Adsorption of Chlorhexidine Digluconate on Acid Modified Fly Ash: Kinetics, Isotherms and Influencing Factors
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Environ. Eng. Res. 2020; 25(2): 205-211 pISSN 1226-1025 https://doi.org/10.4491/eer.2018.412 eISSN 2005-968X Adsorption of chlorhexidine digluconate on acid modified fly ash: Kinetics, isotherms and influencing factors Astha Singh, Sonalika Sonal, Rohit Kumar, Brijesh Kumar Mishra† Department of Environmental Science and Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad-826004, India ABSTRACT Chlorhexidine digluconate (CHD) in the aquatic environment causes irreversible change to microbes, making them resistant to biodegradation, which needs remediation other than biological process. Adsorption study was performed for the removal of CHD on fly ash (FA) as a function of pH and ionic strength. Experimental result has been validated by characterization using Scanning electron microscopy, Fourier Transform-Infrared Spectroscopy and Brunauer-Emmett-Teller. CHD adsorption with FA showed an increasing trend with an increase in pH. Variation in pH proved to be an influential parameter for the surface charge of adsorbent and the degree of ionization of the CHD molecules. The adsorption capacity of CHD decreased from 23.60 mg g-1 to 1.13 mg g-1, when ionic strength increased from to M. The adsorption isotherms were simulated well by the Freundlich isotherm model having R2 = 0.98. The Lagergren’s model was incorporated to predict the system kinetics, while the mechanistic study was better explained by pseudo-second order for FA. On the basis of operational conditions and cost-effectiveness FA was found to be more economical as an adsorbent for the adsorption of CHD. Keywords: Adsorption, Chlorhexidine digluconate (CHD), Fly ash, Isotherm and Kinetics 1. Introduction CHD molecules is also cramped due to its byproduct formation p-chloroaniline, which has rapid adsorption and metabolizing prop- erty, being hemotoxic and carcinogenic [6-7]. Therefore, the content Among the water pollution issues, pharmaceutical and personal of p-chloroaniline in mouthwash and the use of CHD at higher care product have attracted more and more attention as novel emerg- concentration limited by Pharmacopeias [8]. Moreover, CHD has ing contaminants by the scientific community and common public been selected as a target compound due to its accumulation in as well [1]. High pollution load to the aquatic ecosystem contains the aquatic environment, affecting the aquatic life, sewage micro- oodles of disinfectant and antibiotics such as Diclofenac, Naproxen, organisms as well as drinking water quality [6]. Ibuprofen, Sulfamethazine, Sulfamethoxazole, Sulfathiazole and The mode of action and mechanism of pharmaceutical waste Chlorhexidine Digluconate (CHD) [2]. The disposal and degradation (PhW) and personal care products (PCPs) in the aquatic ecosystem of such persistent pollutants by natural means are a difficult attempt, is tremendously uncertain. They are pervasively connected to their although they affect water quality and potentially impact drinking action on molecules, cells, lymphatic organs and human health water supplies [3]. CHD (Fig. S1) is cationic molecules [1,6-bis [6]. Composition and quantity of wastewater generated from the (4-chloro-phenylbiguanido) hexane], a widespread antimicrobial agent used extensively in dentistry and veterinary such as mouth- pharmaceutical industries play a crucial role in their treatment. wash, toothpaste, skin cleanser and some pre-operative skin prepa- Several treatment methods such as chemical oxidation, photolytic, ration, frequently used in daily life. The widespread incorporation photocatalytic treatment, biodegradation can be used to remove of CHD in a vast array of pharmaceutical and personal care product a wide array of pollutant generated from the pharmaceutical industry results in direct discharge into the aquatic environment after their [9-11]. These treatment methods have some drawbacks such as use [4]. Presence of CHD in the aquatic system at higher and lower high cost, generation of a residual or secondary pollutants or concentration reported as “bacteriostatic agent “and “bactericidal by-products, longer duration of treatment and insufficient removal agent”, making them resistant to biodegradation [5]. Stability of efficiency, limiting the use of these treatment technologies [9]. This is an Open Access article distributed under the terms Received November 23 2018 Accepted March 7, 2019 of the Creative Commons Attribution Non-Commercial License † (http://creativecommons.org/licenses/by-nc/3.0/) which per- Corresponding author mits unrestricted non-commercial use, distribution, and reproduction in any Email: [email protected] medium, provided the original work is properly cited. Tel: +91-9471191704 Copyright © 2020 Korean Society of Environmental Engineers ORCID: 0000-0002-4451-1924 205 Astha Singh et al. Conversely, numerous favorable features of adsorption processes (1.19%), MgO (0.612%), and Na2O (0.034%) was used in the present such as efficiency, simplicity, the capability of trace pollutant re- study. The BET surface area and porosity analyzer (Autosorb-1C, moval and no further by-product formation made it an alternative Quanta chrome, USA) were used to obtain surface area, pore size method for removal of PhW and PCPs. Adsorption could be easily and pore volume under the influence of nitrogen gas at particular scaled up from a laboratory to an industrial application with high temperature 77.3 K. The surface morphology and topography of removal efficiency [12-15]. the adsorbent were studied using a FESEM (Zessis, Germany). FTIR The most commercialized adsorbent is activated carbon (AC) spectrophotometer (Perkin Elmer) was used to determine the pres- that has been used for the past few decades. But regeneration ence of the functional groups on the surfaces of the adsorbent, and cost effectiveness play a major role in the use of AC on large participated in the adsorption process. scale is difficult. Fly ash (FA) has received remarkable attention to overcome the cost-related problem. FA modified as a new low-cost 2.3. Batch Experiment for Adsorption AC due to its porosity, sphericity, high strength, non-toxicity and The adsorption experiments were carried out in 250 mL Erlenmeyer light weight property [16]. Use of FA as an adsorbent has dual flasks by mixing 0.2 g L-1 of FA with 100 mL of pharmaceutical benefit: i) removal of pharmaceutical and PCPs from the aquatic synthetic wastewater, containing different amount of CHD (ranging environment and ii) also maintaining the sustainability of the ther- from 10 ppm - 500 ppm). The agitation speed of the mixture was mal power plant by-product generation [17]. Experimental pH and maintained at 200 rpm in orbital rotator shaker (Remi Shaker in- alkaline condition of wastewater generated from the pharmaceutical cubator, CIS-24 PLUS) at a range of 293.15-308.15 K for 60 min. industry play a key role in the selection of adsorbent [18-19]. Easy The pH (Hanna, India) of the solution was adjusted with 1 N NaOH availability of FA for the adsorption process prompts sustainable or 0.1 N HCl solutions. The samples were then filtered through treatment technology as compared to the use of AC. a filter paper (Whatman filter paper 42), and the concentration Adsorption of personal care product including CHD using tradi- of CHD in the filtrate was estimated spectrophotometrically, at tional adsorbents (AC) has been well proved as it could not cause 275 nm using a UV-Vis spectrophotometer (Lab Tech 9100A, China). any by-product formation during adsorption, but the adsorption of compounds like CHD with AC needs pH modification of waste- water of pharmaceutical industry before adsorption process. The × (1) effluent from the pharmaceutical industry is well known for their alkaline nature and pH modification before treatment will cause Where, is the initial concentration of CHD in the solution economic and environmental complication. To overcome this issue (mg L-1), is the concentration of CHD (mg L-1) at time t. the FA has been modified accordingly to achieve adsorption of CHD in alkaline condition. To understand the adsorption mecha- nism of modified FA, isotherm and kinetics studies were carried (2) out and the property of adsorbent was examined by SEM, FTIR and Brunauer-Emmett-Teller (BET) analysis. Where, is the initial concentration of CHD in the solution -1 -1 (mg L ), is the concentration of CHD (mg L ) at time t, 2. Materials and Methods is the volume of solution (L) and is the mass of adsorbent (g), -1 (mg g ) is the adsorption capacity at time t. 2.1. Chemicals and Sample Preparation Standard solution of CHD (20% w/v) was purchased from 3. Results and Discussion Sigma-Aldrich. AC derived from charcoal, Sodium hydroxide (NaOH), Hydrochloric acid (HCl), Sodium chloride (NaCl) was pro- 3.1. Selection of Adsorbent cured from Merck, India. Dissolved accurately weighed standard solution of CHD in 1 L of Milli-Q, RO water (Millipore, USA) To understand the working pH during adsorption process, the to prepare 1,000 mg L-1 CHD stock solution and serial dilution “pHpzc” analysis was carried out for both the adsorbents and found of the samples were carried for the lower concentration. FA was 4.5 and 7.0 for AC and FA, respectively (Fig. S2 and S3). The collected from Maithon Power Plant, Jharkhand. “pHpzc” value for FA was found more favourable for adsorption of a selected pollutant, i.e. CHD as it has cationic property. The 2.2. Adsorbent and Their Characterization working pH of FA as an adsorbent was observed 8.5 which support the adsorption of CHD without further modification in the pH In the present study, the FA was collected and sieved into a fine of wastewater. Keeping this fact, further study for AC was not powder product and samples were washed number of times with investigated, and a detailed study was carried out with FA. warm distilled water (333.15 K) to remove the impurities. Chemical washing of FA was performed by 10% concentrated sulfuric acid 3.2. Characterization of Adsorbent using vacuum filtration system followed by washing with distilled water and kept in the oven at 383.15 K for drying and activation The surface morphology of the adsorbent before and after adsorption before using it as an adsorbent [20].