolic processes.
  • Prevents clogging in other parts of the plant.

b) Granular sludge systems (Nereda®)

• Developed in Delft, Netherlands.
• Millimeter-sized granules (instead of small flocs).
• Dense biofilms form structured zones:
  • Outer aerobic → oxidizes organics and nitrifies.
  • Inner anoxic → denitrifies.
• Self-settling, compact, and energy-efficient.

c) Membrane Bioreactors (MBR)

• Biomass separated by membrane, not clarifier.
• Pros: high biomass concentration, small footprint, better effluent quality.
• Cons: membrane biofouling (biofilm formation) reduces performance.
  • Mitigated via chemical cleaning or air scouring.

d) Biofilters (Trickling filters)

• Wastewater trickles through a medium (sand, stone, plastic) covered with biofilm.
• Once common; now mainly used in industries.

🦠 5. Microbiology and Community Structure

Wastewater systems are ecosystems containing:

• Bacteria: perform organic degradation, nitrification, phosphorus removal.
• Viruses: often 10× more abundant than bacteria, influencing dynamics.
• Protozoa & Metazoa (e.g., ciliates, nematodes): graze on bacteria.
• The system is a complex microbial food web balancing cooperation and competition.

⚙️ 6. Process Stability and Problems

• Good flocs: compact, settle well.
• Problems:
  • Foaming: caused by filamentous bacteria (e.g., Microthrix parvicella), hydrophobic surfaces, or surfactant production.
  • Bulking: poor settling due to overgrowth of filamentous species.
  • Slimy flocs: poor settling due to low density.
• Morphology of bacteria (floc vs. filamentous) strongly influences plant performance.

🧬 7. Danish and Global Microbial Studies

• Danish Microbiome Projects:
  • Long-term monitoring of >200 treatment plants using FISH and later amplicon sequencing.
  • Led to creation of the MiDAS database — a curated reference with long 16S rRNA sequences and placeholder names for uncultured species.
  • Enabled global comparison and standardized classification.

🌐 Global insights:

• ~440 plants worldwide compared.
• ~500 species dominate Danish systems; ~1000 species globally.
• Most genera are universal (e.g., Nitrospira nitrifiers).
• Species vary by location, so transferring process knowledge requires local adaptation.

🧠 8. Understanding Community Dynamics

• Long-term monitoring: microbial communities are stable but dynamic.
• ~80 genera and ~500 species dominate over 10+ years.
• Seasonal variation: many species show periodic abundance changes (winter vs. summer peaks).
  • E.g., Microthrix species differ in seasonal patterns.
• Aggregating data at genus level hides species-level dynamics, which are critical for process control.

📈 9. Data, Prediction, and Control

• Time-series analysis: separates long-term trends, seasonality, and noise.
• Machine learning models: trained on microbial time-series to predict community changes up to 2 months ahead — even without input variables (e.g., substrate, temperature).
  • Successful in both wastewater and human microbiome systems.
• Real-time sequencing: Nanopore technology allows same-day monitoring (≈30 min runtime).
• Goal: “Know your plant.”
  • Establish baseline microbial fingerprint.
  • Detect deviations early → adjust operation before failure.

🧾 10. Summary Concepts