💧 Micropollutants & Wastewater Treatment

1️⃣ What are Micropollutants?

Micropollutants are tiny chemical contaminants found in extremely low concentrations in wastewater. They include:

• 💊 Pharmaceuticals (medicine residues like painkillers, antibiotics)
• 🧴 PCPs (Personal Care Products) – shampoos, soaps, cosmetics
• 🌾 Pesticides & Biocides
• 🏭 Industrial chemicals

Thousands of new compounds are introduced every year, and many end up in wastewater after use.

2️⃣ Wastewater Treatment: What We Do Well 💡

Modern wastewater treatment plants (WWTPs) are designed to remove:

• Macronutrients: Phosphorus (P) and Nitrogen (N)
• Organic matter
• Pathogens

They also often include:

• Anaerobic digesters – to create biogas (energy) ♻️
• Resource recovery – reusing waste to produce sustainable materials

However, when it comes to micropollutants, even advanced plants struggle — only about 50% are removed. The rest flow out with the treated effluent 🌊.

3️⃣ The Swedish Study 🇸🇪

Scientist Per Färløs measured pharmaceutical levels in wastewater:

• Found the same drugs (like painkillers) entering and leaving the plant.
• Example: Diclofenac (a muscle pain reliever) is not removed at all — the amount in = amount out.
• In some cases, concentrations were higher in the effluent than in the influent 🤔

4️⃣ Why Are Some Compounds “Produced” in the Plant? 🧪

Surprisingly, it’s not that new drugs are made in the plant — but rather that:

• Our bodies modify pharmaceuticals before excreting them.
• The kidneys attach sugar or sulfur groups to make the compound water-soluble and easier to excrete (via urine).
• These modified forms are invisible to chemical detectors (like GC–MS).
• Once bacteria in WWTPs remove the sugar group (their “candy” 🍬), the original drug is released again — so we detect more in the effluent than the influent.

⚗️ Toxic Interactions & the Cocktail Effect 🍹

5️⃣ Compound Interactions

Micropollutants rarely act alone. When mixed, they can:

• Have no interaction (additive)
• Have an antagonistic effect (cancel or reduce each other’s impact)
• Have a synergistic effect (together they’re more toxic 😱)

This cocktail effect makes it extremely difficult to predict environmental toxicity because:

• Lab tests can’t reproduce every possible combination.
• Real-world mixtures often act unpredictably.

Scientists visualize this using isobolograms, showing how combined doses affect organisms.

🔬 How Can We Remove Micropollutants?

6️⃣ Removal Mechanisms: Biotic vs Abiotic

There are two major categories:

🧫 Biotic (green) – biological removal

• Microbes biodegrade micropollutants into smaller, harmless compounds.
• This can lead to mineralization (complete breakdown to CO₂, water, etc.)

⚙️ Abiotic (non-living) – physical/chemical removal

1. Volatilization – compounds evaporate into air (causing bad smells 🦨)
2. Sorption – compounds stick to sludge or biofilm surfaces (adsorption/absorption)
3. Photo-oxidation – sunlight breaks them down (limited because wastewater is dark and murky)
4. Chemical oxidation – strong oxidants like ozone break molecules apart
5. Filtration (membranes) – physically separates them, but concentrates pollutants on one side

7️⃣ Which Methods Work Best?

Biodegradation is the most promising because it’s:

• Natural
• Sustainable
• Scalable (we can “train” microbes to do better)

🧴 Case Study: Triclosan (Antibacterial Compound)

8️⃣ What Is Triclosan?

• Once used widely in toothpaste, soap, and cosmetics as an antibacterial agent.
• Works by blocking fatty acid synthesis in bacteria (they can’t make membranes 🧫➡️💀).
• 🚫 Now banned in Denmark & the EU due to toxicity to both microbes and humans.

9️⃣ But… Why Is It Still Found? 🌍

Even though banned locally, triclosan still appears in Danish wastewater because:

• Imported goods (especially from Southeast Asia) are treated with triclosan to prevent biofilm and corrosion during shipping 🚢.

🧾 Triclosan in Wastewater: Where Does It Go?

So, roughly 40% is biodegraded, 60% ends up bound or released.

🧠 Improving Removal – What Matters?

10️⃣ Factors Affecting Biodegradation:

1. Loading rate:
   • The more a compound appears in wastewater, the more microbes adapt to degrade it.
   • 🧍‍♂️ Municipal wastewater (e.g. Aalborg West) has higher human input → higher removal.
   • 🏭 Industrial wastewater (e.g. Aalborg East) → fewer adapted microbes → lower removal.
2. Retention time:
   • Longer contact time between wastewater and bacteria = better degradation.
3. Plant design & operation:
   • Affects oxygen levels, biofilm growth, and microbial community stability.

🌿 Big Picture

Even though WWTPs are complex “black boxes” of microbial activity, data shows:

• Some plants are much better at micropollutant removal than others.
• This means it’s possible to optimize biological systems to enhance degradation.
• By identifying which microbes are responsible, we can engineer better wastewater ecosystems 💚