Application of a heavy metal-resistant Achromobacter sp. for the simultaneous immobilization of cadmium and degradation of sulfamethoxazole from wastewater

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Highlights

  • Strain L3 possessed the abilities of SMX degradation and Cd(II) immobilization.

  • Microbial actions play a key role in the SMX degradation process.

  • Microbial action and BCa sediment adsorption play equally important roles for Cd(II) removal.

  • The SMX degradation pathways were proposed through the intermediate and biochemical principles.

  • SMX degradation and Cd(II) removal follow the same degradation rule.

Abstract

Little information is available regarding the kinetics, products, and pathways of simultaneous SMX degradation and Cd(II) immobilization from wastewater. In this study, a novel bacterium (Achromobacter sp. L3) with SMX degradation and Cd(II) immobilization capabilities was isolated. The boundary conditions of SMX degradation were as follows: initial pH 6–8, temperature 25–30 °C, and SMX concentration 10–40 mg/L−1. The boundary conditions of Cd(II) immobilization were as follows: initial pH 7–9, temperature 25–35 °C, and SMX concentration 10–30 mg/L−1. The maximum SMX degradation and Cd(II) removal were 91.98% and 100%, respectively. The SMX degradation and Cd(II) immobilization data fitted well with the pseudo-first-order kinetic model, indicating that the two pollutants conform to the same degradation rule. Moreover, the microbial degradation, sediment adsorption, and intermediates identified in the experiments were used to explore the mechanisms of SMX and Cd(II) removal. These results indicate that microbial removal and sediment adsorption play equally important roles in Cd(II) immobilization; however, microbial degradation plays a decisive role in SMX degradation. Furthermore, the relationship between aerobic denitrification, SMX degradation, and Cd(II) immobilization was proposed. These results may provide valuable insights for treatment of wastewater polluted by antibiotics and heavy metals.

Introduction

Sulfamethoxazole (SMX) ((CAS: 723–46–6) ) is one of the most frequently detected contaminants in wastewater as reported by the US Geological Survey (Elissavet et al.,2016), and one of the high concentration pharmaceutical identified in a European assessment of pharmaceuticals (Li et al., 2019).

Due to the high consumption in medicine and aquaculture, and WWTPs are not designed to remove these and other xenobiotic chemicals (Nguyen et al., 2018), partly SMX would escape from STPs and enter to the environments (Fekadu et al., 2019). The presence of SMX has directly toxic effects on aquatic organisms (Li et al., 2018). The persistent exposure of microorganisms to SMX also promotes the development of antibiotic resistance genes (ARGs), and enhancement the transfer of ARGs, which lead to long-term threats to human health and animals (Zhang et al., 2020). Therefore, develop the effective and stable for SMX treatment processes has become an emerging and important task for environmental protection (Du et al., 2019).

A lot of research has been used to removal of SMX, such as adsorption, membrane filtration, ion exchange, advanced oxidation and coagulation−flocculation (Li et al., 2017, Liu et al., 2020). While microbial degradation of SMX has some advantages compared to other methods, including low operation costs, eco-friendliness, and wide applicability (Miran et al., 2018). It was found that SMX microbial degradation occurred preferentially under aerobic conditions, such as anaerobic sulfate-reducing (Jia et al., 2017), anaerobically digested (Rauseo et al., 2019), anaerobic methane oxidation with nitrite (Martínez-Quintela et al., 2021) or ironreducing conditions (Bílková et al., 2019).

However, recently researches associated with SMX degradation in aerobic condition including laboratory and full scale studies, are marked with inconsistent results (Cetecioglu et al., 2016). The SMX degradation efficiency ranges from 26% to above 98% in conventional activated sludge (CAS) plant (Radjenovi et al., 2009, Kassotaki et al., 2016). Some conflicting results also appeared in laboratory scale experiments, Xu et al. (2011) showed that approximately 85% of SMX (30 mg/L−1) could be degraded by sediment system. Also, Cetecioglu et al. (2016) observed that SMX degradation ratio was 59% while 40 mg/L−1 of SMX was feeding into the reactors. However, Plósz et al. (2010) found SMX was not readily biodegradable compound during the 28 days laboratory scale experiment. Beside, some SMX degrading strains have been isolated from CAS. For example, Huang et al. (2012) isolated an Achromobacter sp. (S-3) with the ability to degrade SMX, and the SMX removal efficiency reach to 80% when SRT was 25 days. Reis et al. (2014) isolated four bacterial strains, only Achromobacter denitrificans PR1 could degrade SMX, Strain PR1 was able to remove SMX at a rate of 73.6 ± 9.6 μmolSMX·g−1cell dry weight h. These conflicting SMX degradation efficiency can be attributed to various environmental factors (e.g. sludge retention time (SRT), hydraulic retention time (HRT), pH value, and temperature) (Luo et al., 2014). Some research point out that wastewater may containing two or more organic as well as toxic inorganic compounds, and the degradation of a single pollutant may be affected by the other pollutants (Giang et al., 2015).

Nowadays, much attention focused on toxic metals cadmium (Cd), owing to the growing demand of heavy metals (Eichler et al., 2014) and Cd(II) containing in water bodies would cause a series of diseases to the human beings even at trace level (Wan et al., 2020). Microbial induced carbonate precipitation (MICP) technology is a perfect technology for heavy metals in situ remediation (Johnstone et al., 2016, Wang et al., 2019a). Most of Cd(II) can be embed into the structure of calcite through metathesis during the MICP process, and thus immobilized (Wang et al., 2019a). Liu and Lian (2019) used the BCa induced by Bacillus subtilis to adsorb the Cd(II), and the maximum adsorption capacity of BCa was 172.41 mg·g−1. Many studies have proved that MICP process and BCa adsorption were the important factors to affect the Cd(II) immobilisation, but the intensity of their contribution is not clear at present. And no aerobic SMX degradation and Cd(II) immobilisation denitrifier (ASDCID) has been reported to date. In this experiment, SMX was selected as the typical antibiotic pollutant, and Cd(II) was selected as the heavy metal pollutant, to investigate the performance of Achromobacter sp. L3 in the treatment of combined pollution from wastewater.

The five primary goals of this study were designed to address gaps that currently exist in the research. The first goal was to isolate a high efficiency SMX degradation and Cd(II) immobilization strain and to characterize it through both morphological and molecular aspects. The second goal was investigate the effects of temperature, initial pH, and SMX concentration on SMX degradation and Cd(II) immobilization and to determine boundary conditions. Thirdly, we aimed to confirm the SMX degradation and Cd(II) immobilization kinetic models and evaluate the variation in SMX degradation and Cd(II) immobilization kinetics under different conditions. Forth, we explored the mechanisms of SMX degradation and Cd(II) immobilization and proposed the pathway of SMX degradation through intermediate products and biochemical principles. Fifth, we provided some valuable insights for the treatment of wastewater polluted by antibiotics and heavy metals.

Section snippets

Culture medium

An aerobic denitrification bacterial strain (Achromobacter sp. L3) was isolated from the sediments of Datang industrial park area of Foshan, Guangdong, China. Basal media (BM) were used to cultivate the cell suspension, and the detailed components of the BM and trace elements are shown in Table 1. The cadmium chloride (analytically pure, Aladdin, CAS ID 10108-64-2) and SMX (Purity ≥ 98.0%, Sangon Biotech, CAS ID 723–46–6) were used to prepared the BM. After autoclaving (121 °C, 30 min), batch

Identification of the strain L3

A novel bacteria (strain L3) that is able to degrade SMX and immobilize Cd(II) was isolated from industrial wastewater. Microscopic analysis showed that strain L3 is a gram-positive, rod-shaped bacteria. The cells sizes were 1.2–1.5 µm in length and 0.2–0.4 µm in width. The 16S rRNA gene (1436 bp) was acquired from strain L3, and the phylogenetic tree (Fig. 1) was constructed based on gene sequences and homologous strains, and the results revealed that strain L3 (submission ID: SUB7989170)

Conclusions

A novel bacteria with SMX degradation and Cd(II) immobilization capabilities was isolated. The maximum SMX degradation efficiency was 91.98% with a rate constant of 0.022 h−1 at an SMX concentration of 30 mg/L−1. The maximum Cd(II) removal rate was 0.378 mg/L−1·h−1 with a rate constant of 0.101 h−1 at an initial pH of 9.0. The mechanism experiments demonstrated that microbial action and BCa sediment adsorption functions play equally important roles in the process of Cd(II) removal, and

CRediT authorship contribution statement

Donghui Liang: Conceptualization, Methodology, Software, Investigation, Writing - original draft preparation. Yongyou Hu: Validation, Formal analysis, Visualization, Software, Data curation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors gratefully thank the financial support provided by the National Natural Science Foundation of China (No. 21477039, No. U1401235, No. 2016B020240005).

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