Elsevier

Bioresource Technology

Volume 311, September 2020, 123455
Bioresource Technology

Effects of modification and magnetization of rice straw derived biochar on adsorption of tetracycline from water

https://doi.org/10.1016/j.biortech.2020.123455Get rights and content

Highlights

  • Modified magnetic biochar showed enhanced TC adsorption capacity reaching to 98.33 mg/g.

  • Adsorption occurs mainly by hydrogen bonding and pore-filling effect.

  • A stable TC removal rate of 69% was maintained after five cycles.

  • Nitrate nitrogen and phosphorus removal reach to 75.23 mg/g and 83.33 mg/g, respectively.

Abstract

Rice straw derived biochar shows low-cost superiority as a potential adsorbent in tetracycline (TC) removal, but limited by its poor adsorption capacity and N, P leaking risk. Herein, an alkali-acid combined and magnetization method was proposed for its modification. The sorption kinetic and isotherm data showed modification enhanced the performance for tetracycline removal with adsorption capacity up to 98.33 mg·g−1. The strong adsorption mechanisms were dominated by hydrogen bonding and pore-filling effect due to the increase of specific surface area and pore volume. Furthermore, the effect of pH was insignificant over a pH range from 3 to 10. The strong competition between ionic and TC was identified, where Ca2+ and PO43− markedly inhibited the sorption. The enhanced TC adsorption, strong N and P removal, easy magnetic recovery, and good reusability in water samples entrusted it with good potential for wastewater treatment and rice straw resource disposal.

Introduction

Tetracycline (TC), as emerging pollutants, are released into the environment due to abuse of pharmaceuticals, and it is difficult to degrade even with more toxic byproducts (DeVries and Zhang, 2016). The residues of tetracycline pose serious threats to animals and human health (Yang et al., 2018). At present, many technologies have been developed to remove aqueous tetracycline, such as adsorption, photolysis, chemical oxidation. Among them, adsorption is considered as a cost-effective method (Xiang et al., 2019). Biochar is a carbon-rich material produced by pyrolysis of biomass under oxygen-limited atmosphere (Aller, 2016). Due to the wide range of biomass materials and three win-win effects of water remediation, carbon sequestration and reutilization of wastes, biochar shows low-cost superiority over many other adsorbents. The adsorption performance of biochar relies on its raw material and preparation technology.

Rice straw, as a common agricultural waste, was often burned in fields because of the large agricultural production in China, which could easily cause secondary pollution and resources wasting. Nowadays, the rice straw has been frequently used to produce biochar, but the raw biochar showed poor adsorption capacity for tetracycline due to the limited porosity and functional groups. Some strategies of surface modification of the natural derived biochar were provided to enhance the adsorption capacity. It has been reported that rice straw derived biochar modified with manganese oxide could enhance adsorption capacity of Pb (II) ions (Guangqun Tan et al., 2018). The H3PO4 modification enhanced the sorption of TC on rice straw derived biochar (Chen et al., 2018). The magnetic rice straw derived biochar prepared with co-precipitation method showed high efficiency for the removal of Cd (II) (Tan et al., 2017). However, the adsorption capacity of these single modified rice straw derived biochar adsorbents is still unsatisfactory, and few reports have taken the secondary pollution risk into consideration, namely the N and P leaking from biochar into water.

Generally, most of the inorganic salts in rice straw biochar, such as the oxides and salts of Ca, Mg, Mn, Fe and Al, could be removed by acid to form soluble ions (Kai Zhou et al., 2014). Additionally, the biochar usually contains a large number of silicon and ash, which could be removed with thick hot alkali solution (Wang et al., 2018b). In theory, the porosity, surface area and surface functional groups would increase along with the removal of substances. According to previous studies, the increased porosity, surface area and functional groups would improve the adsorption ability of raw biochar. Therefore, based on the properties of rice straw derived biochar, a simple method, alkali-acid modification for raw biochar, could be a promising approach to enhance the adsorption capacity. What’s more, as porous adsorbents, biochar, with strong affinity to organic compounds, however, the adsorbed contaminants are also likely to be released from adsorbents into water (Hao et al., 2018). Consequently, as a practical adsorbent in the water, its effective separation and recycling could be a challenge. In addition, the ability to adsorb organic compounds is limited owing to limited adsorption sites on the surface of biochar. Consequently, recovery processing is required, such as the recent reports of magnetic particles loaded biochar adsorbents (Thines et al., 2017). Magnetic modification method provides a solution for recovery problems of sorbents and further treatment of contaminants. The use of magnetic biochar could enhance the removal of contaminants, and the loaded magnetic particles did not markedly change the contaminants affinity (Bombuwala Dewage et al., 2019, Dong et al., 2018). While our understanding about the effect of magnetic modification on the characteristics, contaminants sorption ability and sorption mechanism of biochar are still developing, the influence of loaded magnetic particles on sorption was also not well understood. In this study, while alkali-acid modification was used to enhance the adsorption capacity of raw biochar, further magnetization provided a route to the recycling of biochar adsorbents and contaminants treatment, the effect of single alkali, acid and magnetic modification and combined modification on the characteristics, contaminants sorption ability and sorption mechanism of biochar are still unclear.

Herein, in this work, an alkali-acid modified magnetic biochar derived from rice straw was prepared, and applied to tetracycline adsorption. And the effects of alkali, acid and magnetic modifications on characteristics of biochar were explored. The TC adsorption behavior, including the adsorption kinetics, isotherms, mechanisms as well as the water environment factors affecting the adsorption capacity were studied. The release risk and potential in N and P removal from water were investigated. As a potential practical adsorbent, the reusability also deserves to be evaluated.

Section snippets

Chemicals and materials

Tetracycline (96% in purity) was purchased from Shanghai Aladdin Bio-chem Technology Co., Ltd; Nitric acid (HNO3, 65%), glacial acetic acid (CH3COOH, 98%) and phosphoric acid (H3PO4, 85%) were purchased from Beijing Chemical Works, China; absolute ethyl alcohol (CH3CH2OH, 99%) was purchased from Beijing Tongguang Fine Chemicals Company; ferrous sulfate (Fe2SO4·7H2O, 99%), ferric chloride (FeCl3·6H2O, 99%), Mono Potassium Phosphate (KH2PO4, 99%), Sodium hydroxide (NaOH, 96%), sodium sulphate

Effects of modification methods

The adsorption of organic pollutants onto adsorbents is greatly affected by surface properties of the adsorbent (Tong et al., 2019). To grasp the surface properties of adsorbent would help to understand adsorption kinetic and mechanisms itself. It had been reported that surface properties of biochar greatly depend on the raw material and process of post-pyrolysis treatment (Liu et al., 2018).

The SEM images illustrate that smooth surface and numerous regular hollow channels were found in virgin

Conclusion

In general, rice straw biochar with alkali-acid combined modification and magnetization was prepared with the enhanced TC adsorption capacity due to increased BET area and pore volume. The results demonstrated different modification methods remarkable influences on biochar’ properties. The mechanisms involved among the adsorption process were dominated by hydrogen bonding and pore-filling effect. The TC sorption was not markedly affected by pH and the bulk of ionic. Besides the strong TC

Future perspectives

There is a growing interest in applications of biochar in wastewater treatment, biochar adsorption could serve as an emergency method for the removal of toxic compounds. Considering magnetic biochar combine the advantages of biochar matrix and magnetic particles, multifunctional potential applications are existed, for instance, catalytic materials couple with magnetic biochar may be applied for simultaneous adsorption-degradation of contaminants and further recycle of biochar-based materials.

CRediT authorship contribution statement

Jiawei Dai: Conceptualization, Methodology, Data curation, Writing - original draft, Writing - review & editing. Xiangfu Meng: Methodology, Validation, Formal analysis, Investigation. Yuhu Zhang: Writing - review & editing, Supervision, Project administration, Funding acquisition. Yunjie Huang: Validation, Resources, 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.

Acknowledgement

The authors would like to thank the support of National Key Research and Development Program, China (2017YFC0406002), Capital Normal University Multidisciplinary Studies Project, China (00719530011010, 00719530012012, 00719530012010), National Science and Technology Support Project (2015BAC02B02) and China Clean Development Mechanism Fund (CDM) Grant Project (NO. 2014108).

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