Elsevier

Bioresource Technology

Volume 225, February 2017, Pages 377-385
Bioresource Technology

Magnetic Fe3O4 nanoparticles induced effects on performance and microbial community of activated sludge from a sequencing batch reactor under long-term exposure

https://doi.org/10.1016/j.biortech.2016.11.130Get rights and content

Highlights

Abstract

The performance and microbial community of activated sludge from a sequencing batch reactor (SBR) were investigated under long-term exposure of magnetic Fe3O4 nanoparticles (Fe3O4 NPs). The COD removal showed a slight decrease at 5–60 mg/L Fe3O4 NPs compared to 0 mg/L Fe3O4 NPs, whereas the NH4+-N removal had no obvious variation at 0–60 mg/L Fe3O4 NPs. It was found that 10–60 mg/L Fe3O4 NPs improved the denitrification process and phosphorus removal of activated sludge. The microbial enzymatic activities of activated sludge could be affected by Fe3O4 NPs, which had similar variation trends to the nitrogen and phosphorus removal rates of activated sludge. The reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release demonstrated that Fe3O4 NPs led to the toxicity to activated sludge and destroyed the integrity of microbial cytomembrane. High throughput sequencing indicated that Fe3O4 NPs could obviously affect the microbial richness and diversity of activated sludge.

Introduction

Metal oxide nanoparticles (NPs) are extensively used in many industrial and consumer products due to their specifically chemical, physical and optical properties. The increasing application of metal oxide NPs will unavoidably increase their environmental release during the processes of manufacture, transportation, utilization and disposal. The potential adverse effects of metal oxide NPs on human health and environmental safety have raised wide attentions in recent years. Previous researches have proved that some metal oxide (e.g. ZnO, CuO and TiO2) NPs have obvious toxicity to microorganism, algae, aquatic invertebrate, terrestrial invertebrate and human tissue cell (Ma et al., 2013, Cerrillo et al., 2016, Bondarenko et al., 2013). Some metal oxide NPs have been found to be released into sewage and wastewater collection systems (Gottschalk et al., 2009), and their possible effects on the performance of different wastewater biological treatment systems have also drawn the researcher’s concerns due to their toxicity to organisms. Zheng et al. (2011) demonstrated that the presence of TiO2 NPs in the influent under long-term exposure impacted on the removals of COD, nitrogen and phosphorus and led to bacterial community shift of activated sludge. Wang et al. (2016) evaluated the long-term effects of ZnO NPs at 0–60 mg/L on the performance, microbial activity and microbial community of activated sludge from a sequencing batch reactor (SBR). Hou et al. (2015) illustrated that the presence of CuO NPs could impact on the flocculating ability of activated sludge and the composition of extracellular polymeric substances from activated sludge. García et al. (2012) reported that CeO2 NPs could inhibit the respiration rate of heterotrophic bacteria, ammonia oxidation bacteria, and anaerobic bacteria from a municipal wastewater treatment plant. Therefore, it is very necessary to evaluate the effects of metal oxide NPs on the performance and microbial community of wastewater biological treatment systems in the future.

Magnetic Fe3O4 nanoparticles (Fe3O4 NPs) have been extensively applied in many fields of biomedicine and bioengineering, such as magnetic cell labeling, magnetic resonance imaging, immunoassay, magnetic target drug delivery, cell separation and cancer therapy. With the rapid increase of the production and application fields, Fe3O4 NPs are increasingly released into wastewater stream during their manufacturing, transport, utilization and disposal process. The adverse effects of Fe3O4 NPs on the environment and human have been investigated in the last few years. Dwivedia et al. (2014) reported that Fe3O4 NPs could induce the cytotoxicity of human lung alveolar epithelial cells under in vitro conditions. Srinivas et al. (2012) found that Fe3O4 NPs might result in the cytotoxicity via the oxidative stress and led to biphasic inflammatory responses in rat. Auffan et al. (2008) analyzed the relation between the redox state of Fe3O4 NPs and their cytotoxicity toward Escherichia coil. Due to the biotoxicity of Fe3O4 NPs, the potential effects of Fe3O4 NPs on wastewater biological treatment system are also a matter worthy of our attention. Ni et al., 2013a, Ni et al., 2013b reported that the short-term exposure of 50–200 mg/L magnetic NPs containing Fe decreased the total nitrogen (TN) removal efficiency and the long-term exposure of 50 mg/L magnetic NPs containing Fe could significantly improve TN removal efficiency (from 69% to 92%), and the activities of nitrite oxidoreductase and key denitrifying enzymes increased after long-term exposure. However, little research has been performed to investigate the long-term effects of magnetic Fe3O4 NPs on the performance, microbial activity and microbial community of activated sludge from wastewater biological treatment system.

The primary aims of the present research were (I) to evaluate the long-term effects of magnetic Fe3O4 NPs on the performance, microbial activity and microbial enzymatic activity of activated sludge from a SBR; (II) to investigate toxicity of Fe3O4 NPs by analyzing the reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release of activated sludge; and (III) to assess the variations of microbial composition, richness and diversity in activated sludge at different Fe3O4 NPs concentrations.

Section snippets

Preparation of Fe3O4 NPs suspension and wastewater compositions

Fe3O4 NPs with a particle size of 20 nm were purchased from Beijing DK Nano Technology Co., Ltd. (Beijing, China). The Fe3O4 NPs suspension was prepared at 500 mg/L according to previous research (Keller et al., 2010). The hydrodynamic diameter, particle size peak, and polydispersity index of Fe3O4 NPs in the suspension were measured to be 1212.6 ± 109.4 nm, 414.7 ± 87.8 nm, and 0.874 ± 0.099 by dynamic light scattering (DLS) using a Malvern Zetasizer Nano ZS90 (Malvern Instruments, UK), respectively.

Long-term effects of magnetic Fe3O4 NPs on the SBR performance

The COD, nitrogen and phosphorus removals of the SBR were evaluated at different Fe3O4 NPs concentrations (Fig. 1). Prior to the addition of Fe3O4 NPs to the influent, the SBR had continually operated for 57 days and kept a stable removal performance of COD, nitrogen and phosphorus. Compared to 0 mg/L Fe3O4 NPs, the COD removal of SBR had no obvious change at 2 and 5 mg/L Fe3O4 NPs (Fig. 1a). However, the COD removal efficiency of SBR under steady states decreased slightly from 92.38 ± 0.44% at 5 mg/L

Conclusions

The Fe3O4 NPs concentration at 5–60 mg/L had no obvious effect on the NH4+-N removal, whereas the COD removal showed a slight decrease. The microbial enzymatic activities had the similar varying trends to the COD, nitrogen and phosphorus removal rates. The ROS production and LDH release increased with the increase of Fe3O4 NPs concentration from 0 to 60 mg/L. The microbial richness and diversity at phyla, class, and genus levels showed some obvious variations at different Fe3O4 NPs

Acknowledgements

The work was funded by Province Key Technologies R & D Program of Shandong (Grants 2007GG10006002) and the National Natural Science Foundation of China (No. 51178437).

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