Effects of ZnO Nanoparticles on Wastewater Biological Nitrogen and Phosphorus Removal

Abstract

With the increasing utilization of nanomaterials, zinc oxide nanoparticles (ZnO NPs) have been reported to induce adverse effects on human health and aquatic organisms. However, the potential impacts of ZnO NPs on wastewater nitrogen and phosphorus removal with an activated sludge process are unknown. In this paper, short-term exposure experiments were conducted to determine whether ZnO NPs caused adverse impacts on biological nitrogen and phosphorus removal in the unacclimated anaerobic-low dissolved oxygen sequencing batch reactor. Compared with the absence of ZnO NPs, the presence of 10 and 50 mg/L of ZnO NPs decreased total nitrogen removal efficiencies from 81.5% to 75.6% and 70.8%, respectively. The corresponding effluent phosphorus concentrations increased from nondetectable to 10.3 and 16.5 mg/L, respectively, which were higher than the influent phosphorus (9.8 mg/L), suggesting that higher concentration of ZnO NPs induced the loss of normal phosphorus removal. It was found that the inhibition of nitrogen and phosphorus removal induced by higher concentrations of ZnO NPs was due to the release of zinc ions from ZnO NPs dissolution and increase of reactive oxygen species (ROS) production, which caused inhibitory effect on polyphosphate-accumulating organisms and decreased nitrate reductase, exopolyphosphatase, and polyphosphate kinase activities.

Effects of CeO2 nanoparticles on biological nitrogen removal in a sequencing batch biofilm reactor and mechanism of toxicity

“…2) suggest that the reduction in nitrogen removal efficiency can be attributed to the inhibitory effects of the CeO 2 NPs on the ammonia oxidation and denitrification phases, rather than the process of nitrite to nitrate. Similar conclusions were also drawn by Zheng et al (2011aZheng et al ( , 2011b, who studied the influences of different kinds of NPs on nitrogen removal in activated sludge systems. Furthermore, due to the complex and special structure of biofilm, the denitrifying bacteria that live deeper in the anoxic biofilm layer with carbon storage would stimulate the SND process (Yang et al, 2014).…”

“…In contrast, the structure of the LB-EPS coating on the outside of sludge particles would permit the NPs to penetrate the deeper layers of the biofilm, and thus, the protective capacity is limited under high concentrations (Hou et al, 2015;Ma et al, 2013). Thus, in this study, the reason for the inhibited denitrification in the SBBR may not have been caused by the denitrifying bacteria, in seeming contradiction to the inhibition of NPs in activated sludge systems (Zheng et al, 2011b).…”

“…Accordingly, a biofilm-based nitrogen-removal reactor is a system that fully exploits the metabolic activities of ammonia-oxidizing, nitrifying, and denitrifying bacteria in the biofilm. For each of these bacteria, enzymes play important roles in effecting metabolic activities (Zheng et al, 2011b). However, limited knowledge is available concerning the influence of NPs on biofilm bacteria or the key enzymes responsible for nitrogen removal.…”

Effects of aluminium oxide nanoparticles on bacterial growth

“…Zheng et al proved that zinc oxide NPs had adverse influence on biological processes of nitrogen removal as well as on denitrifying bacteria and microorganisms responsible for phosphorus elimination called PAO (polyphosphate accumulating organisms). Nitrogen removal efficiency decreased from 81.5% to 75.6% and 70.8%, when concentrations of nano-ZnO equaled 10 mg/l and 50 mg/l, respectively [17]. These results indicate that zinc oxide NPs lead to the disruption of the activated sludge treatment process.…”

Effect of aluminium oxide nanoparticles on the enzymatic activity on microorganisms of activated sludge

“…In the literature there are also a few reports about influence NPs on biological processes of nitrogen and phosphorus removal as well as on denitrifying bacteria and microorganisms responsible for phosphorus elimination, the so-called PAO (polyphosphate accumulating organisms). Zheng et al (2011) showed that, nano-ZnO can induce serious trouble in self-purification of water as well as in biological wastewater treatment [8].…”