Removal of aqueous phenanthrene by brown seaweed Sargassum hemiphyllum: Sorption-kinetic and equilibrium studies
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are aromatic hydrocarbons with two or more fused carbon rings. They are classified as persistent toxic substances (PTS) by United Nations Environmental Programme (UNEP) since they are characterized not only by their ubiquity and persistency in the environment, but also their toxicities to various organisms. Because of their low water solubility [1], PAHs are also commonly known as hydrophobic organic compounds (HOCs). Among these compounds, 16 of them are especially notorious for their mutagenic and carcinogenic properties and named as priority pollutants by the U.S. EPA [2]. Contamination of PAHs in urban runoffs has been found [3], [4], [5] and subsequently to receiving water bodies [5] and edible fish [6] were also reported.
Biosorption is a branch of biotechnology that uses dead or inactive biomass from various origins to reduce chemical concentrations in the aqueous compartment [7]. The cost is lower than ion exchange technology while still retaining comparable removal efficiency on various kinds of pollutants, from heavy metal ions, to soluble toxic chemicals such as phenol in pulp mill or dyes in industrial wastewaters [7]. The use of bacterial biomass as a sorbent to remove aqueous phenanthrene (PHE) was demonstrated by Stringfellow and Alvarez-Cohen [8], however, the removal percentages of PHE varied (42–91%). The effectiveness for removing metallic ions and polar organics in wastewaters by the marine brown seaweed, Sargassum, has long been recognized [9], [10]. In contrast to bacterial biomass, little has been done to examine its potential for PHE sorption. Furthermore, Sargassum possesses other attractive features, such as relative ease of collection, abundant in worldwide coastal areas, stable quality than fermentation originated bacteria and its cellulose structure enabling a minimum pretreatment including immobilization and granulation of microbes [7]. Therefore, it has become one of the popular choices of biosorbents for removing toxicants, especially heavy metals in wastewaters.
Most of the available studies are focused on ionic species such as heavy metals in contaminated wastewaters, and to certain extent, the polar organic pollutants such as organic dyes and phenolics. The characteristics of Stockholm POPs have caught our attention. In this study, we explored the effectiveness of using dried Sargassum hemiphyllum to remove aqueous PHE. PHE was chosen as a model of medium HOCs because of its abundance in the aquatic environment [11]. Various factors such as temperature, shaking rate and initial PHE concentration that may affect the uptake of PHE were also investigated. The sorption-kinetic and equilibrium experiments can provide important information for understanding the dynamic interactions between soption and environmental factors in batch systems and thus optimal conditions for remediation of HOCs by seaweed can be tailored.
Section snippets
Algal sampling and preparation
S. hemiphyllum was harvested as life stocks from Clear Water Bay, Hong Kong. It was rinsed thoroughly with deionized water and dried in oven at 50 °C overnight. Subsequently it was sieved to retain 0.18–1 mm fraction by standard meshes (Endecotts Ltd., London) and stored in desiccator before use.
Standard setup
In order to compare kinetic and equilibrium sorptions caused by different factors, a standard sorption condition was given and only one factor was varied each time while others were kept constant.
Kinetic studies
Table 1 compares the kinetic data among treatments. The data generated was fitted into the linearilzed pseudo-first-order and pseudo-second-order kinetic equations. For most of the conditions investigated, the pseudo-second-order model was able to describe the kinetic behavior of PHE more accurately (r2 = 0.85–1.00) when compared with the pseudo-first-order model (r2 = 0.72–0.99). Thus, we will focus to examine the corresponding rate constant (k2) of pseudo-second-order model further (Table 1).
Environmental effects—agitation rate and sorption temperature
Fig.
Conclusions
It was found that factors affecting sorption rate of PHE by Sargassum were shaking rate of the sorption system, and to less extent, the environmental temperature during sorption. Initial concentration of aqueous PHE, ionic strength and the alkalinity of the solution were factors influencing the sorption capacity of PHE. However, more study is needed to understand how exactly the ionic strength and alkalinity of the solution affect the sorption capacity by Sargassum. Sargassum typically can
Acknowledgments
The authors thank B. Yeung from Department of Biology (CUHK) for collecting macroalgae; Y.K. Chung, from Department of Statistics and Actuarial Science (HKU) and K. So, from School of Computer Science and Engineering (UNSW, Australia) for their advice on using mathematical models and statistical analyses. This study was supported by the Area of Excellence (AoE) Scheme under the University Grants Committee of the Hong Kong Special Administrative Region (CITYU/AoE/0304/02).
References (26)
- et al.
Dynamic behavior of fractional suspended solids and particle-bound polycyclic aromatic hydrocarbons in highway runoff
Water Res.
(2005) - et al.
The residual dynamic of polycyclic aromatic hydrocarbons and organochlorine pesticides in fishponds of the Pearl River delta, South China
Water Res.
(2005) - et al.
Evaluating the relationship between the sorption of PAHs to bacterial biomass and biodegradation
Water Res.
(1999) - et al.
Removal of heavy metals from waters by means of natural zeolites
Water Res.
(1984) - et al.
Effects of temperature, salinity, and dissolved humic substances on the sorption of polycyclic aromatic hydrocarbons to estuarine particles
Mar. Chem.
(2005) - et al.
Adsorption of halogenated aromatic pollutants by a protein released from Bacillus pumilus
Water Res.
(2003) - et al.
Sorption and desorption of Pb2+ ions by dead Sargassum sp. biomass
Biochem. Eng. J.
(2006) - et al.
Kinetic and equilibrium modelling of lead(II) sorption from water and wastewater by polymerized banana stem in a batch reactor
Sep. Purif. Technol.
(2005) - et al.
Adsorption of malachite green onto Pithophora sp., a fresh water algae: Equilibrium and kinetic modelling.
Process Biochem.
(2005) - et al.
Illustrated Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals
(1992)
Priority pollutants. I: A perspecitve view
Environ. Sci. Technol.
Characterization of heavy metals and polycyclic aromatic hydrocarbons in urban highway runoff
Water Sci. Technol.
Urban runoff as a source of polycyclic aromatic hydrocarbons to coastal waters
Environ. Sci. Technol.
Cited by (52)
The desorption of n-hexadecane in calcareous soils from a karst area: Insight into endogenous Cd/Pb
2024, Environmental Technology and InnovationExpansion of marine pollution along the coast: Negative effects on kelps and contamination transference to benthic herbivores?
2023, Marine Environmental ResearchThermally enhanced biodegradation of benzo[a]pyrene and benzene co-contaminated soil: Bioavailability and generation of ROS
2023, Journal of Hazardous MaterialsApplication of constructed wetlands in the PAH remediation of surface water: A review
2021, Science of the Total EnvironmentCitation Excerpt :Within a certain range, increases in temperature increase bioavailability and accelerate microbial and enzyme activity, which has positive effects on PAH biodegradation and phytoremediation (Liu et al., 2017). Sediment adsorption capacity also increases with temperature (Chung et al., 2007). Research at Yanlong Lake CW in China shows a seasonal variation in removal efficiencies of 57.23% in summer and 25.53% in winter (Xu et al., 2019).
- 1
Present address: Water Resources Science Program, University of Minnesota, St. Paul, MN 55108, USA.