Effect of nanosilver particles on biodegradation of laundry surfactants in urban wastewaters systems

Discharge of silver nanoparticles (AgNP) from textiles and cosmetics, todays major application areas for metallic AgNP, into wastewater is inevitable. Transformation in wastewater treatment plants (WWTP) will determine the impact of AgNP on aquatic and terrestrial environments. This study aimed to determine the behavior of AgNP in the sludge at the WWTP by adressing the stability of citrate- coated AgNPs and their interactions with laundry-relevant surfactants (sodium dodecyl sulphate (SDS) and dodecylammonium chloride (DDACl)). The stability of the AgNPs was shown to depend on the charge and concentration of the adsorbed surfactants. The presence of DDACl prevented the formation of AgNP agglomerates even at higher ionic strength. In order to determine the effect of AgNP on biodegradation of laundry surfactants, we employed standardized method for water quality and HRN- EN-ISO-10707:2000 (Evaluation in an aqueous medium of the "ultimate" aerobic biodegradability of organic compounds). Additionally, we evaluated the inhibitory effect of AgNPs on the growth of activated sludge microorganisms (ASMs)). Results showed that AgNPs were toxic to ASMs at very high concentration (>50 mg/L). However, biodegradability of SDS, DDACl and commercial laundry detergent were inhibited by more than 5% and 20% in the presence of 0.1 and 1 mg/L AgNP, respectively. It can be concluded that AgNP discharged to the wastewater stream will influenced overall biodegradability of organic matter at various degrees in the sewer system. Such knowledge is important as it may influence the subsequent transport of AgNPs through different chemical transients and thus their potential bioavailability and toxicity.