biosorben kulit durian

Accepted Manuscript

Title: Utilization of Renewable Durian Peels for Biosorption of Zinc from Wastewater

Authors: Mohammed Ngabura, Siti Aslina Hussain, Wan Azlina W.A. Ghani, Mohammed Saedi Jami, Yen Ping Tan

PII: S2213-3437(18)30173-8

DOI: https://doi.org/10.1016/j.jece.2018.03.052

Reference: JECE 2293

To appear in:

Received date: 14-1-2018 Revised date: 18-3-2018 Accepted date: 27-3-2018

Please cite this article as: Mohammed Ngabura, Siti Aslina Hussain, Wan Azlina W.A.Ghani, Mohammed Saedi Jami, Yen Ping Tan, Utilization of Renewable Durian Peels for Biosorption of Zinc from Wastewater, Journal of Environmental Chemical Engineering https://doi.org/10.1016/j.jece.2018.03.052

This is a PDF file of an unedited manuscript that has been accepted for publication.

As a service to our customers we are providing this early version of the manuscript.

The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

1

Utilization of Renewable Durian Peels for Biosorption of Zinc from Wastewater

Mohammed Ngabura^a, Siti Aslina Hussain ^a,*, Wan Azlina W. A. Ghani ^a, Mohammed Saedi Jami ^b, Yen Ping Tan ^c,

a Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia

b Department of Biotechnology Engineering, Faculty of Engineering, International Islamic University Malaysia, P.O. Box 10, 50728, Kuala Lumpur, Malaysia

c Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia

HIGHLIGHTS

 Zinc ion removal by renewable durian peels from contaminated water is proposed.

 Biosorbent modification with HCl acid improved the Zinc biosorption capacity.

 Temkin, Langmuir and pseudo-second-order models were obeyed in batch scale.

 Biosorbent could be utilized up to 5 cycles and beyond.

 HCl is a good modification reagent and best eluent to recover Zinc from wastewater.

Abstract

Durian peel is among the renewable biomass wastes abundantly available in Malaysia. An implication of untreated biological materials for biosorption process was intensively reported, that prioritize our work towards sorbent modification. The biosorption potentials of hydrochloric acid (HCl) modified durian peels (HAMDP) for removal of Zn (II) from simulated wastewater was investigated. Characterization of HAMDP was performed by ATR-FTIR, SEM and BET.

Spectroscopic studies showed the predominant contributors for Zn (II) biosorption on HAMDP is attributed to hydroxyl, carbonyl, carboxyl and amides groups. Batch adsorption studies revealed optimum conditions of pH 8, 0.5 g biosorbent dose, 4 hours contact time and reaction temperature of 313 K. Non-linear isotherm models suggested applicability of Tempkin and Langmuir models at 313 K. The Langmuir maximum adsorption capacity was 36.73 mg/g. Kinetic studies revealed

ACCEPTED MANUSCRIPT

2

applicability of pseudo-second-order model. Webber-Morris model indicated possible role of diffusion of Zn (II) within the particles of HAMDP during the sorption process. Freundlich constant and activation energy values confirmed the physical nature of the process.

Thermodynamic studies indicated that the process is exothermic and spontaneous. Regeneration studies depicted that HAMDP is economically viable. Conclusively, HCl served two significant purposes, namely; a good modification reagent and best eluent in Zn (II) recovery. Therefore, HAMDP is relatively effective, efficient, economical and most importantly “renewable and sustainable” biosorbent for Zn (II) removal from wastewater.

Keywords: Biosorption, heavy metals, Durian waste, modification, wastewater treatment, biosorbent reusability,

ACCEPTED MANUSCRIPT

3 1.0 Introduction

Water pollution due to natural and anthropogenic activities is an issue of greater concern globally. Pollutants generated from industries are generally classified into organic and inorganic contaminants [1]. Heavy metals happened to be categorized as one of the inorganic pollutants found from industrial effluents with substantial amount. They have deleterious impacts on human health as well as the environment due to possession of two major characteristics, namely, non- biodegradability and persistency [2-5]. Significance of numerous heavy metals in life process of living organism has been reported [6-8]. For instance, zinc [Zn(II)] is one of the most common heavy metals found in industrial effluents. It is an essential metal ion which serves as micronutrient when found in trace amount. However, excessive exposure to such metal is detrimental to human life and the eco system [9]. United States Environmental Protection Agency (USEPA) has set up the maximum contamination level of Zn(II) as 0.8 mg/L for surface or groundwater to be used in drinking water supply [10]. Moreover, World Health Organization, WHO suggested 0.01, 0.05 and 3 mg/L for surface water, groundwater and drinking water, respectively as maximum permissible limit for Zn(II) [11]. Otherwise, an elevated concentration of zinc causes severe health problems such as irritability, muscular stiffness, loss of appetite and nausea [12], vertigo, disharmony, arteriosclerosis, pancreas damages. In addition, Zn(II) is associated with short-term

“metal-fume fever”, diarrhea, depression, lethargy, and neurological signs such as seizures and ataxia [13, 14]. Health disputes such as skin inflammations, fever and vomiting are reported due to exposure to excess zinc in the environment [1]. Therefore, decontamination of Zn(II) especially from industrial wastewater prior to disposal into water bodies is highly essential.

ACCEPTED MANUSCRIPT

4

Zinc ions are mainly discharged to aquatic environment via numerous industrial activities.

Such industries include fabrics, wood, metal coating, mining, ceramics, battery production, drugs, sun blocks and deodorants [13, 7]. Chemical precipitations, chemical coagulation, Ion exchange, electrochemical, membrane filtration, electro dialysis and photo catalysis are among the conventional methods applied for heavy metals decontaminations [6, 7, 10]. However, these methods carried drawbacks in terms of cost effectiveness and inability to treat polluted wastewater especially when the metal ions are in trace concentrations [9]. As a result, effective and efficient wastewater treatment is required to safeguard our life and the eco-system. In answer to that, adsorption process has been proposed as a promising heavy metals decontamination method [6, 7]. Being a renewable resource, agricultural wastes are, therefore, fruitful means for environmental technology when applied in handling of contaminated water bodies.

Durian peel is among the renewable biomass waste especially in Southeast Asia abundantly available as waste material. Malaysia is one of the major producers of durian fruit in the world where about 376 kilo tons (kt) of durian peels annually produced. The average weight of durian fruit is approximately 1.5 kg (3.3 lb). The edible portion of the fruit accounts for merely about 15-30 % of the entire fruit, impliedly 263.2 to 319.6 kt of organic waste are generated as a byproduct from durian fruit industry alone yearly in Malaysia.

The resultant large quantity of durian waste accounts for the feasibility of selecting it as biosobent in this work. More details and elaboration of durian fruit and peels could be found elsewhere [15].

Meanwhile, the implication of untreated biomaterial wastes as adsorbent has been reported [16].

Challenges such as inadequate adsorption capacity, high chemical oxygen demand (COD) and biological oxygen demand (BOD) and total organic carbon due to release of soluble organic compounds from the plant materials could be encountered. Ultimately, it may lead to depletion of

ACCEPTED MANUSCRIPT

5

oxygen content in water and threatens aquatic life. Therefore, biological materials need to be modified using available modification reagents prior to their application to treat wastewater.

Interestingly, HCl has been reported intensively as one of the effective reagents that improve biomass capability in adsorption of heavy metals [6, 14]. Similarly, from our previous work, HCl has the ability of nickel desorption and further improved surface-active sites of mustard oil cake (MOC) led to increment of adsorption efficiency of nickel from polluted water [17]; hence, it was adopted as modification reagent in this work. Therefore, this research focused on sorption of Zn(II) from wastewater using durian peel as potential biosobents.

2.0 Materials and Methods 2.1 Chemical Reagents

Stock solutions of Zn(II) with concentration of 1000 mg/L was prepared using analytical reagent grade of zinc nitrate {Zn (NO3)2.6H2O [purity: 98 %]} which were purchased from Ajax Chemicals, Australia. Similarly, KCl, NaCl, KOH, NaOH, HNO3, H2SO4 and HCl of same quality and corresponding purities of ≥ 99.5 %, ≥ 99 %, 99.99 %, ≥ 98 %, 68-70 %, 95-98%, 37 %, respectively, were prepared accordingly.

2.2 Raw Biomass (Durian waste)

Durian (D24) Durio zibethinus murray used in this study was obtained from local trader along the streets of Serdang area, Selangor Dharul Ehsan, Malaysia (in July 2016). It was collected free of charge and processed systematically as described in the subsequent sub-sections.

2.3 Biosorbent Preparation

ACCEPTED MANUSCRIPT

6

Durian peels as a precursor in this work was thoroughly washed repeatedly with tap water followed by deionized water to remove adhering dirt particles on the surface and cut into smaller pieces;

approximately 1.5 to 2 cm and oven dried at 80°C for 48 hours. The dried biomass was milled using a mechanical grinder (cutting mill Retsch SM200, Germany) and the resultant powder was sieved and the fine particles size below 250 µm were collected, transferred into airtight plastic bag and stored in a desiccator.

2.4 Chemical Modification of Durian peels

A weighed amount (50 g) of pristine powdered durian peels was contacted with 500 mL of 0.1 N HCl solutions in 1000 ml beaker. The mixture was stirredfor 3 hours at 50 °C with a magnetic stirrer. Afterwards, the residue was filtered and rinsed thoroughly with distilled water until neutral pH was observed. It was oven dried at 80°C for 48 hours and labeled as hydrochloric acid modified durian peels (HAMDP) and applied throughout this work.

2.5 Characterizations of Biosorbent

Attenuated total reflection-Fourier transform-infrared (ATR-FT-IR) [Perkin Elmer Spectrum (100 FTIR Spectrometer)] was used and analyzed the functional groups present on the surface of durian peels active in biosorption of Zn(II). Non-modified durian peels NMDP, HAMDP before and after Zn(II) biosorption and after Zn(II) desorption from HAMDP were the considered biosorbent samples and were analyzed within 4000–650 cm^-1 range. The surface morphology of the pristine and HAMDP before adsorption, after Zn(II) adsorption as well as after Zn(II) desorption was determined by scanning electron microscopy (SEM, Hitachi Co., Japan, Model No. S3400N). The samples were mounted on a stub with coating thickness about 30-50 nm gold layers in a vacuum chamber with settings: current 40 mA for 3 minutes; then scanned and

ACCEPTED MANUSCRIPT

7

identified surface morphology of the biosorbent. In addition, surface area and pore size of pristine and HAMDP were examined using Brunauer, Emmett and Teller (BET) single point method. It was analyzed with surface characterization analyzer (Micromeritics 3 flex 1.02, USA, Model No.

170). Degas temperature of 200 °C was adopted [18] and the samples were out-gassed by passing dry nitrogen for a specific duration over the samples in order to clean any unwanted matter, e.g.

moisture content or dust particles that would interfere especially by blocking the pores available on the surface of biosorbent [19].

Point of zero charge (pHpzc) study was performed according to [17] procedure. The experiments were conducted in a series of 50 mL conical flasks with stopper cork each containing 20 mL of 0.01 M KCl solution. The initial pH (pHi) in each flask was adjusted approximately between 2-12 by adding either 0.1 N HCl or 0.1 N NaOH using pH meter (Milwaukee, MW100).

The total volume of the solutions was then adjusted to 25 mL by adding KCl solution of same strength. The pHi of the solutions was accurately measured. Biosorbent of 0.25 g was added to each flask and securely capped immediately. The mixtures were manually shaken at 120 rpm intermittently and allowed to equilibrate for 48 h. The supernatant was collected using filter paper and final pH (pHf) were measured. The difference between pH values (ΔpH = pHi - pHf) was plotted against pHi [Fig 4 (b)]. The point of intersection of the resulting curve with abscissa, at which ΔpH

= 0, gave the pHpzc of the biosorbent.

2.6 Sorption Studies

Series of 250 ml conical flask with stopper cork along with 100 ml treatment solution at desired Zn(II) concentration as well as temperature was adopted under batch adsorption sturdies.

Temperature controlled Water bath shaker (Stuart, Model number: SBS40) and incubator shaker

ACCEPTED MANUSCRIPT

8

(Sastec, model: ST-200R) were used at 120 rpm agitation speed throughout this experiment.

Samples were collected at equilibrium and the residual concentrations were measured using inductive coupled plasma optical emission spectroscopy, ICP-OES (Perkin-Elmer, Optima 7300 DV). The adsorption capacity of chemically modified durian peels at equilibrium qe (mg/g) was determined using:

𝑞_𝑒 = (𝐶₀− 𝐶_𝑒) × 𝑉/𝑊 (1)

Where qe is the amount of Zn(II) adsorbed on HAMDP (mg/g), C0 and Ce were initial adsorbate concentration (mg/L) and adsorbate concentration at equilibrium (mg/L), respectively, V is volume of solution treated, (L) and W is mass of adsorbent (g).

Whereas, percentage adsorption (%) was computed using:

(% 𝐴𝑑𝑠𝑜𝑟𝑝𝑡𝑖𝑜𝑛) =^𝐶0_𝐶^−𝐶𝑒

0 × 100% (2)

2.6.1 Effect of pH

The range of pH considered under this study was 2-12. Fifty milliliter of Zn(II) solution with initial metal concentration of 50 mg/L was introduced into a beaker (100 ml). Hydrochloric acid (0.1 N HCl) and sodium hydroxide (0.1 N NaOH) solutions were used to adjust the treated solution pH to desired initial pH value (pHi). Subsequently, the resulting solution was transferred to 250 ml conical flask and 0.5 g of HAMDP was added. The mixture was placed into temperature- controlled water bath shaker for 24 hours at ambient temperature (27±0.5) with agitation speed of

ACCEPTED MANUSCRIPT

9

120 rpm. Afterward, it was filtered and final concentration of Zn(II) was determined with ICP- OES.

2.6.2 Effect of Contact Time

In this study, series of 250 mL conical flask each containing 0.5 g of adsorbent and 100 mL solution of 50 mg/L of Zn(II) was employed. The mixture was placed in an incubator shaker (303 K) and temperature-controlled water bath shaker (313 and 323 K) at 120 rpm. The supernatants were filtered and collected intoclean glass tubes and Zn(II) concentration in the filtrate was analyzed using ICP-OES.

2.6.3 Effect of Initial metal ions Concentration

Variation of initial Zn(II) concentrations considered ranges between 10-200 mg/L. Each concentration was contacted with 0.5 g of adsorbent dose plus 100 ml treatment solution at optimum temperature and pH in 250 mL stopper corked conical flask. It was placed into temperature-controlled water bath shaker at 120 rpm for 4 hours. Afterward, samples were collected into clean glass tubes and final Zn(II) concentration was analyzed using ICP-OES.

2.6.4 Effect of Biosorbent Dose

Runsof 250 ml conical flask containing 100 ml solution of 50 mg/L Zn(II) concentration were performed at optimum conditions. Biosorbent doses considered is from 0.1 to 2.0 g. The flasks were immediately placed into water bath shaker with agitation speed of 120 rpm for 4 hours.

Subsequently, the solutions were filtered and diluted systematically into clean glass tubes and final concentrations of Zn(II) were analyzed using ICP-OES.

ACCEPTED MANUSCRIPT

10 2.7 Desorption studies

Single and multi-metal ions systems were considered under batch adsorption process. In the case of single metal system, 1.0g of biosorbent was initially saturated with 100 mg/L of Zn(II) concentration. Whereas, pertaining to multi-metal ions system, 100 mg/L of Zn(II) was contacted along with 50 mg/L of each Cu(II), Pb(II), Mn(II) and Ni(II) until equilibrium. In both cases, the mixture was allowed for 4 hours using temperature-controlled water bath shaker at 313 K.

Deionized water was applied to wash the saturated biosorbent thoroughly to remove unadsorbed traces of metal ions in both systems. Eluents used to desorb the heavy metals are HCl (0.05 and 0.1), HNO3 (0.05 and 0.1), NaOH (0.05 and 0.1), KOH (0.05 and 0.1 N), NaCl (0.05 and 0.1) and KCl (0.05 and 0.1 N). Fifty milliliter of eluent solutions was introduced to the saturated adsorbent to elute Zn(II) ions and equilibrated in water bath shaker, afterward filtrations and sample analysis via ICP-OES followed immediately.

2.8 Regeneration Studies

Regeneration studies were performed in series of 250 ml stopper corked conical flasks.

Initially, 100 mL of 100 mg/L of Zn(II) solution was equilibrated with 0.5 g of biosorbent in an incubator shaker at 120 rpm and reaction temperature of 313 K. The mixture was filtered where a sample for the first cycle was collected. Thereafter, adsorbent residue was thoroughly washed with distilled water to remove unadsorbed Zn(II) traces. It was then treated with 100 mL of 0.1 N HCl solutions (best eluent from desorption studies) for 4 hours in incubator shaker under similar

ACCEPTED MANUSCRIPT

11

experimental conditions to desorb the Zn ions adsorbed. Similar procedure was repeated and samples up to five cycles were subsequently collected.

3.0

Results and Discussions

3.1 Characterization

3.1.1 ATR-FTIR analysis of Biosorbent

ATR-FTIR analysis is a powerful tool for dissecting the mechanism of biosorption. It is mainly performed preliminary for quantitative analysis of major functional groups present on HAMDP used as biosorbent of Zn(II) in this work. Therefore, the pattern of biosorption of Zn(II) onto biological material such as durian peels is attributed to the active functional groups and bonds present on the biomass. Basically, the region of spectra of FTIR is categorized into 3 (Table 1), namely; functionalgroups, finger print and nano aromatic structure regions [20]. Comparing the spectra of pristine durian peels [Fig. S1 (a) in supplementary materials], HAMDP before adsorption [Fig. S1 (b) in supplementary materials] and after adsorption of Zn(II) [Fig. S1 (c) in supplementary materials] as well as the spectrum of biomass after desorption of Zn(II) [Fig. S1 (d) in supplementary materials]. It was observed that infrared (IR) peaks have been altered (Table 1).

A broad and intense spectrum band for pristine adsorbent was observed at 3376.14 cm^-1 corresponds to O-H stretching vibrations and H bonding of cellulose, pectin, absorbed water and lignin [21]. This peak shifted to 3380.53 (HAMDP), 3346.64 [after Zn(II) adsorption] and 3385.19 [after Zn(II) desorption]. Thus, the movement of the peak apparently revealed the possible involvement of hydroxyl groups in Zn(II) adsorption onto durian peels. The sharp peak indicated at 2915.24 cm^-1 (Table 1) could be assigned to C-H stretching vibrations of methyl, methylene or methoxy group (C-H asymmetrical stretching). It also shifted to 2918.47 (HAMDP), 2921.81 (after

ACCEPTED MANUSCRIPT

12

adsorption) and 2917.81 (after desorption) shown possibility of aliphatic group involvement in the adsorption process. The peaks located at 2385.84, 2362.67 and 2322.48 are feasibly assigned to N-H or C-H stretching vibrations [21, 22]. The peaks shifted slightly to a different wavelength as further processes took place indicating the possibility of involvement of the aforementioned functional groups. Interestingly, the peak at 2345.26 appeared which was not available in the spectrum of pristine biomass by modifying the surface of durian peels with HCl [Fig. S1. (b)]. It is probably assigned to N-H or C=O stretching vibrations and that signified the positive impact of HCl as a potential modification reagent to improve surface active sites of agricultural wastes such as durian peels. The peak disappeared after biosorption of Zn(II) and reappeared when Zn(II) was desorbed which revealed possible involvement of amine and ketone functional groups. Similar illustration was observed at 1740.07 that assign to carbonyl group and later shifted to 1737.65 and 1741.62 cm^-1 after adsorption and desorption of Zn(II), respectively. The peaks detected at 1628.57, 1511.47, 1376.09, 1246.98 and 1038.32 are assigned to amide band, strong asymmetric carboxylic group, methyl group (bending vibration), aromatic amines and C-O stretching of carboxylic acids, respectively (Table 1). These peaks shifted to different wavelength during the processes implied ability of the active functional groups. Furthermore, at the lower region of the IR spectra (nano aromatic structure region), significant active sites were observed. The peak at 900.16 is attributed to C-C stretching, which was later, shifted to 899.60 after the biosorbent modified using HCl. The peak disappeared after Zn(II) adsorption and reappeared after Zn(II) desorption at wavelength of 899.76. The peak at 847.68 in the spectrum of pristine biomass disappeared after modification and adsorption of Zn(II) occurred and reappeared after Zn(II) was desorbed from the surface of the biosorbent and that spectrum is assigned to alkanes group [20].

The peaks at "781.68, 737.98", 702.46 and 669.11 are assigned to C-Cl stretching of alkyl halides

ACCEPTED MANUSCRIPT

13

[23], strong bending vibration of alkyne and NH wagging, respectively. Shifting of wavelength’s positions, appearance, disappearance and reappearance of their corresponding wavelength locations revealed the possible participation of the functional groups (Table 1). In general, the significant alteration of these specific peaks after Zn(II) biosorption may be attributed to the changes in counter ions associated with carboxylate and hydroxylate anions. Acidic groups, carboxyl, hydroxyl and amides are suggested to be predominantly contributors in metal ions biosorption [21, 23].

3.1.2 SEM Analysis of Durian Peels

The micrograph of the biosorbent showed cavities of irregular surface and microstructures [Fig 1 (a)]. Availability of some pores on the surface of the biosorbent was observed especially after HCl modification [Fig. 1(b)] where Zn(II) occupied pores after biosorption [Fig. 1 (c)].

Similarly, after Zn(II) was desorbed [Fig. 1 (d)] using HCl, the surface of biosorbent regained the porous microstructure which could be able to re-adsorb Zn(II) ions.

3.1.3 BET Analysis.

Adsorbent surface area, pore size distribution and total pore volume were measured by N2

adsorption-desorption isotherm considering degas temperature of 200 °C [18]. Adsorption isotherm was obtained by measuring amount of N2 gas adsorbed to the surface of the biosorbent at 77.26 K, while desorption isotherms were evaluated by removing amount of N2 gas (adsorbed earlier) by means of a gradual pressure reduction. Surface area of pristine durian peel and HAMDP that was ascertained by the means of BET method were presented in Table 2. Apparently, HAMDP has higher porous structure, evidently with larger surface area of 0.8807 (m²/g) compared to the

ACCEPTED MANUSCRIPT

14

pristine durian peels 0.6793(m²/g). This signified the importance of surface modification of raw agricultural waste prior to adsorption studies. Moreover, as observed from the data (Table 2), crucial characteristics in adsorption studies involve high specific surface area and porosity of biosorbent. When a specific surface area of biosorbent is larger, number of available active sites on that biosorbent increases which would yield higher adsorption capacity of metal removal [19].

Durian peels used in this work had a good porous structure capable of adsorbing Zn(II) ions from wastewater. Pores in solid particles have several properties which includes shape, location, connectivity and surface chemistry. The easiest visual property of a pore is it size, i.e., itsextent in a unit spatial dimension. That prioritized particle size of adsorbent to be main property of concern to characterize a pore. Additionally, pore size has the greatest influence on properties of solid adsorbents such as biomass, compared to other parameters e.g., pore shapes. It is useful and convenient to categorically use pore diameter based on pore size distribution as a mean to characterize and compare different porous solids. International Union of Pure and Applied chemistry (IUPAC) classified 3 main categories of pore dimensions [24], namely: (1) micropore if diameter d is less than 2 nm (d < 2 nm); (2) mesopore (d ranges between 2-50 nm); and (3) macropore (d > 50 nm). Evidently, the average pore diameter as presented in Table 2 showed decrement of pore diameter from 1146.04 (pristine durian peels) to 745.03 (HAMDP) nm. The significant difference occurred while the biosorbent passed through acid modification. Since both pore diameter are greater than 50 nm, therefore, this biosorbent can be considered as macropre material, containing predominantly macroporous structure. These results are corroborated by SEM [Fig.1 (a) & (b)] where small amount of the corresponding biosorbent were visualized

ACCEPTED MANUSCRIPT

15

morphologically. Hence, the major contribution of the morphological structure of the HAMDP for the Zn(II) sorption could be attributed mainly to macropores.

3.4 Effect of pH

Irrefutably, solution pH is the most influential parameters among the factors involved in adsorption experiment. Fig. 2 depicted the effect of pH on the biosorption of Zn(II) using HAMDP.

The biosorption capacities were found to be low at lesser pH and increased gradually with increase in solution pH, then decreased as the pH conceded 8 (Fig. 2). At the lower pH, protons dominate competitive race to occupy HAMDP surface led to lower adsorption capacity. Competition between hydrogen ion and Zn(II) onto the surface of durian peels is higher at that pH region. The progressive increase in pH improved Zn(II) adsorption capacities by lowering the electrostatic repulsion between HAMDP and Zn(II) and resulted to decrease in competition for Zn(II) to occupy HAMDP surface. Biosorption capacity slightly decreased after pH of 8 until pH 12. Similar results were reported by numerous researchers [25-29]. Zn(II) is in ionic form below pH 8 [28], at pH greater than 8, decrease in adsorption of Zn(II) was probably due to the formation of soluble hydroxylated complexes and their competition with the active sites [30]. Mechanism of metal uptake based on the concept of Pourbaix diagrams (Eq. 3 & 4) have been explained [30]. For metal- H2O system at 26.5 °C Zn(II) ions transform in M(OH)⁺ or precipitate as M(OH)2 at pH values higher than 8. The maximum biosorption capacity observed was 11.2 mg/g at pH of 8.

M²⁺ + OH¯ MOH⁺ (3)

MOH⁺ + OH¯ M (OH)2 (4)

ACCEPTED MANUSCRIPT

16

The observed point of zero charge pHPZC of HAMDP was 3.9 (Fig. S2 in supplementary materials).

At pH < pHPZC, hydrogen ions occupied the surface of HAMDP with apparent preponderance over Zn (II), alternatively, at pH > pHPZC, biosorption of Zn(II) would be higher [38, 41].

3.5 Biosorbent Dose

Biosorbent dose has a greater impact on adsorption process under certain experimental conditions. Sorption of Zn(II) on HAMDP increased from 47 % to 86.2% with an increase of adsorbent dose from 0.1 to 2.0 g at optimum conditions, however, biosorption capacity decreased from 26.77 to 2.45 mg/g (Fig. 3). Increment of biosorbent dose led to sufficient generation of active sites resulted to increase biosorption efficiency. On the other hand, decrease in biosorption capacity was due to the fact that some of the biosorption sites remained unsaturated. Similar results were reported in the investigations of Zn(II) adsorption on a rapeseed [28], biosorption of Zn(II) by rice bran [29], Pseudevernia furfuracea as biosorbent for removal of Zn(II) [26] and biosorption of Zn(II) using orange peels [27]. The drastic decrement of biosorption capacities minimize significantly after 0.5 g biosorbent dose, afterwards, the difference in reduction of uptake capacities are quite negligible. Therefore, from economical aspect of wastewater treatment point of view, biosorbent dose of 0.5 g was adopted for the subsequent studies.

3.6 Contact Time Studies

ACCEPTED MANUSCRIPT

17

This study indicated a remarkable increase in biosorption capacity with increase in contact time and reaction temperature [Fig. S3 (a & b) in supplementary materials]. Initially, most of the biosorbent surface was unsaturated; therefore, biosorption of Zn(II) was fast. Meanwhile, as the surface of adsorbent was getting saturated gradually with increase in contact time, biosorption capacities apparently increased until equilibrium achieved. Interestingly, increment in reaction temperature has contributed significantly to the enhancement of Zn(II) uptake as well as reduction of equilibrium time. Fig. S3 (a) revealed that increasing contact time (1 to 360 min) increased adsorption capacity from 2.75 to 5.64 mg/g at the temperature of 303 K. In addition, Fig. S3 (b) showed increment of biosorption capacity from 4.81 to 5.34 mg/g as the contact time increased from 5 to 240 minutes at 313 K. Moreover, variation of contact time from 1 to 360 minutes at temperature of 318 K led to increment of biosorption capacity of Zn(II) from 4.59 to 7.03 mg/g [Fig. S3 (a)]. Furthermore, Zn(II) biosorption increased from 4.29 to 4.52 mg/g along with contact time variation from 5 to 240 minutes at 323 K [Fig. S3 (b)]. It is obvious that Zn(II) adsorption onto HAMDP is quite rapid at the lower contact time and the impact of reaction temperature is of paramount importance. To avoid biomass degradation at higher temperature, moderate temperature (313 K) was chosen to be optimum and was adopted for further studies. Similarly, contact time of 4 hours is reasonable to achieve equilibrium.

3.7 Effect of Initial Zn(II) Concentration

The biosorption capacity of Zn(II) on HAMDP as a function of initial adsorbate concentration of 10 to 200 mg/L at optimum conditions was studied. Apparently, biosorption capacities increased with increase in initial Zn(II) concentration [Fig. 4 (a)] as the amount of Zn(II) increases, nevertheless, the process efficiency decreased from 80 to circa 40 % [Fig. 4 (b)].

ACCEPTED MANUSCRIPT

18

Increment of initial Zn(II) concentrations provides driving force i.e. concentration gradient between solid and solution phase overcoming mass transfer resistance [32, 28]. On the other hand, decrease in the biosorption efficiency is a clear indication of insufficient sorption sites to accept excess adsorbate on to the biosorbent [33, 34]. Similar effects have been reported on the biosorption of Zn (II) using potato peels [35], dead biomass of isolated yeast species (Candida rugosa and Candida laurentii) [36], rapeseed waste [28]. Therefore, biosorption of Zn(II) is significantly dependent on it concentration in wastewater, hence, dilution of effluent containing excess metal ions is highly recommended to improve purification of wastewater. The biosorption capacity increased from 2.05 to 23.41 mg/g as initial Zn(II) concentration increased from 10 to 200 mg/L [Fig. 4(a)].

3.8 Biosorption Isotherm

The mechanism of biosorption systems are usually understood by data revealed using adsorption isotherm models. Basically, adsorption isotherms model has certain significance such as representations of equilibrium distribution of adsorbate between solid and liquid phase, liquid phase concentrations and correlation definition with amount of solute adsorbed in the solvent [37].

Experimental data obtained in this study were ascertained using three prominent adsorption isotherm models, namely Langmuir, Freundlich and Tempkin isotherms. Langmuir models assumed the surface of the adsorbent is energetically homogenous and formation of

ACCEPTED MANUSCRIPT

19

monomolecular layer during adsorption process, neglecting interaction between the adsorbed molecules. Non-linearized form of Langmuir isotherm is signified as [38]:

𝑞_𝑒 = ^𝑞_1+𝑏𝐶^{𝑚𝑏𝐶𝑒}

𝑒 (5)

Where qe is the equilibrium amount of solute adsorbed per weight of biosorbent (mg/g); Ce is the equilibrium concentration of solute in the bulk solution (mg/L); qm is the maximal monolayer adsorption capacity under the experimental conditions (mg/g); b is the constant related to the free energy of adsorption. Linearized form of the model is expressed as:

𝐶_𝑒

𝑞_𝑒 = 1

𝑏𝑞_𝑚+ 1

𝑞_𝑚× 𝐶_𝑒 (6)

This model can be accessed by it essential feature known as separation factor (RL) which is a dimensionless constant denoted mathematically as:

𝑅_𝐿 = _1+𝑏𝐶¹

0 (7)

Where C0 is the initial concentration of Zn(II) (mg/L). The value of RL theoretically reflects the nature of the biosorption isotherm in the actual process. If RL > 1, the biosorption process is unfavorable, for the values ranges between 0 < RL < 1, it indicates favorable adsorption process. If the value RL = 1, that refers to linear biosorption process, and when RL = 0, the process is irreversible. The values of RL at different initial Zn(II) concentrations are given in Table S1 (in

ACCEPTED MANUSCRIPT

20

supplementary materials). The values computed ranges between 0-1 indicated that Langmuir adsorption isotherm is highly favorable at all experimental conditions investigated.

Contrasting Langmuir isotherms, multilayer sorption and heterogeneous surface properties are the basic assumptions stretch out by Freundlich adsorption isotherm model. It is also an empirical expression which suggests exponential decrease in biosorption energy with saturation of sorption sites on the adsorbent [17, 27]. The non-linear form of Freundlich isotherm model is given as [39]:

𝑞_𝑒 = 𝐾_𝑓𝐶_𝑒^1/𝑛 (8)

Where qe is the equilibrium amount of solute adsorbed per unit weight of biosorbent (mg/g); Kf, the constant indicative of the relative adsorption capacity of biosorbent (mg/g); n, the constant related to intensity of the adsorption (dimensionless) and represent biosorption deviation from linearity and nature of adsorption process. If n = 1, < 1 and > 1, the adsorption process is said to be Linear, chemisorption and physisorption, respectively [30, 39]. Linearized form of the model is expressed as:

log 𝑞_𝑒 = log 𝐾_𝑓+1

𝑛𝑙𝑜𝑔𝐶_𝑒 (9)

In addition, Tempkin model is chiefly based on linear decrement of biosorption energy rather than decreasing exponentially as inferred by Freundlich isotherm. Biosorbents saturation in sorption process is taken into account. Temkin isotherm model consists of a factor that explicitly considers

ACCEPTED MANUSCRIPT

21

the adsorbing species-adsorbate interaction. Non-linear form of the isotherm model is represented as [40]:

𝑞_𝑒 = 𝐵_𝑇𝑙𝑛(𝐾_𝑇𝐶_𝑒) (10)

𝐵_𝑇 = ^𝑅𝑇_𝑏 (11)

Where BT is the constant related to the heat of sorption (dimensionless); R is the universal gas constant (8.314 J/mol-K); b, a Tempkin constant related to the biosorption energy (KJ/mol); KT, the binding constant at equilibrium corresponding to the maximum binding energy (L/g).

Linearized form of the isotherm is denoted mathematically as:

𝑞_𝑒 = 𝐵_𝑇𝑙𝑛𝐾_𝑇+ 𝐵_𝑇𝑙𝑛𝐶_𝑒 (12)

Experimental data of linear biosorption isotherm models were computed (Table 3) and compared with that of non-linear isotherm models (Table 4). Microsoft Excel SOLVER software was used to evaluate non-linear isotherm parameters. An error function known as sum of squares error (SSE) is required in the optimization procedure [17]. Its significance was to be able to evaluate the fitness of the equation to the experimental data. SSE can be evaluated as:

𝑆𝑆𝐸 = ∑(𝑞_{𝑒,𝑐𝑎𝑙}− 𝑞_{𝑒,𝑒𝑥𝑝})²

𝑛

𝑖=1

(13)

ACCEPTED MANUSCRIPT

22

Where qe,cal and qe,exp are calculated and experimental biosorption capacities at equilibrium, respectively and n is number of observations.

Comparison between linear [Fig. S4 (a-c) in supplementary materials] and non-linear isotherm [Fig. 5 (a-c)] parameters for different models at various temperatures was scrutinized. As a result, Temkin isotherm model fitted well to the experimental data at temperature 303-323 K. It was confirmed evidently by higher R² values particularly by considering non-linear isotherm models (Table 4). Also, the values of Temkin constants (BT and KT) for both linear and non-linear isotherm models at all temperatures were in good covenant. Similarly, Freundlich model exhibited good R² values at 313 K (Linear isotherm model) which confirmed the fitness of the model.

The Langmuir constant, qm increased with rise in temperature from 303 to 313 K and decreased rapidly as the temperature augmented to 323 K (Table 3 and Table 4). The increment of the adsorption capacities might be due to rise in the kinetic energy of the biosorbent particles;

consequently, collision frequency between HAMDP and Zn(II) improved and therefore enhanced the process performance [28]. In addition, the temperature of 313 K might cause rupturing of bonds that are present on the surface of HAMDP led to an increase in number of active sites resulted in enhancement of biosorption capacity of linear isotherm model from 20.2020 to 34.8432 mg/g.

Non-linear Langmuir model revealed maximum adsorption capacity of 36.73 mg/g at 313 K. At higher temperature (323 K), the biosorption capacity drastically reduced to 15.64 mg/g (table 4), this might be due to damages caused by the reaction temperature to some of the valuable active sites present on the surface of HAMDP [28]. Similar instance was observed at higher temperature considering the other 2 isotherms studied in this work. The RL values of Langmuir isotherm model (Table 3) ranges from 0-1 indicating favorable biosorption process. The Freundlich constant (n) were greater than unity confirming physical nature of the sorption process.

ACCEPTED MANUSCRIPT

23 3.9 Biosorption kinetics study

Kinetic biosorption models are generally applied to analyze experimental outcomes to ascertain the biosorption mechanisms and identify the process rate limiting step. The limiting stage defines the speed of the biosorption process, possibly due to chemical reactions, diffusion or mass transfer via the medium interface. Pseudo-first-order, pseudo-second-order and Webber-Morris models have been applied. These models could be classified into reaction based and diffusion- based (Table 5).

Pseudo-first-order model is given by Lagergren can be expressed mathematically as [41]:

𝑑𝑞_𝑡

𝑑𝑡 = 𝑘₁(𝑞_𝑒− 𝑞_𝑡) (14)

Where k1 (1/min) is the rate constant of pseudo-first-order, qe and qt (mg/g) adsorption capacities at equilibrium and time t, respectively. Equation (14) can be re-written in Linearized form as:

log(𝑞_𝑒− 𝑞_𝑡) = 𝑙𝑜𝑔𝑞_𝑒− 𝑘₁

2.303𝑡 (15)

Pseudo-second-order kinetic model can be represented as [42]:

ACCEPTED MANUSCRIPT

24 𝑑𝑞_𝑡

𝑑𝑡 = 𝑘₂(𝑞_𝑒− 𝑞_𝑡)² (16)

The linear form of equation (16) is:

𝑡 𝑞_𝑡 =1

ℎ+ 1

𝑞_𝑒𝑡 (17)

Also, ℎ = 𝑘₂𝑞_𝑒² (18)

Where k2 (g/mg-min) is the pseudo-second-order rate constant and h (mg/g-min) is initial sorption rate.

Weber-Morris (intraparticle diffusion) model was given as [43]:

𝑞_𝑡 = 𝑘_𝑖𝑡^1⁄2+ 𝐶 (19)

The Kinetic data were fitted to these models [Fig. 6 (a) and (b) and Fig. S5 in supplementary materials]. The corresponding kinetic parameters and correlation coefficient values computed from the slope and intercept of the kinetic plots are tabulated (Table 6). Based on the regression coefficients (R²) values, it is concluded that Zn(II) sorption onto HAMDP can be described more appropriately by pseudo-second order reaction model than pseudo-first-order model. Similarly, the values of qe, exp and qe, cal of pseudo-second-order model are approximately equal (Table 6), proving the fitness of the model. In addition, higher regression values obtained

ACCEPTED MANUSCRIPT

25

from Webber-Morris (Table 6) especially at temperature of 323 K indicated possible role of diffusion of Zn (II) within the particles of HAMDP during the sorption process [44]. Several steps are involved for an adsorbate to transport from solution phase to the surface of the biosorbent particles. The biosorption process is generally controlled by single or more steps, for instance, film or external diffusion, a pore diffusion, surface diffusion and adsorption on the pore surface, or even combination of more than a step. Therefore, a process is said to be diffusion controlled if its rate is solely dependent upon the rate at which components diffuse towards one another. Fig. 6 (b) depicted the intra-particle diffusion model plot and the details are summarized in Table 6.

Considering the plot at 313 and 323 K, it is concluded that the plot satisfies the linear relationship with the experimental data; impliedly the sorption process may be controlled by intra particle diffusion. However, the plot at 303 K exhibited multi-linear plots, which suggested the involvement of two or more steps influencing the sorption process. Moreover, the data points are related to single strait lines i.e., at 313 and 323 K and multiple straight lines at 303 K. At 323 K, the straight line is quite smooth compared to the plot at 313 K depicting meso-pore diffusion, while the plot at later temperature with little variation in terms of smoothness representing both macro- pore and meso-pore diffusion [45]. Nevertheless, at 303 K, the multiple straight lines could be due to lower temperature and does not fit this model well, evidently with lower regression coefficient (Table 6). Extension of the linear portions of the plot towards vertical axis gives the intercepts which provides the magnitude of the boundary layer thickness. Apparently, the straight lines from Fig. 6 (b) deviated from the origin; this may be due to change in rate of mass transfer in the initial and final stages of the biosorption process. Furthermore, such deviation is a clear indication that the pore diffusion is not the sole rate-controlling step. The slope of the intraparticle diffusion plots

ACCEPTED MANUSCRIPT

26

between qt against t^0.5 is defined as rate parameter. It characterized the biosorption rate in that region where intraparticle diffusion is rate controlling process.

The kinetic parameters of Zn(II) biosorption were improved by increasing temperature from 303 to 323 K (Table 6) evidently by increment of pseudo-second-order rate constant (k2) and that is another indication of physisorption process [45]. In addition, physical adsorption of Zn(II) onto HAMDP was supported by calculating activation energy of adsorbate biosorption using:

𝑘₁ = 𝑘. 𝑒^{(−𝑅𝑇)𝐸𝑎} (20)

Where K1 is the rate constant for pseudo-first-order kinetics (g mg⁻¹ min⁻¹), k the temperature- dependent factor (g mg⁻¹ min⁻¹), Ea the activation energy of sorption (kJ mol⁻¹), R the universal gas constant (8.314 J mol⁻¹ K) and T the solution temperature (K). A graph of ln k1 versus 1/T was plotted (Fig. not shown) and the activation energy of Zn(II) sorption on HAMDP was calculated from the slope of the straight line obtained. Basically, the magnitude of activation energy has been typically applied to differentiate between physiosorption and chemisorption of adsorption process.

The activation energy for Zn(II) adsorption in this study was discovered to be 10.55 kJ mol⁻¹ for initial concentration of 50 mg/L. That finally confirmed Zn(II) ions are physically adsorbed on HAMDP [44,45].

ACCEPTED MANUSCRIPT

27 3.10 Biosorption Thermodynamic studies

Experimentation was performed for temperature range from 303 to 323 K with initial metal concentration from 50-250 mg/L. The equilibrium constant (Kc) values were calculated using:

𝐾_𝑐 =𝐶_𝐴𝑒

𝐶_𝑒 (21)

Where CAe (mg/L) and Ce (mg/L) are the amount of adsorbate on the biosorbent at equilibrium and amount of adsorbate remained in the solution at equilibrium, respectively.

Gibbs free energy (ΔG°) was computed as:

𝛥𝐺° = 𝑅𝑇𝑙𝑛𝐾_𝑐 (22)

Where T (K) is the absolute temperature and R is universal gas constant (8.314 J/mol-K).

The values of enthalpy (ΔH°) and entropy (ΔS°) changes were calculated using Van’t Hoff equation given as:

𝑙𝑛𝐾_𝑐 = 𝛥𝑆°

𝑅 −𝛥𝐻°

𝑅𝑇 (23)

ACCEPTED MANUSCRIPT

28

A plot of lnKc versus 1/T (Fig. not shown) was used to evaluate the values of ΔH° and ΔS°. The result (Table S1. In supplementary materials) showed exothermic and spontaneous reactions with negative entropy change that partially “retard” adsorption process [46] which also decreases in solid/solution interface randomness [47]. The spontaneity of the biosorption process at initial Zn(II) concentrations increases with increase in reaction temperature.

3.11 Desorption Studies

Batch desorption experimentations were conducted in a single metal ion system containing 100 mg/L of Zn(II) and multi-metal ions system of Zn(II) 100 mg/L along with other heavy metals precisely Cu(II), Pb(II), Mn(II) and Ni(II) each of equal concentrations of 50 mg/L. The main idea behind multi-metal ion system is; in raw industrial effluents, the constituent involves several pollutants, impliedly not only single heavy metal is usually discharged. Therefore, the ability of other heavy metal ions hindering the adsorption of the pollutant in question is the basic concept described by multi-metal ions system. Eluents applied to remove Zn(II) on the surface of HAMDP are acids (HCl and HNO3), alkaline (NaOH and KOH) and saline (NaCl and KCl) using different concentrations of each compound (0.05 N and 0.1 N) and the outcome was summarized [Table 7 (a) and (b)]. To check out the leaching of Zn(II) ions from AMPD, a control experiment was run in deionized water. The biosorption of Zn(II) on HAMDP in single metal ion system was 94±0.1

% [Table 7 (a)] while, in multi-metal system, the biosorption was 63.31 % [Table 7(b)]. The decrease in adsorption efficiency of Zn(II) in multi-metal system might be due to the hindrance caused by the other heavy metals present in the treated solution while competing with Zn(II) to

ACCEPTED MANUSCRIPT

29

occupy active biosorbent surface. Based on controlled experiment using deionized water as an eluent, no traceable amount of Zn(II) ions in both single and multi-metal systems were leached from HAMDP. The desorption of Zn(II) in single and multi-metal systems by alkaline solutions at different concentrations ranged between 0 - 8.5 %. In addition, desorption in saline was between 15-46.5 % which is much higher than that of alkaline. Recovery of Zn(II) in single metal system data using acids gave a remarkable performance. Almost 100 % of the adsorbed Zn(II) was removed from HAMDP when HCl solution at different concentrations was applied showing involvement of ion-exchange mechanism for the process [Table S7 (a)]. However, in multi-metal system, desorption in acidic medium was reduced to 54 % [Table 7(b)]. Comparing the performance of HCl with that of HNO3 [Table 7(a)], the earlier acid is considered as best reagent to desorb and possibly recover Zn(II) ions adsorbed on HAMDP. Therefore, HCl served two significant purposes in this work, namely; good modification reagent as well as better eluent to recover Zn(II) adsorbed on HAMDP.

3.12 Regeneration Studies

To investigate the reusability of HAMDP, regeneration studies were carried out in batch adsorption process. For five consecutive cycles, biosorption of Zn(II) observed ranged 91.75 to 90.55 % (Fig.

7), showing a negligible variation. That depicted the possibility to reuse the biosorbent making the process economically viable. Similarly, desorption of Zn(II) was almost 100 %, confirming the performance of HCl as a fruitful eluent as described in desorption studies. This study also revealed that HCl has the potential to modify the surface of HAMDP and desorb Zn(II) attached to the biosorbent without altering the surface-active sites of the biosorbent. That further ratifies the two significant roles that HCl played in this work. Additionally, since the variation in adsorption of

ACCEPTED MANUSCRIPT

30

Zn(II) on HAMDP for the first five cycles is quite negligible, it could further be reused beyond fifth cycle.

3.13 Comparison with other Biosorbents

The current biosorption result was compared with reported outcomes in the literature. Table 8 summarized the values of maximum adsorption capacities from different biosorbents. The value of adsorption capacity in the present work is significantly considerable compared to the amount reported. However, sulfured orange peel is the biosorbent with higher uptake capacity (80 mg/g) among the list. Sulfured orange peels abided by several modification procedures, i.e., pretreatment by 1 % of NaOH, ethanol as well as mercaoto-acetic acid solutions [27]. Similarly, Guo and his co-authors reported KCl modified orange peel as fruitful biosorbent in treatment of Zn(II) from wastewater [48]. Prior to pretreatment of the biosorbent with KCl, it also passed through ethanol and NaOH treatment which led to maximum adsorption capacity of 45 mg/g. While HAMDP used in this work undergo a simple HCl pretreatment yielded maximum adsorption capacity of 36.73 mg/g. Thus, the present work revealed that HAMDP is an effective, efficient, economical and most importantly “renewable and sustainable” biosorbent for treatment of Zn(II) from wastewater.

ACCEPTED MANUSCRIPT

31 4.0 Conclusions

Biosorption of Zn(II) on HAMDP was investigated by batch adsorption studies.

Spectroscopic characterization of the biosorbent revealed that the biosorption process is influenced by the functional groups and bonds active on the durian peels. Adsorption isotherm indicated that the process is highly dependent on certain operating parameters not limited to solution pH, HAMDP dose, contact time, initial Zn(II) concentration and reaction temperature. The optimum conditions were pH of 8, biosorbent dose of 0.5 g, 4 hours contact time, and 313 K reaction temperature. Applicability of Tempkin Isotherm model was observed in non-linear isotherm model, evidently with higher regression coefficient value (1.00) at all investigated reaction temperatures. Maximum adsorption capacity was described by Langmuir isotherm which is 36.73 mg/g at 313 K. Kinetic studies showed applicability of pseudo-second-order model where the adsorption process is physical in nature. Thermodynamic studies indicated that the process is exothermic and spontaneous. Batch desorption studies revealed maximum removal of Zn(II) on HAMDP when HCl was used as eluent. Regeneration studies depicted that HAMDP is economically viable. Finally, HCl was considered to be a good modification reagent as well as best eluent in Zn(II) recovery. Therefore, the present investigation revealed that HAMDP is relatively effective, efficient, economical and most importantly “renewable and sustainable”

biosorbent for treatment of Zn(II) from wastewater.

Acknowledgements

ACCEPTED MANUSCRIPT

32

This work was financially supported by Ministry of Higher Education of Malaysian Government and University Putra Malaysia (GP-IPS/2016/9482900).

References

[1] C.F. Carolin, P.S. Kumar, A. Saravanan, G.J. Joshiba, M. Naushad, Efficient techniques for the removal of toxic heavy metals from aquatic environment: a review, J. Environ Chem Eng. (2017) 2782-2799.

[2] J. Zhang, F. Bi, Q. Wang, W. Wang, B. Liu, S. Lutts, W. Wei, Y. Zhao, G. Wang, R. Han, Characteristics and influencing factors of cadmium biosorption by the stem powder of the invasive plant species Solidago canadensis, Ecol. Eng. (2017) https://doi.org/10.1016/j.ecoleng.2017.10.001.

[3] J. Milojković, L. Pezo, M. Stojanović, M. Mihajlović, Z. Lopičić, J. Petrović, M. Stanojević, M. Kragović, Selected heavy metal biosorption by compost of Myriophyllum spicatum-A chemometric approach, Ecol. Eng. 93 ( 2016) 112–119.

[4] K.S. George, K.B. Revathi, N. Deepa, C.P. Sheregar, T.S. Ashwini, S. Das, A Study on the potential of moringa leaf and bark extract in bioremediation of heavy metals from water collected from various lakes in Bangalore, Procedia Environ Sci. 35 (2016) 869-880.

[5] A. Verma, S. Kumar, S. Kumar, Biosorption of lead ions from the aqueous solution by Sargassum filipendula: equilibrium and kinetic studies, J. Environ. Chem. Eng. 4 (2016) 4587–4599.

[6] A. Bhatnagar, M. Sillanpää, A. Witek-Krowiak, Agricultural waste peels as versatile biomass for water purification–A review, Chem. Eng. J. 270 (2015) 244–271.

[7] V. Mishra, Biosorption of zinc ion: a deep comprehension, Appl. Water Sci. 4 (2014) 311–332.

[8] S. Srivastava, S.B. Agrawal, M.K. Mondal, A review on progress of heavy metal removal using adsorbents of microbial and plant origin, Environ. Sci. Pollut. Res. 22 (2015) 15386–15415.

[9] Y. Yi, J. Lv, N. Zhong, G. Wu, Biosorption of Cu 2+ by a novel modified spent Chrysanthemum：kinetics, isotherm and thermodynamics, J. Environ. Chem. Eng. 5 (2017) 4151–4156.

[10] T.A.H. Nguyen, H.H. Ngo, W.S. Guo, J. Zhang, S. Liang, Q.Y. Yue, T.V. Nguyen, Applicability of agricultural waste and by-products for adsorptive removal of heavy metals from wastewater, Bioresour. Technol. 148 (2013) 574–585.

[11] World Health Organization (W.H.O.), Guidelines for Drinking-Water Quality, Fourth ed.

World Health Organization, Geneva, (2011) pp. 433-434.

[12] L. Sellaoui, T. Depci, A.R. Kul, S. Knani, A.B. Lamine, A new statistical physics model to interpret the binary adsorption isotherms of lead and zinc on activated carbon, J. Mol. Liq.

214 (2016) 220–230.

[13] S. Malamis, E. Katsou, A review on zinc and nickel adsorption on natural and modified zeolite, bentonite and vermiculite: examination of process parameters, kinetics and isotherms, J. Hazard. Mater. 252 (2013) 428–461.

ACCEPTED MANUSCRIPT

33

[14] M. Fomina, G.M. Gadd, Biosorption: current perspectives on concept, definition and application, Bioresour. Technol. 160 (2014) 3–14.

[15] Y.Y. Voon, N.S.A. Hamid, G. Rusul, A. Osman, S.Y. Quek, Characterisation of Malaysian durian (Durio zibethinus Murr.) cultivars: relationship of physicochemical and flavour properties with sensory properties, Food Chem. 103 (2007) 1217–1227.

[16] S. Patel,. Potential of fruit and vegetable wastes as novel biosorbents: summarizing the recent studies, Rev. Environ. Sci. Bio/Technology 11 (2012) 365–380.

[17] M.A. Khan, M. Ngabura, T.S. Choong, H. Masood, L.A. Chuah, Biosorption and desorption of Nickel on oil cake: batch and column studies, Bioresour. Technol. 103 (2012) 35–42.

[18] A. Ismail, H. Sudrajat, D. Jumbianti, Activated carbon from durian seed by H3PO4 activation:

preparation and pore structure characterization. Indones. J. Chem. 10 (2010) 36–40.

[19] E.L. Cochrane, S. Lu, S.W. Gibb, I. Villaescusa, A comparison of low-cost biosorbents and commercial sorbents for the removal of copper from aqueous media, J. Hazard. Mater. 137 (2006) 198–206.

[20] R.M. Silverstein, F.X. Webster, Spectrometric identification of organic compounds, Sixth Edition. ed. John wiley & sons (1998) pp. 71-109.

[21] N. Feng, X. Guo, S. Liang, Y. Zhu, J. Liu, Biosorption of heavy metals from aqueous solutions by chemically modified orange peel, J. Hazard. Mater. 185 (2011) 49–54.

[22] N.V. Farinella, G.D. Matos, M.A.Z. Arruda, Grape bagasse as a potential biosorbent of metals in effluent treatments, Bioresour. Technol. 98 (2007) 1940–1946.

[23] S.M. Anisuzzaman, C.G. Joseph, D. Krishnaiah, A. Bono, L.C. Ooi, Parametric and adsorption kinetic studies of methylene blue removal from simulated textile water using durian (Durio zibethinus murray) skin, Water Sci. Technol. 72 (2015) 896–907.

[24] T.J. Mays, A new classification of pore sizes, Stud. Surf. Sci. Catal. 160 (2007) 57–62.

[25] U. Israel, U.M. Eduok, Biosorption of zinc from aqueous solution using coconut (Cocos nucifera L) coir dust, Arch. Appl. Sci. Res. 4 (2012) 809–19.

[26] Z. Kılıç, O. Atakol, S. Aras, D. Cansaran-Duman, E. Emregul, Biosorption properties of zinc (II) from aqueous solutions by Pseudevernia furfuracea (L.) Zopf, J. Air Waste Manage.

Assoc. 64 (2014) 1112–1121.

[27] S. Liang, X. Guo, Q. Tian, Adsorption of Pb ²⁺ and Zn ²⁺ from aqueous solutions by sulfured orange peel, Desalination 275 (2011) 212–216.

[28] C. Paduraru, L. Tofan, C. Teodosiu, I. Bunia, N. Tudorachi, O. Toma, Biosorption of zinc (II) on rapeseed waste: equilibrium studies and thermogravimetric investigations, Process Saf.

Environ. Prot. 94 (2015) 18–28.

[29] X.S. Wang, Y. Qin, Z.F. Li, Biosorption of zinc from aqueous solutions by rice bran: kinetics and equilibrium studies, Sep. Sci. Technol. 41 (2006) 747–756.

[30] S. Pap, J. Radonić, S. Trifunović, D. Adamović, I. Mihajlović, M.V. Miloradov, M.T. Sekulić, Evaluation of the adsorption potential of eco-friendly activated carbon prepared from cherry kernels for the removal of Pb²⁺, Cd²⁺ and Ni²⁺ from aqueous wastes, J. of Environ.

Manag. 184 (2016) 297–306.

[31] M. Ahmaruzzaman, Industrial wastes as low-cost potential adsorbents for the treatment of wastewater laden with heavy metals, Adv. Colloid Interface Sci. 166 (2011) 36–59.

[32] V.O. Arief, K. Trilestari, J. Sunarso, N. Indraswati, S. Ismadji, Recent progress on biosorption of heavy metals from liquids using low cost biosorbents: characterization, biosorption parameters and mechanism studies, CLEAN–Soil, Air, Water. 36 (2008) 937–962.

ACCEPTED MANUSCRIPT

34

[33] P. King, N. Rakesh, S.B. Lahari, Y.P. Kumar, V. Prasad, Biosorption of zinc onto Syzygium cumini L.: equilibrium and kinetic studies, Chem. Eng. J. 144 (2008) 181–187.

[34] C. Yang, J. Wang, M. Lei, G. Xie, G. Zeng, S. Luo, Biosorption of zinc (II) from aqueous solution by dried activated sludge, J. Environ. Sci. 22 (2010) 675–680.

[35] G. Taha, A. Arifien, S. El-Nahas, Removal efficiency of potato peels as a new biosorbent material for uptake of Pb(II) Cd(II) and Zn(II) from their aqueous solutions, The JSWTM, 37 (2011) 128–140. https://doi.org/10.5276/JSWTM.2011.128

[36] D. Das, G. Basak, V. Lakshmi, N. Das, Kinetics and equilibrium studies on removal of zinc (II) by untreated and anionic surfactant treated dead biomass of yeast: batch and column mode, Biochem. Eng. J. 64 (2012) 30–47.

[37] Metcalf & Eddy Inc., Wastewater engineering: treatment and reuse (Fourth Edition), New York McGraw Hill, (2003) pp. 1138-1141.

[38] I. Langmuir, The constitution and fundamental properties of solids and liquids, Part I. Solids, J. Am. Chem. Soc. 38 (1916) 2221–2295.

[39] H.M.F. Freundlich, Over the adsorption in solution, J. Phys. Chem. 57 (1906) 385-470.

[40] M.I. Tempkin, V. Pyzhev, Kinetics of ammonia synthesis on promoted iron catalyst, Acta Phys. Chim. USSR, (1940) 12, 327.

[41] S. Lagergren, About the theory of so-called adsorption of soluble substances. K. Sven.

Vetenskapsakad, Handl. 24 (1898) 1–39.

[42] Y.S. Ho, G. McKay, The kinetics of sorption of divalent metal ions onto sphagnum moss peat, Water Res. 34 (2000) 735–742.

[43] W.J. Weber, J.C. Morris, Kinetics of adsorption on carbon from solution, J. Sanit. Eng. Div.

89, (1963) 31–60.

[44] N.S. Randhawa, D. Dwivedi, S. Prajapati, R.K. Jana, Application of manganese nodules leaching residue for adsorption of nickel (II) ions from aqueous solution, Int. J. Environ.

Sci. Technol. 12 (2015) 857–864.

[45] V.C. Srivastava, I.D. Mall, I.M. Mishra, Characterization of mesoporous rice husk ash (RHA) and adsorption kinetics of metal ions from aqueous solution onto RHA, J. of Hazard. Mater.

134 (2006) 257–267.

[46] A. Ramesh, D.J. Lee, J.W.C. Wong, Thermodynamic parameters for adsorption equilibrium of heavy metals and dyes from wastewater with low-cost adsorbents, J. Colloid Interface Sci. 291 (2005) 588–592.

[47] Y. Chang, J.Y. Lai, D.J. Lee, Thermodynamic parameters for adsorption equilibrium of heavy metals and dyes from wastewaters: research updated, Bioresour. Technol., 222 (2016) 513–

516.

[48] X.Y. Guo, S. Liang, Q.H. Tian, Removal of heavy metal ions from aqueous solutions by adsorption using modified orange peel as adsorbent, in: Advanced Materials Research, Trans Tech Publ, 236-238 (2011) 237–240. https//doi.org/10.4028/www.scientific.net/AMR.236- 238.237

[49] M. Iqbal, A. Saeed, I. Kalim, Characterization of adsorptive capacity and investigation of mechanism of Cu²⁺, Ni²⁺ and Zn²⁺ adsorption on mango peel waste from constituted metal solution and genuine electroplating effluent, Sep. Sci. Technol. 44 (2009) 3770–3791.

[50] W.E. Oliveira, A.S. Franca, L.S. Oliveira, S.D. Rocha, Untreated coffee husks as biosorbents for the removal of heavy metals from aqueous solutions, J. Hazard. Mater. 152 (2008) 1073–

1081.

ACCEPTED MANUSCRIPT

35

[51] Y.P. Kumar, P. King, V. Prasad, Zinc biosorption on Tectona grandis Lf leaves biomass:

equilibrium and kinetic studies, Chem. Eng. J. 124 (2006) 63–70.

[52] F.A. Abu Al-Rub, Biosorption of zinc on palm tree leaves: equilibrium, kinetics, and thermodynamics studies, Sep. Sci. Technol. 41 (2006) 3499–3515.

ACCEPTED MANUSCRIPT

36 (a)

(b)

ACCEPTED MANUSCRIPT

37 (c)

(d)

Fig. 1. (a) Pristine durian peel, 10.9 mm x 1.00k SE; (b) HAMDP, 11.2mm x 3.0k SE;

(c) biosorbent after Zn(II) adsorption, 11.2mm x 3.00k SE and (d) biosorbent after Zn(II) desorption, 11.3mm x 1.00k SE.

ACCEPTED MANUSCRIPT

38

Fig. 2. Effect of pH on biosorption of Zn(II) on HAMDP at room temperature (27 ± 0.5) and 0.5 g adsorbent dose

0 2 4 6 8 10 12

0 2 4 6 8 10 12

qe(mg/g)

pH (-)

0 10 20 30 40 50 60 70 80 90 100

0 5 10 15 20 25 30

0 0.5 1 1.5 2

Removal (%)