The effects of engineered nanoparticles on nitrification during
biological wastewater treatment
Abstract
Technological advancements in the past few decades have made it possible
to manufacture nanomaterials at large scale and ENPs are increasingly
found in consumer products such as cosmetics, sports products and LED
displays. A large amount of these ENPs are in wastewater and potentially
impact the performance of wastewater treatment plants (WWTPs). One
important function of the WWTP is nitrification, which is carried out by
the actions of two groups of bacteria, ammonia-oxidizing bacteria (AOB)
and nitrite-oxidizing bacteria (NOB). Since most ENPs are found to have
or are designed to have antimicrobial activities, it is a legitimate
concern that ENPs entering WWTPs may have negative impacts on
nitrification. In this paper, the effects of ENPs on nitrification is
discussed, focusing mainly on autotrophic nitrification by AOBs and
NOBs. This review also covers ENPs effects on ANAMMOX. Generally,
nitrifiers in pure and mixed culture can be inhibited by a variety of
ENPs, but stress response mechanisms may attenuate toxicity. Long-term
studies demonstrated that a wide range of NPs can cause severe
deterioration of AOBs and/or NOBs when the influent concentration
exceeded an inhibition threshold. Proposed mechanisms include the
generation of reactive oxygen species, dissolved metals, physical
disruption of cell membranes, bacterial engulfment, and intracellular
accumulation of ENPs. Future research needs are also discussed.