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MgO nanoparticles (NPs) are widely used in bactericides, fuel cells and electronic materials and are frequently detected in aquatic environments. Anaerobic ammonium oxidation (anammox) is a highly efficient and economical autotrophic nitrogen removal process. To date, the effects of MgO NPs on anammox granular sludge have remained unknown. This work systematically evaluated the short- and long-term effects of MgO NPs on anammox process performance and explored an effective strategy to relieve stress. The half maximal inhibitory concentration (IC50) of MgO NPs to anammox granular sludge was 69.5 mg L−1. During the long-term experiment, the anammox process experienced a reduction in nitrogen removal ability under the stress of 50.0 mg L−1MgO NPs. Moreover, the enzymatic activity and synthesis of heme c significantly decreased. Adding 40.0 mg L−1bull serum albumin (BSA) effectively relieved the stress caused by 50.0 mg L−1MgO NPs, and the anammox activity recovered to 97.0% of the original level. Multiple spectral analyses verified the adsorption of MgO NPs by BSA. Furthermore, the formation of an eco-corona was observed by transmission electron microscopy, which also contributed to decreasing the biotoxicity of the MgO NPs. The results of this study provide guidance for treating NP-containing wastewater during the anammox process.

The development and application of anammox-based nitrogen removal technology is thought to have the potential to boost the evolution of wastewater treatment to a more sustainable model. However, due to the long doubling time and vulnerability to the varying operating conditions of anammox bacteria, the actual application of this technology remains restrained. Nanomaterials have been proposed as external suppliers to stimulate the activity of anammox bacteria. To date, although there are lots of experimental results, the actual effects relating to different types of nanomaterials still remain unclear. Moreover, besides artificially added nanoparticles, anammox may be inhibited by nanomaterials released during the use of nanotechnology products. Addressing the above challenges requires a better understanding of the performance, fate, and mechanism of interaction between various nanomaterials and anammox bacteria. Herein, this review describes the effects of various engineered nanomaterials on the nitrogen removal performance and metabolic properties of anammox bacteria. Also, the intoxication routes of nanomaterials and the detoxification mechanisms of anammox are analyzed and discussed. Finally, future development trends and research directions in this field are proposed.

Nonphotosynthetic microorganisms are typically unable to directly utilize light energy, but light might change the metabolic pathway of these bacteria indirectly by forming intermediates such as reactive oxygen species (ROS). This work investigated the role of light on nitrogen conversion by anaerobic ammonium oxidation (anammox) consortia. The results showed that high intensity light (>20000 lx) caused ca. 50% inhibition of anammox activity, and total ROS reached 167% at 60,000 lx. Surprisingly, 200 lx light was found to induce unexpected promotion of the nitrogen conversion rate, and ultraviolet light (<420 nm) was identified as the main contributor. Metagenomic and metatranscriptomic analyses revealed that the gene encoding cytochrome cperoxidase was highly expressed only under 200 lx light. 15N isotope tracing, gene abundance quantification, and external H2O2addition experiments showed that photoinduced trace H2O2triggered cytochrome cperoxidase expression to take up electrons from extracellular nonfermentative organics to synthesize NADH and ATP, thereby expediting nitrogen dissimulation of anammox consortia. External supplying reduced humic acid into a low-intensity light exposure system would result in a maximal 1.7-fold increase in the nitrogen conversion rate. These interesting findings may provide insight into the niche differentiation and widespread nature of anammox bacteria in natural ecotopes.