Here’s your fun yet detailed educational summary of Paul et al. (2021) — “Biopolymers Production from Wastes and Wastewaters by Mixed Microbial Cultures (MMC)” 🎓🌍
Biopolymers are natural macromolecules (proteins, polysaccharides, PHAs, etc.) made by living organisms — they’re biodegradable, biocompatible, and renewable. Unlike fossil-based plastics, they can reduce waste and CO₂ emissions.
But… 💸 they’re still expensive to make! So scientists want to produce them from organic wastes using open mixed microbial cultures (MMC) — microbial “teams” that thrive without sterilization and handle complex substrates.
To be sustainable, a substrate should be:
Examples: food waste, wastewater sludge, paper mill residues. High C:N or C:P ratios trigger microbes to store carbon as polymers when nutrients are limited.
This fits perfectly into the circular economy, turning “trash into treasure.”
MMC = a community of microbes, not a single strain. They offer: ✅ resilience ✅ substrate flexibility ✅ natural contamination resistance …but also ❗challenges in control and reproducibility.
Key idea: “Everything is everywhere, but the environment selects.” → Reactor conditions (O₂, nutrients, SRT, pH, etc.) decide which microbes dominate.
Microbial polyesters (e.g., PHB, PHBV). Stored as intracellular carbon & energy reserves when nutrients like N or P are limited. ✅ Biodegradable plastics ✅ Tunable properties (short-chain vs medium-chain monomers)
➡️ MMCs can make PHAs cheaply using waste carbon sources (VFAs, glycerol, whey, etc.). Pilot projects like PHA2USE (Netherlands) show industrial feasibility.
Microbes secrete exopolysaccharides (EPS) for protection and adhesion. EPS have gelling, flocculating, and coating abilities — great for paper, bioplastics, and water treatment.
Key idea: – Carbon excess + nutrient limitation → EPS production. – Different substrates → different EPS structures and properties.
Modern interest: extracting EPS from aerobic granular sludge (AGS) — already used industrially as Kaumera Nereda® Gum in the Netherlands 🧪.
Dried microbial biomass rich in protein (43–95% DW). Can replace fishmeal and soy in animal feed — especially in aquaculture.
Made from wastes like:
Bonus: low land use and minimal environmental footprint.
Microbial “consortia engineering” = tuning conditions to favor desired microbes.
r-strategists (fast growers) vs K-strategists (efficient scavengers). Other interactions include mutualism, predation, and quorum sensing 🧠 — microbes “chat” via chemical signals to coordinate EPS or PHA synthesis!
Short feast (plenty of carbon) → long famine (none). Selects microbes that store carbon internally as PHAs for survival.
Optimal conditions:
Used for wastes like whey, molasses, pulp mill effluent, and food waste.
Alternating oxygen levels selects PAOs and GAOs — bacteria that store PHAs or glycogen while removing N & P. Example: pilot WWTPs achieving 49% PHAs content + nutrient removal.
Continuous reactor under dual limitation (C + P) selects PHA-accumulators with high phosphorus affinity (e.g. Malikia sp., Acinetobacter sp.). → Up to 80% PHB in cells. P-limitation is a powerful selective pressure!
Municipal sludge already contains PHA-storing microbes. Under N or P limitation, direct feeding with VFAs can yield ≈ 70% PHB in biomass.
Halophilic archaea like Haloferax mediterranei thrive in salty media, reducing contamination risk and water use. Produce both PHAs and anionic polysaccharides.
Granules = tiny, self-organized bio-balls 🟢 that trap bacteria and EPS. They:
Optimized by alternating anaerobic/aerobic phases, short settling times, and high shear forces. → Slow-growing PAOs & GAOs dominate → stable granules + valuable EPS.
Classic routes:
→ High protein (up to 70% DW), low cost, sustainable fish-feed alternative.
MMC systems = nature-inspired factories for circular biotechnologies 🌍 Advantages:
Challenges ahead:
In short: 🌿 Waste → Microbes → Biopolymers → Sustainable Future. MMC systems could turn our wastewater plants into true bio-refineries of the circular economy! 🔁💧🧫
Would you like me to make a diagram-style cheat sheet (A4 layout) summarizing these points visually — with icons for each biopolymer type and process flow?