Water Air Soil Pollut (2007) 183:355–365 DOI 10.1007/s11270-007-9384-2
Removal of Pentachlorophenol by Adsorption on Magnetite-immobilized Chitin K. M. Pang & S. Ng & W. K. Chung & P. K. Wong
Received: 8 October 2006 / Accepted: 13 March 2007 / Published online: 30 March 2007 # Springer Science + Business Media B.V. 2007
Abstract The application of magnetite-immobilized chitin in pentachlorophenol (PCP) removal was demonstrated in this study. The physicochemical parameters for immobilization of chitin by magnetite, and for PCP adsorption using magnetite-immobilized chitin were optimized. For chitin immobilization, the optimized conditions were: magnetite to chitin (m:c) ratio at 1:2, initial pH 6, 25°C, 200 rpm and 60 min in batch system. The immobilization efficiency (IE) was 99.4% and immobilization capacity (IC) was 2.0 mg chitin mg−1 magnetite. High initial pH (pH>11) and temperature (>30°C) lowered the IE and IC. For PCP (10 mg l−1) adsorption, the optimized conditions were: 1,500 mg l−1 immobilized chitin, initial pH 6, 25°C, 200 rpm and 60 min in batch system. The removal efficiency (RE) was 57.9% and removal capacity (RC) was 5.4 mg g−1. K. M. Pang : W. K. Chung : P. K. Wong Department of Biology, The Chinese University of Hong Kong, Shatin, NT, Hong Kong S. Ng International Chitin Production Inc., 8596 Fraser Street, Vancouver, BC, Canada P. K. Wong (*) Environmental Science Programme, The Chinese University of Hong Kong, Shatin, NT, Hong Kong e-mail:
[email protected]
The adsorption ability of immobilized chitin decreased with pH and temperature increased. However, increasing the amount of immobilized chitin (24,000 mg l−1) can increase the RE up to 92%. Both chitin immobilization and PCP adsorption exhibited Langmuir and Freundlich adsorption isotherms. Results in this study indicated that magnetite-immobilized chitin was a cost-effective and environmental friendly adsorbent to remove environmental pollutants such as PCP. Keywords Adsorption . Pentachlorophenol . Chitin . Magnetite . Immobilization
1 Introduction Pentachlorophenol (PCP), a highly chlorinated aromatic organic compound, was widely used as a biocide to kill broad spectrum of microorganisms and is now restricted to be used as a wood preservative (Environmental Health Criteria 1987; ATSDR 2001). PCP is a toxic, ubiquitous and persistent environmental pollutant (Proudfoot 2003). It is listed as a priority pollutant and classified as a probable human carcinogen (Group B2) by the U.S. Environmental Protection Agency (ATSDR 2001). Due to its toxicities, PCP is banned or severely restricted in many countries (Environmental Health Criteria 1987). However, it is still prevalent in the environment and present in over one-fifth of the contaminated sites on the National Priorities List of the
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United States (ATSDR 2001). Thus, biological and chemical methods to degrade PCP were extensively studied (Tanjore and Viraraghavan 1994), however, most of them are either ineffective or non-economical. Biodegradation is a relatively slow treatment method. Because of high toxicity and recalcitrant nature of PCP to the organisms (Annachhatre and Gheewala 1996), biodegradation is ineffective at high concentrations (Gautam et al. 2003). Chemical treatments can destroy the compound in a short time and independent of the concentration of compound. Ozonation (Hong and Zeng 2002), UV irradiation (Ho and Bolton 1998) and Fenton’s reaction (Fukushima and Tatsumi 2001) are the commonly used methods. However, for the high operating cost and safety reason, more environmental friendly remediation method is needed. Adsorption of PCP by bacteria (Jacobsen et al. 1996), activated sludge biomass (Wang et al. 2000a, b), chitin (Chan 2002) and activated carbon (Hu et al. 1998) have been investigated to prevent spreading of the pollutant, or to preconcentrate the pollutant for further treatments (Wang et al. 2000a,b). However, in order to make adsorption process more economically feasible, non-living adsorbents are preferable because of the lack of toxicity limit, culture requirement and ease of regeneration (Brady et al. 1994). Chitin, the second most abundant natural polysaccharide, is an ideal adsorbent to remove inorganic (Zhou et al. 2004) and organic compounds (Trung et al. 2003; Zheng et al. 2004). Chitin is biocompatible (Zhou et al. 2004), nontoxic (Chui et al. 1996) and inexpensive (Trung et al. 2003). However, the separation of adsorbate-bounded chitin after adsorption by traditional methods such as centrifugation and filtration are expensive, timeconsuming and require large space (Šafaříková et al. 2005). Therefore, magnetite-immobilized chitin is introduced in this study to overcome the costly separation problem. Magnetite (Fe3O4) is regarded as a copolymer of Fe3+ and Fe2+ oxides and has been used for immobilization of bacteria (Wang et al. 2000a, b) and chitosan (Liu et al. 2000). To the best of our knowledge, the use of magnetite-immobilized chitin for adsorption of an organic compound has not been reported. The present study focuses on immobilization of chitin by magnetite and PCP adsorption by magnetiteimmobilized chitin. The effect of physicochemical parameters such as solution pH, temperature, contact time, concentrations of adsorbate and adsorbent, and
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agitation rate on immobilization of chitin by magnetite, and PCP adsorption using magnetite-immobilized chitin were determined.
2 Materials and Methods 2.1 Immobilization of Chitin by Magnetite 2.1.1 Sources and Pretreatment of Chitin and Magnetite The chitin in 100 mesh (0.15 mm) was produced by International Chitin Production Inc. (ICPI, Vancouver, Canada). The chitin was pretreated by washing with Milli-Q water (Millipore, Bedford, UK) in a ratio of 1:15 (w/v) for 1 h at 200 rpm by an orbital shaker (Lab-line 4628-1, Melrose Park, USA) and then collected by centrifugation with a Beckman J2-M1 centrifuge machine (Beckman, Fullerton, USA) at 14,000 rpm and 4°C for 30 min. Then the washed chitin were lyophilized by a freeze-dryer (Labconco, Kansas City, USA) at 0°C under reduced pressure for 5 days. The freeze-dried adsorbents were stored in a desiccator (Eureka AD-75B, Taipei, Taiwan) for later experiments. And, the magnetite (Fe3O4, 98% purity,
