Removal of Methylene Blue from Aqueous Effluent Using Fixed Bed of Groundnut Shell Powder

Removal of methylene blue from aqueous solution using a low-cost adsorbent groundnut shell powder (GNSP) was studied using �xed bed. Bed service depthmodel andomasmodel were employed to study the adsorption kinetics and to predict break-through curves for the system. Both models �t the experimental data very well with very high R values. Percentage color removal increased with increase in bed height. It was found that adsorption potential of GNSP was in the range of 0.238 to 0.272 kg/kg of adsorbent. ese results show that the GNSP can be effectively used as low-cost alternate adsorbent for the removal of pollutants from aqueous streams.


Introduction
Dyes are widely used by several industries like plastics, textile, and paper, to color their �nal products [1].Presence of dyes in industrial effluent poses serious threat to the environment.It interferes with the normal photosynthetic activities of aquatic life [2][3][4].Majority of dyes are recalcitrant and usually take very long time for biodegradation.Moreover, it is reported that the intermediates formed during biodegradation of the dyes are more toxic than the original molecules.Photochemical oxidation can mineralize the compounds efficiently, but it is energy intensive and therefore not preferred for largescale applications.Similarly, many other physicochemical techniques available for color removal are either costly or inefficient.Among them adsorption is proven to be one of the most efficient techniques [5,6].However, as cost of conventional adsorbents is too high, it is necessary to search for low cost adsorbents.Scientists are now exploring the possibilities of using low-cost agro wastes as alternate adsorbents.Agro wastes like rice husk [7][8][9], wheat husk [10,11], saw dust of various trees [12][13][14], peels of fruits [15], seeds [16,17], and leaves of various plants [18][19][20][21][22] have been studied recently.In this work, groundnut shell powder (GNSP) is used for the adsorption of methylene blue from aqueous effluent.
Groundnut shell is a byproduct of groundnut oil industry.It is a solid waste to be disposed off properly.If this material could be effectively used as an alternate adsorbent, then it can have double-fold advantage.In order to assess the adsorption potential of the GNSP, equilibrium studies were performed in batch mode.However, continuous adsorption is preferred over batch adsorption for large-scale applications owing to higher efficiency and effective utilisation of adsorbent capacity.erefore, in this work �xed bed packed with GNSP was employed for adsorption of methylene blue from aqueous solution.

Adsorbate. Methylene blue (MB, chemical formula:
C16H18N3SCl; FW: 320 g mol −1 ,  max = 662 nm, class: thiazine, CI classi�cation number: 52015) was obtained from the Ranbaxy Laboratories Limited (India) and used without further puri�cation.MB is not regarded as acutely toxic, but it can have various harmful effects.On inhalation, it can give rise to short periods of rapid or difficult breathing, while by ingestion through the mouth it produces a burning sensation and may cause nausea, vomiting, diarrhea, and gastritis [23,24].Stock solutions were prepared as described in Ponnusami et al. [19].Frequently in adsorption studies, MB is used as model dye for two reasons [18]: (i) MB is one of the commonly used commercial dye and (ii) MB is well known for its adsorption characteristics.
2.2.Adsorbent.e groundnut shell was �rst washed thoroughly with unpuri�ed water to remove adhering foreign particles from the surface and then dried in solar light.en it was dried in hot-air oven at 70 ∘ C for about 24 h.Aer drying, the adsorbent was crushed in ball mill and then size separated using sieve shaker.Particles of size BSS # −60 + 72 were collected and then stored in a plastic container for further use.Physical characteristics of the GNSP were determined, and results are summarized in Table 1.pH zero point charge (pH zpc ) of the adsorbent was determined by powder addition method [25].
Infrared spectrum of the sample was obtained using PerkinElmer spectrum RX I model Fourier transform infrared spectrometer by KBr pellet method in the range of 400 to 4000 cm −1 , with a resolution of 1 cm −1 .FT-IR spectrum is shown in Figure 1.e reported result is average of 20 scans.e deep absorption peak at 3398 cm −1 corresponds to -OH stretching vibrations.Peak at 2929 cm −1 corresponds to alkane stretching.Peaks at 1600 cm −1 and 1363 cm −1 indicate C=C stretching and -CH 3 bending vibration, respectively.As MB is a cationic dye, -OH functional groups on the surface of GNSP may increase the interaction between adsorbent and adsorbate and contribute for the adsorption of MB.

Batch Equilibrium
Studies. 100 mL of MB solution of desired concentration (0.02, 0.04, 0.06, 0.08, 0.1, 0.125, 0.15, and 0.2 kg/m 3 ) was taken in a 500 mL conical �ask.0.5 g of adsorbent was added to the solution, and the mixture was kept in an orbital shaker at constant temperature (303, 313, and 323 K) and 200 RPM for 24 h to ensure equilibrium.Aer 24 h samples were taken from each �ask using a �ne tip syringe to avoid carryover of solid particles.e samples were then centrifuged to collect clear supernatant solution.Concentration of MB was estimated using UV-Vis spectrophotometer, by measuring the optical density at 660 nm.Optical density was then converted into concentration units using calibration chart [18].ough the pH zpc of the GNSP was found to be 7.5, for adsorption studies pH was maintained at 7 throughout this study to minimise the addition of chemicals.
Equilibrium data was analysed with most frequently used Langmuir isotherm [26] which is given by   =  max     /(1 +     ).Here,   is equilibrium solid-phase concentration of MB (kg/kg),  max is monolayer adsorption capacity of the adsorbent (kg/kg),   is equilibrium liquid phase concentration of MB (kg/m 3 ), and   is the Langmuir equilibrium constant (m 3 /kg).e Langmuir isotherm parameters   and  max were determined by nonlinear regression [27,28] using Curve expert 1.40 (Microso corporation, 1993).Chi-square, de�ned as  2 = (  −   ) 2 /  , was used as the error function while determining isotherm parameters by non-linear regress analysis [27].Here,   stands for the equilibrium solid phase concentration of MB (kg/kg) as predicted by the model.

Column Experiments.
Bulk removal of MB onto GNSP was investigated using a packed bed of BSS # −60 + 72 size GNSP particles.Larger-size particles were chosen to reduce excessive pressure drop and to ensure plug �ow.A 2 cm diameter glass column was used for this study.e column was �tted with �ve sampling ports located at regular intervals of 5 cm.At the bottom of the column, 2 cm high layer of glass beads (3 mm dia.) was used to ensure proper distribution of inlet �ow.�ye solution (0.2 kg/m 3 ) was introduced at the bottom of the column in upward direction at a rate of 1 l/h using a peristaltic pump.Samples were collected at regular time intervals from the sampling points located at 5, 10, and 15 cm heights.Performance of the column operation is described by break-through curves.Break-through time and shapes of break-through curves are very important characteristics of the column for determining the operation and dynamic response of the bed.Volume of effluent ( eff ) processed is calculated as: where  = volumetric �ow rate in l/h and  total is the service time of the column in h.Exhaustive time is taken as the service time ( total ) of the column for the purpose of calculating  eff      total , and %.Total amount of dye adsorbed in the column (  , kg) for a given feed concentration and �ow rate is calculated using the formula where  0 is initial concentration in kg/m F 1: FTIR of groundnut shell powder.
e equation can be expressed as: where   ,  0 ,  0 ,  0 ,  0 ,   , and   are break-through time (h), bed capacity (kg/m 3 ), bed height (m), initial dye concentration (kg/m 3 ), super�cial velocity through bed (m/h), kinetic constant (m 3 /kg h), and break-through concentration (kg/m 3 ), respectively.In spite of ignoring the intra-particle mass transfer resistance and external �lm resistance, the model �ts many packed bed adsorption systems well and provides information ( 0 and   ) useful for scale up of given adsorption system [24].
2.6.e omas Model.Prediction of concentration-time pro�le and maximum adsorption capacity is important for satisfactory design of a column adsorption.e omas model [18,24] is one of the most general and widely used models to describe packed bed adsorption.It assumes (i) Langmuir's isotherm, (ii) no axial dispersion, and (iii) second-order adsorption kinetics.Linear form of the model is given by the equation [29,30]: e kinetic parameters   (m 3 kg −1 h −1 ) and  0 (kg/kg) were determined from the slope and intercept of the plot of ln ( 0 /  −1) versus t at a given �ow rate.3 shows the break-through curve for the adsorption of MB using a �xed bed of GNSP.Break-through concentration was �xed as 10% of initial concentration (that is 0.02 kg/m 3 ).Break-through time increased with increase in bed height in consistent with the theory.Values of  0 and   are found to be 77.99 kg/m 3 and 0.45 m 3 kg −1 h −1 , respectively.Percentage color removal was calculated be 67, 77, and 79, respectively, for bed heights 5, 10, and 15 cm.Percentage color removal increases with increase in bed height as utilisation of bed improves with increase in bed height [24].(2).is shows that the prediction of the omas model is close enough to the actual values.e difference seen here is largely due to the deviation of the omas model during the initial period.It is seen that the height of the bed did not show any de�nite effect on  0 .is suggests plug �ow conditions prevailed in the column and the axial dispersion was negligible.is is comparable to other low-cost adsorbents reported in the literature [24].is indicates that the GNSP has good adsorption potential and it can be employed as an alternate adsorbent.

Conclusion
Continuous removal of methylene blue from aqueous solution was studied using a �xed bed packed with of groundnut shell powder.Up to 80% color removal was possible with the �xed bed.omas model could satisfactorily predict the adsorption break-through curve.Adsorption capacity of the bed was found to be in the range of 0.238 to 0.272 kg/kg.ese results demonstrate that groundnut shell powder possesses good adsorption capacity and can be effectively used as a low cost alternate adsorbent for the removal of pollutants like methylene blue from industrial effluents.
T 1: Physical and chemical properties of GNSP used in the experiments.
Model.e omas model plot is shown in Figure4.emodelparameters and  0 are presented in Table3.High  2 values obtained indicate that omas model �ts the experimental data well for this system.Comparison of experimental and predicted break-through curves is shown in Figure3.e values of   decreased with increase in bed height.Values of  0 predicted by the omas model were in the range of 0.272, 0.238, and 0.241 kg/kg.ese