Long-Term Effects of Copper
Nanoparticles on Wastewater Biological Nutrient Removal and N<sub>2</sub>O Generation in the Activated Sludge Process
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Abstract
The increasing use of copper nanoparticles (Cu NPs) raises
concerns about their potential toxic effects on the environment. However,
their influences on wastewater biological nutrient removal (BNR) and
nitrous oxide (N<sub>2</sub>O) generation in the activated sludge
process have never been documented. In this study the long-term effects
of Cu NPs (0.1–10 mg/L) on BNR and N<sub>2</sub>O generation
were investigated. The total nitrogen (TN) removal was enhanced and
N<sub>2</sub>O generation was reduced at any Cu NPs levels investigated,
but both ammonia and phosphorus removals were not affected. The mechanism
studies showed although most of the Cu NPs were absorbed to activated
sludge, the activated sludge surface was not damaged, and the released
copper ion from Cu NPs dissolution was the main reason for TN removal
improvement and N<sub>2</sub>O reduction. It was also found that the
transformation of polyhydroxyalkanoates and the activities of ammonia
monooxygenase, nitrite oxidoreductase, exopolyphosphatase, and polyphosphate
kinase were not affected by Cu NPs, whereas the decreased metabolism
of glycogen and the increased activities of denitrification enzymes
were observed. Further investigation revealed that Cu NPs increased
the number of denitrifiers (especially N<sub>2</sub>O reducing denitrifiers)
but decreased nitrite accumulation. All these observations were in
correspondence with the enhancement of TN removal and reduction of
N<sub>2</sub>O generation