Background: A large amount of silver chloride residue is produced from the Mohr's experiments in the industrial and educational laboratories. Considering the environmental problems caused by the release and accumulation of silver chloride, this study aimed to design an efficient method for the recovery of silver nanoparticles in laboratory waste with antibacterial activity.

Materials and Methods: This bench-scale experimental study was conducted on silver chloride waste samples accumulated during one semester from teaching laboratories in a batch system. Formalin and polyvinylpyrrolidone were used as the reducing and stabilizing agents, respectively. The size of nanoparticles, size distribution and stability of silver nanoparticles were investigated using transmission electron microscopy, dynamic light scattering and UV-visible spectroscopy techniques, respectively. The antibacterial activity of silver nanoparticles was assessed by measuring minimum inhibition concentration (MIC) with a serial concentration method.

Results: The results showed that the optimum silver recovery with small size and narrow size distribution was achieved in 0.7 mol ammonia solution and the formalin/silver chloride mole ratio of 2. The MIC value against Gram-negative (E.coli ATCC25922) and Gram-positive (S.aureus ATCC29213) reference strains was 50 ppm, whereas the MIC of nanoparticles against the clinical isolate pathogen (Acinetobacterbaumanii) was 25 ppm.

Conclusion: The proposed method is a simple and efficient method for the recovery of silver nanoparticles in laboratory waste. Moreover, the obtained silver nanoparticles have the powerful antibacterial activity.