BIOSORPTION AND DESORPTION OF CHROMIUM FROM IMMOBILIZED MICROALGAE BIOSORBENT
3. Results and Discussion
3.1 Moisture Content
Moisture content is determined for understanding the biosorbent hygroscopic properties in adsorbing water and air around the pores in the surface of the adsorbent (Fernando, 2009).
Moisture content will determine the freshness and durability of materials. According to Pari et al. (2008), high moisture content resulting in ease of bacteria, molds, and yeasts to proliferate, causing a change in the material and will decrease the absorption of either the gas or liquid. In general, the larger the surface area will increase the absorption biosorbent to a substance, so that the molecules of water vapor from the air will be more adsorbed hence increasing water content (Hasfita, 2011). Low water content indicate that the moisture content of free and bound water in material has evaporated during the heating process or carbonation. Analysis result of moisture content of immobilized biosorbent from microalgae as much as 91.2%.
3.2 Ash Content
Ash content analysis indicates the amount of metal oxides remaining after heating at high temperature around 600oC. The formed ashes derived from minerals that is firmly attached to the charcoal, such as calcium, potassium, and magnesium (Rumidatul, 2006). The existence of excess ash can blocking biosorbent pores that reduce the surface area of biosorbent.
Analysis by using gravimetry method revealed that the ash content of immobilized biosorbent of 2.2%.
3.3 Biosorption
Biosorption analysis against contact time is important because it relates to process capacity, operational application, and economics. Generally, biosorption take place in a short time to reach equilibrium (Wang, 2006). Figure 1 shows the increasing of Cr(VI) removal against contact time. Until 30 minutes, biosorbent could remove Cr(VI) up to 58.61% and gradually increase to 80.1 % at 150 minutes. However, the removal percentage decrease to 74.99% and 72.23% at 165 minutes and 180 minutes, respectively. It might be explained due to there is no more surface active biosorbent which able to bind heavy metals. It also caused by the reversible process towards equilibrium that causing the metal ions released back into the solution.
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Figure 1. Concentration and percent removal vs time
3.4 Freundlich and Langmuir Isotherm
Figure 2a shows the correlation values as much as 0.957. Value of n1 as much as 0.515 and Kf
as much as 1.21. Kf represent of parameter Freundlich capacity (mg sorbate/gram sorbent)(L solution /mg sorbate)1/n. Value of n1 represent intencity of Freundlich parameter which has no unit. According to the calculation, we can have matematic equation based on Freundlich isotherm as Equation 6.
q = 1.21 Ce 0,515 (6)
Kf is constanta if only n = 1 it often called as distribution coeficient which equivalent with Kd value. Value of 1n is important parameter. It represent compatibility of biosorption in Freundlich isotherm. If value 1n less than one, so isotherm represent suitable isotherm.
Figure 2b shows correlation values as much as 0.9985. Using linearization of equation with q = (1:Kads Ce)qm Kads Ce, we can have slope value which represent biosorption capacity equation or qm and Kads as much as 20.284 mg Cr(VI)/gram sorbent and 0.002825 respectively. Kads shows level afinity between sorbate and biosorbent. According analysis we can get Equation 7.
q = 1:0.002825 Ce0.05729 Ce (7)
0 10 20 30 40 50 60 70 80 90
0 10 20 30 40 50 60 70 80 90 100
0 15 30 45 60 75 90 105 120 135 150 165 180 t (min)
% Removal (%)
C (mg/L)
Biosorption % Removal
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Figure 2. Isotherm: a. Freundlich; b. Langmuir
3.5 Desorption
Desorption was conducted to recover chromium metal from biosorbent. The process was performed by using several types of eluent such as acid and alkaline. The eluents for desorption are HNO3 0.1; 1 N, H2SO4 0.1; 1; 4 N, KOH 0.1; 1 N, NaOH 0.1; 1 N as much as 100 mL for desorp 10 gram biosorbent. Percent desorption have been calculated using Equation 5. The result of desorption percentage and desorption capacity can be seen at Figure 4.
According to the Figure 3, we can see that desorption using H2SO4 4N for 24 hours shows the capability of recovery up to 31.181 ppm. While, using HNO3 1N, recovery was as much as 19.386 ppm at 24 hours. However, desorption using alkaline eluent which represent by KOH 1N and NaOH 1N show recovery up to 30.984 and 22.597 ppm respectively.
The results of desorption percentage at optimum value can be seen at Figure 4. According to the figure, the highest desorption was achieved by using H2SO4 4N with 78.84% recovery, while the lowest one at HNO3 0.1N as much as 41.53%. Choudury et al. (2014) reported that NaOH, KOH, HCl, H2SO4, HNO3 1M could recover chromium from groundnut shell up to 60%: 87%; 7.8%; 5%, and 12.8%, respectively, with initial concentration of 100 mL Cr(VI) of 200 μg/L, at agitation speed of 60 rpm for 2 hours.
(a) (b)
0 10 20 30 40 50
0 500 1000
C (ppm)
t (min) C Tot
0 10 20 30 40 50
0 500 1000
C (ppm)
t (min) C Tot
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(c) (d)
Figure 3. Chromium concentration in desorption process using various eluents:
(a) H2SO4 4 N; (b) HNO3 1N; (c) KOH 1N; (d) NaOH 1N
Figure 4. Percent and capacity of desorption
3.6 Desorption Kinetics
Kinetics study has important role in biosorption and desorption analysis. It has the ability to provide information regarding of required time to reach equilibrium. Kinetics reaction are determined to know the order of the reaction that occurs in the process. In this research the desorption kinetics was conducted by sampling at minutes-10, 30, 60, 90, 120, 180, 240, 1440. The ploting from concentration vs contact time we can get the kinetic equation and correlation coefficient at Figure 5, Table 1, and Table 2.
0 10 20 30 40 50
0 30 60 90 120 150 180 210 240
C (ppm)
t (min)
C tot
0 10 20 30 40 50
0 30 60 90 120 150 180
C (ppm)
t (min)
C tot
55,28
70,98
57,73 56,42
41,53 48,40 48,40
64,11
78,84
0 1 2 3 4
0 10 20 30 40 50 60 70 80 90 100
KOH 0.1 N KOH 1 N NaOH 0.1 N NaOH 1 N HNO3 0.1N HNO3 1N H2SO4 0.1N H2SO4 1N H2SO4 4N Desorption capacity (mg/gr)
Percent of Cr Desorption (%)
Types of Eluent
Percent of Cr Desorption (%) q (mg/g)
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Table 1. Comparison of pseudo first order and pseudo second order equation for kinetics reaction of alkaline eluent
Eluent Pseudo-first-order Pseudo-second-order
Equations R2 Equations R2
KOH 0.1N 0.002x + 0.0664 0.6101 -0.3689x – 10.883 0.8631 KOH 1N 0.003x + 0.0365 0.9101 -0.2459x – 13.926 0.9035 NaOH 0.1N 0.0015x + 0.2539 0.5229 0.3235x – 4.1028 0.9961 NaOH 1N 0.0032x – 0.0548 0.8586 -0.2673x – 18.93 0.8401 Table 2. Comparison of pseudo first order and pseudo second order equation for
kinetics reaction of acid eluent
Eluent Pseudo-first-order Pseudo-second-order
Equations R2 Equtions R2
HNO3 0.1N 0.0002x – 0.7378 0.2530 2.798x – 133.7 0.9954 HNO3 1N 0.0004x – 0.7305 0.7050 1.6634x – 193.85 0.9854 H2SO4 0.1N 7.10-05x – 0.2717 0.8129 -1.4644x – 17.002 0.9999 H2SO4 1N 0.0003x – 0.4425 0.7176 -1.0737x – 77.759 0.9897 H2SO4 4N 0.0002x – 0.4315 0.3869 -1.5046x – 34.6 0.9998
(a) (b)
(c) (d)
Figure 5. Desorption kinetics: (a) alkaline eluent order I; (b) Alkaline eluent order II;
(c) Acid eluent order I; (d) Acid eluent order II.
-0,2 -0,1 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
0 30 60 90 120 150 180
log (qe-qt)
t (min)
KOH 0,1 N KOH 1 N NaOH 0,1 N NaOH 1 N
-90 -80 -70 -60 -50 -40 -30 -20 -10 0
0 30 60 90 120 150 180
t/qt
t (min)
KOH 0,1 N KOH 1 N NaOH 0,1 N NaOH 1 N
-1,2 -1 -0,8 -0,6 -0,4 -0,2 0
0 500 1000
log (qe-qt)
t (min)
HNO3 0,1N HNO3 1N H2SO4 0,1N H2SO4 1N H2SO4 4N
-4500 -4000 -3500 -3000 -2500 -2000 -1500 -1000 -500 0
0 500 1000
t/qt
t (min)
HNO3 0,1N HNO3 1N H2SO4 0,1N H2SO4 1N H2SO4 4N
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According to the Table 1 and Table 2, we can see the correlation value close to 1 are obtained at second order kinetics model. So, based on the comparison of the correlation kinetics coefficient, the kinetics model follow the second-order reaction kinetics model.
3.6 Biosorption Cycle
Biosorption-desorption repetitions were perfomed to determine the performance of biosorption after desorption. Biosorption-desorption were performed up to 3 cycles. The performance of biosorption after desorption using HNO3 1N, H2SO4 4N, KOH 1N, dan NaOH 1N can be seen at Figure 6.
Biosorption-desorption cycle for eluent H2SO4 4N shows good performance which could remove chromium up to 12.863 ppm after 90 minutes. While at biosorption III could remove up to the efluent concentration as much as 9.678 ppm. While biosorption cycle using alkaline were conducted only up to two times. The performance of biosorption II decreased due to the damage of biosorbent. Cabating et al. (2001) reported that desorption using 1 N NaOH against S. siliquosum cause leaching of some biosorbent components that damage the cell structure.
a. b.
c. d.
Figure 6. Biosorption-desorption cycles: a. eluent HNO3 1N; b. eluent H2SO4 4N; c.
eluent KOH 1N; d. eluent NaOH 1N
0 20 40 60 80 100
0 60 120 180 240 300 360 420 480
C (mg/L)
t (min) Bio I HNO3 1N II HNO3 1N III
0 20 40 60 80 100
0 60 120 180 240 300 360 420 480
C (mg/L)
t (min) Bio I H2SO4 4 N II H2SO4 4 N III
0 20 40 60 80 100
0 60 120 180 240 300
C (mg/L)
t (min) Bio I KOH 1 N II
0 20 40 60 80 100
0 60 120 180 240 300
C (mg/L)
t (min)
Bio I NaOH 1 N II
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