BAB V. KESIMPULAN PENELITIAN
3. RESULTS AND DISCUSSION
Table 1 compares the characteristics of biochar in experiment with SNI standards. The biomass samples exhibit large variations in the proximate analysis, especially in the volatile matter and fixed carbon. From the carbon content and mass yield, the carbon yield representing the amount of carbon remaining in the biochar can be calculated. Biochar have carbon yields of about 61-65% while the rest have values in the range of 65%.
Tabel 1. Characteristics of biochar compared with SNI standards
Parameters Value
Biochar SNI
standards
Moisture content (%) 3.97 Max. 15
Ash content (%) 3.78 Max. 10
Volatile matter (%) 30.91 Max. 25
Fixed carbon (%) 65.27 Min. 65
Iodium number (mg/g) 875.97 Min. 750
Benzena number (%) 25.94 Min. 25
Sumihar (2015)
The main role of biochar in the soil is the increased retention of nutrients in addition to the direct supply of nutrients. Therefore, the microscopic surface area is one of the crucial properties for biochar, which determines the capability of nutrients and water absorption.
3.1. Soil properties
The soil samples were collected from horticultural land and analyzed in order to evaluate the soil texture and pH value. Table 2 shows the results obtained from these tests. From table 2, it was noticed that the silt percentage is larger than that in the clay.
Organic carbon is relatively high (4.07 and 4.22%) which reduced the adsorption of pesticides. Sorption of pesticides to soil generally increases with soil organic matter content (Tiwari and Guha, 2012).
Tabel 2. Physical and chemical soil properties Parameters Sukanalu Korpri Texture
sand (%) 62.87 59.05 silt (%) 33.41 33.50
clay (%) 3.72 7.46
pH (H2O) 5.30 5.70
Organic material
C (%) 4.07 4.22
N (%) 0.78 0.82
P-Bray (ppm) 541.00 448.00
Base saturation (%) 29.91 28.96 CEC (meq/100 g) 32.97 32.45 K-exch (meq/100 g) 6.51 5.39 Ca-exch (meq/100 g) 1.57 2.50 Mg-exch (meq/100 g) 1.31 1.63 Na-exch (meq/100 g) 0.18 0.15
The results of the analysis of both physical and chemical properties soil samples in both groups, namely Sukanalu and Korpri shown in Table 2. The soil samples Sukanalu contains 62.87% sand, 33.41% silt, and 3.72% clay. The pH value of the water is 5.30 and relatively acid. Organic matter content C includes high at 4.07%, while the organic matter content of N is very high, 0.78%. P content is obtained by extracting Bray classified as very high at 541.00 ppm. While the CEC and base saturation values obtained are respectively 32.97 meq / 100 g (high) and 29.91%
(lower). The composition of cation in the soil samples Sukanalu includes K at 6.51 meq /100 g (very high), Ca at 1.57 meq /100 g (very low), Mg at 1.31 meq /100 g (moderate), and Na of 0.18 meq /100 g (low). The soil samples of Korpri contain 59.05% of sand, 33.50% of silt and 5.7% of clay. The pH value of the water is 5.70 and the relatively acid. Organic matter content C includes high at 4.22%, while the organic matter content of N is very high, 0.82%. P content is obtained by extracting Bray classified as very high at 448.00 ppm. While the CEC and base saturation values obtained are respectively 32.45 meq /100 g (high) and 28.96% (lower). The composition of cation in the soil samples of Korpri includes K at 5.39 meq /100 g (very high), Ca at 2.50 meq /100 g (low), Mg of 1.63 meq /100 g (moderate), and Na 0.15 meq /100 g (low). In general, both the soil samples have physical and chemical properties are no different.
3.2. Cypermethrin adsorption isotherms
Tabel 3. The residual values of adsorption by activated biochar on some concentrations of cypermethrin
Sample of soil
C0 (ppm)
Ce (ppm)
Cads (ppm)
Xm/m (mg/g)
Ce/(X/m
) log Ce log Xm Sukanal
u 3 1.39 1.61 0.81 1.7267 0.1430
- 0.0942
6 2.08 3.92 1.96 1.0612 0.3181 0.2923
9 3.16 5.84 2.92 1.0822 0.4997 0.4654
12 4.02 7.98 3.99 1.0075 0.6042 0.6010
Korpri 3 1.13 1.87 0.94 1.2086 0.0531
- 0.0292
6 1.60 4.40 2.20 0.7273 0.2041 0.3424
9 2.18 6.82 3.41 0.6393 0.3385 0.5328
12 2.63 9.37 4.69 0.5614 0.4200 0.6707
The process of absorption or adsorption by an adsorbent is influenced by many factors and patterns within specific adsorption isotherm. Factors that influence in the adsorption process, i.e the type of adsorbent, the type of substance that is absorbed, the surface area of the adsorbent, the substance concentration and temperature. Because of these factors, each adsorbent which absorbs a substance one with another substance would not have the same pattern of the adsorption isotherm (Handayani and Sulistiyono, 2009).
Table 3 shows that the greater the concentration of pesticides was, the greater the mass of pesticide was adsorbed by biochar. In concentration of 3 ppm of cypermethrin, pesticide was adsorbed by biochar about 0.81 mg/gram for Sukanalu and 0.94 mg/gram for Korpri. In concentration of 6 ppm, pesticide was adsorbed by biochar about 1.96 mg/gram for Sukanalu and 2.20 mg/gram for Korpri. In concentration of 9 ppm, pesticide was adsorbed by biochar about 2.92 mg/gram for Sukanalu and 3.41 mg/gram for Korpri. In concentration of 12 ppm, pesticide was adsorbed by biochar
about 3.99 mg/gram for Sukanalu and 4.69 mg/gram for Korpri. Generally, the absorption of pesticide residues in soil samples of Korpri was larger than the soil samples of Sukanalu. This condition occured because the soil samples of Korpri have a clay structure that was larger than the soil samples of Sukanalu, so that the absorption of pesticide residues was also influenced by the structure of clay in the soil (Tu, 2001).
Figure 1. Langmuir plot for the Cypermethrin adsorption onto biochar
Figure 2. Freundlich plot for the Cypermethrin adsorption onto biochar Table 4. Equilibrium adsorption isotherm values for
cypermethrin pesticide
Soil samples Isotherm Isotherm
parameters Value Sukanalu Langmuir
a (mg/g) 4.464
b 0.224
R2 0.590
Korpri Langmuir
a (mg/g) 2.525
b 0.396
R2 0.801
Sukanalu Freundlich
k (mg/g) 1.786
n 0.688
R2 0.963
Korpri Freundlich
k (mg/g) 1.247
n 0.534
R2 0.983
y = -0.224x + 1.817 R² = 0.59
y = -0.396x + 1.531 R² = 0.801 0.0
0.5 1.0 1.5 2.0
0.0 1.0 2.0 3.0 4.0 5.0
Ce/(Xm/m)
Ce
Sukanalu Korpri
y = 1.454x - 0.252 R² = 0.963 y = 1.873x - 0.096
R² = 0.983
-0.20 0.00 0.20 0.40 0.60 0.80
0.00 0.20 0.40 0.60 0.80
Log Ce/Xm
Log Ce
Sukanalu Korpri
The Langmuir adsorption isotherms showed that it is not linear relationship on the present results shown in Figs. 1, but the Freundlich adsorption isotherms showed linear relationship present results shown in Figs. 2. R2 of the Freundlich adsorption isotherms is larger than that in Langmuir adsorption isotherms and close to 1. It means that this Freundlich model was obeyed by adsorption of cypermethrin as shown in Figs.
2.
Adsorption tends to have n between 1 and 10. Larger value of n implies stronger interaction between the soil and the pesticides (Öztürk and Bektas, 2004). The n values were 0.688 and 0.534 for Sukanalu and Korpri respectively in Freundlich isotherm model, showing that adsorption process was unfavorable and this has to do with low percentage of the clay (3.72 and 7.46) and due to the organics material available in the horticultural soil. The multilayey capacity factor of both pesticides (k) is higher than one which shows the good interaction between the soil and the pesticides with more interaction in Sukanalu than Korpri. The Langmuir adsorption isotherm is commonly applied to monolayer chemisorptions of gases. This isotherm is mainly applied when no strong adsorption is expected and when the adsorption surface is uniform. The Langmuir isotherm shows that adsorption will increase with increasing pesticides concentration up to a saturation point, in which all of the sites are occupied (Fig. 1) (Jodeh, et.al., 2013).
3.3. Chlorpyrifos adsorption isotherms
Tabel 5. The residual values of adsorption by activated biochar on some concentrations of chlorpyrifos
Sample of soil
C0 (ppm)
Ce (ppm)
Cads (ppm)
Xm/m (mg/g)
Ce/(Xm/
m) log Ce log Xm
Sukanalu 3 1.82 1.18 0.59 3.0847 0.2601 -0.2291
6 3.06 2.94 1.47 2.0816 0.4857 0.1673
9 5.30 3.70 1.85 2.8649 0.7243 0.2671
12 7.30 4.70 2.35 3.1064 0.8633 0.3710
Korpri 3 2.03 0.97 0.49 4.1856 0.3075 -0.3143
6 3.43 2.57 1.29 2.6693 0.5353 0.1089
9 4.37 4.63 2.32 1.8877 0.6405 0.3645
12 6.57 5.43 2.72 2.4199 0.8176 0.4337
Table 3 shows that the greater the concentration of pesticides was, the greater the mass of pesticide was adsorbed by biochar. In concentration of 3 ppm of chlorpyrifos, pesticide was adsorbed by biochar about 0.59 mg/gram for Sukanalu and 0.49 mg/gram for Korpri. In concentration of 6 ppm, pesticide was adsorbed by biochar about 1.47 mg/gram for Sukanalu and 1.29 mg/gram for Korpri. In concentration of 9 ppm, pesticide was adsorbed by biochar about 1.85 mg/gram for Sukanalu and 2.32 mg/gram for Korpri. In concentration of 12 ppm, pesticide was adsorbed by biochar about 2.35 mg/gram for Sukanalu and 2.72 mg/gram for Korpri. Generally, the absorption of chlorpyrifos residues in soil was smaller than the adsorption of cypermethrin.
Figure 3. Langmuir plot for the chlorpyrifos adsorption onto biochar
Figure 4. Freundlich plot for the chlorpyrifos adsorption onto biochar Tabel 6. Equilibrium adsorption isotherm values for
chlorpyrifos pesticide
Soil samples Isotherm Isotherm
parameters Value Sukanalu Langmuir
a (mg/g) 15.15
b 0.066
R2 0.112
Korpri Langmuir
a (mg/g) 2.755
b 0.363
R2 0.494
Sukanalu Freundlich
k (mg/g) 2.529
n 1.066
R2 0.905
Korpri Freundlich
k (mg/g) 5.395
n 0.653
R2 0.929
y = 0.066x + 2.494 R² = 0.112
y = -0.363x + 4.281 R² = 0.494
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
0.00 2.00 4.00 6.00 8.00
Ce/(Xm/m)
Ce
Sukanalu Korpri
y = 0.938x - 0.403 R² = 0.905 y = 1.531x - 0.732
R² = 0.929
-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6
0.0 0.2 0.4 0.6 0.8 1.0
Log Xm/m
Log Ce
Sukanalu Korpri
The Langmuir adsorption isotherms showed that it is not linear relationship on the present results shown in Figs. 3, but the Freundlich adsorption isotherms showed linear relationship present results shown in Figs. 4. R2 of the Freundlich adsorption isotherms is larger than that in Langmuir adsorption isotherms and close to 1. It means that this Freundlich model was obeyed by adsorption of chlorpyrifos as shown in Figs.
4.
Adsorption tends to have n between 1 and 10. Larger value of n implies stronger interaction between the soil and the pesticides (Öztürk and Bektas, 2004). The n values were 1.066 and 0.653 for Sukanalu and Korpri respectively in Freundlich isotherm model, showing that adsorption process was unfavorable and this has to do with low percentage of the clay (3.72 and 7.46) and due to the organics material available in the horticultural soil. The multilayey capacity factor of both pesticides (k) is higher than one which shows the good interaction between the soil and the pesticides with more interaction in Korpri than Sukanalu. The Langmuir adsorption isotherm is commonly applied to monolayer chemisorptions of gases. This isotherm is mainly applied when no strong adsorption is expected and when the adsorption surface is uniform.
Generally, the effect of organic matter content in the soil into adsorption residue as the influence of soil clay content. The greater the content of organic material is, the greater the adsorption. Pesticides have the speed for different decay (half-life). The half- life of this will affect the resistance properties of the residue in the soil. The greater half-life is the longer it will stay in the soil and more difficult to be degraded. Activated biochar which has been incorporated into the soil will have different adsorption power compared to the initial state. This is due to the possibility of activated biochar adsorb other compounds.