Towards a simultaneous combination of ozonation and biodegradation for enhancing tetracycline decomposition and toxicity elimination

https://doi.org/10.1016/j.biortech.2020.123009Get rights and content

Highlights

  • A novel simultaneous combination of ozonation and biodegradation (SCOB) system was fabricated.

  • Excess ozone caused disinfection but not enough to cause biological poisoning.

  • TCH removal rate was 29% advanced over than ozonation alone at 2.0 mg-O3/(L·h).

  • SCOB products exhibited no toxicity to S. aureus after 8 h TCH treatment.

Abstract

In this study, a new intimately coupling technology of advanced oxidation and biodegradation was proposed, called simultaneous combination of ozonation and biodegradation (SCOB), which uses ozonation in place of traditional photocatalysis. SCOB was evaluated for its ability to degrade and detoxify tetracycline hydrochloride (TCH). Biodegradation alone only resulted in negligible TCH removal, while ozone alone caused less effective performance, with TCH degradation rate constants of 29–171% lower than those of SCOB. The optimal ozone dose was 2.0 mg-O3/(L·h), and it contributed to remove 97% of the TCH within 2 h under SCOB operation. The SCOB effluent was not toxic to S. aureus after 8 h of exposure. During six SCOB operation cycles, the biomass in the biofilm remained stable, and cell structure was relatively intact. SCOB significantly improved TCH degradation and reduced toxicity of the effluent.

Introduction

Antibiotics are widely used to treat bacterial infections in humans and animals (Chen et al., 2019) and have played a significant role in the development of modern society. Nevertheless, antibiotics are widely detected in the aquatic environment due to overuse (Chi et al., 2019, Wang et al., 2011). A confounding factor is that municipal sewage treatment plants are often ineffective at removing antibiotics (Cheng et al., 2018, Tran et al., 2018), which pass through as contaminants of rivers, lakes, groundwater, and drinking water (Zhang et al., 2015). The presence of these antibiotics harms the aquatic ecology and human health due to the proliferation of antibiotic resistance among bacteria exposed to the bulk water (Boovaragamoorthy et al., 2019, Wang et al., 2020). Tetracycline hydrochloride (TCH) is one of the most widely used antibiotics (Liu et al., 2019), but it is also an environmental challenge due to its high biological toxicity, chemical stability, and stimulation of antibiotic resistance genes (Xiong et al., 2018).

Traditional biological treatments, such as activated sludge, are ineffective for removing TCH from wastewater (Ganesan et al., 2019). Advanced oxidation processes (AOPs) have wide-ranging ability to remove complex organic compounds that are refractory to biodegradation (Zhi et al., 2020). TCH is directly attacked by strong oxidants, such as ozone, or indirectly by reactive oxygen species, such as hydroxyl radicals (radical dotOH) and superoxide anions (radical dotO2) (Wang & Zhuan, 2020). AOPs add O-containing groups that make products more biodegradable (Babu et al., 2019). However, acting alone, advanced oxidation dose little for mineralization and generates toxic byproducts, and consumes energy (Van Aken et al., 2017, Xiong et al., 2017).

One way to overcome these disadvantages is to couple AOP and biodegradation processes: biodegradation could mineralize the advanced oxidation products; thus, mitigating the problems of toxic byproducts and high costs. The traditional way to combine the processes is sequential, but this is often ineffective due to excessive and non-selective oxidation and the resulting formation of inhibitory products (Di Iaconi, 2012, Gómez-Pacheco et al., 2011). In this context, Rittmann’s lab presented the concept of intimate coupling of photocatalysis and biodegradation (ICPB) by integrating photocatalysis and biodegradation in time and space (Marsolek et al., 2008). In ICPB, the photocatalysts are attached to the outer surface of sponge carriers, and biofilms are attached to the interior to avoid inhibition from toxic reactants, free radicals and UV light (Rittmann, 2018). In the process of intimate coupling, photocatalytic reaction products are rapidly biodegraded by protected bacteria, which mineralize without excessive advanced oxidation. ICPB has been reported to successfully remove and mineralize chlorophenol (Zhang et al., 2017), dyes (Li et al., 2012) and antibiotics (Wang et al., 2019b). However, photocatalysis limits the practical application of ICPB under poor light penetration situation.

Could ozonation be substituted for photocatalytic oxidation of ICPB? A key prerequisite to stable intimate coupling reactions is a short quenching time of the active species produced by advanced oxidation. This not only meets the requirements of the attacking target organic compounds, but also quenches before mass transfer to the biofilm inside the porous carrier to produce a bactericidal effect (Zhang et al., 2010). In addition to generating radical dotOH, ozonation leaves a certain amount of ozone due to radical dotOH conversion efficiency. The life-time of ozone is 15–25 min (Mansas et al., 2020). which is much longer than the quenching time of key photocatalytic oxidation active species including radical dotOH (4 × 10−9 s) and radical dotO2 (2 × 10−10 s) (Zhao et al., 2018a).

This study aims to establish a system which is called simultaneous combination of ozonation and biodegradation (SCOB) to significantly reduce toxicity of the effluent and the concentration of TCH. SCOB is an applicable technology that substitutes ozonation for photocatalytic oxidation of ICPB due to its advantages of cleanliness and good light penetration. Above all, the main challenge for constructing SCOB is whether ozone exerts a stress effect on the biofilm. Solving this problem requires optimizing the ozone dose in the SCOB system. In this study, the effects of excessive ozone residue on SCOB-reactor biofilms was examined. Additionally, the effects of ozone dose on the removal rate of TCH, reduction in toxicity, and biofilm status were determined. The results indicate that this SCOB shows significant advantages over either ozone alone or biodegradation alone. SCOB was established successfully for the first time by achieving stable ozonation and biodegradation in one unit.

Section snippets

Biofilm culture

The biofilm carrier used here was a porous honeycomb polyurethane cube with a side length of 2 mm (Hayi-diverse, Yixing, China), a porosity of 87%, and pore sizes of 0.1–0.3 mm. After being soaked in activated sludge (obtained from the aerobic tank of Beijiao Wastewater Treatment Plant in Changchun, China) for 24 h, the sponge carrier was cultured in a well-mixed continuous flow reactor as described in our previous publication (Zhou et al., 2013). The synthetic influent consisted of (mg/L)

TCH removal by ozonation alone in different ozone doses

TCH degradation under ozonation is the basis of the biodegradation reaction, and also determines the efficiency of SCOB for TCH degradation. Therefore, it is necessary to identify TCH removal by ozonation for different ozone doses. As shown in Fig. 2, with increasing dose of ozone from 0.4 mg-O3/(L·h) to 4.0 mg-O3/(L·h), the removal rate of TCH in 4 h increased from 68.79% to 100%. Notably, for an ozone dose of 3.0 mg-O3/(L·h), the removal rate did not increase. Additionally, the reaction rate

Conclusions

SCOB was successfully established for the first time with stable operation of simultaneous ozonation and biodegradation. The TCH ozonation intermediates were utilized by protected microorganisms in carries during SCOB, accelerating degradation and detoxification of TCH. For an ozone dose of 2.0 mg-O3/(L·h), the TCH removal rate reached 97% within 2 h with SCOB. The SCOB degradation rate constant was 29% higher than that of ozonation alone. Furthermore, the SCOB effluent did not inhibit S. aureus

CRediT authorship contribution statement

Yuanyu Su: Conceptualization, Methodology, Software, Investigation, Data curation, Writing - original draft. Xiansheng Wang: Writing - review & editing. Shuangshi Dong: Resources, Supervision, Data curation, Writing - review & editing. Shaozhu Fu: Validation, Formal analysis, Visualization, Software. Dandan Zhou: Conceptualization, Methodology, Resources, Data curation, Writing - review & editing, Supervision, Project administration, Funding acquisition. Bruce E. Rittmann: Writing - review &

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.

Acknowledgments

The authors thank the National Natural Science Foundation of China (51722803, 51578117, 51678270) and the Fundamental Research Funds for the Central Universities (2412018ZD013, 2412018ZD042) for their financial support.

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