🚰 Big Picture: Why Wastewater Matters

• Wastewater treatment isn’t just about clean water—it’s about energy and resource recovery.
• Microbes are the workforce: they recycle carbon (C), nitrogen (N), phosphorus (P), and even help handle micropollutants.
• Goal = link clean water production with bioenergy + nutrient recovery → supports UN Sustainable Development Goals (SDG 6 & 7).

🏭 State of the Art

• Activated sludge process = most common system → removes C, N, P, pathogens, micropollutants.
• Surplus sludge often goes to anaerobic digesters, producing biogas (mainly methane).
  • In Denmark 🇩🇰, many WWTPs are now energy neutral or even net producers ⚡.
• Bonus: phosphorus recovery (as struvite 💎 or fertilizer from sludge).
• Online resource: MiDAS database 📚 tracks who’s who in microbial communities.
• New discoveries change the game: e.g., comammox organisms (can oxidize ammonium all the way to nitrate alone).

🔬 Needs and Perspectives

1. Microbial Knowledge Gap

• Only ~100–200 genera dominate WWTP communities worldwide.
• But many are still poorly characterized—functions unknown 🤔.
• Especially digesters: often unstable, foamy, or low gas-yield → linked to microbial balance.

2. Stability of Ecosystems

• If microbial communities collapse, the whole process fails.
• Need ecological theories to guide engineering (not just trial and error).

3. Greenhouse Gas Concerns

• N-removal sometimes produces N₂O (nitrous oxide), a strong greenhouse gas.
• Which microbes make it? Still uncertain ❓

4. Antibiotic Resistance Genes (ARGs)

• WWTPs may be hotspots for ARG spread. Debate: how dangerous is this really?

5. Phosphorus Recovery

• EBPR (Enhanced Biological P Removal) is essential for sustainable P recycling.
• Still unclear which species are the real P-heroes in full-scale plants.

6. Filamentous Microbes

• Cause poor settling, foaming, and fouling.
• Some are known and controllable ✅, but many remain mysterious 🚫.

🌟 Novel and Exciting Processes

• DAMO (Denitrifying Anaerobic Methane Oxidation): methane + nitrate → energy + less pollution.
• SANI process: integrates sulfate reduction, autotrophic denitrification, nitrification → for saline wastewater 🌊.
• Potential for new sustainable hybrid systems.

⚡ Beyond Biogas

• Biogas (CH₄) is good but maybe too low-value.
• Alternatives:
  • Biohydrogen (clean fuel 🚀)
  • Organic acids, alcohols, lipids (chemicals + bioplastics industry 🧪)
  • Even proteins for feed/food 💪.

🧬 The Omics Revolution

• DNA sequencing + meta-omics (metagenomics, metatranscriptomics, etc.) = game-changer.
• Soon we’ll have complete genomes of all key WWTP microbes.
• Tools like Oxford Nanopore MinION → real-time, on-site monitoring ⚡.
• Data → used for surveillance and microbial community control.

✅ Take-Home

• Wastewater treatment is shifting from waste disposal → resource factory (circular economy).
• Microbial biotechnology is central:
  • Optimize existing systems 🔧
  • Develop novel processes 🌱
  • Harness “omics” for smarter control 🎛️
• Future = clean water, energy, nutrients, and valuable products, all from “waste.”