Biosorption of nickel onto treated alga (Oedogonium hatei): Application of isotherm and kinetic models

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Abstract

Oedogonium hatei was developed into an effective and efficient adsorbent for the removal of Ni(II) ions from aqueous solution. The adsorption studies of untreated and treated algal biomass (with 0.1 M HCl) were compared in batch mode. Optimum biosorption conditions were determined as a function of pH, biomass dosage, contact time, and temperature and the Langmuir and Freundlich isotherms were found applicable in terms of relatively high regression values. The maximum monolayer adsorption capacity of the biosorbents (untreated and acid-treated algae), as obtained from the Langmuir adsorption isotherm, was found to be 40.9 and 44.2 mg/g, respectively at 80 min contact time, 5.0 pH, 0.7 g/L algal dose, and 298 K temperature. The thermodynamic parameters showed that the adsorption of Ni(II) ions onto algal biomass was feasible, spontaneous, and exothermic under the studied conditions. Kinetics of adsorption followed both first- and second-order rate equations and the process involving the rate-controlling step is complex involving boundary layer as well as intraparticle diffusion processes. The FTIR results of algal biomass showed that biomass has different functional groups and these functional groups are able to react with metal ion in aqueous solution. Biosorbent could be regenerated using 0.1 M NaOH solution, with up to 70% recovery. The performance of this biosorbent was then compared with many other reported biosorbents for nickel removal and it was observed that the proposed adsorbent is effective in terms of its performance.

Graphical abstract

Effect of pH on the uptake of Ni(II) Cr(VI) onto untreated and acid-treated Oedogonium hatei algal biomass.

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Introduction

Heavy metals continue to pose a serious threat to biota, due to their acute toxicity, nonbiodegradable nature, and buildup of high concentrations in water bodies all over the world. Hence, developing strategies for their control and reducing the levels of heavy metals to their permissible limits in waste waters are major challenges for environmental scientists. Nickel(II) ion is one such heavy metal frequently encountered in raw wastewaters streams from industries such as electroplating, battery manufacturing, mineral processing, steam–electric power plants, paint formulation, porcelain enameling, and so on [1]. Ni(II) belongs to the so-called “essential” metals and is identified as a component in a number of enzymes, participating in important metabolic reactions, such as ureolysis, hydrogen metabolism, methane biogenesis, and acidogenesis [2]. But, nickel(II) ion intake over the permissible levels results in different types of disease such as pulmonary fibrosis, renal edema, skin dermatitis, and gastrointestinal distress (e.g., nausea, vomiting, diarrhea) [2]. The US Environmental Protection Agency (EPA) requires nickel in drinking water not to exceed 0.5 mg/L [3]. It is therefore, essential to remove Ni(II) from wastewater before disposal.

A number of workers have used different adsorbent systems, developed from various industrial waste materials, for the removal of toxic heavy metals and organic waste pollutants [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]. There still exists a need to develop a low-cost and efficient adsorbent material for the removal of pollutants. Recently, a biological method of heavy metal removal, termed biosorption, has been suggested as a cheaper and more effective alternative to existing treatment techniques [17], [18]. Biosorption utilizes the ability of dead/inactive biomass to remove heavy metals from solutions. The use of dead/inactive biomass is preferred over active/live biomass because living biomass cells often require the addition of fermentation media which increases the biological oxygen demand (BOD) or chemical oxygen demand (COD) in the effluent [19]. In addition, nonliving biomass is not affected by the toxicity of the metal ions, they can be subjected to different chemical and physical treatment techniques to enhance their performance, and adsorbed metals can be easily recovered from the biomass by many chemical and physical methods, leading to repeated use of the biomass and better process economy [20], [21]. The major advantages of the biosorption technology are its effectiveness in reducing the concentration of heavy metal ions to very low levels and the use of inexpensive biosorbent materials [22].

A variety of different biomass types including bacteria, fungi, algae, yeast, and aquatic plants as the biosorbent have been studied by various investigators for Ni(II) biosorption [3], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28]. Among the biomasses, algae possess relatively high binding capacities [29], [30]. They are much higher than those of activated carbon and natural zeolite, and are comparable to those of some ion-exchange resins. This is due to the presence of carboxylic, amino, and hydroxy groups in algal cell wall polysaccharides which can act as binding sites for metals [31]. There is evidence that some phenomena for metal binding, such as adsorption, complexation, ion-exchange, coordination, chelation, inorganic precipitation, and/or a combination of these take place in the cellular membrane of microorganisms [31]. External factors such as pH, temperature, concentration of metal ion, biosorbent dose, and contact time always affect the sorption of metal ions.

From a thorough literature survey, very few investigations have been reported for biomonitoring nickel pollution with green filamentous algae [2], [22], [28]. Also, nickel is a metal whose recovery is one of the poorest; thus, it would be interesting to find a selective biomass able to adsorb this metal from highly contaminated effluents. So, in the present study, the feasibility of using Oedogonium hatei, filamentous alga found in submerged waters in many tropical countries of the world as a potential biosorbent for removing nickel from aqueous solutions is planned. This new material was chosen as biosorbent in this study as it is natural, easily available, and thus a low-cost biomass for dissolved metal ions. Also, this material has shown good biosorption ability for Pb(II), Cd(II) and Cr(VI) metal ions in our earlier communications [32], [33], [34]. It is pretreated with acid to enhance the sorption performance and also to strengthen it for sorption process applications. So, the untreated and acid-treated forms of alga O. hatei were utilized for the removal of toxic nickel metal ion. Optimum biosorption conditions were determined and various equilibrium isotherms and kinetic models were applied. In addition, nickel(II) ion desorption studies using 0.1 M NaOH were performed for three adsorption–desorption cycles to evaluate the sorbent for reuse. The information obtained from these studies was expected to indicate whether the untreated and acid-treated forms of alga have the potential for the removal and recovery of Ni(II) ions from aqueous solutions.

Section snippets

The test alga

O. hatei is an epiphytic or epilithic alga, collected from a nearby pond, and washed several times with Milli-Q water for removing from its surface interfering ions and other undesired materials, such as sand particles and debris. The alga is sun-dried for 3 days followed by heating the biomass at 343 K for 40 min and thereafter referred to as untreated alga. The native algal biomass is also transferred into 0.1 M. HCl solutions and the mixtures were stirred at 200 rpm for 8.0 h at room temperature;

Characterization of the biosorbent

The physical and chemical properties of the algal biomass were determined by the standard methods as reported in our earlier publications [32], [33], [34], [35]. Changes in the functional groups and surface properties of the biosorbent were confirmed by FTIR spectra. The spectra revealed biosorbent heterogeneity, evidenced by different characteristic peaks with the possible presence of amino, carboxylic, hydroxyl, and carbonyl groups. The IR absorption bands and corresponding possible groups

Summary

The batch studies conducted in the present study provide significant information regarding the biosorption of Ni(II) ion onto untreated and acid-treated O. hatei in terms of optimum pH, temperature, and biomass dose for the maximum removal of nickel from the aqueous solutions. The results indicate that Oedogonium sp. is an effective biosorbent for Ni(II) removal. The maximum adsorption capacity of untreated and treated algal biomass (40.9 and 44.2 mg/g) was found to have greater or comparable

Acknowledgment

The authors are thankful to MHRD, New Delhi, for providing financial assistance for this work.

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