Elsevier

Bioresource Technology

Volume 336, September 2021, 125320
Bioresource Technology

Evaluating the effect of fluoxetine on mesophilic anaerobic dark biohydrogen fermentation of excess sludge

https://doi.org/10.1016/j.biortech.2021.125320Get rights and content

Highlights

Abstract

Recently, the influence behavior of new pollutants in the environment has been widely concerned. However, the effect of antidepressants widely detected in excess sludge (ES) on biohydrogen production from anaerobic dark fermentation has never been explored. To fill this gap, fluoxetine (FLX), a typical antidepressant, was selected to evaluate its effect on ES mesophilic anaerobic dark biohydrogen fermentation. The results showed that FLX reduced biohydrogen production even at low content (0.1 mg/Kg). The biohydrogen yield was only 12.8 mL/g in the 1.8 mg/Kg (based on total suspended solids) FLX group, decreased by about 34.7%, compared with the control group (without FLX). Further mechanism investigation implied that high levels (more than 0.6 mg/Kg) of FLX reduced every step associated with the biohydrogen production. FLX reduced the concentration of ammonia nitrogen and phosphate in fermentation broth. FLX also had a significant negative effect on enzyme activity in ES dark fermentation.

Introduction

Excess Sludge (ES) is an important part of urban solid waste. It was reported that in 2015, the production of ES was about ~34 million tons in China (Wang et al., 2019a). It is very expensive to treat the large amount of sludge. It is reported that the treatment cost of ES can account for 60% of the operation cost of sewage (Low et al., 2000). In addition, ES contains a considerable amount of biodegradable organic matter, for instance, protein, polysaccharide and grease (He et al., 2019). Therefore, ES is an ideal reusable resource and the organic matter in ES can be recovered by anaerobic digestion, gasification and composting (Wei et al., 2018, Godlewska et al., 2017).

Usually, ES is anaerobic digested for methane production because methane is a valuable energy gas (Li et al., 2019, Li et al., 2020, Zhao et al., 2021a). However, the collection and purification of methane is the key step to limit the reuse of ES derived biogas. Hydrogen may be obtained from organic matter by (steam) reforming and anaerobic digestion (Živković et al., 2020, Obradović et al., 2013a, Obradović et al., 2013b, Kuang et al., 2020a). Biohydrogen is the key intermediate product in the anaerobic digestion process of ES, which has high calorific value and poor explosiveness in the process of collection (Wang et al., 2019b). Therefore, in recent years, the application of ES to produce biohydrogen has attracted wide attention (Kuang et al., 2020a). The production of biohydrogen is a complex and continuous biological reaction process, which includes the key steps of pyrolysis, hydrolysis, acidification and methonogenesis (Wei et al., 2019, Hu et al., 2018, Chen et al., 2012). Alkaline dark fermentation has been proved to be an efficient pretreatment strategy to promote biohydrogen production and inhibit methanogenic archaea (Wei et al., 2019, Wan et al., 2016). Previous studies on ES anaerobic biohydrogen production mainly focused on process optimization, pretreatment selection and operation conditions (Yin and Wang, 2021, Liu et al., 2020). Anaerobic production of biohydrogen from organic matter is also affected by the characteristics of fermentation substrate. ES is a special form of microbial self condensation. In addition to the degradable organic components, ES also contains a variety of pollutants that contained in sewage (Dubey et al., 2021, Zhao et al., 2020, Kuang et al., 2020b, Zhang et al., 2021). However, there are few reports on the effect of emerging pollutants contained in ES on biohydrogen production from anaerobic dark fermentation.

Antidepressants are a kind of common psychiatric prescription drugs. With the continuous improvement of chemical analysis level, trace level of drug active components and their by-products are widely detected in polluted water, and become an important kind of water pollutants (Stackelberg et al., 2004, Choi et al., 2018, Castillo-Zacarías et al., 2021). Fluoxetine (FLX), an antidepressant, is widely used in clinic because of its excellent effect. In view of the special risk assessment characteristics of pollutants, FLX has been listed as the top 20 pollutants of pharmaceuticals and personal care products (PPCP) by the US Environmental Protection Agency (Munari et al., 2014). The mass production and use of FLX would inevitably lead to its release and existence in the environment. In a sewage plant in northern Spain, the detection FLX concentration in the influent reached 3100 ng/L (Alvarino et al., 2015). The removal or degradation efficiency of FLX was limited (less than 8%) by the activated sludge treatment process applied in the existing sewage treatment plants (MacLeod et al., 2007). Therefore, FLX in the influent sewage will be transferred to ES by adsorption and accumulated in ES for a long time. Radjenović et al.(2009) showed that the content of FLX in sludge of a sewage treatment plant was up to 174.1 ng/g. Moreover, scientists found that the content of FLX can reach 1033 ng/g when determining the content of antidepressants in sewage sludge from Canada (Lajeunesse et al., 2012). With the increasing use of FLX, its side effects on the human body or aquatic organisms have also been continuously disclosed, including gastrointestinal dysfunction, anorexia, mental disorders, sexual dysfunction, decreased sperm activity, etc (Fong and Ford. 2014). For example, de Abreu et al. (2014) found FLX reduced the hormone synthesis of zebrafish at environment-related concentrations, which led to the obstruction of emergency response. The influence of FLX on aquatic organisms and human beings has been explored for many years, however, the impact of FLX in ES on the resource utilization of ES is rarely reported. Recently, our research group has shown that FLX had a serious inhibitory effect on enhanced biological phosphorus removal, the release and excessive absorption of phosphate, and the synthesis of intracellular polymer polyhydroxyalkanoates had been reduced to varying degrees (Zhao et al., 2021b). It should be noted that up to now, the influence of FXL on biohydrogen production from ES has never been reported. Also, the relevant mechanism has not been revealed yet. Although Zhao et al (2021a) explored the effect of FLX on ES anaerobic methanogenesis using sequencing batch reactor under neutral conditions. The effect of FLX on the production of biohydrogen from ES alkaline dark fermentation has not been reported. On the one hand, the alkaline environment can inhibit the consumption of hydrogen by methanogenic archaea (Wan et al., 2016). On the other hand, the alkaline environment can accelerate the release of organic matter and improve the efficiency of hydrogen production (Cai et al., 2004). Biohydrogen production by ES anaerobic fermentation and methane production from ES anaerobic fermentation are two different bioreaction systems. There are some differences in microbial communities and key enzyme activities involved in the two biochemical processes. Therefore, it is necessary to explore the effect of FLX on the dark fermentation of ES to produce bio hydrogen.

The main purpose of this work was to explore the impact of FLX on the production of biohydrogen from ES dark fermentation. Firstly, the production of biohydrogen from ES alkaline fermentation in the presence of different doses of FLX was compared. Then, the influence mechanism of FLX on biohydrogen production was systematically revealed. Finally, the significance of FLX to the actual sewage treatment plant was elaborated.

Section snippets

Materials

The ES was taken from a semi continuous flow reactor for phosphate removal in the laboratory. The influent of the wastewater treatment reactor is synthetic, and the wastewater did not contain FLX. ES was first filtered through a colander (2.0 mm) to eliminate the large particles of impurities that were difficult to digest, and then the ES was left standing for 12 h and the supernatant was removed manually for standby. The main features of ES are displayed in Table 1.

The inoculum was taken from

Comparison of hydrogen production in different reactors in the presence of FLX

The cumulative production of biohydrogen produced from ES alkaline dark fermentation with different levels of FLX was shown in Fig. 1. It can be clearly seen that in the control, the biohydrogen production increased sharply in the first 5 d, increased slowly in 6–15 d, and did not increase after 18 d. In the control, the maximum biohydrogen production was about 21.6 mL/g (calculated by VSS), and the value was higher than that reported in the literature (Xiao and Liu. 2009), which proved that

Conclusion

The effect of FLX on the production of biohydrogen from ES mesophilic anaerobic dark fermentation was systematically explored in this work. The results showed that FLX had a remarkable effect on the accumulation of bio hydrogen from ES dark fermentation, and as the FLX exposure dose elevated from 0.1 to 1.8 mg/Kg, the cumulative production of biohydrogen decreased from 16.8 mL/g to 12.8 mL/g. High level of FLX inhibited every step related to biohydrogen production, and the higher the content of

CRediT authorship contribution statement

Ying Gao: Investigation, Data curation. Jianwei Zhao: Conceptualization, Funding acquisition. Chengzhi Qin: Review & editing. Qingjiang Yuan: . Jiangwei Zhu: . Yingjie Sun: Resources, Visualization. Chenggang Lu: Writing- review & editing.

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

This research was financially supported by the project of National Natural Science Foundation of China (NSFC) (No. 51908305), the Open Fund of Innovation Institute for Sustainable Maritime Architecture Research and Technology (iSMART), Qingdao University of Technology (Nu. 2020-042), the project funded by China Postdoctoral Science Foundation (No. 2019M660162), Shanghai Engineering Research Center of Biotransformation of Organic Solid Waste (No. SERC2020C05), Shandong Province Key Research and

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