NSave Nature to Survive

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1 ISSN: NSave Nature to Survive : Special issue, Vol. 1; QUARTERLY DEVELOPMENT OF CONTROL RELEASE PHOSPHATIC FERTILISER FROM PALM FRUIT HUSK M. Vinolia Thamilarasi et al. KEYWORDS Palm fruit husk Phosphate Control Release Fertilizer Paper presented in 3rd International Conference on Climate Change, Forest Resource and Environment (ICCFRE, 2011) December 09-11, 2011, Thiruvananthapuram, organized by Department of Environmental Sciences, University of Kerala in association with National Environmentalists Association, India 335

2 NSave Nature to Survive QUARTERLY M. VINOLIA THAMILARASI, P. ANILKUMAR AND M. V. SURESHKUMAR* Department of Chemistry, KPR Institute of Engineering and Technology Coimbatore , INDIA ABSTRACT The surface of palm fruit husk, an agricultural solid waste was modified using a cationic surfactant, hexadecyltrimethylammonium bromide (HDTMA) and the modified palm fruit husk was investigated to assess the capacity for the removal of phosphate from aqueous solution. Optimum ph for maximum phosphate adsorption was found to be 4.0. Langmuir and Freundlich were used to model the adsorption equilibrium data. The batch desorption studies indicated that the sorbed phosphate can be slowly released under different ph conditions. Column leaching studies showed that leaching of phosphate was very slow. The results, from the standpoint of batch and column phosphate release, show evidences that using phosphate loaded modified palm fruit husk as a slow-releasing fertilizer is feasible INTRODUCTION In the past few decades, excess phosphorus (P) has been recognized as a non point- source of agricultural pollutant throughout the world due to the overapplication of both synthetic and animal based fertilizers. Eutrophication as well as the over growth of cyanobacteria due to the excess P in recreational, industrial, and drinking water could greatly threaten human and ecological health. Before discharging the phosphate containing wastewaters, it is essential to treat them and the effluent must meet the discharge limit of mg/l P (Yeoman et al., 1988). Adsorption techniques are widely used to remove certain classes of pollutants from waters, especially such as anionic contaminants. A range of adsorbents has been investigated for phosphate adsorption. However, several factors, including variability in composition, source, and low sorption capacities have limited their use despite their low cost. So there is always a hunt for new lowcost and easily available adsorbent materials for the phosphate removal. Palm fruit husk (PFH) is one such material which is disposed as waste after the consumption of palm fruit mesocarp. Large amount of palm fruit husk thrown on the roadside generates solid wastes. It consists mainly of cellulose, pentosan and lignin. In solution, lignin and cellulose, lose hydrogen ions and form a particle surface with a negative potential (Chen et al., 2001). Cationic surfactant, such as hexadecyltrimethylammonium (HDTMA) bromide, has strong affinity for palm husk, making them suitable for surfactant modification. Cationic surfactant modified natural materials have shown greater affinity for anions (Namasivayam and Sureshkumar, 2005). After modification, PFH exhibits high sorption capacity for anionic contaminants. After treatment, the adsorbent is loaded with phosphate. This phosphate-loaded adsorbent can be used as control release fertilizer (CRF). Nitrate loaded surfactant modified zeolite (SMZ) was used as a low-cost CRF to control nitrate release (Li, 2003) So the objective of this study is two fold, one is to examine the adsorption of phosphate by surfactant modified PFH and find out its applicability to the removal of phosphate from wastewaters and the next is to explore the possibility of using the spent adsorbent as CRF. Experimental MATERIALS AND METHODS All reagents used are of analytical grade chemicals and were obtained from Merck. The experimental solutions were prepared from stock 1000 mg/l phosphate solution, which was prepared using analytical grade potassium dihydrogen phosphate obtained from s.d. Fine Chemicals, Mumbai, India. *Corresponding author Preparation and characterization of surfactant modified palm fruit husk (MPFH) Waste PFH was dried in sunlight. Then it was crushed and sieved to get the particle size of μm. The PFH was modified as follows: 10 g of PFH and 200 ml of 0.2% HDTMA solution was taken in a 500 ml conical flask. The mixture was agitated using a shaker machine for 6 h at 200 rpm. Then the suspension was left undisturbed to separate the liquid and PFH. The liquid was 336

3 PHOSPHATIC FERTILISER FROM PALM FRUIT HUSK decanted and the modified PFH was washed with distilled water several times. The modified PFH was dried in a hot air oven at 60ºC for 12 h. Then it was characterized by CHNS Analysis (Vario EL III, Germany). Leaching of the surfactant was studied by agitating a known weight of the adsorbent with 50 ml of distilled water, at different ph values for 2 h. After agitation, the supernatant was decanted and the adsorbent was filtered using Whatman filter paper and washed gently with water to remove any superficially held surfactant. Then it was dried in hot air oven. Batch mode adsorption studies Batch mode adsorption studies were carried out by shaking 100 ml conical flasks containing 0.2 g of MPFH and 50 ml of phosphate solution of desired concentration. Then the suspension was agitated on an orbital shaker machine at 200 rpm, 32ºC and at an initial ph 4. The solution ph was adjusted with 0.1M HCl and 0.1M NaOH solutions using a ph meter (Elico, Mode LI-107, Hyderabad, India). At the end of the adsorption period the supernatant solution was separated by centrifugation at 10,000 rpm for 30 minutes. Then the concentration of the residual phosphate was determined by stannous chloride method (APHA, 1985) using UV Visible spectrophotometer. Effect of ph on the adsorption of phosphate onto MPFH was studied for the PO 4 concentration of 10 and 30 mg/l. The effect of contact time was studied by withdrawing the samples from the shaker at predetermined time intervals and residual PO 4 concentration was measured as above. Langmuir and Freundlich isotherms were used to study the adsorption capacity of the adsorbent. Batch mode desorption studies The adsorbent used for the adsorption of 10 and 30 mg/l of PO 4 solution was separated from the solution by filtration using Whatmann filter paper and washed gently with water to remove unadsorbed PO 4. Batch desorption experiments were conducted as a function of desorbing solution ph or ionic strength. To each 100 ml conical flask, 0.2g of phosphate loaded adsorbent and 50 ml of desorbing solution at ph 2-11 (adjusted using 1M HCl/NaOH solutions). Then the desorbed PO 4 was estimated as before. Column phosphate leaching test The column used was a 10 ml glass syringe sleeve. Column was filled with 5 g of phosphate loaded MPFH and was flushed with double distilled water. The effluent phosphate concentration was analyzed colorimetrically at every one-pore volume. The pore volume was determined by the difference between the wet weight and the dry weight of the columns packed with phosphate loaded MPFH divided by the density of water. The detailed flow and column conditions can be seen in Table 1. RESULTS AND DISCUSSION Characterization of the adsorbent The per cent of C, H and N present in the modified and unmodified PFH is given in Table 2. The increase in the C, H and N is due to the adsorption of HDTMA on to PFH surface. The BET surface area of MPFH (4.9 m 2 /g) is lower than that of unmodified PFH (7.3 m 2 /g). Sorption of HDTMA on MPFH causes a decrease in the surface area relative to the PFH. Apparently, the adsorption process leads to a constriction of the pore channels, as a result of attachment of the surfactant moieties to the internal framework surfaces. Similar reduction in the BET surface area was also observed during the modification of montmorillonite with HDTMA (Krishna et al., 2000). Effect of ph Effect of ph on the removal of phosphate is shown in Fig. 1. The percent adsorption of phosphate increased with the increase of ph from 2.0 to 4.0 and then remained almost the same upto ph 6.0 and then decreased to zero at ph Phosphate speciation depends on solution ph (Xia et al., 2002). The low removal at ph less than 3 is due to the predominant undissociated H 3 PO 4 species. At ph , - H 2 PO 4 species, which is predominant, is adsorbed. As the ph is increased above 7.0, PO 4 species is not favoured for adsorption due to the presence of OH - ions. Adsorption kinetics The adsorption kinetic data of phosphate are analyzed using the Lagergran rate equation (Lagergren, 1898): log (q e -q) = log q e k 1 t/ (1) where q e and q are the amount of phosphate adsorbed (mg/g) at equilibrium and at time t (min), respectively, and k 1 is the Lagergran rate constant of first order adsorption (1/min). The q e and rate constant k 1 were calculated from the slope of the plots of log (q e -q) vs t (Figure not shown). It was found that the calculated q e values do not agree with the experimental q e values (Table 3). This suggests that the adsorption of phosphate does not follow first order kinetics. The second order kinetic model (Ho and Mckay, 1998) can be represented as: 2 t/q= 1/k 2 q e + t/q e... (2) where k 2 is the rate constant of second order adsorption (g/ mg/min). Values of k 2 and q e were calculated from the plots of t/q vs t. Table 3 shows that the calculated q e values agree with the experimental q e values and the correlation coefficients are These results indicate that the adsorption process studied obeys the second order kinetic model. Similar result have been Table 1: Flow conditions for column phosphate leaching tests Column Phosphate loaded MPFH Adsorbent weight, g 5 Pore volume, ml 5 Flow rate, ml/min 1 Phosphate input, mm Phosphate output, mm Phosphate recovery, % 30 Table 2: Elemental composition of (a) PFH, (b) MPFH and (c) MPFH after leaching at different ph Sample C% H% N% (a) PFH (b) MPFH (c) MPFH after leaching at (i) ph 2 (ii) ph (iii) ph

4 M. VINOLIA THAMILARASI et al., Table 3: Comparison of first order and second order adsorption rate constant and calculated and experimental q e values for different initial phosphate concentrations and temperatures Initial PO 4 conc (mg/ L) *qe (exp) (mg g -1 ) First order kinetic model Second order kinetic model k 1 (1/min) q e (cal)(mg/g) R 2 k 2 X 10 3 (g/ mg q e (cal)(mg/g) R 2 / min) * Conditions: Temperature, 32 0 C; Adsorbent dose, 0.20 g /50 ml ph 4.0 Table 4: Langmuir and Freundlich constants Langmuir Freundlich Q 0 (mg/g) b(l/mg) R 2 k f (mg 1-1/n L 1/n /g) n R %Adsorption mg/l 30 mg/l Initial ph Figure 1: Effect of ph on the adsorption and desorption of phosphate by MPFH observed in the adsorption of phosphorous onto ZnCl 2 activated coir pith carbon (Namasivayam and Sangeetha, 2004). Adsorption isotherms The equilibrium adsorption isotherm is fundamental in describing the interactive behavior between adsorbates and adsorbent and is important in the design of adsorption systems. Langmuir isotherm is represented by the following equation: (Langmuir, 1918) C e /q e = l/q o b + C e /Q o... (3) where C e is the concentration of phosphate solution (mg/l) at equilibrium. The constant Q o signifies the adsorption capacity (mg/g) and b is related to the energy of adsorption (L/mg). Linear plot of C e /q e vs C e shows that adsorption follows Langmuir isotherm. Values of Q o and b were calculated from the slope and intercept of the linear plots and are presented in Table 4. The applicability of the Langmuir isotherm suggests the monolayer coverage of the phosphate on the surface of MPFH. The essential characteristics of Langmuir isotherm can be expressed by a dimensionless, constant called equilibrium parameter, R L (Weber and Chakkravorti, 1974) R L =1 / (1 + bc 0 )... (4) where b is the Langmuir constant and C 0 is the initial phosphate %Desorption concentration (mg/l), R L values indicate the type of isotherm. The calculated R L values between zero and one indicate favorable adsorption for all concentrations. Freundlich isotherm was also applied for the adsorption of phosphate (Freundlich, 1906) log 10 (x/m) = log 10 k f + (1/n) log 10 C e... 5) where x is the amount of phosphate adsorbed (mg), m is the weight of the adsorbent used (g), C e is equilibrium concentration of phosphate in solution (mg/l), k f and n are constants incorporating all factors affecting the adsorption process (adsorption capacity and intensity of adsorption). Linear plots of log 10 (x/m) vs log 10 C e show that the adsorption also follows Freundlich isotherm. In general, as the k f value increases the adsorption capacity of the adsorbent for the phosphate increases. Values of k f and n were calculated from the intercept and slope of the plots and are presented in Table 4. Desorption studies To explore the possibility of using spent adsorbent as CRF, desorption studies were performed. Desorption of phosphate is shown in the Fig. 1. At the desorbing ph of 2.0, the per cent desorption of phosphate was 80%. At this ph, H + ions protonate the adsorbed phosphate ions and desorbs it from the surface. Desorption was lowered in the ph range of But above ph 7.0, the desorption starts to increase and reaches upto 80 % at ph Above ph 7, the OH - ions replace the phosphate ions from the surface of the adsorbent and hence there is an increased desorption. The batch Effluent phosphate concerntra Number of Accumulated pore volume Figure 2: Phosphate release from column packed with phosphate loaded MPFH. Data are duplicates with each type of symbols representing a single column 338

5 PHOSPHATIC FERTILISER FROM PALM FRUIT HUSK desorption results indicate that sorbed phosphate on MPFH can be readily desorbed at a particular rate in the ph range of 5-8, which is the ph range of irrigation waters. This makes phosphate loaded MPFH as a good candidate for CRF. Column leaching tests To further explore the possibility of using spent adsorbent as CRF, column leaching tests were performed to monitor the effluent solution concentration with time, so that accumulative desorption could be determined. The initial phosphate concentration was 0.16 mm at first pore volume and the leaching decreased to 0.01 mm at fifth pore volume. The effluent phosphate concentration was still around mm after the columns packed with phosphate loaded MPFH was flushed with more than 10 pore volumes of water. More than 30 % of phosphate still remained on the MPFH after 10 pore volumes of flushing through MPFH columns (Fig. 2). The phosphate recovery is comparable to nitrate recovery by SMZ (Li, 2003). It is clear from the results that slow phosphate release can be achieved using phosphate loaded MPFH. CONCLUSION The present study showed that the agricultural solid waste palm fruit husk can be modified using a cationic surfactant and can be used as low cost adsorbent for the removal of phosphate. Maximum removal occurred in the ph range of 4.0 to 6.0. Analysis of kinetic data showed that the uptake of phosphate by modified MPFH followed second order kinetics. Equilibrium adsorption data obeyed both Langmuir and Freundlich isotherms. The batch desorption studies indicated that the sorbed phosphate can be slowly released under different ph conditions. Column leaching studies showed that leaching of phosphate was very slow. The results, from the standpoint of batch and column phosphate release, show evidences that using phosphate loaded MPFH as a slow-releasing fertilizer is feasible. REFERENCES APHA, Standard Methods for the examination of Water and Wastewater American Public Health Association, American Water Works association and Water Pollution Control Federation. Washington. DC. Chen, B. Chi Wai Hui and McKay, G Pore-Surface diffusion modeling for dyes from effluent on pith. Langmuir. 17: Freundlich, H. M. F Uber die adsorption in losungen. Z. Phys. Chem. 57A: Ho, Y. S. and Mckay, G Sorption of dye from aqueous solution by peat. Chem. Eng. J. 70: Krishna, B. S. Murty, D. S. R. and Jaiprakash, B. S Thermodynamics of chromium(vi) anionic species sorption onto surfactant-modified montmorillonite. J. Colloid Interface Sci. 229: Lagergren, S Zur theorie der sogenannten adsorption geloester stoffe, Kungliga Svenska Vetenskapsakad. Handl. 24: Langmuir, I The adsorption of gases on plane surfaces of glass, mica and platinum. J. Amer. Chem. Soc. 40: Li, Z Use of surfactant modified zeolite as fertilizer carriers to control nitrate release. Microporous and Mesoporous Materials. 61: Namasivayam, C. and Sureshkumar M. V Surfactant Modified Coir Pith, an Agricultural Solid Waste as Adsorbent for Phosphate Removal and Fertilizer Carrier to Control Phosphate Release. J. Environ Sci Engg.. 47: Namasivayam, C. and Sangeetha, D Equilibrium and kinetic studies of adsorption of phosphate onto ZnCl 2 activated coir pith carbon. J. Colloid Interface Sci. 280: Weber, T. W. and Chakkravorti, P Pore and solid diffusion models for fixed-bed adsorbers. AIChE J. 20: 228. Xia, L. R., Jinlong, G. and Hongxiao, T Adsorption of fluoride, phosphate and arsenate ions on a new type of ion exchange fiber. J. Colloid Interface Sci. 248: Yeoman, S. Stephenson, T. Lester, J. N. and Perry, R The removal of phosphorous during wastewater treatment: A review. Environ. Poll. 49:

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