Adsorption of Copper (II) by Chitosan Immobilized on Sand - CiteSeerX

— 96 嘉南— 學報第三十Adsorption 三期 of Copper (II) by Chitosan Immobilized on Sand 第 96～106 頁，民國九十六年 CHIA-NAN ANNUAL BULLETIN V O L . 3 3 , P P. 9 6 － 1 0 6 , 2 0 0 7

Adsorption of Copper (II) by Chitosan Immobilized on Sand Meng-Wei Wan*, Chi-Chuan Kan*, Ching-Han Lin**, Buenda D. Rogel*** and Chun-Hao Wu* *Department of Environmental Engineering and Science, **Department of the Introduction of Applied Chemistry, Chia-Nan University of Pharmacy and Science, Tainan, Taiwan 71710, R.O.C. ***Department of Environmental Engineering University of Philippines-Diliman Diliman, Quezon City, Philippines

ABSTRACT Because of the dramatic develop of industry, heavy metal pollution has become a global environmental considerations. The heavy metals in the soil and groundwater have endangered our environment and human body by direct or indirect pathway. Thus, how to solve efficiently the heavy metal pollution in groundwater has become the most essential issue around the world. Theoretically, the traditional remediation method is physicalchemical processes, which resulted in high capital cost and serious damage in contaminated sites. Currently, bioremediation is a developing biologic process that offers the possibility to destroy or render harmless various contaminants using natural biological activity. As such, it uses relatively low-cost, low-technology techniques, which generally have a high public acceptance and can often be carried out on site. Biopolymer is a biodegradable material, and becomes a newly developing tendency for many industries. Those materials can be degraded by landfill process, which provides the nutrient for microorganisms, plants and animals. Based on this concept, obtaining form insects, the shell of aquatic crustaceans (crab and shrimp), and the cell wall of fungus. Chitin and Chitosan have widely applied in the adsorption study of heavy metal based on their chemical structures, reaction characteristics and modification properties. This research is based on the ideal of green design and using biodegradable material (chitosan) coated with sand. Nature materials such as sand, soil, clay and chitosan used as adsorbent to examine by Cu2+ adsorption capability and isotherms analysis using Langmuir isotherm. In the considerations of real scale and cost-effective applications, sand was immobilization on chitosan to uptake the Cu2+ ions in aqueous solution. Moreover, the adsorption capacity of 5 % chitosan-coated sand (10.87 mg/g) was a better adsorbent compared to chitosan used alone (7.55 mg/g), 1% (3.38 mg/g) and 2.5% (4.50 mg/g) weight percentages coasted with chitosan. It is suggested that using 5 % chitosan-coated sand as a bioadsorbent in wastewater treatment process. Key words：Chitosan, Biopolymer, Adsorption, Heavy Metal, Natural materials, Subsurface Remediation

Meng-Wei Wan, Chi-Chuan Kan, Ching-Han Lin, Buenda D. Rogel and Chun-Hao Wu

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INTRODUCTION As a result of today’s widely industrialized society, many industrial processes discharge aqueous effluents containing heavy metals. The existence of heavy metals in the aquatic system can be detrimental to a variety of living species(1). Copper (Cu2+) ions are found in low concentrations in some biological systems and high concentrations of these metals are lethal. Although copper can exist as Cu(0), Cu(I), and Cu(II), the main species of concern in aqueous solution is Cu(II)(2). Cu2+ binds easily to organic and inorganic matters in aqueous solution based on solution pH(3), which pose a significant threat to aquatic life and render natural water unsuitable for the public use. Moreover, Copper is used extensively by electrical industries, in fungicides and in anti-fouling paints. When Cu is ingested at high concentrations it can become toxic to humans, causing cancer and promoting oxidation. The present method for removal of Cu is to precipitate copper hydroxide by liming. But with this process, residual Cu remains a problem(4). Over the years, a wide range of clean-up technologies have been developed to remove toxic metals from water(5) and soils(6). Currently, the most widely used remediation technologies are based on physicalchemical processes, including filtration, chemical precipitation, ion exchange, adsorption, electrodeposition, and membrane systems for water treatment, and excavation followed by burial at a hazardous waste site for soil treatment. These technologies have a series of problems, stemming from their high cost, disruptive nature, and inadequacy at removing trace levels of metals in most cases. Recently, biological technologies such as bioremediation and phytoremediation are regarded as future solutions to many contamination problems, because of the many advantages they possess such as, being cost-efficient, nondisruptive, and easy to maintain. However, there are still problems with these methods, as microorganisms do not have the ability to degrade metals but rather to transform them, and phytoremediation is only effective for low to moderate contamination and may take long periods of time(7). The development of innovative metal clean-up technologies remains a big challenge. To accomplish this mission, many studies of chelating materials holding great potential for metal adsorption and removal from both water and soils have been widely applied in wastewater and contaminated soil treatment through the world. In recent years, many natural adsorbents have been investigated for the removal of heavy metals from water. A review of more than 70 natural and synthetic adsorbents and their potential uses for metal removal has been reported(8). Among these, there are various natural adsorbents such as chitin, chitosan, natural zeolites, perlite, and agricultural wastes applied for metal ion removal from contaminated water. Chitosan, a biopolymer of glucosamine, has received considerable attention for metal ion removal due to its excellent metal binding capacities and its ready availability(9). It has been used widely as an adsorbent for transition metal ions and organic species. The chemical structure of chitosan is shown in Fig. 1. The amino (NH2) and hydroxy (OH) groups on chitosan chains can serve as coordination and reaction sites(10–13). In addition, chitosan is economically attractive, since it can be obtained from the deacetylation of chitin, and chitin is the second most abundant biopolymer in nature, next to cellulose(13). In nature, the main sources of chitin/chitosan are from the animal and plant kingdoms, including the shells of crustaceans and mollusks, the algae commonly known as marine diatoms, and the cell walls of fungal species.

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Adsorption of Copper (II) by Chitosan Immobilized on Sand

Fig. 1 The chemical structure of chitosan. Various studies of metal ion adsorption by chitosan have been undertaken in recent years, such as the removal of Cu2+ ions from aqueous solution onto chitosan and cross-linked chitosan beads(7,14). The equilibrium sorption studies of Cu2+ ions onto chitosan were found to follow the Langmuir model(7,15). In addition, chitosan can be used to achieve adsorption of chromium(16), cadmium(17), iron(18), nickel(19,20) and lead(20) ions from aqueous solution. Such investigations, although appealing in theory, have limited potential for practical applications. This is because in order to remediate contaminated waste streams, filters must be built along the stream, which would require large quantities of chitosan, if used alone, and the entire process would be expensive. However, if a proper and inexpensive material is used as immobilization support for chitosan, much lower quantities of chitosan are needed to build the filters, while the overall metal adsorption capacity may not be affected. In spite of the inherent practical advantages, there is no literature reference of adsorption studies using chitosan immobilized on a geologically readily available support. The aim of this study is to examine the metal adsorption capacity on various nature materials, as well as sand, clay, soil and chitosan itself. Moreover, this study also executed the investigation for different weight percentages of chitosan immobilized on sand. The metals used were Cu2+ in CuSO4 solution. Adsorption isothermal data could be interpreted by the Langmuir isotherm equations. Batch studies were carried out to identify the copper isotherm by determining the maximum capacity of the different aforementioned adsorbents used. Finally, adsorption studies were performed to determine the possibility of stable copper removal from chitosan-coated sand system.

MATERIALS AND METHODS Materials In this study the following reagents were used: chitosan with a high purity reflected by a nitrogen content of 7.57 % (MegaCare Inc., S. El Monte, CA); copper sulfate (CuSO4.5H2O); hydrochloric acid (HCl); sodium hydroxide (NaOH); acetic acid (HAc); sand (EM Science, Gibbstown, NJ), soil (Garden soil), Clay (Montmorillonite). All of the reagents used were of a highly pure grade. The deionized water was used for all reagent solutions. Preparation of chitosan-coated sand 5.0 g chitosan was mixed with 100 g sand, and 300 mL 5% HCl (pH = 1.5) was added. The acid was added for chitosan solubilization, allowing its uniform distribution on sand particles. The mixture was then stirred for 5 hours at room temperature. The resulting solution was neutralized with NaOH (1N, pH =13), which was added drop by drop until chitosan-coated sand was formed by precipitating the chitosan from solution on sand surface. Then, it was filtered from the solution, washed and dried in a vacuum oven. After


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grinding and sieving, the particles were passed through ASTM sieve size # 35 and particles greater than 0.425 mm were collected and used as the adsorbent for the isotherm analysis. Coated sand increases the surface area of chitosan. All pH values were measured with pH meter (ORION, Model 1230). Cu2+ Adsorption studies on various natural materials Cu2+ solutions of different concentrations (100 mg/L, 500 mg/L, 1000 mg/L and 2000 mg/L) were prepared in deionized water using CuSO4. The batch adsorption equilibrium studies of Cu were carried out at room temperature and with CuSO4 of pH 4.2, beakers filled with 2.5 g different bioadsorbents (chitosancoated sand with 1%, 2.5% and 5% by weight chitosan content, chitosan, sand, clay and soil) and 30 mL metal solution (of each concentration used). The contact times were two and four hours. A shake machine, reaching a static speed of 50 rpm, provided continuous mixing. After sample filtration, Cu concentration in the supernatant was analyzed with an atomic adsorption (AA) spectrophotometer (Perkin Elmer AAnalyst300). The percentage adsorption of Cu was calculated according to: Percentage Adsorption =

(C 0 − C )100 C0

where C0 is the initial Cu2+ concentration (mg/L) and C is the final Cu2+ concentration (mg/L). The adsorption capacity was calculated for each adsorbent (reported per g chitosan or different bioadsorbents), based on the difference of Cu2+ concentration in aqueous solutions before and after adsorption, the volume of aqueous solution, and the amount of adsorbent used by weight, according to: Adsorption Capacity =

(C 0 − C )V W

where C0 is the initial Cu2+ concentration (mg/L), C is the final Cu2+ concentration (mg/L), V is the volume (L) of Cu2+ solution, and W is the weight (g) of the adsorbent used. Equilibrium isotherms studies Equilibrium isotherms are used to determine the capacity for different bioadsorbents for Cu2+ ions. The bioadsorbent was stirred with fixed volumes (30 mL) of metal ion solutions varying the initial concentrations (100 mg/L, 500 mg/L, 1000 mg/L and 2000 mg/L) in four hours contact time. The relation between the amount of adsorbed metal and the metal ion concentration remaining in solution is described by the isotherm studies.

RESULT AND DISCUSSION Copper adsorption studies on various natural materials Natural materials knowing as sand, clay and soil have the trend to adsorb metallic ions from aqueous solutions. Gecol et al. has clarified that clay has the capability to attract metal ions because of the negative charge on the structure of clay minerals. Among clay minerals, montmorillonite has the highest cation exchange capacity(21). Therefore, clay (mostly montmorillonite) was tested for their effectiveness in the removal of metal ions (such as Zn2+, Pb2+, and Cd2+) from aqueous solutions(21). Moreover, based on many literature reviews, one of the first applications for chitosan was the use of chelating materials for metal ions in wastewater treatment. The ability of chitosan to adsorb metallic ions from aqueous solutions has been

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extensively studied in several metals, such as Cu, Pb, Au, Cr, and Cd. In such studies, chitosan was either used alone, as cross-linked chitosan, or in the form of several derivatives (e.g., carboxymethyl and hydroxamic acid derivatives). There is no literature reference of adsorption studies using chitosan immobilized on a geologically readily available support. Therefore, the investigation of different weight percentages of chitosan immobilized on sand as compared to chitosan and natural materials used alone has been seriously examined and compared. The Cu adsorbability and its adsorption capacity on different biosdsorbents are the main parameters derived from the adsorption studies. These parameters are presented in Table 1 for the studies with pure chitosan, sand, clay, soil, and different weight percentage of chitosan-coated sand in four hours contact time, respectively. The best Cu adsorption capacity was obtained for the highest Cu concentration used in all current studies of 2000 mg/L, regardless of the adsorbent type. However, different values of Cu adsorption capacity were obtained for each adsorbent used in this study. The best adsorption capacity was obtained in the case of chitosan-coated sand with a value of 260 mg Cu adsorbed per g chitosan (5 % chitosan-coated sand), followed by chitosan with 184 mg Cu adsorbed per g chitosan (used alone). Sand only resulted in 2.04 mg Cu adsorbed per g sand. Clay resulted in 6.17 mg Cu adsorbed per g clay. Among three natural materials, soil executed the best result in 7.89 mg Cu adsorbed per g soil. This was both surprising and encouraging at the same time. Thus, by coating the sand with chitosan, this study created an adsorbent that is not only less expensive than chitosan, but also displays much better adsorption capacity than any of its components used alone (sand or chitosan). Table 1 Copper adsorption parameters from studies with different bioadsorbents in four hours contact time

Sand

100

16 (0.20)*

500

13 (0.78)

*

12 (1.39)

*

1000 2000 *

Cu2+ Adsorbability, % (Cu2+ Adsorption Capacity, mg Cu2+/g chitosan)

Cu2+ Iron Conc. (mg/L)

Clay

8.50 (2.04)

Soil

Chitosan

72.1(0.87) * 98.2(1.18) *

*

49.8(2.99)

*

42.3(5.07)

*

25.7(6.17)

*

Chitosan-Coated Sand 1%

2.5 %

5%

99 (24.9)

15.9(19.1)

20.8(10.0)

99 (25.1)

68.1(4.08)

*

92 (116.2)

13.0(77.8)

17.8(42.8)

99 (124.5)

47.9(5.75)

*

66 (165.9) 10.8(130.1) 12.9(62.1)

93 (235.4)

32.9(7.89)

*

36 (184.2)

8.5(203.5)

12.4(118.8) 52 (260.5)

2+

In this case mg Cu /g of natural material only (sand, clay and soil)

The explanation may lie in the three dimensional structure, which is different for each of the adsorbents used, and thus may fit differently with Cu’s ionic size. It is well knowing that the amine groups in chitosan possess the best active sites for the formation of complexes with metallic ions, which are stabilized by coordination(22). The maximum binding capacity of chitosan to heavy metals may decrease as the amount of acetyl groups in its structure increases. As the adsorption of heavy metals onto chitosan is stabilized by the interaction between amine groups and metallic cations, it can be considered that when the amount of amine groups increases, in case of decreasing acetyl groups by connecting with sand particles in


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the chitosan network, the maximum binding capacity also increases. Equilibrium isotherms studies for Cu2+ ions The Langmuir isotherm assume that the adsorption occurs in monolayer or may only occur in a fixed number of definitive localized sites on the surface, and that each site may adsorb only one molecule (monolayer). All sites are equivalent and no interaction may be observed between adsorbed moieties and adjacent molecules. The Langmuir isotherm considers that the energies and enthalpy resulting from the adsorption phenomenon are the same(20). The equation for this isotherm is represented by:

Cads =

KLCeq C max bCeq = 1 + bCeq 1 + bCeq

where, C max b = K L 1 1 b = + C ads K L K L Ceq Where Cads = amount of Cu (II) adsorbed (mg/g); Ceq = equilibrium concentration of Cu (II) in solution (mg/L); KL = the Langmuir equilibrium constant (L/g); b = the Langmuir constant (L/mg). The constant b in the Langmuir equation is related to the energy or the net enthalpy of the adsorption process, while the constant KL can be used to determine the enthalpy of adsorption. In our case, the experimental values of the isotherms were used in the linear forms of the Langmuir equation. This equation is valid for monolayer adsorption. The model contains a limited number of sites and predicts a homogeneous distribution of adsorption energies. The Langmuir isotherms for pure chitosan, sand, clay, and soil are shown in the Fig. 2(a), and its liner repolts were evaluated by correlation coefficients (R2) was obtained from Fig. 2(b). Figure 3(a) shows the Langmuir isotherms analysis for different weight percentage of chitosan-coated sand, and its liner replots were classified as Fig. 3(b). The Langmuir isotherms constants studied were Cads Ceq, kL, b, and R2 which are summarized in Table 2.

Fig. 2 (a)Adsorption isotherm for pure chitosan, sand, clay and soil (b)Langmuir replots of Cu2+ adsorption onto pure chitosan, sand, clay and soil

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Fig. 3 (a)Adsorption isotherm for different weight percentage of chitosan-coated (b)Langmuir replots of Cu2+ adsorption onto different weight percentage of chitosan-coated

Table 2 Langmuir isotherms parameters from adsorption studies with different bioadsorbents R2

kL

b

Cmax

Sand

0.9994

0.0025

0.0008

3.27

Clay

0.9814

0.0683

0.0136

5.04

Soil

0.9816

0.8092

0.1440

5.62

Pure Chitosan

0.9968

1.2555

0.1662

7.55

1 % CCS

0.9999

0.0024

0.0007

3.38

2.5% CCS

0.9989

0.0033

0.0007

4.50

5 % CCS

0.9984

2.9762

0.2738

10.87

There are many studies indicating that adsorption of metals by chitosan is described by different experimental models, depending on the metal. Most studies in the case of Cu, reported the Langmuir model as best describing the equilibrium isotherms. Within the concentration range studied, the equilibrium data in this study fit very well for both bioadsorbents and different weight percentages of chitason coated sand using the Langmuir model with very high correlation coefficients. Therefore, it is assumed that the adsorption of copper ions occurs through monolayer on homogenous adsorption sites of both bioadsorbents and chitason coated sand. In the comparisons of natural materials (sand, clay, soil and chitosan), the maximum monolayer amount (Cmax) of copper adsorbed on chitosan shows the highest value (7.55 mg/g) among all kinds of bioadsorbents. Moreover, sand, clay, and soil exhibit their maximum adsorption capacities as 3.27 mg/g, 5.04 mg/g, and 5.62 mg/g, respectively. Based on the previous study, Ali Awan et al. indicated that the amount of metal adsorbed to form monolayer on sand, obtained from Langmuir isotherm, exhibited the preference of metals for sand in the order Pb>Cr>Cu>Zn. The metal adsorption on sand can be illustrated on the basis of the interaction between surface functional group of silicates (sand) and the metal ions. It is deduced that sand can be used as a low cost adsorbent for the removal of heavy metal from wastewater(23).


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Clay has the capability to attract metal ions because of the negative charge on the structure of clay minerals. Among clay minerals, montmorillonite has the highest cation exchange capacity(21). Soil is the natural material which contains sand, silt and clay. In this study, clay and soil as bioadsorbent illustrated higher adsorption capacities than sand. It is deduced that clay and soil have higher potential to be immobilized on chitosan as geologically readily available supports. However, the object of this study is to exhibit the most cost-effective solution by investigating a new adsorbent material based on chitosan immobilized on natural materials. Sand is a proper and inexpensive material and often used as the filter component in the wastewater treatment process. For practical and economic consideration, sand was firstly chosen as immobilization support for chitosan. 1%, 2.5% and 5% of chitosan-coated sand exhibit their maximum adsorption capacities as 3.38 mg/g, 4.50 mg/g, and 10.87 mg/g, respectively. The best adsorption capacity was obtained in the case of 5% chitosan-coated sand, which is better than chitosan used alone (7.55 mg/g). This Langmuir analysis indicated that the site homogeneity on bioadsorbent may result from the chitosan NH3+ groups being the main active adsorption sites. The sand particles with appropriate weight distribution onto chitatson increase the amounts of amine groups, which finally enhance the maximum binding capacity with metallic ions in the chitosan-sand network. Concerning the ratio of nitrogen concentration to that of Cu in the chitosan-sand network for each adsorbent used after the completion of adsorption studies, the calculation result was shown as Table 3. It is believed that the smaller the ratio the better the adsorbent capacity, as most of the amino groups would bind Cu. Thus, 5 % chitosan-coated sand was, from this perspective, a better adsorbent compared to chitosan used alone and the other weight percentages coasted with chitason. Therefore, the results of this study illustrated that the potential for copper removal in aqueous solution by 5% chitosan-coated sand, which can be considered as the important practical implications when building filters along a contaminated stream of groundwater or the applications of wastewater treatment. Table 3

The ratio of N/Cu from different Cu adsorption studies Bioadsorbents

Chitosan-Coated Sand

N/Cu(II)

1 % weight percentage

4.83

2.5 % weight percentage

3.63

5 % weight percentage

1.50

Pure Chitosan

2.28

CONCLUSION Different natural materials, including sand, soil, clay and chitosan, have been carefully examined by Cu adsorption study and Langmuir isotherms analysis. The results confirmed that clay (5.04 mg/g) and soil (5.62 mg/g) illustrated higher adsorption capacities than sand (3.27 mg/g). In the real applications, sand is a proper and inexpensive material and often used as the filter component in the wastewater treatment process. For practical and economic consideration, sand was chosen as immobilization support for chitosan to uptake the metallic ions in this study. 2+

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Different weight percentages of chitason-coated sand (1%, 2.5% and 5%) on Cu2+ adsorption study have been executed. The adsorption capacity of 5 % chitosan-coated sand (10.87 mg/g) was a better adsorbent compared to chitosan used alone (7.55 mg/g), 1% (3.38 mg/g) and 2.5% (4.50 mg/g) weight percentages coasted with chitason. Thus, this result also illustrated that the potential for copper removal in aqueous solution by 5% chitosan-coated sand, which can be considered as the important practical implications when building filters along a contaminated stream of groundwater or the other applications in wastewater treatment.

ACKNOWLEDGEMENT This work is supported by National Science Council (Project Number: 96-2221-E-041-003). In addition, we would like to express our deep appreciation to Professor Teh-Fu Yen in Department of Civil and Environment Engineering, University of Southern California, USA for his kindly assistance in consulting and technical supports.

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ANNUAL BULLETIN V O L . 3 3 , P P. 9 6 － 1 0 6 , 2 0 0 7

使用幾丁聚醣固化於天然物質吸附水中銅金屬之研究萬孟瑋* 甘其銓* 林敬涵** Buenda D. Rogel*** 吳君豪* *嘉南藥理科技大學環境工程與科學系 **嘉南藥理科技大學醫藥化學系 ***菲律賓大學地利門分校環境工程系

摘

要

隨著工業快速的發展，重金屬污染已形成了一種全球性的危害。存在於土壤及地下水中的重金屬，經由直接或間接的管道，造成環境及人體的傷害，因此，如何有效的處理地下水之重金屬污染之問題，已成為現今環工界之重要課題。水中重金屬污染整治可分為「控制」及「處理」二個部分，而傳統的復育技術著重於化學物理處理方法，成本較高且易破壞污染現地；而生物復育技術是一經由管理或自然發生的過程中，以微生物將污染物降解或轉移成較低毒性或無毒性的型態，藉此降低或排除環境污染物，且處理技術本身不會造成環境二度傷害，是一成本低廉且政府、社會大眾接受度高的處理方式。生物高分子聚合物(Biopolymer)，為生物可分解材料(Biodegradable Materials)，已成為許多產業未來研發的趨勢。生物可分解材料的製成是以天然的生物材料為基質，如：微生物、植物與動物等。生物可分解材料於使用後，可用堆肥的方式回歸於大自然，滋養微生物、植物與動物，所以原料來源可不斷重複取得，符合「永續再生」的原則。有鑑於此，從昆蟲、水生甲殼類動物(蝦、蟹等)之外殼及真菌類之細胞壁中取得之幾丁質與幾丁聚醣，因其化學結構、反應特性及可塑性性質，已廣泛的被應用於重金屬之吸附試驗。本計畫以綠色設計為概念，使用生物可分解之材料，如：幾丁聚醣、黏土(Clay) 及沙子(Sand)等，進行重金屬的吸附可行性研究。首先，找尋研製不同重量比的幾丁聚醣結合沙子為吸附劑之最佳化操作條件，並針對重金屬銅(Cu)進行吸附及等溫吸附模式之探討及評估。實驗結果顯示：沙子具有吸附銅金屬的能力(Langmuir等溫吸附之最大吸附量：3.27 mg/g)；基於經濟因素及實用性考量，選用沙子與幾丁聚醣之結合，當其重量比率為5%時具有最高的吸附容量(10.87 mg/g)，甚至高於幾丁聚醣單獨使用之最大吸附量(7.55 mg/g)，故5%的幾丁聚醣－沙子聚合物可以考量作為廢水處理技術中吸附重金屬之生物吸附劑。關鍵字：幾丁聚醣、生物高分子聚合物、吸附、重金屬、天然物質、地下水污染復育