How Bacteria Transform Wastewater into Gold
Every day, millions of tons of nitrogen-rich wastewater flow from our homes, farms, and industries into rivers and oceans.
Traditional wastewater treatment consumes 2-3% of global electricity.
Toxic algae blooms from nitrogen pollution suffocate marine life and contaminate drinking water.
This invisible flood fuels toxic algae blooms that suffocate marine life, contaminate drinking water, and destabilize ecosystems. For decades, wastewater treatment relied on energy-hungry processes guzzling 2-3% of global electricity. But nature has evolved a smarter solution: microbial communities that transform ammonia into harmless nitrogen gas without oxygen or excessive energy. Welcome to the frontier of aerobic-anaerobic ammonium oxidation—where bacteria collaborate like microscopic alchemists to turn wastewater into environmental gold 3 7 .
Ammonia-oxidizing bacteria (AOB) and archaea (AOA) kickstart nitrogen removal by converting ammonia (NHâ‚„âº) to nitrite (NOâ‚‚â») using oxygen. Recently discovered "comammox" bacteria (genus Nitrospira) perform this in one step—challenging a century-old dogma that required separate microbes 2 5 .
In oxygen-free zones, anammox bacteria (e.g., Brocadia, Kuenenia) fuse ammonia and nitrite into nitrogen gas (Nâ‚‚). Their unique anammoxosome organelle contains ladderane lipids that trap toxic intermediates, making them living chemical reactors 3 .
| Microbe Type | Function | Key Genera | Electron Acceptor |
|---|---|---|---|
| AOB | Converts NH₄⺠to NO₂⻠| Nitrosomonas | Oxygen |
| Anammox | Converts NH₄⺠+ NO₂⻠to N₂ | Brocadia, Kuenenia | Nitrite |
| Comammox | Converts NH₄⺠to NO₃⻠in one step | Nitrospira | Oxygen |
| Feammox bacteria | Oxidizes NH₄⺠using iron | Acidimicrobiaceae A6 | Fe(III) |
In 2025, researchers uncovered a radical shortcut: Feammox. Here, bacteria like Acidimicrobiaceae sp. A6 use rust (Fe³âº) instead of oxygen to oxidize ammonia, producing nitrogen gas or nitrate. This process thrives in wetlands and now in engineered systems, slashing energy needs by 60% 1 .
When aerobic and anaerobic microbes team up, magic happens. Partial Nitritation/Anammox (PNA) cuts aeration costs by 60% and organic carbon demand by 100% 3 7 . Biofilm engineering allows spatial separation that prevents slow-growing anammox bacteria from washing out 7 .
While Feammox excels in natural sediments, harnessing it for wastewater required cultivating these elusive bacteria. In 2025, Xueyuan et al. pioneered a study using two sludge types as "microbe nurseries":
From oxygen-free digesters.
From aerated tanks 1 .
ADS and CAS collected from a plant treating 500 tons/day of municipal wastewater.
Fed with organic-rich reject water (simulating food-processing waste) and synthetic wastewater with controlled nitrogen/iron levels.
Tracked nitrogen loss, iron reduction, and microbial DNA over 160 days.
| Parameter | ADS with RW | CAS with RW | ADS with SW |
|---|---|---|---|
| Start-up time | 48 days | 66 days | 55 days |
| Max Feammox rate | 11 mg N/L/day | 8 mg N/L/day | 6 mg N/L/day |
| Nitrogen removal | 93% | 72% | 73% |
| Dominant microbes | Acidimicrobiaceae, IRB | Proteobacteria, IRB | Acidimicrobiaceae |
ADS sludges in organic-rich RW achieved 93% nitrogen removal—rivaling natural wetlands. Organic matter boosted Feammox by acidifying the environment and releasing soluble iron.
Microbial shifts revealed teamwork: Iron-reducing bacteria (IRB) like Geobacter pre-processed iron oxides, while Acidimicrobiaceae executed Feammox 1 .
Critical finding: Excess organics triggered "dissimilatory iron reduction," stealing electrons from Feammox. Optimal carbon levels proved essential 1 .
| Reagent/Material | Function | Real-World Application |
|---|---|---|
| Ferrihydrite (Fe(OH)₃) | Electron acceptor for Feammox | Replaces oxygen, cutting aeration costs |
| Anthraquinone-2,6-disulfonate (AQDS) | Electron shuttle | Boosts Feammox rates by 40% 1 |
| Anammox biofilm carriers | Biomass retention | Plastic/ceramic surfaces retain slow-growing bacteria in IFAS systems 7 |
| Ladderane lipid biomarkers | Anammox detection | Tracks anammox abundance in complex sludge |
| qPCR primers for nxrB gene | Quantifies NOB | Suppressing nitrite oxidizers is critical for PNA success |
| Phenylfosinopril | C30H40NO7P | |
| Ketazolam-13C,d3 | C20H17ClN2O3 | |
| Keap1-Nrf2-IN-18 | C27H29FN2O4 | |
| PARP1/c-Met-IN-1 | C40H33FN8O4 | |
| Biotin-D-Glucose | C16H26N2O8S |
Current systems work best for concentrated "side-stream" wastewater. Scaling to "mainstream" municipal sewage requires battling NOB invaders (Nitrospira) that outcompete anammox at low ammonia levels 7 .
Synthetic microbial communities with division of labor: Brocadia for anammox, Candidatus Accumulibacter for phosphorus removal, and denitrifying PAOs for carbon-efficient nitrate removal 7 .
NASA explores anammox for Mars missions—its low oxygen, energy, and biomass production aligns with closed-loop life support 3 .
Aerobic-anaerobic ammonium oxidation epitomizes sustainability: turning waste into water safety using nature's smallest engineers.
As we decode microbial alliances—from iron-dependent Feammox to biofilm-enabled PNA—we reimagine wastewater not as pollution but as a resource. In the words of systems microbiologists: "The next clean-water revolution will be written in the language of genes, biofilms, and electron transfers." 6 .
Microbial nitrogen removal already cuts treatment costs by 60%. With engineered consortia, future plants could generate energy from waste—proving that true gold lies in microbial ingenuity.
NH₄⺠→ NO₂⻠using oxygen
NH₄⺠+ NO₂⻠→ N₂ (anaerobic)
NH₄⺠oxidation using Fe³âº
Anammox: 60% less energy
Feammox: 60% energy reduction
PNA: 100% less organic carbon
Anammox discovered in wastewater
Comammox bacteria identified
Feammox engineered for wastewater