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