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Comparative analysis of floating and submerged macrophytes for heavy metal (copper, chromium, arsenic and lead) removal: sorbent preparation, characterization, regeneration and cost estimation

Comparative analysis of floating and submerged macrophytes for heavy metal (copper, chromium,... GeoloGy, ecoloGy, and landscapes, 2018 Vol . 2, no . 2, 61–72 https://doi.org/10.1080/24749508.2018.1452460 INWASCON OPEN ACCESS Comparative analysis of floating and submerged macrophytes for heavy metal (copper, chromium, arsenic and lead) removal: sorbent preparation, characterization, regeneration and cost estimation † † Akhilesh Bind   , Lalit Goswami   and Veeru Prakash d epartment of Biochemistry and Biochemical engineering, s.H.U.a.T.s, allahabad, India ABSTRACT ARTICLE HISTORY Received 20 a ugust 2017 In this study, a comparative evaluation of floating and submerged macrophytes was performed. a ccepted 15 d ecember 2017 Azolla filiculoides (free floating) and Hydrilla verticillata (submerged) aquatic macrophytes were utilized for arsenic, copper, chromium and lead removal from the respective metallic ion KEYWORDS solutions. Batch experiments were performed initially with optimization of different physical Biosoption; heavy metals; parameters viz., pH, initial heavy metal concentration, biosorbent dosage, contact time, aquatic macrophytes; temperature and agitation speed. Submerged (Hydrilla verticillata) had depicted better removal Azolla filiculoides; Hydrilla efficiency in comparison to the floating macrophyte (Azolla filiculoides). Field emission scanning verticillata electron microscopy equipped with energy dispersive spectroscopy and Fourier transform infrared spectroscopy analysis was performed for the characterization of the metal loaded biosorbents. Biosorption of the respective heavy metal was clearly depicted in the FESEM-EDX spectrum, although not much change in the morphology of the biosorbents were examined. FTIR spectra of the biosorbents obtained after the experiments confirmed the involvement of C–H bend, –CH –(C=O), N–H, –C–O, R –C= bending and –C–C=O on the biomass. Furthermore, 2 2 the biosorbent regeneration followed by heavy metal biosorption confirmed the reusability of the prepared biosorbent for at least two consecutive cycles without much significant change in the heavy metal biosorption capacity. 1. Introduction flocculation, electro-flotation, electrochemical treat- ment, ion exchange, reverse osmosis, advanced oxi- e ra Th pid increase in the anthropogenic activities such dation and membrane separation have been utilized as mining operations, smelting, chemical, paint, ferti- (Anastopoulos & Kyzas, 2015). Among aforementioned lizer, pesticide processing plant, leather industries and techniques, biosorption is  found to be the most eco- electronic manufacturing discharge has increased the nomical, efficient, passive and widely accepted process, amount of metal-containing wastewater into the aquatic as biosorbents are eco-friendly, effective, readily avail- environment (Goswami, Manikandan, Pakshirajan, & able in huge quantity and also does not produces any Pugazhenthi, 2017; Yu, Li, & Liu, 2017). The discharge by-products aer t ft he treatment (Yu et al., 2017). of heavy metals into the environment without any prior Various literatures have been reported with the aim treatment is diminishing the water quality to frighten- of utilizing different biosorbents, such as chitosans, ing levels, thereby posing its lethal effect on to the liv- nano-biosorbents, barks, wastes from food and edible ing organisms (Martin, Turnbull, Rissmann, & Rieger, oil industries and agricultural wastes, for the heavy metal 2017). Heavy metals tend to accumulate and concentrate removal (Anastopoulos & Kyzas, 2015). Taking into in the living tissues through the food chain, imposing consideration of the above-mentioned aspects, present its adverse impact on human health (Etesami, 2018). work was emphasized on heavy metal removal from the Henceforth, treatment of wastewater containing heavy simulated aqueous heavy metal solutions individually by metals prior to their discharge is mandatory due to the utilizing macrophytes. Earlier several researches had per- increasingly restrictive legislation (Arul Manikandan, formed this phenomenon by accounting macrophytes Alemu, Goswami, Pakshirajan, & Pugazhenthi, 2016). as a potential biosorbent and some have been enlisted For the treatment of wastewater contaminated in Table 1. An attempt was made for the comparative with heavy metals, numerous treatment technologies analysis between two different categories of macrophytes viz., floating and submerged and hence was performed viz., adsorption, coagulation, chemical precipitation, CONTACT akhilesh Bind akhilesh.bind@shiats.edu.in equal author contribution. © 2018 The a uthor(s). published by Informa UK limited, trading as Taylor & Francis Group. This is an open a ccess article distributed under the terms of the creative c ommons a ttribution license (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 62 A. BIND ET AL. Table 1. literature reports on Azolla filiculoides and Hydrilla verticillata utilization for heavy metal removal. Maximum uptake S. No. Biosorbent Heavy metal capacity pH Isotherm Removal (%) References 1. Azolla filiculoides cs 195 8 Freundlich – Mashkani and Ghazvini sr 212.1 9 – – (2009) 2. Azolla filiculoides au 98 – – 98.2 Umali, d uncan, and Burgess (2006) 3. Azolla filiculoides au – 2 – 100 antunes, Watkins, and d uncan (2001) 4. Azolla filiculoides ni 45.32 7.8 langmuir – ahmady, Mohammadi, Bahrami, Monfared, and Jafari (2011) 5. Azolla filiculoides cu 363 – – 75 Fogarty et al. (1999) (Immobilized) 6. Azolla filiculoides cr 10.6 2 langmuir, Freundlich 83.34 Babu, sumalatha, Ven- kateswarulu, das, and Kodali (2014) 7. Azolla filiculoides Zn 45.2 6.0 – – Zhao et al. (1999) 8. Azolla filiculoides ni 43.4 6.5 Batch and c olumn 60 Zhao and d uncan (1998) study 9. Hydrilla verticillata pb 2.14 5.0 pseudo-second-order 85.7 chathuranga et al. (2014) 10. Hydrilla verticillata as 11.65 6 langmuir – n igam Vankar, and Gopal (2013) 11. Hydrilla verticillata cd 15 5 langmuir – Bunluesin et al. (2007) 12. Hydrilla verticillata cd 50 6 – – Huang et al. (2010) 13. Hydrilla verticillata cr 29.43 4 langmuir and – Mishra, Tripathi, and Rai ni 48.72 Freundlich (2014) 14. Hydrilla verticillata cr 8–69.9 1 langmuir >60 pilli , Goud, and Mohanty 15. Hydrilla verticillata cr 89.32 – – – Mishra, Tripathi, and Rai ni 87.18 (2016) 16. Hydrilla verticillata cr 247 3 langmuir – Baral, das, chaudhury, and das (2009) to examine the removal efficiencies. The heavy metals River). The samples were washed thrice with deionized tested in this study were copper (Cu (II)), chromium (Cr water (approximately 18.1 Ω resistance) to remove extra- (VI)), arsenic (As (III)) and lead (Pb (II)). Optimization neous materials (each time; 50 mL for 20 min) and was of the batch study was performed individually to deter- air-dried. Azolla and Hydrilla species (as the non-living mine the optimal biomass dose, heavy metal concentra- biomass) were then crushed in mortar-pestle and sieved tion, pH, contact time and temperature for heavy metal to the powder form (size – 0.075 mm) prior to their uti- removal from the aqueous solution. Furthermore, the lization. Pre-treatment for the activation of the samples heavy metal removal process was further investigated was performed by soaking 2 g of each sample in NaOH employing field emission scanning electron microscopy (1.0 M) at pH 9.5 for 5 h. Already it is well established (FESEM) equipped with energy dispersive spectroscopy that demethylation of pectin results in enhancement (EDX) and Fourier transform infrared spectroscopy of –COOH groups, and may be catalysed using alkali (FTIR) analyses. solutions (Rakhshaee, Khosravi, & Ganji, 2006). Pectin is protonated to remove excess cations such as Na or 2+ Ca that could interfere with heavy metal sorption and 2. Materials and methods to generate a more distinct and suitable biosorbent. 2.1. Metal stock solution preparation Subsequently, for removing the excess sodium (Na), the samples were washed twice with deionized water Analytical grade chemical salts and reagents were uti- (50  mL, 5  min). Further, the samples were soaked in lized throughout the experiment procured from Merck 250 mL of CaCl solution with the total concentration (Mumbai, India). Individual heavy metal stock solutions of 2 M and volume ratio of 2:1:1, respectively. pH was of Cu (II), Cr (VI), As (III) and Pb (II) of concentra- −1 adjusted with 0.5  M HCl at 7.0  ±  0.2. These activated tion 1000 mg L each were prepared using CuCl ·H O, 2 2 samples were oven-dried at 65° ± 2 °C for 8 h i.e., until K Cr O , As O and PbNO , respectively, in deionized 2 2 7 2 3 3 they reached a constant weight. The agitation rate for the distilled water. Subsequent volume of metal solution was activation was fixed at 150 rpm at 25° ± 2 °C. Followed prepared with proper dilution. by drying, grinding and sieving the samples for their further utilization in the absorption experiments. 2.2. Collection and pre-treatment of fresh water macrophytes 2.3. Biosorbent characterization Freshwater macrophytes, Azolla filiculoides (free e Th prepared biosorbents (aer ft the pre-treatment) were floating) and Hydrilla verticillata (submerged), as the further characterized chemically, physically and mor- potential biomass were collected from the pond surface phologically as detailed ahead. near Salori, Allahabad, India (eastern shore of Yamuna GEOLOGY, ECOLOGY, AND LANDSCAPES 63 e a Th sh content of the two biosorbents was analysed pH of the solution (2–7), solution temperature (293, by following the ASTM D1762-84 standard. 1 g of each 303 and 313 K), initial metal concentration (10, 20 and −1 −1 sample was incinerated at 650 °C in presence of air for 50  mg L ), biosorbent dose (1–5  g L ), contact time 12 h in a muffle furnace (LabTech, India). The elemental (0–180 min) and agitation speed (50–300 rpm). All the compositions of the biosorbents were determined using flasks were kept in the rotary shaker with the respective an elemental analyzer (Eurovector EA3000, Germany). process parameters for determining the biosorption effi - e zet Th a potential (ZP) and average particle size were ciency. A brief schematic of the overall experiment is TM measured using a laser particle size analyzer (Delsa shown in Figure 1. Nano, Beckman Coulter). For examining the contact angle (CA), the sessile drop method was followed 2.5. Heavy metal quantification (Bachmann, Goebel, & Woche, 2013). e q Th uantification of heavy metals aer ft the batch shake Surface morphology of the biosorbents was analysed experiments was reported in the percentage removal by utilizing field emission scanning electron microscope according to the equation (1). Heavy metal concentra- at ultra-high resolution (FESEM, Zeiss, Sigma, Germany) tions were analyzed by atomic absorption spectroscopy equipped with energy dispersive spectroscopy (FESEM- (Perkin Elmer Analyst 400, England) as per the American EDX). The sample was surmounted onto the copper Public Health Association standards (American Public stub using a carbon tape and a fine doubled-coating of Health Association [APHA], 2005). gold were performed prior to the analysis for making the samples more conductive. The sample images were C − C o e recorded at an operating condition of 3.0 kV (Goswami, Heavy metal removal (%) = × 100 (1) Kumar, Arul Manikandan, Pakshirajan, & Pugazhenthi, 2017). where C and C , the initial and final heavy metal concen - For determining the surface functional groups pres- o e −1 trations (mg L ) present in the solutions, respectively. ent in the two biosorbents was analysed using a Fourier transform infrared (FTIR) spectrophotometer (IR Affinity, Shimadzu, U.S.A.). An average of five scans was 2.6. Regeneration of the exhausted biosorbents −1 collected for each analysis (400–4000 cm ) (Goswami, and cost estimation Tejas Namboodiri, Vinoth Kumar, Pakshirajan, & For determining a process to be cost-effective, desorp- Pugazhenthi, 2017). tion experiments were performed using 0.5 N HCl and 0.5  N NaOH solutions as the stripping agents. Metal 2.4. Experimental set-up loaded biomass aer t ft he biosoption was further trans- ferred to the flasks and kept in an orbital shaker for 24 h. All the batch biosorption experiments were performed Following this, filtrates were further analysed to examine in the 250 mL Erlenmeyer flasks with a working volume the percentage fraction of desorbed Cu (II), Cr (VI), As of 100 mL. For determining the effect of process param - (III) and Pb (II) metal ions to examine the percentage eters onto the biosorption phenomena, all the exper- fraction of desorbed. Successive biosorption–desorption iments were performed by taking one parameter at a cycles were repeated thrice for the similar biosorbents time. The various process parameters were as follows: Figure 1. a brief schematic of the overall experiment. 64 A. BIND ET AL. (Kaur, Singh, Khare, Cameotra, & Ali, 2013). Desorption positive capillary pressure, thus allowing water to enter efficiency for both the biosorbents was further evaluated into the pores. from the quantitative amount of metal ions desorbed FTIR is an imperative to comprehend the chemical to the metal ions adsorbed in the desorption medium, nature of individual components which controls the as per the expression (2) (Yoonaiwong, Kaewsarn, & biosoption of the heavy metals. FT-IR spectra of the Reanprayoon, 2011): prepared biosorbent samples which depict various vibra- tional frequencies due to various functional groups pres- Amount of metal ion desorbed Desorption efficiency (%) = × 100 ent in the biosorbents. Table 3 presents the respective Amount of metal ion adsorbed functional group involved in biosoption phenomenon. (2) 3. Results and discussion 3.2. Effect of different parameters on biosoption capability e ra Th w biomass of both the aquatic macrophytes were washed, dried and crushed to the desired size and both 3.2.1. Effect of pH the prepared biosorbents were further physical, chemical pH, an important parameter for the heavy metal sorption and morphological characterized. on to the biosorbent from an aqueous solution. It decides the surface charge of biosorbent, the degree of ionization and speciation of absorbate (Gupta, Pathania, Agarwal, 3.1. Biosorbent characterization & Sharma, 2013; Huang & Zhu, 2013). The functional Table 2 presents the elemental compositions and sur- groups present on the cell wall plays a significant role face properties of the two prepared biosorbents. FESEM in heavy metal biosoption (Sarada, Prasad, Kumar, & image of the two biosorbent is depicted in Figure 2 that Murthy, 2014). Biosoption mechanism involves the com- reveals a smooth and clear morphology of the mate- plex mechanism of ion exchange, chelation, biosorption rial. Also, the elemental composition of the biosorbent by physical forces, and ion entrapment (Sarada et al., materials with carbon, hydrogen and nitrogen values was 2014). In this study, the biosoption of tested heavy met- −1 evaluated. The zeta potential values of 2.19 and 3.42 mV, als was examined in the range of 10–50 mg L . Figure for Azolla and Hydrilla species, respectively, indicated 3 shows the effect of pH on biosoption heavy metal that both the biosorbent surfaces were covered with pos- through macrophytes. For heavy metal biosoption at itively charged species. low pH, there is competition between heavy metal and e a Th verage particle size of Azolla and Hydrilla spe- H ions for the absorption sites, ae ff cting the ionization cies was found to be 1042.9 and 948.2 nm with a total of functional groups onto the biosorbent surface, i.e., at 2 −1 surface area of 4.29 and 2.23 m g , respectively. Total low pH, the acidic surface functional groups tend to be ash content was found to be 67.12 and 56.28% for Azolla protonated, and henceforth, not considerably contribute and Hydrilla species, respectively. Further, the contact to adsorption reactions (Wahab, Jellali, & Jedidi, 2010). angle of Azolla and Hydrilla species was found out to be As the surface gets positively charged, therefore making 34.6° and 27.9°, respectively. In general, the hydrophilic (H ) ions compete efficiently with metal ions resulting surfaces have a contact angle less than 90° and impose in a decrease in the amount of heavy metal sorption. The maximum removal of heavy metals was found at a pH of 4 for Pb, 7 for As,  6 for Cu and 2 for Cr, respectively. These pH values were found to be sim- Table 2. elemental composition, surface and magnetic proper- ilar to the studies of prior researchers (Sarada et al., ties of the biosorbent. 2014; Swarnalatha & Ayoob, 2016). Increase in pH Elemental Surface area and from 2 to 5 had resulted in low percentage removal composition (%) pore diameter Density and above pH 6.0, complex formation of metal ions (a) Hydrilla verticillata occurs resulting in precipitation of heavy metals c (%) 62.4 BeT surface 4.29 Bulk density 0.43 area occurs (Sulaymon, Mohammed, & Al-Musawi, 2013a; 2 −1 (m  g ) Swarnalatha & Ayoob, 2016). It can well be related to H (%) 3.55 porosity 19.7% Moisture 8.72 the fact that the insoluble metal hydroxide precipitation content n (%) 1.92 pore volume 0.19     occurs at the higher pH values (Sulaymon et al., 2013a). 3 −1 (cm  g ) Whereas biosoption efficiencies of Cr (VI) for both the H/c 0.057         macrophytes was maximum at low pH (2.0) and have (b) Azolla filliculoides c (%) 53.8 BeT surface 2.23 Bulk density 0.39 been reported in the literature by many authors. Cr area 2− (VI) ions are frequently found in chromates (CrO ), 2 −1 (m  g ) 2− − H (%) 3.15 porosity 15.8 Moisture 11.2 dichromates (Cr O ) and bichromates (HCrO ) forms 2 7 4 content depending upon the pH (Gupta et al., 2013). At low n (%) 2.75 pore volume 0.09     2− 3 −1 pH, the concentration of Cr O increases whereas, at (cm  g ) 2 7 H/c 0.037         higher pH (6.0), Cr (VI) is present in solution in the GEOLOGY, ECOLOGY, AND LANDSCAPES 65 Figure 2. Micrographs of Azolla filiculoides and Hydrilla verticillata (scale bar = 500 μm). Table 3. FTIR absoption bands and their corresponding possi- other literature for the removal of tested heavy metals ble functional groups. (Kaur et al., 2013; Muthusamy, Venkatachalam, Jeevamani, & Rajarathinam, 2014). Beyond the optimum Azolla filiculoides Hydrilla verticillata Frequency Functional group −1 dosage, there was a decline in the removal efficiencies (cm ) (Free floating) (Submerged) stretch by both the biosorbents due to saturation of active pore 3500–3200 3280 3277 o –H (hydroxyl) 3000–2850 2845 2921 –c–H (alkanes) sites at the surface of biosorbent (Kamsonlian, Suresh, 1750–1735 – 1737 –c=o (aldehyde) Majumder, & Chand, 2013). Although the optimum bio- 1650–1580 1641 1610 n–H (primary amine) 1400–1370 1400 1363 –so (sulphoxide) 3 sorbent dosages of the heavy metals were attained at 2 g 1280–1150 – 1227 –c– o (alcohol, car - −1 −1 −1 L and 2.5 g L , respectively, 5 g L of the biosorbent boxylic acid, esters, ethers) dose was selected for the comparative removal efficien- 1250–1020 1019 – –c–n (aliphatic cies of heavy metal at exhaust points. Nevertheless, an amines) 900–865 873 877 –c–H (alkene) optimum biosorbent dose has been utilized for the fur- 850–830 838 – R –c= (trisubstituted ther studies. Table 1 also clearly depicts the optimized alkene) parameters for different heavy metals and macrophytes. 560–510 542 526 –c– c=o (aldehyde) pH, contact time and initial heavy metal ion concen- tration of the aqueous solution were kept invariable at 2− form of CrO (Samuel, Abigail, & Ramalingam, 2015). the optimum values for both the biosorbents as attained The presence of negatively charged sites onto the sur - from the earlier experimental results. face of biosorbent does not favour biosoption owing to the electrostatic repulsions (Gupta et al., 2013). These 3.2.3. Effect of contact time optimized pH values were chosen as further studies. Removal of As (III), Cu (II), Pb (II) and Cr (VI) at dif- It might be attributed to the decrease in the solubil- ferent contact time were studied for metal concentra- −1 ity of heavy metals at high pH (Huang & Zhu, 2013). tion (10 mg L ) at different optimum pH for respective Considering these results into account, respective pH at metals with both the macrophytes. The effect of contact which maximum removal efficiency of biosorbent was time on biosorption of As (III), Cu (II), Pb (II) and Cr attained was selected further for all the experiments. (VI) is shown in Figure 5. Uptake of metal ions occurred rapidly within 20 min and equilibrium was attained in 3.2.2. Effect of biosorbent dosage 60  min for chromium with Azolla with 88.76% and Effect of biosorbent dosage on the biosoption efficien- 40 min for Hydrilla with 91.41% and becomes constant cies of tested heavy metals by the two biosorbents were thereaer ft . (Lim, Priyantha, Tennakoon, & Dahri, 2012; determined in the range of 0.5–5  g (Figure 4). The Singha & Das, 2012) Similar fashion was observed with outcomes clearly revealed that removal (%) of all the other three heavy metal whose equilibrium time varies: four heavy metal ions boosts with an increase in the Copper showed equilibrium time of 60 min and 80.14% adsorbent dosage (Kamsonlian et al., 2012). The max- with Azolla while 30  min and 84.36% with Hydrilla, imum removal efficiency for Hydrilla verticillata was Arsenic showed 180  min of equilibrium time with −1 found at 2  g L of biosorbent dose while Azolla filli - 78.94% with Azolla and 240 min with 92.75% Hydrilla −1 culoides shows promising removal at 2.5  g L . These and lead showed 83.66% of removal at equilibrium time outcomes can well be correlated with the increase in of 90 min and 90.13% at equilibrium time of 120 min absorbent dose leading to increase in the surface area with Hydrilla. Therefore, optimized contact time was and accessibility of biosoption sites up to 2.5  g (Kaur taken for all the further experimentation (Gupta et al., et al., 2013). Similar kind of trend was depicted by several 2013). 66 A. BIND ET AL. (a) (a) Arsenic Chromium Copper Lead 23 4 56 7 pH 100 (b) (b) Arsenic Chromium Copper Lead 23 45 67 pH Figure 4. eec ff t of biosorbent dosage on heavy metal removal (%); (a) Azolla and (b) Hydrilla. Figure 3.  eec ff t of pH on heavy metal removal (%); (a) Azolla and (b) Hydrilla. could be due to electrostatic interactions among active groups and probability of higher interaction among 3.2.4. Effect of initial concentration of heavy metal them (Gupta et al., 2013; Muthusamy et al., 2014). ion However, per cent adsorption of As (III) decreased With the change in the initial concentration of Cr (VI), −1 from 87.5% and 83.5% to 44.23 and 38.8%, for Cu Cu (II), Pb (II) and As (III) from 10 mg L to 300 mg −1 (II); 80.5 and 83.3 to 41.59 and 34.25%, for Pb (II); 71 L which was analysed initially, were treated with opti- and 80.7 to 29.9 and 36.6% and for Cr (VI); 91.88 and mum biosorbent dose (0.125 g per 50 mL) of Azolla fil - 89.79% to 51.26 and 43.92% for Hydrilla and Azolla liculoides and 0.1 g per 50 mL of Hydrilla verticillata for species, respectively. This increase might be because of 40–180  min for optimized contact time of respective rapid saturation of metal functional sites on the bio- metal ions at constant biosorbent dose and temperature sorbent (Shukla & Vankar, 2012). With the increase (30 ± 2 °C). Further, the results are presented in Figure 6, in the concentration of heavy metal, the binding sites depicting the percentage removal versus initial heavy of the biosorbent are becoming more saturated and metal concentration. after a certain concentration, there will be no further es Th e results shown here are the augmentation absorption. Furthermore, for the dilute solutions, of metallic uptake on increasing Cr (VI), Cu (II), Pb metal ions have a very high mobility and therefore, the (II) and As (III) ion concentrations with both the bio- interaction with the biosorbent is very high. Here, the sorbents. The maximum uptake values correspond to −1 increase in the initial concentration of Cr (VI) and Zn 76.895, 62.38, 35.908 and 66.35 mg g of the biosorbents (II) results in the saturation of the biosorbent surface in case of Cr (VI), Cu (II), Pb (II) and As (III), respec- faster that leads to decrease in absoption (Muthusamy tively for Hydrilla verticillata and 52.7, 41.12, 54.9 and −1 et al., 2014). 46.6  mg  g for Cr (VI), Cu (II), Pb (II) and As (III), Also, at a higher concentration, the heavy metals dif- respectively, for Hydrilla verticillata correspondingly fuse on the surface of the biosorbent by intra-particle with an initial heavy metal concentration of 300  mg −1 L . The observed heavy metal removal augmentation diffusion and also the highly hydrolyzed ions will diffuse Removal (%) Removal (%) GEOLOGY, ECOLOGY, AND LANDSCAPES 67 (a) (a) (b) (b) Figure 5.  eec ff t of contact time on heavy metal removal (%); (a) Azolla and (b) Hydrilla. Figure 6.  eec ff t of initial concentration of heavy metal on it’s removal (%); (a) Azolla and (b) Hydrilla. at a slower rate. This specifies the probable monolayer formation of As (III) and Cr (VI) ions on the outer surface. be several reasons that could be ascribed: the relative increase in escaping tendency from solid to bulk phase of 3.2.5. Effect of temperature heavy metals and rupture of bonds leads to surface deac- Effect of temperature on the equilibrium sorption poten- tivation of biosorbent/weakening of forces involved in tial for Pb (II), Cr (VI), Cu (II) and As (III) ions were bond formation (Samuel et al., 2015). It could be inferred investigated in the temperature range 20–50 °C with an from results that the sorption of heavy metals/metalloids −1 initial heavy metal concentration of 10 mg L and at all onto macrophytes is an endothermic process. the previously optimized conditions. Figure 7 depicts Hence, the submerged aquatic macrophyte, H. ver- the percentage removal of heavy metals at different tem - ticilata might be efficiently utilized for arsenic removal peratures. Maximum percentage of removal of the four with very promising results (Nigam et al., 2013). In metals was attained at 30 °C. From the obtained result, it compared to the commercial adsorbents present in the could be inferred that biosorption between macrophyte market, the cost of processing this weed i.e., drying, biomass and the heavy metals might be due to prob- grinding, packaging as well as transportation, incurs the able involvement of chemical interaction and physical absolutely negligible cost. Previous studies on H. verti- adsorption (Gupta et al., 2013; Sulaymon, Mohammed, & cillata species seems to be very economical as well as an Al-Musawi, 2013b). efficient biosorbent for the removal of Cr (VI) from the With the rise in temperature (up to 30 °C), availabil- aqueous solutions. ity of surface area increases due to enlargement of pore size and leads to decrease in viscosity of the solution. 3.2.6. Effect of agitation speed Enlargement of pore size present on macrophyte aug- e b Th iosoption capacities of the two macrophytes for ments adsorption and diffusion of metal ions within the heavy metal removal in a single component solution at pores (Sulaymon et al., 2013b). A further rise in temper- different agitation speeds (50–200 rpm) were evaluated. ature (above 35 °C) leads to a decline in the percentage With the increase in the agitation speed the biosoption removal efficiency through biosorption. There might of heavy metal increases as there is an  enhancement 68 A. BIND ET AL. in the diffusion of heavy metal ions towards the bio- (a) sorbent surface .These outcomes can well be associated with the fact that the agitation speed in the range of 150–250 rpm is sufficient enough for making the surface binding sites available for heavy metal uptake for both the biosorbents (Srividya & Mohanty, 2009). Therefore, 250 rpm was chosen as the optimum agitation speed for both the biosorbent. Although Azolla took 30, 60, 90 and 180  min for copper, chromium, lead and arsenic, respectively, while Hydrilla have taken 30, 40, 120 and 240 min. Nadeem et al. (2008) reported similar results for different heavy metal biomass system. The attrac- tive forces between heavy metal and the biosorbent viz., vander waal forces, electrostatic forces and rapid pore diffusion into the intra-particle matrix help in attaining (b) the equilibrium (Gupta et al., 2013). 3.3. Characterization of the biosorbents 3.3.1. FESEM-EDX analysis For analyzing the difference in the morphology and elemental composition of the two biosorbents aer t ft he experiments, FESEM–EDX analyzes of the control bio- sorbent and the metal loaded biosorbent were carried out. From FESEM-EDX spectrum (Figure 8), clearly revealed the occurrence of the additional peak of the respective individual metal ions on the biosorbent. This further confirmed the biosoption phenomena of the heavy metal on the biosorbent surface. There were not many morphological differences were observed during Figure 7.  eec ff t of temperature on heavy metal removal (%); (a) Azolla and (b) Hydrilla. the FESEM analysis of the biosorbent. Figure 9 depicts the micrograph showing FESEM elemental mapping analysis of different metals (for lead experiment with repetitive extraction-elution cycles and reuse potential Azolla filiculoides ). (Bunluesin, Kruatrachue, Pokethitiyook, Upatham, & Lanza, 2007; Samuel et al., 2015). Desorption experi- 3.3.2. FTIR spectroscopy analysis ments were carried out in 3 cycles and with each cycle e t Th wo biosorbent depicted wide band spectra at the loss in weight of adsorbent was observed. In first two −1 around 3250  cm , which is characteristic of the cycles, loss was significant which may be due to washing hydroxyl groups (O–H) (Arul Manikandan et al., 2016) of soluble material and in the last cycle, no significant −1 (Figure 10). At 2921 cm , another band was observed weight loss due leftover biosorbent might have resistant −1 due to –CH followed by a band spectrum at 1737 cm material. A steady decrease in sorption with an increase (only in Hydrilla) corresponding to the carbonyl of ester in the number of cycles was also noticed which may due −1 groups; peak at 1641 cm was assigned to the primary to corrosive nature of acid and washing away of func- amine band spectra. The absorption band in the range −1 tional group. (Bunluesin et al., 2007; Kaur et al., 2013; 1650–1580  cm signifies the N–H (primary amine). Zhao, Duncan, & Van Hille, 1999). In addition, the FTIR spectra reveal –C–O, –C–C=O, Desorption of adsorbed As (III), Cu (II), Pb (II) and and R –C=band stretch corresponding to the functional Cr (VI) on A. filliculoides and H. verticillata biomass groups alcohol/carboxylic acid, alkene and aldehyde, were studied using 0.1 N H SO , 0.1 N HCl, 0.1 N HNO . respectively. 2 4 3 e p Th ercentage desorption varied between 65.2% for Cu, 59.45% for Pb, 71–72.6% for Cr (VI) and 81.3% for As 3.3.3. Regeneration/reusability studies of the (III) with H. verticillata. 0.1 N HCl found to be better for exhausted biosorbent desorption of chromium (VI) for H. verticillata, 0.1 N Regeneration studies were further performed to calculate HCl > 0.1 N HNO  > 0.1 N H SO whereas 0.1 N HNO the reusability potential of the bioabsorbent. The ec ffi ient 3 2 4 3 showed better desorption of adsorbed heavy metal in desorption of absorbed heavy metals from A. filliculoides and H. verticillata biomass were deemed indispensable order of 0.1 N HNO  > 0.1 N H SO . > 0.1 N HCl with 3 2 4 to make sure their sustainability for long-term usage for A. filliculoides and percentage of desorption was not GEOLOGY, ECOLOGY, AND LANDSCAPES 69 Figure 8. FeseM-ed X of Azolla filiculoides (a) control biomass and metal loaded biomass (b) chromium, (c) arsenic and (d) l ead. Figure 9. FeseM micrographs along with metal mapping of Azolla filiculoides loaded with (at 500 μm) (a) arsenic, (b) chromium and (c) l ead; depicting the respective elemental mapping. 70 A. BIND ET AL. (a) 4. Conclusions With the ease and mass availability and low processing cost, the aquatic macrophytes could be among the most promising candidate in the heavy metal removal from the wastewater. Further, the feasibility of the adsorp- tion technology could be explored by up-scaling all the parameters. Henceforth, it might be finally concluded that submerged aquatic macrophyte is a better candidate when compared with its floating counterpart and the present investigation is in sync with the previous studies. Acknowledgements e a Th uthor would like to thank the Instrumentation Facilities at IIT Kanpur and MNIT Jaipur, for the sample analyses. (b) Authors also thank all the reviewers for their critically valua- ble suggestions in the review process. Disclosure statement No potential conflict of interest was reported by the authors. ORCID Akhilesh Bind   http://orcid.org/0000-0002-4851-5906 Lalit Goswami   http://orcid.org/0000-0003-2119-568X References Ahmady, A.S., Mohammadi, M., Bahrami, A., Monfared, Figure 10.  FTIR spectra of control biomass and metal loaded A.L., & Jafari, N. (2011). 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Comparative analysis of floating and submerged macrophytes for heavy metal (copper, chromium, arsenic and lead) removal: sorbent preparation, characterization, regeneration and cost estimation

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GeoloGy, ecoloGy, and landscapes, 2018 Vol . 2, no . 2, 61–72 https://doi.org/10.1080/24749508.2018.1452460 INWASCON OPEN ACCESS Comparative analysis of floating and submerged macrophytes for heavy metal (copper, chromium, arsenic and lead) removal: sorbent preparation, characterization, regeneration and cost estimation † † Akhilesh Bind   , Lalit Goswami   and Veeru Prakash d epartment of Biochemistry and Biochemical engineering, s.H.U.a.T.s, allahabad, India ABSTRACT ARTICLE HISTORY Received 20 a ugust 2017 In this study, a comparative evaluation of floating and submerged macrophytes was performed. a ccepted 15 d ecember 2017 Azolla filiculoides (free floating) and Hydrilla verticillata (submerged) aquatic macrophytes were utilized for arsenic, copper, chromium and lead removal from the respective metallic ion KEYWORDS solutions. Batch experiments were performed initially with optimization of different physical Biosoption; heavy metals; parameters viz., pH, initial heavy metal concentration, biosorbent dosage, contact time, aquatic macrophytes; temperature and agitation speed. Submerged (Hydrilla verticillata) had depicted better removal Azolla filiculoides; Hydrilla efficiency in comparison to the floating macrophyte (Azolla filiculoides). Field emission scanning verticillata electron microscopy equipped with energy dispersive spectroscopy and Fourier transform infrared spectroscopy analysis was performed for the characterization of the metal loaded biosorbents. Biosorption of the respective heavy metal was clearly depicted in the FESEM-EDX spectrum, although not much change in the morphology of the biosorbents were examined. FTIR spectra of the biosorbents obtained after the experiments confirmed the involvement of C–H bend, –CH –(C=O), N–H, –C–O, R –C= bending and –C–C=O on the biomass. Furthermore, 2 2 the biosorbent regeneration followed by heavy metal biosorption confirmed the reusability of the prepared biosorbent for at least two consecutive cycles without much significant change in the heavy metal biosorption capacity. 1. Introduction flocculation, electro-flotation, electrochemical treat- ment, ion exchange, reverse osmosis, advanced oxi- e ra Th pid increase in the anthropogenic activities such dation and membrane separation have been utilized as mining operations, smelting, chemical, paint, ferti- (Anastopoulos & Kyzas, 2015). Among aforementioned lizer, pesticide processing plant, leather industries and techniques, biosorption is  found to be the most eco- electronic manufacturing discharge has increased the nomical, efficient, passive and widely accepted process, amount of metal-containing wastewater into the aquatic as biosorbents are eco-friendly, effective, readily avail- environment (Goswami, Manikandan, Pakshirajan, & able in huge quantity and also does not produces any Pugazhenthi, 2017; Yu, Li, & Liu, 2017). The discharge by-products aer t ft he treatment (Yu et al., 2017). of heavy metals into the environment without any prior Various literatures have been reported with the aim treatment is diminishing the water quality to frighten- of utilizing different biosorbents, such as chitosans, ing levels, thereby posing its lethal effect on to the liv- nano-biosorbents, barks, wastes from food and edible ing organisms (Martin, Turnbull, Rissmann, & Rieger, oil industries and agricultural wastes, for the heavy metal 2017). Heavy metals tend to accumulate and concentrate removal (Anastopoulos & Kyzas, 2015). Taking into in the living tissues through the food chain, imposing consideration of the above-mentioned aspects, present its adverse impact on human health (Etesami, 2018). work was emphasized on heavy metal removal from the Henceforth, treatment of wastewater containing heavy simulated aqueous heavy metal solutions individually by metals prior to their discharge is mandatory due to the utilizing macrophytes. Earlier several researches had per- increasingly restrictive legislation (Arul Manikandan, formed this phenomenon by accounting macrophytes Alemu, Goswami, Pakshirajan, & Pugazhenthi, 2016). as a potential biosorbent and some have been enlisted For the treatment of wastewater contaminated in Table 1. An attempt was made for the comparative with heavy metals, numerous treatment technologies analysis between two different categories of macrophytes viz., floating and submerged and hence was performed viz., adsorption, coagulation, chemical precipitation, CONTACT akhilesh Bind akhilesh.bind@shiats.edu.in equal author contribution. © 2018 The a uthor(s). published by Informa UK limited, trading as Taylor & Francis Group. This is an open a ccess article distributed under the terms of the creative c ommons a ttribution license (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 62 A. BIND ET AL. Table 1. literature reports on Azolla filiculoides and Hydrilla verticillata utilization for heavy metal removal. Maximum uptake S. No. Biosorbent Heavy metal capacity pH Isotherm Removal (%) References 1. Azolla filiculoides cs 195 8 Freundlich – Mashkani and Ghazvini sr 212.1 9 – – (2009) 2. Azolla filiculoides au 98 – – 98.2 Umali, d uncan, and Burgess (2006) 3. Azolla filiculoides au – 2 – 100 antunes, Watkins, and d uncan (2001) 4. Azolla filiculoides ni 45.32 7.8 langmuir – ahmady, Mohammadi, Bahrami, Monfared, and Jafari (2011) 5. Azolla filiculoides cu 363 – – 75 Fogarty et al. (1999) (Immobilized) 6. Azolla filiculoides cr 10.6 2 langmuir, Freundlich 83.34 Babu, sumalatha, Ven- kateswarulu, das, and Kodali (2014) 7. Azolla filiculoides Zn 45.2 6.0 – – Zhao et al. (1999) 8. Azolla filiculoides ni 43.4 6.5 Batch and c olumn 60 Zhao and d uncan (1998) study 9. Hydrilla verticillata pb 2.14 5.0 pseudo-second-order 85.7 chathuranga et al. (2014) 10. Hydrilla verticillata as 11.65 6 langmuir – n igam Vankar, and Gopal (2013) 11. Hydrilla verticillata cd 15 5 langmuir – Bunluesin et al. (2007) 12. Hydrilla verticillata cd 50 6 – – Huang et al. (2010) 13. Hydrilla verticillata cr 29.43 4 langmuir and – Mishra, Tripathi, and Rai ni 48.72 Freundlich (2014) 14. Hydrilla verticillata cr 8–69.9 1 langmuir >60 pilli , Goud, and Mohanty 15. Hydrilla verticillata cr 89.32 – – – Mishra, Tripathi, and Rai ni 87.18 (2016) 16. Hydrilla verticillata cr 247 3 langmuir – Baral, das, chaudhury, and das (2009) to examine the removal efficiencies. The heavy metals River). The samples were washed thrice with deionized tested in this study were copper (Cu (II)), chromium (Cr water (approximately 18.1 Ω resistance) to remove extra- (VI)), arsenic (As (III)) and lead (Pb (II)). Optimization neous materials (each time; 50 mL for 20 min) and was of the batch study was performed individually to deter- air-dried. Azolla and Hydrilla species (as the non-living mine the optimal biomass dose, heavy metal concentra- biomass) were then crushed in mortar-pestle and sieved tion, pH, contact time and temperature for heavy metal to the powder form (size – 0.075 mm) prior to their uti- removal from the aqueous solution. Furthermore, the lization. Pre-treatment for the activation of the samples heavy metal removal process was further investigated was performed by soaking 2 g of each sample in NaOH employing field emission scanning electron microscopy (1.0 M) at pH 9.5 for 5 h. Already it is well established (FESEM) equipped with energy dispersive spectroscopy that demethylation of pectin results in enhancement (EDX) and Fourier transform infrared spectroscopy of –COOH groups, and may be catalysed using alkali (FTIR) analyses. solutions (Rakhshaee, Khosravi, & Ganji, 2006). Pectin is protonated to remove excess cations such as Na or 2+ Ca that could interfere with heavy metal sorption and 2. Materials and methods to generate a more distinct and suitable biosorbent. 2.1. Metal stock solution preparation Subsequently, for removing the excess sodium (Na), the samples were washed twice with deionized water Analytical grade chemical salts and reagents were uti- (50  mL, 5  min). Further, the samples were soaked in lized throughout the experiment procured from Merck 250 mL of CaCl solution with the total concentration (Mumbai, India). Individual heavy metal stock solutions of 2 M and volume ratio of 2:1:1, respectively. pH was of Cu (II), Cr (VI), As (III) and Pb (II) of concentra- −1 adjusted with 0.5  M HCl at 7.0  ±  0.2. These activated tion 1000 mg L each were prepared using CuCl ·H O, 2 2 samples were oven-dried at 65° ± 2 °C for 8 h i.e., until K Cr O , As O and PbNO , respectively, in deionized 2 2 7 2 3 3 they reached a constant weight. The agitation rate for the distilled water. Subsequent volume of metal solution was activation was fixed at 150 rpm at 25° ± 2 °C. Followed prepared with proper dilution. by drying, grinding and sieving the samples for their further utilization in the absorption experiments. 2.2. Collection and pre-treatment of fresh water macrophytes 2.3. Biosorbent characterization Freshwater macrophytes, Azolla filiculoides (free e Th prepared biosorbents (aer ft the pre-treatment) were floating) and Hydrilla verticillata (submerged), as the further characterized chemically, physically and mor- potential biomass were collected from the pond surface phologically as detailed ahead. near Salori, Allahabad, India (eastern shore of Yamuna GEOLOGY, ECOLOGY, AND LANDSCAPES 63 e a Th sh content of the two biosorbents was analysed pH of the solution (2–7), solution temperature (293, by following the ASTM D1762-84 standard. 1 g of each 303 and 313 K), initial metal concentration (10, 20 and −1 −1 sample was incinerated at 650 °C in presence of air for 50  mg L ), biosorbent dose (1–5  g L ), contact time 12 h in a muffle furnace (LabTech, India). The elemental (0–180 min) and agitation speed (50–300 rpm). All the compositions of the biosorbents were determined using flasks were kept in the rotary shaker with the respective an elemental analyzer (Eurovector EA3000, Germany). process parameters for determining the biosorption effi - e zet Th a potential (ZP) and average particle size were ciency. A brief schematic of the overall experiment is TM measured using a laser particle size analyzer (Delsa shown in Figure 1. Nano, Beckman Coulter). For examining the contact angle (CA), the sessile drop method was followed 2.5. Heavy metal quantification (Bachmann, Goebel, & Woche, 2013). e q Th uantification of heavy metals aer ft the batch shake Surface morphology of the biosorbents was analysed experiments was reported in the percentage removal by utilizing field emission scanning electron microscope according to the equation (1). Heavy metal concentra- at ultra-high resolution (FESEM, Zeiss, Sigma, Germany) tions were analyzed by atomic absorption spectroscopy equipped with energy dispersive spectroscopy (FESEM- (Perkin Elmer Analyst 400, England) as per the American EDX). The sample was surmounted onto the copper Public Health Association standards (American Public stub using a carbon tape and a fine doubled-coating of Health Association [APHA], 2005). gold were performed prior to the analysis for making the samples more conductive. The sample images were C − C o e recorded at an operating condition of 3.0 kV (Goswami, Heavy metal removal (%) = × 100 (1) Kumar, Arul Manikandan, Pakshirajan, & Pugazhenthi, 2017). where C and C , the initial and final heavy metal concen - For determining the surface functional groups pres- o e −1 trations (mg L ) present in the solutions, respectively. ent in the two biosorbents was analysed using a Fourier transform infrared (FTIR) spectrophotometer (IR Affinity, Shimadzu, U.S.A.). An average of five scans was 2.6. Regeneration of the exhausted biosorbents −1 collected for each analysis (400–4000 cm ) (Goswami, and cost estimation Tejas Namboodiri, Vinoth Kumar, Pakshirajan, & For determining a process to be cost-effective, desorp- Pugazhenthi, 2017). tion experiments were performed using 0.5 N HCl and 0.5  N NaOH solutions as the stripping agents. Metal 2.4. Experimental set-up loaded biomass aer t ft he biosoption was further trans- ferred to the flasks and kept in an orbital shaker for 24 h. All the batch biosorption experiments were performed Following this, filtrates were further analysed to examine in the 250 mL Erlenmeyer flasks with a working volume the percentage fraction of desorbed Cu (II), Cr (VI), As of 100 mL. For determining the effect of process param - (III) and Pb (II) metal ions to examine the percentage eters onto the biosorption phenomena, all the exper- fraction of desorbed. Successive biosorption–desorption iments were performed by taking one parameter at a cycles were repeated thrice for the similar biosorbents time. The various process parameters were as follows: Figure 1. a brief schematic of the overall experiment. 64 A. BIND ET AL. (Kaur, Singh, Khare, Cameotra, & Ali, 2013). Desorption positive capillary pressure, thus allowing water to enter efficiency for both the biosorbents was further evaluated into the pores. from the quantitative amount of metal ions desorbed FTIR is an imperative to comprehend the chemical to the metal ions adsorbed in the desorption medium, nature of individual components which controls the as per the expression (2) (Yoonaiwong, Kaewsarn, & biosoption of the heavy metals. FT-IR spectra of the Reanprayoon, 2011): prepared biosorbent samples which depict various vibra- tional frequencies due to various functional groups pres- Amount of metal ion desorbed Desorption efficiency (%) = × 100 ent in the biosorbents. Table 3 presents the respective Amount of metal ion adsorbed functional group involved in biosoption phenomenon. (2) 3. Results and discussion 3.2. Effect of different parameters on biosoption capability e ra Th w biomass of both the aquatic macrophytes were washed, dried and crushed to the desired size and both 3.2.1. Effect of pH the prepared biosorbents were further physical, chemical pH, an important parameter for the heavy metal sorption and morphological characterized. on to the biosorbent from an aqueous solution. It decides the surface charge of biosorbent, the degree of ionization and speciation of absorbate (Gupta, Pathania, Agarwal, 3.1. Biosorbent characterization & Sharma, 2013; Huang & Zhu, 2013). The functional Table 2 presents the elemental compositions and sur- groups present on the cell wall plays a significant role face properties of the two prepared biosorbents. FESEM in heavy metal biosoption (Sarada, Prasad, Kumar, & image of the two biosorbent is depicted in Figure 2 that Murthy, 2014). Biosoption mechanism involves the com- reveals a smooth and clear morphology of the mate- plex mechanism of ion exchange, chelation, biosorption rial. Also, the elemental composition of the biosorbent by physical forces, and ion entrapment (Sarada et al., materials with carbon, hydrogen and nitrogen values was 2014). In this study, the biosoption of tested heavy met- −1 evaluated. The zeta potential values of 2.19 and 3.42 mV, als was examined in the range of 10–50 mg L . Figure for Azolla and Hydrilla species, respectively, indicated 3 shows the effect of pH on biosoption heavy metal that both the biosorbent surfaces were covered with pos- through macrophytes. For heavy metal biosoption at itively charged species. low pH, there is competition between heavy metal and e a Th verage particle size of Azolla and Hydrilla spe- H ions for the absorption sites, ae ff cting the ionization cies was found to be 1042.9 and 948.2 nm with a total of functional groups onto the biosorbent surface, i.e., at 2 −1 surface area of 4.29 and 2.23 m g , respectively. Total low pH, the acidic surface functional groups tend to be ash content was found to be 67.12 and 56.28% for Azolla protonated, and henceforth, not considerably contribute and Hydrilla species, respectively. Further, the contact to adsorption reactions (Wahab, Jellali, & Jedidi, 2010). angle of Azolla and Hydrilla species was found out to be As the surface gets positively charged, therefore making 34.6° and 27.9°, respectively. In general, the hydrophilic (H ) ions compete efficiently with metal ions resulting surfaces have a contact angle less than 90° and impose in a decrease in the amount of heavy metal sorption. The maximum removal of heavy metals was found at a pH of 4 for Pb, 7 for As,  6 for Cu and 2 for Cr, respectively. These pH values were found to be sim- Table 2. elemental composition, surface and magnetic proper- ilar to the studies of prior researchers (Sarada et al., ties of the biosorbent. 2014; Swarnalatha & Ayoob, 2016). Increase in pH Elemental Surface area and from 2 to 5 had resulted in low percentage removal composition (%) pore diameter Density and above pH 6.0, complex formation of metal ions (a) Hydrilla verticillata occurs resulting in precipitation of heavy metals c (%) 62.4 BeT surface 4.29 Bulk density 0.43 area occurs (Sulaymon, Mohammed, & Al-Musawi, 2013a; 2 −1 (m  g ) Swarnalatha & Ayoob, 2016). It can well be related to H (%) 3.55 porosity 19.7% Moisture 8.72 the fact that the insoluble metal hydroxide precipitation content n (%) 1.92 pore volume 0.19     occurs at the higher pH values (Sulaymon et al., 2013a). 3 −1 (cm  g ) Whereas biosoption efficiencies of Cr (VI) for both the H/c 0.057         macrophytes was maximum at low pH (2.0) and have (b) Azolla filliculoides c (%) 53.8 BeT surface 2.23 Bulk density 0.39 been reported in the literature by many authors. Cr area 2− (VI) ions are frequently found in chromates (CrO ), 2 −1 (m  g ) 2− − H (%) 3.15 porosity 15.8 Moisture 11.2 dichromates (Cr O ) and bichromates (HCrO ) forms 2 7 4 content depending upon the pH (Gupta et al., 2013). At low n (%) 2.75 pore volume 0.09     2− 3 −1 pH, the concentration of Cr O increases whereas, at (cm  g ) 2 7 H/c 0.037         higher pH (6.0), Cr (VI) is present in solution in the GEOLOGY, ECOLOGY, AND LANDSCAPES 65 Figure 2. Micrographs of Azolla filiculoides and Hydrilla verticillata (scale bar = 500 μm). Table 3. FTIR absoption bands and their corresponding possi- other literature for the removal of tested heavy metals ble functional groups. (Kaur et al., 2013; Muthusamy, Venkatachalam, Jeevamani, & Rajarathinam, 2014). Beyond the optimum Azolla filiculoides Hydrilla verticillata Frequency Functional group −1 dosage, there was a decline in the removal efficiencies (cm ) (Free floating) (Submerged) stretch by both the biosorbents due to saturation of active pore 3500–3200 3280 3277 o –H (hydroxyl) 3000–2850 2845 2921 –c–H (alkanes) sites at the surface of biosorbent (Kamsonlian, Suresh, 1750–1735 – 1737 –c=o (aldehyde) Majumder, & Chand, 2013). Although the optimum bio- 1650–1580 1641 1610 n–H (primary amine) 1400–1370 1400 1363 –so (sulphoxide) 3 sorbent dosages of the heavy metals were attained at 2 g 1280–1150 – 1227 –c– o (alcohol, car - −1 −1 −1 L and 2.5 g L , respectively, 5 g L of the biosorbent boxylic acid, esters, ethers) dose was selected for the comparative removal efficien- 1250–1020 1019 – –c–n (aliphatic cies of heavy metal at exhaust points. Nevertheless, an amines) 900–865 873 877 –c–H (alkene) optimum biosorbent dose has been utilized for the fur- 850–830 838 – R –c= (trisubstituted ther studies. Table 1 also clearly depicts the optimized alkene) parameters for different heavy metals and macrophytes. 560–510 542 526 –c– c=o (aldehyde) pH, contact time and initial heavy metal ion concen- tration of the aqueous solution were kept invariable at 2− form of CrO (Samuel, Abigail, & Ramalingam, 2015). the optimum values for both the biosorbents as attained The presence of negatively charged sites onto the sur - from the earlier experimental results. face of biosorbent does not favour biosoption owing to the electrostatic repulsions (Gupta et al., 2013). These 3.2.3. Effect of contact time optimized pH values were chosen as further studies. Removal of As (III), Cu (II), Pb (II) and Cr (VI) at dif- It might be attributed to the decrease in the solubil- ferent contact time were studied for metal concentra- −1 ity of heavy metals at high pH (Huang & Zhu, 2013). tion (10 mg L ) at different optimum pH for respective Considering these results into account, respective pH at metals with both the macrophytes. The effect of contact which maximum removal efficiency of biosorbent was time on biosorption of As (III), Cu (II), Pb (II) and Cr attained was selected further for all the experiments. (VI) is shown in Figure 5. Uptake of metal ions occurred rapidly within 20 min and equilibrium was attained in 3.2.2. Effect of biosorbent dosage 60  min for chromium with Azolla with 88.76% and Effect of biosorbent dosage on the biosoption efficien- 40 min for Hydrilla with 91.41% and becomes constant cies of tested heavy metals by the two biosorbents were thereaer ft . (Lim, Priyantha, Tennakoon, & Dahri, 2012; determined in the range of 0.5–5  g (Figure 4). The Singha & Das, 2012) Similar fashion was observed with outcomes clearly revealed that removal (%) of all the other three heavy metal whose equilibrium time varies: four heavy metal ions boosts with an increase in the Copper showed equilibrium time of 60 min and 80.14% adsorbent dosage (Kamsonlian et al., 2012). The max- with Azolla while 30  min and 84.36% with Hydrilla, imum removal efficiency for Hydrilla verticillata was Arsenic showed 180  min of equilibrium time with −1 found at 2  g L of biosorbent dose while Azolla filli - 78.94% with Azolla and 240 min with 92.75% Hydrilla −1 culoides shows promising removal at 2.5  g L . These and lead showed 83.66% of removal at equilibrium time outcomes can well be correlated with the increase in of 90 min and 90.13% at equilibrium time of 120 min absorbent dose leading to increase in the surface area with Hydrilla. Therefore, optimized contact time was and accessibility of biosoption sites up to 2.5  g (Kaur taken for all the further experimentation (Gupta et al., et al., 2013). Similar kind of trend was depicted by several 2013). 66 A. BIND ET AL. (a) (a) Arsenic Chromium Copper Lead 23 4 56 7 pH 100 (b) (b) Arsenic Chromium Copper Lead 23 45 67 pH Figure 4. eec ff t of biosorbent dosage on heavy metal removal (%); (a) Azolla and (b) Hydrilla. Figure 3.  eec ff t of pH on heavy metal removal (%); (a) Azolla and (b) Hydrilla. could be due to electrostatic interactions among active groups and probability of higher interaction among 3.2.4. Effect of initial concentration of heavy metal them (Gupta et al., 2013; Muthusamy et al., 2014). ion However, per cent adsorption of As (III) decreased With the change in the initial concentration of Cr (VI), −1 from 87.5% and 83.5% to 44.23 and 38.8%, for Cu Cu (II), Pb (II) and As (III) from 10 mg L to 300 mg −1 (II); 80.5 and 83.3 to 41.59 and 34.25%, for Pb (II); 71 L which was analysed initially, were treated with opti- and 80.7 to 29.9 and 36.6% and for Cr (VI); 91.88 and mum biosorbent dose (0.125 g per 50 mL) of Azolla fil - 89.79% to 51.26 and 43.92% for Hydrilla and Azolla liculoides and 0.1 g per 50 mL of Hydrilla verticillata for species, respectively. This increase might be because of 40–180  min for optimized contact time of respective rapid saturation of metal functional sites on the bio- metal ions at constant biosorbent dose and temperature sorbent (Shukla & Vankar, 2012). With the increase (30 ± 2 °C). Further, the results are presented in Figure 6, in the concentration of heavy metal, the binding sites depicting the percentage removal versus initial heavy of the biosorbent are becoming more saturated and metal concentration. after a certain concentration, there will be no further es Th e results shown here are the augmentation absorption. Furthermore, for the dilute solutions, of metallic uptake on increasing Cr (VI), Cu (II), Pb metal ions have a very high mobility and therefore, the (II) and As (III) ion concentrations with both the bio- interaction with the biosorbent is very high. Here, the sorbents. The maximum uptake values correspond to −1 increase in the initial concentration of Cr (VI) and Zn 76.895, 62.38, 35.908 and 66.35 mg g of the biosorbents (II) results in the saturation of the biosorbent surface in case of Cr (VI), Cu (II), Pb (II) and As (III), respec- faster that leads to decrease in absoption (Muthusamy tively for Hydrilla verticillata and 52.7, 41.12, 54.9 and −1 et al., 2014). 46.6  mg  g for Cr (VI), Cu (II), Pb (II) and As (III), Also, at a higher concentration, the heavy metals dif- respectively, for Hydrilla verticillata correspondingly fuse on the surface of the biosorbent by intra-particle with an initial heavy metal concentration of 300  mg −1 L . The observed heavy metal removal augmentation diffusion and also the highly hydrolyzed ions will diffuse Removal (%) Removal (%) GEOLOGY, ECOLOGY, AND LANDSCAPES 67 (a) (a) (b) (b) Figure 5.  eec ff t of contact time on heavy metal removal (%); (a) Azolla and (b) Hydrilla. Figure 6.  eec ff t of initial concentration of heavy metal on it’s removal (%); (a) Azolla and (b) Hydrilla. at a slower rate. This specifies the probable monolayer formation of As (III) and Cr (VI) ions on the outer surface. be several reasons that could be ascribed: the relative increase in escaping tendency from solid to bulk phase of 3.2.5. Effect of temperature heavy metals and rupture of bonds leads to surface deac- Effect of temperature on the equilibrium sorption poten- tivation of biosorbent/weakening of forces involved in tial for Pb (II), Cr (VI), Cu (II) and As (III) ions were bond formation (Samuel et al., 2015). It could be inferred investigated in the temperature range 20–50 °C with an from results that the sorption of heavy metals/metalloids −1 initial heavy metal concentration of 10 mg L and at all onto macrophytes is an endothermic process. the previously optimized conditions. Figure 7 depicts Hence, the submerged aquatic macrophyte, H. ver- the percentage removal of heavy metals at different tem - ticilata might be efficiently utilized for arsenic removal peratures. Maximum percentage of removal of the four with very promising results (Nigam et al., 2013). In metals was attained at 30 °C. From the obtained result, it compared to the commercial adsorbents present in the could be inferred that biosorption between macrophyte market, the cost of processing this weed i.e., drying, biomass and the heavy metals might be due to prob- grinding, packaging as well as transportation, incurs the able involvement of chemical interaction and physical absolutely negligible cost. Previous studies on H. verti- adsorption (Gupta et al., 2013; Sulaymon, Mohammed, & cillata species seems to be very economical as well as an Al-Musawi, 2013b). efficient biosorbent for the removal of Cr (VI) from the With the rise in temperature (up to 30 °C), availabil- aqueous solutions. ity of surface area increases due to enlargement of pore size and leads to decrease in viscosity of the solution. 3.2.6. Effect of agitation speed Enlargement of pore size present on macrophyte aug- e b Th iosoption capacities of the two macrophytes for ments adsorption and diffusion of metal ions within the heavy metal removal in a single component solution at pores (Sulaymon et al., 2013b). A further rise in temper- different agitation speeds (50–200 rpm) were evaluated. ature (above 35 °C) leads to a decline in the percentage With the increase in the agitation speed the biosoption removal efficiency through biosorption. There might of heavy metal increases as there is an  enhancement 68 A. BIND ET AL. in the diffusion of heavy metal ions towards the bio- (a) sorbent surface .These outcomes can well be associated with the fact that the agitation speed in the range of 150–250 rpm is sufficient enough for making the surface binding sites available for heavy metal uptake for both the biosorbents (Srividya & Mohanty, 2009). Therefore, 250 rpm was chosen as the optimum agitation speed for both the biosorbent. Although Azolla took 30, 60, 90 and 180  min for copper, chromium, lead and arsenic, respectively, while Hydrilla have taken 30, 40, 120 and 240 min. Nadeem et al. (2008) reported similar results for different heavy metal biomass system. The attrac- tive forces between heavy metal and the biosorbent viz., vander waal forces, electrostatic forces and rapid pore diffusion into the intra-particle matrix help in attaining (b) the equilibrium (Gupta et al., 2013). 3.3. Characterization of the biosorbents 3.3.1. FESEM-EDX analysis For analyzing the difference in the morphology and elemental composition of the two biosorbents aer t ft he experiments, FESEM–EDX analyzes of the control bio- sorbent and the metal loaded biosorbent were carried out. From FESEM-EDX spectrum (Figure 8), clearly revealed the occurrence of the additional peak of the respective individual metal ions on the biosorbent. This further confirmed the biosoption phenomena of the heavy metal on the biosorbent surface. There were not many morphological differences were observed during Figure 7.  eec ff t of temperature on heavy metal removal (%); (a) Azolla and (b) Hydrilla. the FESEM analysis of the biosorbent. Figure 9 depicts the micrograph showing FESEM elemental mapping analysis of different metals (for lead experiment with repetitive extraction-elution cycles and reuse potential Azolla filiculoides ). (Bunluesin, Kruatrachue, Pokethitiyook, Upatham, & Lanza, 2007; Samuel et al., 2015). Desorption experi- 3.3.2. FTIR spectroscopy analysis ments were carried out in 3 cycles and with each cycle e t Th wo biosorbent depicted wide band spectra at the loss in weight of adsorbent was observed. In first two −1 around 3250  cm , which is characteristic of the cycles, loss was significant which may be due to washing hydroxyl groups (O–H) (Arul Manikandan et al., 2016) of soluble material and in the last cycle, no significant −1 (Figure 10). At 2921 cm , another band was observed weight loss due leftover biosorbent might have resistant −1 due to –CH followed by a band spectrum at 1737 cm material. A steady decrease in sorption with an increase (only in Hydrilla) corresponding to the carbonyl of ester in the number of cycles was also noticed which may due −1 groups; peak at 1641 cm was assigned to the primary to corrosive nature of acid and washing away of func- amine band spectra. The absorption band in the range −1 tional group. (Bunluesin et al., 2007; Kaur et al., 2013; 1650–1580  cm signifies the N–H (primary amine). Zhao, Duncan, & Van Hille, 1999). In addition, the FTIR spectra reveal –C–O, –C–C=O, Desorption of adsorbed As (III), Cu (II), Pb (II) and and R –C=band stretch corresponding to the functional Cr (VI) on A. filliculoides and H. verticillata biomass groups alcohol/carboxylic acid, alkene and aldehyde, were studied using 0.1 N H SO , 0.1 N HCl, 0.1 N HNO . respectively. 2 4 3 e p Th ercentage desorption varied between 65.2% for Cu, 59.45% for Pb, 71–72.6% for Cr (VI) and 81.3% for As 3.3.3. Regeneration/reusability studies of the (III) with H. verticillata. 0.1 N HCl found to be better for exhausted biosorbent desorption of chromium (VI) for H. verticillata, 0.1 N Regeneration studies were further performed to calculate HCl > 0.1 N HNO  > 0.1 N H SO whereas 0.1 N HNO the reusability potential of the bioabsorbent. The ec ffi ient 3 2 4 3 showed better desorption of adsorbed heavy metal in desorption of absorbed heavy metals from A. filliculoides and H. verticillata biomass were deemed indispensable order of 0.1 N HNO  > 0.1 N H SO . > 0.1 N HCl with 3 2 4 to make sure their sustainability for long-term usage for A. filliculoides and percentage of desorption was not GEOLOGY, ECOLOGY, AND LANDSCAPES 69 Figure 8. FeseM-ed X of Azolla filiculoides (a) control biomass and metal loaded biomass (b) chromium, (c) arsenic and (d) l ead. Figure 9. FeseM micrographs along with metal mapping of Azolla filiculoides loaded with (at 500 μm) (a) arsenic, (b) chromium and (c) l ead; depicting the respective elemental mapping. 70 A. BIND ET AL. (a) 4. Conclusions With the ease and mass availability and low processing cost, the aquatic macrophytes could be among the most promising candidate in the heavy metal removal from the wastewater. 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Journal

Geology Ecology and Landscapes – Taylor & Francis

Published: Apr 3, 2018

Keywords: Biosoption; heavy metals; aquatic macrophytes; Azolla filiculoides; Hydrilla verticillata

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