Figure
Figure 1: A schematic showing the types of ENPs commonly found in the
WWTPs and their fate and effects on the microorganisms in the activated
sludge. Several processes may happen to ENPs entering the WWTP: 1)
aggregation including both intra- and inter-species aggregation; 2)
dissolution which produces metal ions that could be toxic; 3)
transformation such as the loss of surface coating; and 4) organics
adsorption, NPs with large surface area may be covered by organics in
the wastewater due to adsorption. Products of these processes, along
with the original ENPs can cause damage to the microorganisms by several
organisms: 1) weakening cell membrane by adsorption and aggregation onto
the membrane; 2) extracellular ROS damage the membrane through lipid
oxidation; 3) piercing through the membrane; 4) dissolved ions interact
with important enzymes; 5) intracellular ROS damages damage the DNA,
protein and other vital biomolecules; 6) dislodging the EPS from the
bacteria by strong adsorption; 7) ENPs internalized into bacteria and
damage biomolecules and metabolic functions; 8) wrapping around the
bacteria to trap and isolate it from the microenvironment.
Figure 1: The fate and effects of ENPs in activated sludge