Enhancement of ozonation of seawater-based wastewater containing pharmaceutical compounds by total residual oxidants: Salinity, ammonia, and organic matter

doi:10.1016/j.chemosphere.2020.127513

Chemosphere

Volume 259, November 2020, 127513

https://doi.org/10.1016/j.chemosphere.2020.127513 Get rights and content

Highlights

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Bromine (HOBr/OBr⁻) is produced by ozonation of bromide-containing water.
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Total residual oxidants were studied in presence of Cl⁻, NH₃, and humic acid.
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NH₃ and humic acid depress the removal efficiency of pharmaceutical compounds.

Abstract

The ozonation process has recently been proposed as an effective treatment method for removing pharmaceutical compounds from seawater-based wastewater discharged from fish farms or hatcheries. Seawater ozonation can lead to the production of secondary stable oxidants such as bromine (HOBr/OBr⁻), which can be expressed as a total residual oxidants (TRO) owing to the high reaction rate constant with respect to ozone and bromide ion. TRO formation depends on water quality, in terms of aspects such as salinity, ammonia, and organic matter content; therefore, it is important to understand the variations in the ozone chemistry of bromide-containing water by considering the factors influencing TRO formation. In addition, the removal of pharmaceutical compounds in bromide-containing water should be evaluated owing to the different oxidation efficiency between TRO and pure aqueous ozone. This study aims to investigate the factors influencing the formation of TRO and the removal of pharmaceutical compounds during the ozonation of bromide-containing water. The results show that salinity increased the TRO formation rate by 6%, while ammonia and organic matter decreased the TRO formation rate by 51% and 39%, respectively. The removal efficiency of pharmaceutical compounds by TRO was higher compared with that by only ozone. Ammonia and organic matter inhibited the ozonation of bromide-containing water. These results indicate that TRO can be broadly used in the field of seawater ozonation; however, additional case studies on the removal of pharmaceutical compounds from seawater-based wastewater are needed to elucidate the oxidation mechanisms of various TRO.

Introduction

Pharmaceutical compounds present in untreated seawater-based wastewater, such as fish farm or hatchery water, have received increasing attention as an emerging threat, with the development of analytical methods for assessing water quality, growing concerns over public health, and advancements in medical science (Arpin-Pont et al., 2016; Kovalakova et al., 2020). Despite being present in low concentrations (μg/L or less), pharmaceutical compounds present potential to adversely affect human health and aquatic ecosystems subjected to constant exposure (Fisher et al., 1999; Bolong et al., 2009).

Conventional wastewater treatment processes allow for pharmaceutical compounds to be detected and not completely degraded in aquatic ecosystems (Sim et al., 2011; Nam et al., 2014; Kim and Zoh, 2016). To solve this problem, oxidation processes, such as chlorination, ozonation, ultraviolet radiation, and Fenton oxidation have been applied (Vollmuth and Niessner, 1995; Sharma, 2008; Klavarioti et al., 2009; Zheng et al., 2010; Tokumura et al., 2016). Previous studies have shown that ozonation is the most suitable method for effectively degrading and oxidizing pharmaceutical compounds in wastewater (Klavarioti et al., 2009).

Ozone chemistry of seawater is considerably different from that of freshwater owing to the high concentration of ions (e.g., chloride ion, bromide ion, magnesium, and sulfate) (Jung et al., 2013). The most significant difference is that the concentration of bromide ion in seawater is 65 mg/L, while that in freshwater is < 1 mg/L (Pilson, 1998). As shown in Fig. S1, although the chloride ion concentration of seawater is high (18 000 mg/L), its reaction rate constant is much lower (0.003 M⁻¹ s⁻¹) compared with that of bromide ion (Siddiqui, 1996; Jung et al., 2014). The reaction between ozone and bromide ion leads to the formation of oxidants, bromine, i.e., hypobromous acid and hypobromite ion (HOBr/OBr⁻), because of the high reactivity ( $k_{O_{3}, B r^{-}}$ = 160 M⁻¹s⁻¹) (Haag and Holgne, 1983; von Gunten and Holgne, 1994). Even though chlorine (HOCl/OCl⁻) is formed in seawater ozonation, it was instantly converted into bromine at a rate of 2.95 $\times$ 10³ M⁻¹s⁻¹ (Siddiqui, 1996; Jung et al., 2014). The bromine was fractionated into HOBr and OBr⁻ at pKa value of 8.8. The typical pH of seawater is 8; therefore, HOBr is the dominant form of bromine and is quantified as the total residual oxidants (TRO), which shows more stable oxidant properties than those of ozone (Sayato et al., 1990; Shah et al., 2015).

The half-life of ozone in seawater is only few seconds, and it is converted into relatively stable secondary oxidants such as TRO, including bromine. This means that the residual oxidation efficiency for seawater ozonation would be different from that for freshwater ozonation. Previous research suggests that TRO formation varies according to seawater with different properties (Perrins et al., 2006). Regarding seawater ozonation, TRO formation can be affected by other compounds such as sodium chloride (salinity), ammonia, organic matter (OM), and suspended solids (SS) (Hoigne et al., 1985). Moreover, the degradation efficiency of pharmaceutical compounds during seawater ozonation can vary depending on the presence of these compounds. For the proper treatment of seawater-based wastewater, the effects of influencing factors that can promote or inhibit TRO formation and removal efficiency of pharmaceutical compounds should be studied.

Although studies on seawater ozonation have been previously performed via examination of TRO or oxidant species, only the general observation using actual seawater was studied; the influencing factors affecting TRO formation have not been discussed specifically in the context of seawater condition (Perrins et al., 2006; Jung et al., 2014; Gonçalves and Gagnon, 2018). To the best of our knowledge, few studies have investigated the removal efficiency of pharmaceutical compounds from seawater in consideration of various influencing factors (Benitez et al., 2011). It is important to identify the effects of these influencing factors on TRO formation and degradation of pharmaceutical compounds during the ozonation of bromide-containing water. Given the limitations of previous research, a lab-scale ozone dissolution system was designed to produce TRO in consideration of the effects of influencing factors, such as chloride ion (as salinity), ammonia, HA (as OM), and SS.

Therefore, the objectives of this study are (1) to investigate the effect of influencing factors (chloride ion, ammonia, HA, and SS) on the TRO formation rate during ozonation of bromide-containing water; (2) to evaluate the degradation of pharmaceutical compounds by drawing a comparison between the oxidation efficiencies of pure ozone and TRO; and (3) to investigate the TRO removal efficiency at various concentrations of influencing factors. It is important to understand how influencing factors affect seawater ozonation as they determine the optimal ozone concentration for the effective treatment of seawater-based wastewater.

Section snippets

Reagents and pharmaceutical compounds

The bromide-containing water for ozonation was obtained by dissolving sodium bromide (NaBr) in deionized (DI) water. Sodium chloride (NaCl), ammonium chloride (NH₄Cl), humic acid (HA), and SS standard solution were added individually at various concentrations to the bromide-containing water to examine the effect of influencing factors on TRO formation. The pharmaceutical compounds, i.e., atenolol (ATN), antipyrine (ATP), and florfenicol (FFC), were selected as the representative compounds

Effects of ions on TRO formation

Before the effect of influencing factors on TRO formation by ozonation was investigated, the changes in TRO concentration were measured depending on ozonation time at various bromide ion concentrations (10, 29, and 65 mg/L Br⁻). As shown in Fig. S3, the reaction rate (r) of TRO formation linearly increased with ozonation time and bromide ion concentration. This means that initial concentration of bromide ion can affect the TRO formation rate, and a high initial concentration of bromide ion can

Conclusions

In this study, the effects of influencing factors on the ozonation of bromide-containing water were investigated with respect to TRO formation and degradation of pharmaceutical compounds. The factors influencing TRO formation were found to be chloride ion, ammonia, and HA. In the presence of chloride ion (>15 g/L NaCl), the TRO formation rate was 6% higher than that in the case of only a single bromide-ion was present. Ammonia and HA decreased the TRO formation rate to 51% and 39%,

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

This research was a part of the project titled ‘Development of a water treatment system to remove harmful substances of ecological disturbances emitted from quarantine stations screening up imported fishery products,’ funded by the Ministry of Oceans and Fisheries, Korea.

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Enhancement of ozonation of seawater-based wastewater containing pharmaceutical compounds by total residual oxidants: Salinity, ammonia, and organic matter

Highlights

Abstract

Introduction

Section snippets

Reagents and pharmaceutical compounds

Effects of ions on TRO formation

Conclusions

Declaration of competing interest

Acknowledgement

Chemosphere

Desalination

Water Res.

Water Res.

Mar. Pollut. Bull.

Chem. Eng. J.

Environ. Int.

Chemosphere

Chemosphere

Aquacult. Eng.

Mar. Pollut. Bull.

Chemosphere

Chemosphere

Water Res.

Chemosphere

Chemosphere

Chemosphere

Water Res.