Inhibition Kinetics of Ammonia Oxidation Influenced by Silver Nanoparticles

Silver nanoparticles (AgNPs) have significantly increased in production and use for anti-microbial propose. This agent, after used, is released into sewerage system resulting in possibility to inactivate non-targeted microorganisms in wastewater treatment plants. In this study, the inhibitory effect of AgNPs on ammonia oxidation was investigated using respirometric assay. The initial concentrations of AgNPs and ammonia ranged 0.25?C10.00 and 14?C280?mg/L, respectively. Half saturation constant (K _s) for ammonia oxidation was found to be 15.9?mg?N/L. Under the presence of AgNPs, the maximum oxygen uptake rate and K _s declined. The effect of AgNPs was proved to follow an uncompetitive-like inhibition kinetic type with the inhibition coefficients (K _i) of 5.5?mg/L. Increasing AgNPs from 0.25 to 10.00?mg/L inhibited 4 to 50?% of ammonia-oxidizing activities at the initial ammonia concentrations from 14 to 280?mg/L. Based on transmission electron microscopic observation, AgNPs could damage the microbial cells. All findings indicated that AgNPs substantially reduced ammonia-oxidizing microorganisms and their activities. Thus, special attention should be made to manage discharge of AgNPs into the environment.     

Sorption of 17α-Methyltestosterone onto Soils and Sediment

In aquafarming, 17??-methyltestosterone (MT) is widely used as an anabolic steroid to induce the sex of Nile tilapia fry to male in order to increase production yield. Nile tilapia fry is fed at a rate of 0.06?mg of MT/kg of feed during the first 21?days after hatching. MT not consumed by the fish fry may be sorbed onto the sediment in the fish ponds which may contaminate the environment when released from the ponds. Using soils and sediment from a Nile tilapia masculinization pond as sorbents in batch sorption experiments, the linear sorption coefficients (K _d) of MT were found to range from 1.2 to 168.8?L/kg with an average K _oc value of 9,450?L/kg. The linear sorption coefficients of MT were found to correlate with the organic carbon contents of the sorbents. Sorption of MT onto sand, garden soil, and sediment was not impacted by pH, but the sorption of MT onto sediment was found to be impacted by the salinity of the water. The salting out coefficient of MT in saline water was found to be approximately 0.87?L/mol.