Transformation of AgCl nanoparticles in a sewer system--A field study

Area of Science:

• Environmental Science
• Environmental Chemistry
• Nanotechnology

Background:

• Silver nanoparticles (Ag-NP) are prevalent in consumer goods, posing risks to aquatic environments.
• Previous research focused on metallic Ag(0)-NP, overlooking other forms like silver chloride (AgCl).
• AgCl is released in greater quantities than Ag(0) from sources like textiles.

Purpose of the Study:

• To investigate the release and transformation of AgCl-NP from an industrial laundry into the sewer system.
• To track the fate of silver during transport and within a municipal wastewater treatment plant (WWTP).
• To quantify the removal efficiency of silver in WWTPs.

Main Methods:

• Field study monitoring AgCl-NP release from an industrial laundry.
• Electron microscopy and X-ray absorption spectroscopy for Ag speciation analysis.
• Analysis of Ag concentrations in sewer systems, WWTP influent, effluent, and sludge.

Main Results:

• Industrial laundry discharged ~85 g Ag/day, primarily as AgCl-NP and silver sulfide nanoparticles (Ag2S-NP).
• AgCl-NP transformed into Ag2S-NP during 800m transport in the sewer system.
• WWTP demonstrated high Ag removal efficiency (>95%), with low effluent concentrations (<0.5 μg L(-1)).

Conclusions:

• AgCl-NP from industrial laundries are a significant source of silver in wastewater.
• Silver undergoes transformation to Ag2S-NP within sewer systems.
• WWTPs are effective in removing silver, mitigating its release into aquatic ecosystems.