Application of agro-waste rice husk ash for the removal of phosphate from the wastewater

Application of agro-waste rice husk ash for the removal of phosphate from the wastewater

Accepted Manuscript Application of Agro-waste Rice Husk Ash for the Removal of Phosphate from the Wastewater Suman Mor, Kalzang Chhoden, Ravindra Khai...

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Accepted Manuscript Application of Agro-waste Rice Husk Ash for the Removal of Phosphate from the Wastewater Suman Mor, Kalzang Chhoden, Ravindra Khaiwal PII:

S0959-6526(16)30157-3

DOI:

10.1016/j.jclepro.2016.03.088

Reference:

JCLP 6937

To appear in:

Journal of Cleaner Production

Received Date: 22 December 2015 Revised Date:

16 February 2016

Accepted Date: 11 March 2016

Please cite this article as: Mor S, Chhoden K, Khaiwal R, Application of Agro-waste Rice Husk Ash for the Removal of Phosphate from the Wastewater, Journal of Cleaner Production (2016), doi: 10.1016/ j.jclepro.2016.03.088. 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.

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Word Count: 5098 Application of Agro-waste Rice Husk Ash for the Removal of Phosphate from the Wastewater

Department of Environment Studies, Panjab University (PU), Chandigarh, 160014, India 2 Centre for Public Health, Panjab University (PU), Chandigarh 160025, India 3 School of Public Health, Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, 160012, India *Corresponding Author E-mail: [email protected], [email protected] ABSTRACT

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Suman Mor 1,2, Kalzang Chhoden1, Ravindra Khaiwal3*

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Discharge of phosphate into aquatic environment by various human activities such as agricultural runoff, animal waste, sewage, industry and detergents, lead to the deterioration of water quality. Hence, the effective removal of phosphate from wastewater is essentially required. Considering this, the efficiency of locally available agro-waste rice husk was examined in batch mode for the removal of phosphate using synthetic wastewater. Characterization of adsorbent was done using Fourier transform infrared, X-ray fluorescence and X-ray diffraction spectrophotometeric

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analysis, which indicates the crystalline silica nature and presence of Si-O-Si group. The effect of various parameters i.e. contact time, adsorbent dose, pH and temperature were studied. Up to 89% phosphate removal was achieved at pH 6 using 2g/L dose in 120 min of contact time. The equilibrium adsorption data shows best fit for the Langmuir isotherm model (R2=0.991) and

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pseudo-second order kinetic model (R2 = 0.978). Thermodynamic parameters (ΔG, ΔH and ΔS) were also calculated and they indicate that adsorption process is exothermic. Scanning electron

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microscopy reveals the rough surface of absorbent, which may increases the adsorption capacity. Based on the current study, activated rice husk ash offers efficient and cost- effective removal of phosphate from wastewater.

Key words: Agricultural waste, Activated rice husk ash, Phosphate removal, Wastewater, Adsorption isotherms, Adsorption kinetics

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1. INTRODUCTION Phosphorus is mainly used in agriculture sector as fertilizer and in households as detergent, resulting in release of phosphate into the environment (Rout et al., 2014). The other major sources of phosphate includes weathering of rocks as well as industrial activities (Baghel et al.,

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2006). Phosphate is essential for the growth of aquatic life and plants, however high concentration of phosphate in water leads to the algal bloom and anoxic condition (Hussain et al., 2011; Peltzer et al., 2008). Eutrophication mainly occurs when the phosphate concentration is higher than the 0.02 mg/l in water bodies (Kilpimaa et al., 2014) and several studies reports

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that even the groudwater quality in the region is deteriorated (Mor et al., 2003, 2009; Kumar et

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al., 2011).

Leaching of phosphate into the ground water through the subsoil also affect the drinking water quality leading to potential risk to human health and animals Mor et al., 2006a,b; WiumAndersen et al., 2013, Ravindra et al., 2007, 2015). Kidney damage and osteoporosis have been reported due to the consumption of high concentration of phosphate (Oliveira et al., 2012). The continuous discharge of phosphate level in water system stimulates the growth of toxins in the

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water bodies (Zhang et al., 2011). Hence, there is a need to develop a process for both removal and recovery of phosphate from domestic and industrial wastewater. A number of studies have been reported using physical, chemical and biological processes for the removal of phosphate from wastewater (Huang et al., 2008). Although, advance techniques such as electrodialysis,

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reverse osmosis, membrane process, flocculation are considered successful (Huang et al., 2015), but they require high capital investment and operation cost. Therefore, most of the researchers are efficient, viable and cost effective

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look for locally available adsorbent as they offer solutions.

Various studies have shows the application of different waste materials such as red mud (Akay et al., 1998), fly ash ( Yildiz et al., 2004), coal fly ash ( Pengthamkeerati et al., 2008), waste scallop shell ( Yeom et al., 2009), wheat residue ( Xu et al., 2009), carbon fibre ( zhang et al., 2011), lanthanum doped carbon (Liu et al., 2011), calcine egg ( Kosi et al., 2011), nanocomposite ( Oliveira et al., 2012), ), Fe-Al-Mn (Li et al., 2013), ), modified carbon residue (Kilipma et al., 2014), ground burnt patties ( Rout et al., 2014), red seaweed (Rathod et al., 2

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2014), fruit juice residue (Yadav et al., 2015), aerobic digestion (Huang et al., 2015),

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dung ash (Kaur et al., 2016)for the removal of phosphate from the wastewater. Agro residue rice husk is the outer covering of paddy and accounts for 20–25% of its weight. It

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accounts for about one fifth of the gross rice production of 545 million metric ton of the worldwide (Mohamed et al., 2015). The annual generation of rice husk in India is in the range of 18–22 million tons (Srivastava et al., 2006 ). Rice husk ash is an agricultural waste obtained from the rice mill. Rice husk removal during rice refining, creates disposal problem due to its

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low commercial value. Also the handling and transportation of rice husk ash is problematic due to its low density. Much of the rice produced from the processing of rice is either burnt or dumped as waste. Burning of rice husk in open fields cause environmental and health problems

fully utilize the rice husk ash.

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in the surrounding areas especially in developing countries. Therefore, it is very important to

In recent years, attention has been focused on the utilization of unmodified and modified rice husk as adsorbent for the removal of various contaminants (Manique et al., 2012). The present study deals with the utilization of agro-waste rice husk ash for the removal of phosphate from

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wastewater. Batch mode adsorption studies were performed to study the influences of various experimental parameters like pH, adsorbent dosage, contact time and the effect of temperature using activated rice husk ash (ARHA). Various kinetic and isotherm models were also applied to

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investigate the adsorption capacity of ARHA for phosphate removal from wastewater. 2. MATERIALS AND METHODS

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2.1. Preparation and characterization of adsorbent Rice husk ash (raw material) for the experiment was obtained from a rice mill from Panipat and passed through sieve (IS 460:1962, 710µm) before the pretreatment. The Rice husk ash was washed properly using distilled water and heated at 500oC for 2 hours in muffle furnaces. The rice husk ash was than activated to modify the surface characteristics using HCl (1N). The mixture of HCl and rice husk ash (1:1 ratio) was kept for 24 hours at room temperature to prepare the ARHA. Thereafter, ARHA was washed with distilled water until neutral pH was obtained and later dried at 110oC in oven for 24 hours to achieve constant weight and sieved 3

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again to ensure uniform particle size. Characterization of adsorbent was done using x-ray fluorescence spectrometer (XRF), to examine the major and trace element present in the adsorbent. The sample was analyzed in

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Wavelength Dispersive X-Ray Fluorescence (WD-XRF, Model: S8 TIGER, Make Bruker, Germany). The X-ray diffraction (XRD) technique was used to know the crystalline and noncrystalline nature of the material. XRD of the rice husk ash was done using Panalytical D/Max2500 X-ray diffractrometer equipped with Cu-K radiation (1.5406 Å) operating at 40 kV, 50 mA

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with scanning rate of 0.02 s−1. Scanning electron microscopy (SEM) analysis of the adsorbent is also done by using (HITACHI JAPAN Model no 3400 YEN) in the range of 10.1 mm x 8.00k – 10.00 mm x 250 SE magnification. FTIR spectrometer (Thermo Nicolet, Model Magna 760) was

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used to determine the functional groups using pellet (pressed-disk) method. The spectral range varied from 4000 to 400 cm−1. Fourier transform infrared (FTIR) study identify the specific functional groups in adsorption interaction. 2.2. Batch adsorption Experiments

Adsorption experiments were carried out in batch mode by using different amount of ARHA

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with 25 ml of synthetic wastewater in 100 ml of conical flask and then shaked on rotary shaker at 150 rpm at 25oC temperature. Phosphate stock solution (1000ppm) was prepared by dissolving 4.39 g potassium dihydrogen phosphate (KH2PO4) in 1L of distilled water. Further serial dilutions were made to have synthetic wastewater of desired phosphate concentration (10 ppm).

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Adsorption studies were performed ranging pH from 2-10 with dose varying from 0.4g/L to 4g/L and having contact time of 60-240 min. After adsorption, the solution was filtered through

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the whatsman filter paper (42 No: 125mm) and phosphate concentration from treated solution was analyzed spectrophotometerically (Make: Shimadzu-1800) at adsorption range of 690 nm using stannous chloride method. The percentage removal of phosphate was calculated by using the formula given below:

% R emoval efficiency =

Co − Ce X 100 Co

... (1)

Where Co is the initial concentration (mg/l) and Ce is the final concentration of phosphate (mg/L). 4

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2.3. Adsorption isotherms and kinetics Adsorption isotherm experiments were conducted varying contact time from 60-240 min with initial phosphate concentration of 10 ppm at different temperature. Adsorption isotherms show

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the relation between the adsorbate and extent of adsorbate adsorbed on the surface of the adsorbent at constant temperature (Inyang et al., 2012). The different isotherms and kinetics were used to determine the adsorption capacity of the adsorbent.

Langmuir isotherm determines the adsorption of ions on the surface of the adsorbent on the

given below:

....(2)

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Ce C 1 = b+ e q e q max q max

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monolayer and equivalent sites on the surface ( Wang & Qin, 2006). The Langmuir adsorption is

Where qe is the total ions adsorbed on the adsorbent (mg/g), Ce represents equilibrium concentration of ions (mg/l), b is Langmuir constant (L/mg), qmax indicates total number of binding sites or alternatively represents the maximum amount of ion per unit mass of adsorbent.

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Fruindlich isotherm is based on the multilayer adsorption with heterogenous surfaces and can be define as below:

1 log Ce n

… (3)

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log Qe = log k +

Where k is Freundlich constant that depends upon the nature of adsorbate and adsorbent and n

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indicates the adsorption capacity of adsorbent and the intensity of adsorption. Tempkin

isotherm

model

involves

a

factor

that

allows

for

interactions between adsorbents and adsorbates. The adsorption heat of all molecules present in the layer linearly decreases with the coverage due to adsorbent–adsorbate interactions. Uniform distribution of binding energies up to maximum binding energy, is used to characterize the adsorption (Javadian, 2014). The Tempkin model equation is explained below: q e = B1 ln K T + B1 ln Ce

... (4)

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Where KT is equilibrium binding constant and B1 related to the heat of the adsorption. The value of KT and B1 are obtained by using linear plot qe against the lnCe. The nature of adsorption process may also be analyzed using Dubinin-Redushkevich isotherm as

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detailed below: ln qe = K 2 e + ln q DR

………… (5)

Polani potential (ε) is given as:



1 Ce

  

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ε = RT ln1 +

…………… (6)

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Where qs is the maximum amount of adsorbate that can be adsorbed on adsorbent, B is the constant related to energy, R is the universal gas constant (8.314 J mol-1 K-1) and t is temperature. The Dubinin-Redushkevich constant can give the mean free energy of adsorption by the equation. 1 (2 B ) 1 / 2

……………….. (7)

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Ε=

Mean adsorption energy (E) value gives the information about the chemical or physical properties of the adsorption mechanism.The study of adsorption kinetics includes the careful

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monitoring of experimental condition which influences the speed of a chemical reaction and hence helps to attain the equilibrium in a reasonable period of time. Different kinetic models like pseudo-first order, pseudo-second order have been used to identify the dynamics of the

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adsorption process. Pseudo-first order kinetics equation is given below (Han et al., 2013): log( qe − qt ) = log qe −

k1 t 2.303

… (8)

Where qe and qt are the amount of phosphate adsorbed at equilibrium and at time t. The pseudofirst order rate constant is represented as k1. Adsorption kinetics were calculated using pseudo-second order method which can be determined by using following equation ( Wang et al., 2010). 6

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t 1 1 = + t 2 qt k 2 q e qe

... (9)

Where qe is the equilibrium adsorption, qt shows adsorption at time t, K1 and K2 are rate

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constants for pseudo-first order and pseudo-second order, respectively.

3. RESULTS AND DISCUSSION 3.1 Characterization of adsorbent

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XRF analysis shows that the major composition includes oxides of silica along with the various other elements as shown in Table 1. Phase analysis and the nature of ash were confirmed using

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XRD technique. Diffraction pattern of the treated ash confirmed the presence of silicon (Si) and observed to be the major phase in the adsorbent after the chemical treatment (Katal et al., 2012). Silica was found to be the only major constituent as shown by the highest peak located and some other elements were also observed but in traces, as shown by small peaks (Fig 1). The sharp peak indicates the cristobalite, a crystalline phase of silica at 20-40 2-Theta degree (Foletto et al., 2009). ARHA powder was observed to be crystalline as seen in Fig.1 (a). SEM shows the

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morphology of ARHA and indicates the presence of needle shape structure and porous and rough surface (Fig. 2a). The presence of fine particle after chemical activation of rice husk ash is also shown in (Fig 7b). FTIR results show that mainly four peaks were detected in all cases of ARHA as visible in Fig. 1(b). It could also be observed that adsorption peaks around 3476.26 cm-1

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indicate the presence of free hydroxyl groups (Bansal et al., 2009). The peaks around 1096.91, 792.80, 1884.15 cm-1 corresponds to Si-O-Si, Si-H, C=O groups respectively (Dey et al., 2013;

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Srivastava et al., 2006). The presence of polar groups on the surface increases the cation exchange capacity of the adsorbents. FTIR analysis of rice husk ash also showed the presence of silica content which has a high adsorptive capacity.

3.2 Effect of adsorbent dose and contact time The removal of phosphate was studied using synthetic wastewater containing 10 ppm of phosphate. Adsorption of phosphate using ARHA was investigated varying contact time (60-240 min) and adsorbent dose (0.4 g/L – 4g/L) at 25oC and 150 rpm of agitating speed. It was observed that the removal efficiency increases with increasing the contact time. Maximum 7

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89.1% removal was observed using 2g/L dose in 120 minutes (Fig.3). The result indicates that the adsorption of phosphate ions increases with the increase in the contact time and after achieving maximum removal desorption process starts. Hence, increase in the adsorbent dose

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does not increase the adsorption of phosphate showing that equilibrium was achieved. In agreement with current work, several other studies also reported that sorption of phosphate increases as contact time increases (Lu et al., 2013; Rahman et al., 2011). Similar results were also observed by Kose & Kıvanc (2011) using eggshell for the removal of phosphate. High

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adsorbent dose increases the percentage removal of phosphate as it provide more free sites leading to increase in net surface area of adsorbent. However, further increase in the adsorbent

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dose may cause aggregation of adsorbent resulting in decrease in available adsorption sites.

3.3 Effect of pH

The degree of ionization and speciation of adsorbate is mainly affected by pH of solution (Chaudhary et al., 2013, Liu et al., 2013). Hence the removal of phosphate was studied using

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synthetic wastewater containing 10 ppm of phosphate and ranging pH from 2.0 to 10.0. The results show that the percentage removal decreases with increases in pH of the solution (Fig. 4). Maximum removal up to 91.7% was observed at pH 2.0 indicating that the phosphate removal is more efficient under acidic condition and it declines with increase in pH of solution.

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Previous studies also show that with the increase in pH, adsorption capacity of the adsorbent reduces. (Huang et al., 2008; Xiong et al., 2008). High pH leads to dissociation of functional

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groups thereby carries more negative ions which resist phosphate ions interacting with the surfaces, thus decreasing phosphate adsorption. Mor et al. (2007) also highlight that adsorption is also affected by the type and ionic state of the functional group present in the adsorbent and the chemistry of the adsorbate solution. At lower pH the attraction of positive ions towards the PO 43− ions to form the stable ion is more hence pH of solution also affects the removal percentage of phosphate. Decrease in removal of phosphate ions at higher pH is probably due to the higher concentration of hydroxyl ions, present in the reaction mixture which competes with the PO 43− ions for the sorption sites (Rathod et al., 2014). Xiong et al., 2008 also report 8

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maximum phosphate adsorption at pH 5.5 using steel slag and mentioned that lower adsorption of phosphate at higher pH may be due the increased repulsion between the more negatively charged PO43− species and negatively charged surface sites.

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3.4 Effect of temperature

The effect of temperature on the removal of phosphate ions was also investigated as a function of contact time. Experiments were conducted at different temperature keeping the dose (2g/L) and pH (6) constant and varying the temperature from 25oC to 40oC.. Maximum phosphate removal

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of 75.5% was observed at 30oC at 120 minute of contact time (Fig. 5). El-Naas et al., (2010) reported that with increase in temperature adsorption capacity increases. However, in the current

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study, when the temperature was increased 30 oC to 40 oC; decrease in adsorption of phosphate from 75.5% to 55.2 % was observed. This indicates the exothermic nature of adsorption process as detailed in section 3.5. Further, decrease of adsorption with increasing temperature may be due to the weakening of the sorptive forces between the active sites on the sorbent and the adsorptive species.

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3.5 Determination of thermodynamic parameters

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The thermodynamics parameters of the adsorption process are obtained from experiments at various temperatures. The free energy change (∆G◦) for adsorption process was calculated using

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the equation:

∆ G◦ = −RT ln Kb

[1]

Where b is the Langmuir constant, R is the universal gas constant and T is temperature in Kelvin. The value of enthalpy change (∆H◦) and entropy change (∆So) are determined from the slope and intercept of the following equations.

∆G◦ = ∆H◦ − T∆S◦

[2]

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The calculated value of thermodynamic parameters is presented in Table 2. The negative value of ∆G◦ indicates the decrease in Gibbs free energy and hence the adsorption process was favorable and spontaneous. Negative value of ΔH◦ (Fig 6) also confirms the exothermic nature of adsorption process. The positive value of ΔSo suggests increase in randomness at the interface of

exothermic nature of the adsorption process.

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3.6 Adsorption isotherms and kinetics

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solid-liquid interaction. Thus, the values of ΔG◦, ΔH◦ and ΔS◦ confirm the spontaneous and

In order to determine the adsorption of phosphate over ARHA, the experimental data was

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applied to the Langmuir, Fruendlich, Tempkin, Dubinin-Redushkevichand kinetics models to find out the best fitted model as shown in Fig. 7a,b,c. The calculated adsorption data and correlation coefficient (R2) for the isotherms models were interpreted (Table 3) and based on the correlation-coefficient value for these isotherms models, it can be suggested that experimental data of phosphate removal using ARHA can be best described by the Langmuir isotherm model as it has highest R2 value. Various parameters obtained from different isotherms and kinetics

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are also shown in Table 3. As depicted in Fig 8, for Dubinin-Redushkevich isotherm, a straight line graph between Lnqe vs Log (1+1/Ce) gives the intercept and slope which yield the adsorption capacity of the adsorbent. Dubinin-Redushkevich isotherm determined the E value of

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4.05 KJ/mol, indicating that physisorption control the sorption mechanism in the current case as E is <8 KJ/mol (Fig 8). Higher value of E (>8 KJ/mol) predicts the chemisorptions in the

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adsorption process.

The adsorption kinetics describes uptake rate of the solute and governs the duration time of the adsorption process (Yadanaparthi et al., 2009). To evaluate the mass transfer process during the phosphate adsorption, Pseudo-first order and Pseudo-second order kinetic models were applied. The equilibrium data was well represented by the pseudo-second order model at 30oC. According to the linear correlation coefficient (R2) values at optimum pH, temperature and time pseudosecond order kinetics was found to be the best fitted model for phosphate removal. Pseudosecond order kinetic plot of adsorption of phosphate on rice husk ash is presented in Fig.9 (a, b).

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The Rice husk ash is a agricultural waste which is locally available in large quantity. The result indicates that chemically treated rice husk ash enhanced the adsorption capacity of phosphate and showed the maximum removal (up to 89%) of phosphate at pH 6 using 2g/L dose for 120

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min. Langmuir isotherms and pseudo-second order model depicts the best fits to the experimental data. The XRF analysis shows the presence of silica whereas XRD and FTIR study indicates the presence of crystalline silica and Si-O-Si group. SEM results show the rough surface of adsorbent which increases the adsorption capacity. Thus, the result of the study

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suggests that the ARHA ash has the potential to be used as a low-cost adsorbent for the treatment of water and wastewater treatment. Further, the utilization of agro-waste rice husk based

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absorbent will also solve its disposal problem.

Acknowledgements

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Author are thankful to the UGC, New Delhi for providing the financial assistance to carry out the research work. Author also acknowledges the Central instrumentation laboratory (CIL), Panjab University, Chandigarh for the elemental analysis. SM would like to acknowledge DST PURSE grant for partial financial assistance. RK would like to thank Department of Health Research (DHR), Indian Council of Medical Research (ICMR), Ministry of Health and Family Welfare, for providing the Fellowship Training Programme in Environmental Health under Human Resource Development Health Research Scheme.

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Manique, M. C., Faccini, C. S., Onorevoli, B., Benvenutti, E. V., & Caramão, E. B. (2012). Rice husk ash as an adsorbent for purifying biodiesel from waste frying oil. Fuel, 92(1), 56–61. http://doi.org/http://dx.doi.org/10.1016/j.fuel.2011.07.024

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Mohamed, R. M., Mkhalid, I. A., & Barakat, M. A. (2015). Rice husk ash as a renewable source for the production of zeolite NaY and its characterization. Arabian Journal of Chemistry, 8(1), 48–53. http://doi.org/10.1016/j.arabjc.2012.12.013 Mor, S., Bishnoi, M.S., Bishnoi A., (2003). Assessment of groundwater quality of Jind City. Indian Journal of Environmental Protection 23, 673-679.

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Mor, S., Singh, S., Yadav, P., Rani, V., Rani, P., Sheoran, M., ... & Ravindra, K. (2009). Appraisal of salinity and fluoride in a semi-arid region of India using statistical and multivariate techniques. Environmental geochemistry and health, 31(6), 643-655.

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Mor, S., Ravindra, K., De Visscher, A., Dahiya, R.P. and Chandra, A., (2006a). Municipal solid waste characterization and its assessment for potential methane generation: a case study. Science of the Total Environment, 371(1), pp.1-10. Mor, S., Ravindra, K., Dahiya, R. P., & Chandra, A., (2006b). Leachate characterization and assessment of groundwater pollution near municipal solid waste landfill site. Environ. Monit. Aassess. 118(1-3), 435-456.

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Mor, S., Ravindra, K., & Bishnoi, N. R. (2007). Adsorption of chromium from aqueous solution by activated alumina and activated charcoal. Bioresour Technol, 98(4), 954–957. http://doi.org/10.1016/j.biortech.2006.03.018 Oliveira, M., Machado, A. V, & Nogueira, R. (2012). Phosphorus Removal from Eutrophic Waters with an Aluminium Hybrid Nanocomposite. Water, Air, & Soil Pollution, 223(8), 4831–4840. http://doi.org/10.1007/s11270-012-1239-9

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Peltzer, P. M., Lajmanovich, R. C., Sánchez-Hernandez, J. C., Cabagna, M. C., Attademo, A. M., & Bassó, A. (2008). Effects of agricultural pond eutrophication on survival and health status of Scinax nasicus tadpoles. Ecotoxicology and Environmental Safety, 70(1), 185–97. http://doi.org/10.1016/j.ecoenv.2007.06.005

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Pengthamkeerati, P., Satapanajaru, T., & Chularuengoaksorn, P. (2008). Chemical modification of coal fly ash for the removal of phosphate from aqueous solution. Fuel, 87(12), 2469–2476. http://doi.org/10.1016/j.fuel.2008.03.013 Rahman, M. H., Lund, T., & Bryceson, I. (2011). Salinity impacts on agro-biodiversity in three coastal, rural villages of Bangladesh. Ocean & Coastal Management, 54(6), 455–468. http://doi.org/10.1016/j.ocecoaman.2011.03.003 Ravindra, K., & Garg, V. K. (2007). Hydro-chemical survey of groundwater of Hisar city and assessment of defluoridation methods used in India. Environmental Monitoring and Assessment, 132(1-3), 3343.

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Ravindra, K., Kaur, K., & Mor, S.,2015. System analysis of municipal solid waste management in Chandigarh and minimization practices for cleaner emissions. J. Clean. Prod., 89, 251-256.

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Rathod, M., Mody, K., & Basha, S. (2014). Efficient removal of phosphate from aqueous solutions by red seaweed, Kappaphycus alverezii. Journal of Cleaner Production, 84, 484–493. http://doi.org/10.1016/j.jclepro.2014.03.064 Rout, P. R., Bhunia, P., & Dash, R. R. (2014). Modeling isotherms, kinetics and understanding the mechanism of phosphate adsorption onto a solid waste: Ground burnt patties. Journal of Environmental Chemical Engineering, 2(3), 1331–1342. http://doi.org/10.1016/j.jece.2014.04.017

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Shen, J., Liu, X., Zhu, S., Zhang, H., & Tan, J. (2011). Effects of calcination parameters on the silica phase of original and leached rice husk ash. Materials Letters, 65(8), 1179–1183. http://doi.org/10.1016/j.matlet.2011.01.034

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Srivastava, V. C., Mall, I. D., & Mishra, I. M. (2006). Characterization of mesoporous rice husk ash (RHA) and adsorption kinetics of metal ions from aqueous solution onto RHA. Journal of Hazardous Materials, 134(1-3), 257–67. http://doi.org/10.1016/j.jhazmat.2005.11.052 Wang, D., Silkie, S. S., Nelson, K. L., & Wuertz, S. (2010). Estimating true human and animal host source contribution in quantitative microbial source tracking using the Monte Carlo method. Water Res, 44(16), 4760–4775. http://doi.org/10.1016/j.watres.2010.07.076

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Wang, X.-S., & Qin, Y. (2006). Removal of Ni(II), Zn(II) and Cr(VI) from aqueous solution by Alternanthera philoxeroides biomass. Journal of Hazardous Materials, 138(3), 582–8. http://doi.org/10.1016/j.jhazmat.2006.05.091 Wium-Andersen, T., Nielsen, A. H., Hvitved-Jacobsen, T., Brix, H., Arias, C. A., & Vollertsen, J. (2013). Modeling the eutrophication of two mature planted stormwater ponds for runoff control. Ecological Engineering, 61, 601–613. http://doi.org/10.1016/j.ecoleng.2013.07.032

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Yadanaparthi, S. K., Graybill, D., & von Wandruszka, R. (2009). Adsorbents for the removal of arsenic, cadmium, and lead from contaminated waters. J Hazard Mater, 171(1-3), 1–15. http://doi.org/10.1016/j.jhazmat.2009.05.103 Yadav, D., Kapur, M., Kumar, P., & Mondal, M. K. (2015). Adsorptive removal of phosphate from aqueous solution using rice husk and fruit juice residue. Process Safety and Environmental Protection, 94, 402–409. http://doi.org/10.1016/j.psep.2014.09.005 Yeom, S. H., & Jung, K.-Y. (2009). Recycling wasted scallop shell as an adsorbent for the removal of phosphate. Journal of Industrial and Engineering Chemistry, 15(1), 40–44. http://doi.org/10.1016/j.jiec.2008.08.014 Yildiz, E. (2004). Phosphate removal from water by fly ash using crossflow microfiltration. Separation and Purification Technology, 35(3), 241–252. http://doi.org/10.1016/S1383-5866(03)00145-X 15

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Zhang, L., Wan, L., Chang, N., Liu, J., Duan, C., Zhou, Q., … Wang, X. (2011). Removal of phosphate from water by activated carbon fiber loaded with lanthanum oxide. J Hazard Mater, 190(1-3), 848– 855. http://doi.org/10.1016/j.jhazmat.2011.04.021

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Word Count: 0339 50 4000

(b) 40

Intensity (Counts)

3000 2500

Transmittance (%)

30

2000

20

1500 1000

10

0 10

15

20

25

30

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500

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3500

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(a)

35

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2-Th eta (deg ree)

0 4000 3500 3000 2500 2000 1500 1000 500

W avenu m b ers (cm

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)

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Fig 1: X-ray diffraction (a) and Fourier transform infrared (b) of activated rice husk ash

Fig 2: Scanning electron micrograph of activated rice husk ash (a,b)

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100 0 .4 0 .8 2 .0 3 .2 4 .0

Percentage removal (%)

95

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90 85 80 75

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70 65 60 60

80

100 120 140 160 180 200 220 240 260 T im e ( m in )

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40

Fig 3: Phosphate removal efficiency of activated rice husk ash at different contact time and dose in g/L (phosphate concentration: 10 ppm, temperature: 25oC, pH: 6.0)

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Percentage removal (%)

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40

40

60

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120 140 T im e (m in )

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180

200

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Fig4: Effect of pH on phosphate removal using activated rice husk ash (phosphate concentration: 10 ppm, adsorbent dosage: 2g/L, temperature; 25oC)

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25 o C 30 o C

80 70

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35 o C 40 o C

60 50 40 60

80

100

120 140 Tim e (m in )

160

180

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40

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Percentage removal (%)

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Fig 5: Phosphate removal at different temperature using activated rice husk ash (phosphate concentration =10 ppm, adsorbent dosage: 2g/L,, pH=6.0)

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-500 -1000

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∆ G (KJ/mol)

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-3500

304

306

308 Tem p (K )

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312

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314

Fig 6: Thermodynamic plot for the adsorption of phosphate on activated rice husk ash at

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(a )

4 .5

(c )

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3 .5 log Ce

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Fig. 7: Langmuir (a), Fruindlich (b) and Tempkin (c) isotherms plots for phosphate removal at 30oC using activated rice husk ash

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1 2 .0

log Qe

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Ce/qe

1 5 .0

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1.620 1.615

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1.610

Lnqe

1.605 1.600 1.595

1.585 0.8

1.0

1.2

1.4

1.6

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1.580 0.6

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1.590

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Fig 8: Dubinin-Redushkevich isotherm plot for the adsorption of phosphate onto activated rice husk ash

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Fig. 9: Pseudo-first order (a) and Pseudo-second order (b) model for phosphate removal using activated rice husk ash

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Table 1: Composition of adsorbent using X-ray fluorescence technique

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Elemental composition SiO Al2O3 K2O Fe2O3 CaO MgO TiO2 P2O5 Na2O Re MnO SO3 BaO SeO2 ZrO2

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1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

Percentage (%) 87.81 % 5.98 % 2.56 % 1.16 % 0.72 % 0.48 % 0.43 % 0.3% 0.22 % 0.07 % 0.05 % 0.04 % 0.02 % 0.02 % 0.02 %

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S.No.

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Table 2: Thermodynamic parameters for the adsorption of phosphate onto activated rice husk ash ΔGo (kJ/mol)

303

-3541.91

308

-1439.40 -916.78

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313

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Temperature (K)

ΔHo (kJ/mol)

ΔSo (kJ/mol)

-82843.8

262.6

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Table 3: Adsorption isotherms and kinetics models for the adsorption of phosphate

Langmuir

Qmax (mg/g) B (l/mg) R2 K (mg/g) n R2 B (J/mol) KT R2 qDR E (KJ/mol) R2 Qe (mg/g) Kt R2 K2(g/mg) Qe(mg/g) R2

Freundlich

Tempkin

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Dubinin-Redushkevich

Activated Rice Husk Ash

Pseudo-first order

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Pseudo-second order

0.736 4.081 0.991 0.341 0.074 0.962 2.271 4.100 0.987 1.574 4.05 0.711 1.235 0.016 0.868 0.043 1.329 0.978

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Parameters

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Equations

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Novelty Statement / Research Gap / Contribution

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Rice husk ash has good adsorptive properties and it has been used for the removal of various dyes, heavy metals, phenols, pesticides and other compounds in previous studies but till now no study has reported the application of rice husk ash as adsorbent for the removal of phosphate. The current study examines the potential use of agricultural waste i.e. activated rice husk ash for the removal of phosphate from wastewater in batch mode. The results show that activated rice husk ash has the capacity to remove significant fraction of phosphate from water and wastewater.

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Highlights

The adsorbent ability of activated rice husk ash was assessed to remove phosphate from wastewater.



89% phosphate removal was achieved at pH 6 (dose - 0.05 g) in 120 min of time for 25 ml of solution.



Langmuir isotherms and pseudo-second order model depicts the best fits to the experimental data.



XRD and FTIR analysis indicates the crystalline silica nature and presence of Si-O-Si group.



SEM image show the rough surface of absorbent which increases the adsorption capacity.



The study proposes cost-effective technique for the treatment of urban and rural

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wastewater.

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