Nanoparticle Interactions in Wastewater Treatment Systems

Engineered nanoparticles (NPs) are increasingly detected in municipal and industrial wastewater streams, raising questions about their fate during conventional treatment. Within treatment plants, NPs engage in a complex interplay of physical, chemical and biological processes. Key mechanisms include aggregation and sedimentation, surface adsorption to activated sludge flocs and extracellular polymeric substances (EPS), and transformation through redox reactions or dissolution. Biofilms lining reactor surfaces act as dynamic sinks, where EPS matrices trap and immobilise NPs, potentially altering particle size, surface charge and reactivity. These interactions influence not only the removal efficiency of organic and nutrient pollutants but also the viability and community structure of microbial consortia. For example, metal-oxide NPs may inhibit nitrifying bacteria, leading to reduced ammonia removal, while stabilised NPs can persist in effluent streams or accumulate in biosolids. Seasonal changes in pH, ionic strength and organic matter further modulate NP behaviour, affecting aggregation kinetics and transport. Understanding these processes is essential for predicting environmental release, guiding plant operation and informing regulatory frameworks to safeguard human health and ecosystem services.

Research from Nature Portfolio

Recent studies have employed metagenomic profiling to assess how zinc oxide nanoparticles influence microbial diversity in activated sludge. Exposure across a gradient of nanoparticle concentrations led to a marked decline in operational taxonomic units, indicating loss of both dominant and rare taxa. Changes were observed at multiple taxonomic levels, with lower concentrations selectively suppressing sensitive phyla and higher concentrations triggering broader community collapse. These shifts correlated with declines in nutrient removal performance, emphasising the link between microbiome integrity and treatment efficacy. The work highlights the need for advanced molecular tools to monitor NP-induced perturbations and to develop mitigation strategies that preserve essential microbial functions.

Nanoparticle Interactions in Wastewater Treatment Systems publication trend

The graph below shows the total number of articles in nanoparticle interactions in wastewater treatment systems across all publications each year (not limited to Nature Index journals).

Technical terms

Nanoparticle (NP): Particle with at least one dimension between 1 and 100 nm, possessing unique surface and reactivity properties.

Activated sludge: Flocculated biomass of microorganisms used in aerobic treatment to degrade organic pollutants in wastewater.

Biofilm: Structured community of microorganisms embedded within a self-produced matrix adhering to surfaces in treatment reactors.

Extracellular polymeric substances (EPS): Complex mixture of polysaccharides, proteins and nucleic acids secreted by microbes, forming the biofilm scaffold.

Flocculation: Process by which colloidal particles aggregate into larger flocs, facilitating sedimentation and removal in secondary clarifiers.

References

1. When nanoparticles meet biofilms—interactions guiding the environmental fate and accumulation of nanoparticles. Frontiers in Microbiology (2015).
2. The impact of zinc oxide nanoparticles on the bacterial microbiome of activated sludge systems. Scientific Reports (2016).
3. Fate, behaviour, and implications of ZnO nanoparticles in a simulated wastewater treatment plant. Water SA (2016).
4. Insights into the effect of mixed engineered nanoparticles on activated sludge performance. FEMS Microbiology Ecology (2015).