Accelerating peat fiber decomposition by bacteria Pseudomonas taiwanensis and its impact on the physical properties and shear strength of fibrous peat in Palangkaraya

. Peat soil is formed through the accumulation of undecomposed plant organic matter, resulting in a high fiber content that leads to poor physical properties and low shear strength. Consequently, peat soil is identified as problematic and detrimental in infrastructure construction. One proposed method to improve its physical properties and enhance shear strength is biological soil stabilization through biotechnology, with bioaugmentation as an environmentally friendly alternative. The objective of this research is to accelerating the decomposition of peat fiber by Pseudomonas taiwanensis bacteria, thereby accelerating soil compaction and improving its physical properties and shear strength. The subject of this research is fibrous peat soil in Bereng Bengkel Village, Palangkaraya, Central Kalimantan. From the experimental results, it was found that the addition of 15% Pseudomonas taiwanensis bacteria to fibrous peat can significantly improve the physical properties and shear strength. Thus, Pseudomonas taiwanensis bacteria can be used as an environmentally friendly alternative to improve the geotechnical properties of fibrous peat.


Introduction
Indonesia has the largest distribution of peatlands in Southeast Asia, covering 20.6 million hectares or about 10.8% of Indonesia's total land area [1,2].The existence of these vast peatlands poses a challenge to the infrastructure construction in Indonesia as fibrous peat is a geotechnically problematic soil [3,4].Indonesian peat has a very high fiber content, making it known as fibrous peat [5].This high fiber content causes the high-water content in fibrous peat [6] because the peat fiber itself presents micropores (pores between soil grains) and macropores (pores inside peat fibres) that are able to absorb and retain water, so fibrous peat is always in a saturated condition [7].The high-water content causes the compressibility index of fibrous peat to be very high [8] and the shear strength to be very low [9].Therefore, fibrous peat has a very low bearing capacity [10], making it unsuitable as a subgrade material in infrastructure construction [11,12].
In general, peatlands in Indonesia are cultivated for agriculture [13].As time goes by, the need for residential land and transportation facilities is increasing, while the supply of land for infrastructure development is limited [14].This situation often happens, especially on the islands of Sumatra, Kalimantan and Papua, which have a significant distribution of peatlands [15].Therefore, infrastructure development on peatlands is often unavoidable [16].Formerly, construction work on peatlands often involved replacing the subgrade with sand or better soil [17].However, natural resources are limited to fulfil the replacement of subgrade soil in any infrastructure construction work on peatlands [18].Therefore, fibrous peat stabilization is an alternative to address peat soil problems in infrastructure construction work in Indonesia.
The chemical stabilization of peat soils continues to be attempted in an effort to improve the quality of fibrous peat for construction in Indonesia [19].However, in the practice of fibrous peat stabilization that has been carried out so far, a major mistake has been made.The mistake is that the peat soil stabilization practices that have been carried out so far use the wrong method.In previous study, before stabilization was carried out, the peat soil was dried in oven or under the sun [20][21][22][23].This is very wrong, because in the stabilization process, the natural properties of peat soil, which has a very high-water content, are ignored [24].However, there are studies that have stabilized fibrous peat without drying it first [25].But the study showed that chemical soil stabilization could not improve the geotechnical properties of fibrous peat soils while the decomposition process was still ongoing.This is due to the fact that when the stabilized soil undergoes decomposition, the volume of the soil will decrease and the organic matter that hardens with the chemicals will decompose.In other words, when the decomposition process in stabilized soil reaches its peak, hardening only occurs with the chemicals, not with the soil.In addition, the use of chemicals materials is considered not environmentally friendly because it can pollute groundwater [26,27].
Based on this discussion, chemical stabilization is not effective and not environmentally friendly if applied to fibrous peat.Therefore, in the current study, accelerating the peat fibres decomposition, which are considered to be the main cause of the high-water content in fibrous peat, was conducted [28].Accelerating the decomposition of peat fibres can be achieved through biological soil stabilization using biotechnology.One of the biotechnologies that can be applied to accelerate the peat fiber decomposition process is the bioaugmentation method [28][29][30].Bioaugmentation is a process of adding microorganisms such as fungi, bacteria or algae that are capable of degrading certain pollutants [31].
In case of accelerating peat fiber decomposition, lignocellulolytic bacteria are utilized as these bacteria are capable of producing enzymes to degrade cellulose, which is a component of plant tissue such as peat fiber [29].Previous study has proposed that there are indigenous lignocellulosic bacteria from fibrous peat that can be utilized for its potential as an agent of bioaugmentation because it has a high decomposition performance reaches 90% [30].The indigenous bacteria are Pseudomonas taiwanensis, which was first identified in Taiwan [32].Pseudomonas taiwanensis bacteria are gram-negative rod-shaped bacteria, measuring about 2.7-2.2µm, have one or three polar flagella, do not form spores, and have rounded rod ends [33].This bacterium can survive in a tough environment, whereby this bacterium can exist in peat environments that have high acidity and low oxygen [30,32].
Therefore, in the present research, peat soil improvement was carried out using biological soil stabilization by applying biotechnology, namely bioaugmentation with the bacterial agent Pseudomonas taiwanensis to accelerate the peat fibres decomposition.The objective of this research was to investigate the effect of Pseudomonas taiwanensis bacteria addition on the physical properties and shear strength of fibrous peat from Bereng Bengkel Village, Palangkaraya, Central Kalimantan.This research is the first to utilize the potential of Pseudomonas taiwanensis bacteria in biological stabilization to accelerating the peat fibres decomposition of fibrous peat in Palangkaraya.

Materials and methods
This research is a laboratory test conducted from June 2023 to August 2023 (3 months) at Politeknik Negeri Bandung.This research was conducted with 5 main stages which can be seen in the following description.

Peat soil sampling
The fibrous peat samples for this research were taken from Bereng Bengkel Village, Palangkaraya, Central Kalimantan.A visual observation was performed in accordance with ASTM D2488-09a while sampling the peat soil.Soil samples were taken by digging at a depth of 0.5-1 meters because the target of this fibrous peat stabilization in the future is for pavement subgrade where the pavement subgrade is at least 1 meter.There are two types of soil samples taken: undisturbed samples and disturbed samples.Undisturbed samples refer to soil that retains its original structure, while disturbed samples refer to soil whose original structure has been modified.The soil sampling procedure is in accordance with ASTM D 7015-04, although in practice, there are some modifications to the instrument used to collect undisturbed samples.Undisturbed samples were taken using a 4-inch PVC tube with a length of 20 cm, as shown in Figure 1a.Instead of Shelby tubes, PVC tubes were used to avoid corrosion of the Shelby tubes.This was also due to the very soft and watery texture of the peat soil, which made taking undisturbed samples with Shelby tubes impossible.Meanwhile, disturbed samples were taken using polybags covered with two layers to maintain the water content of the peat soil.This is to ensure that during the soil stabilization process with disturbed samples, the original physical properties of the peat soil, especially its water content, is not too much different from its original condition in the field because the water content of fibrous peat greatly affects the behaviour of fibrous peat.The polybag filled with soil was then put into a sack, as shown in Figure 1b.

Preliminary testing
The preliminary tests were conducted to determine the physical and mechanical properties of the initial peat soil with the parameters as follows: • Water content test, according to ASTM D-2216;

Bacterial Culture
The stabilization material used in this study is the bacteria Pseudomonas taiwanensis isolated from the Seed of Plant agricultural agent.To obtain sufficient stabilization material, a bacterial culture process was carried out at the Bioprocessing Laboratory of Politeknik Negeri Bandung based on conventional bacterial culture or liquid culture method using MERCK brand nutrient broth media, as shown in Figure 3a.In general, 8 grams of nutrient broth is dissolved in 1 litter of water (without minerals), commonly using Amidis brand bottled water.Then, the culture medium is autoclaved to make it sterile, as shown in Figure 3b.After the autoclaving process is complete, this cultivation medium is ready to be inoculated with bacterial isolates in a sterile laminar air flow, as shown in Figure 3c.Afterwards, the media solution that has been inoculated with bacteria is placed in a shaker incubator and incubated for 24 hours, as shown in

Peat soil stabilization process
In this research, there were 5 peat soil samples with a weight of 4000 grams each, placed in a plastic box.Then, the peat soil samples were added with Pseudomonas taiwanensis bacteria solution by mixing, as shown in Figure 4.The variation of bacteria addition to the peat soil samples can be seen in Table 1.Furthermore, these samples were observed and tested every 7 days, 14 days and 28 days to see the effect of curing period on its physical properties and shear strength.

Final testing
The final testing was conducted to determine the physical properties and shear strength of the stabilization samples.This final test consists of: • Water content test, according to ASTM D-2216; • Testing fiber content and fiber size distribution, based on the reference Peat Testing Manual 1979; • Soil pH value testing, carried out using the iTuin brand digital soil pH meter; • Direct shear testing, based on ASTM D-3080;

Analysis of physical and mechanical properties of initial peat soil
According to visual observations, it is known that the soil taken in Palangkaraya is fibrous peat.This is evident from the colour of the soil, which is dark brown-black, has clearly visible fibres, and has water content [34], as shown in Figure 5.According to ASTM D2488-09a, these are the characteristics of fibrous peat.Fibrous peat has a dark brown-black colour due to the presence of dark humic or organic compounds that appear as a result of the decomposition of peat fibres.These characteristics exist because peat soils are formed from the accumulation of organic matters such as leaves, twigs, and roots [35] that have not undergone a complete decomposition process [36].Table 2 shows the physical and engineering properties of the fibrous peat under study.The results obtained from the laboratory soil testing are in accordance with the results of previous studies [7,9,28,29,37].Based on Table 2, it is known that Palangkaraya fibrous peat has a water content of 704.02%.This shows that fibrous peat is able to absorb water as much as 6-7 times its dry weight.Therefore, it is certain that most of the pores of the peat soil are filled with water.As a result, peat soil is very sensitive to the load carried on it [38].This was also reported by [39], that buildings built on peat soils are very sensitive to settlement.The high water-absorbing ability of peat soil is due to the presence of micropores and macropores in peat soil that contain fiber [25].Both of these pores can absorb water, thus maintaining the peat soil in a saturated condition [40].The higher water content also indicates that the decomposition process in peat soil is still ongoing.As for the results of the specific gravity test on the peat soil under review, a value of 1.6 was obtained.This indicates that the specific gravity of the fibrous peat soil is very small.
In addition, the test results also obtained a bulk density value of 1.14 gr/cm³ for the peat soil.According to [41], the bulk density value is influenced by the degree of decomposition of peat fibres.It was reported in previous research that if the fiber content in peat soil is less, then the weight content value increases.Usually, soils that have a small bulk density also have a low bearing capacity [42].The calculation of the void ratio of fibrous peat shows a high void ratio, namely 9.3.The previous research showed that fibrous peat has a void ratio ranging from 5-15 [38].This causes peat soil to have a small bulk density value.The void ratio in fibrous peat affects its ability to absorb/retain water.The high void ratio, the higher the water content.As a result, fibrous peat is always in a saturated condition, which makes the environment anaerobic (oxygen-poor).Even during the dry season, fibrous peat will not easily lose its water content.In practice, it takes at least 3-4 days to dry peat soil under sunlight.The previous study reported that the void ratio of fibrous peat is influenced by the high fiber content [8].The higher the fiber content, the higher the void ratio.This is due to the presence of pores known as micropores in the peat fiber itself [7].
The acidity of the fibrous peat was tested using a digital soil pH meter.The results of the test showed that fibrous peat has a very high acidity level, pH 3.2.This is due to the long decomposition process in fibrous peat, which causes organic compounds to form, making the acidity level of fibrous peat very high [43].From this parameter, Bereng Bengkel peat soil can be classified according to ASTM D-4427-07.In terms of acidity, the Bereng Bengkel peat soil is classified as highly acidic peat because the acidity of the soil is < 4.5 pH.Ash content testing was also carried out by oven drying the fibrous peat samples at 750°C for 3 hours.From the test results, it was found that fibrous peat has an ash content of 2.47%.This is in line with previous research which states that fibrous peat has an ash content of around 3% [41,42].According to ASTM D-4427-07, Palangkaraya fibrous peat can be classified as low ash peat because it has an ash content of <5%.The organic content of fibrous peat can be obtained after the ash content is determined.From the calculation, it is known that the organic content of Palangkaraya fibrous peat reaches 97.53%.In previous research, the organic content of fibrous peat reached 75% [39].This is influenced by the different maturity levels of the peat in each location.The high organic content of fibrous peat is very reasonable considering that peat soil is formed from the accumulation of decomposed plant organic matter [35].
Based on the test results, the fiber content of the fibrous peat was 61.14%.According to ASTM D-4427-07, Palangkaraya fibrous peat is classified as "hemic peat" or "moderate fibrous peat", because it has a fiber content ranging from 33-67%.The high fiber content in fibrous peat is caused by the very long decomposition process [13].This means a higher decomposition rate means less fiber content.The high fiber content in fibrous peat enables it to absorb and retain a high amount of water.Based on this, it can be concluded that the higher the fiber content, the more water the fibrous peat contains.Fiber size distribution testing was also conducted to determine the size of the fibres present in the fibrous peat.From the test results, it can be seen that the crude fiber content has the highest percentage.This means that the degree of decomposition of Palangkaraya fibrous peat is very small.The results of the fiber size distribution test are as follows: • Crude fiber content = 45.08% • Medium fiber content = 31.69% • Fine fiber content = 23.23As for the engineering properties of fibrous peat, the shear cohesion value (c) from the direct shear test was 0.029 kg/cm2 with a shear angle of 29.19º.Several previous studies have reported that fibrous peat have low shear strength values [12].The low shear strength of fibrous peat soil is influenced by the high void ratio.Meanwhile, the results of fibrous peat consolidation testing with a standard oedometer, obtained a compression value of 5.5 mm.In geotechnical practice, fibrous peat has been acknowledged as soils with unusual settlement, due to their very high compressibility index [8].The compressibility index of fibrous peat is strongly influenced by its high fiber content.The higher the fiber content, the higher the compressibility index.There are four stages of compression that occur in fibrous peat soils, namely: (1) immediate compression (Si) which is an immediate compression and occurs very quickly, (2) primary compression (Sp) which is the process of releasing water in the macropores, (3) secondary compression (Ss) which is the of water in the micropores of the peat soil, and (4) tertiary compression (St) which is the process of weathering the peat fibres due to the very reduced water in the peat pores [38].This results in very long compression times in fibrous peat because initial compression occurs immediately after the application of load, while primary compression, secondary compression and tertiary compression are time dependent [44].

Fiber content of stabilized peat
Based on Figure 6, it is known that in the variation of adding 15% Pseudomonas taiwanensis bacteria in the 28-day curing period experienced the highest decrease in fiber content, from the initial fiber content of 61.14% to 12.33%.However, in other variations of addition, there was also a consistent and significant decrease in fiber content.The results of the decrease in fiber content in each sample are also not much different from each other.This confirms the results of research by [30] which states that Pseudomonas taiwanensis bacteria have the potential to accelerate the decomposition of peat fiber.The results also showed that the fiber content decreased as the curing period increased.This is in line with the results of research by [29], where in the variation of adding 10% solution of decomposer bacterial consortium, the fiber content decreased consistently as the curing period increased.Thus, it can be concluded that the curing has a good influence on the decrease in peat fiber content.

Fiber size distribution of stabilized peat in the 7-days curing period
Figure 7 shows the fiber size distribution of the stabilized peat during the 7-day curing period.During the 7-day curing period, it was found that the highest decrease in coarse fiber content and medium fiber content occurred with the addition of 10% Pseudomonas taiwanensis bacteria.In addition, in the variation of adding 10% Pseudomonas taiwanensis bacteria, there was also the highest increase in fine fiber content.However, in other samples there was also a decrease in crude fiber content which was not much different from each other.While in the variation of 20% addition of Pseudomonas taiwanensis bacteria, there was an increase in medium fiber content although not so significant.This may be due to the different percentage of Pseudomonas taiwanensis bacteria added to each sample.The decrease in crude fiber content indicates that there is a process of peat fiber decomposition that occurs after the addition of Pseudomonas taiwanensis bacteria.In general, a decrease in coarse fiber content will be followed by an increase in medium fiber content and fine fiber content.The difference in the percentage of Pseudomonas taiwanensis bacteria addition affects the biological process that occurs, as happened in the variation of 5% Pseudomonas taiwanensis bacteria addition, where the fine fiber content was very low compared to other samples.This indicates that the smaller the percentage of Pseudomonas taiwanensis bacteria addition, the less optimal the decomposition process.

Fiber size distribution of stabilized peat in the 14-days curing period
Figure 8 presents the fiber size distribution of stabilized peat during the 14-day curing period.During the 14-day curing period, it was found that there is a decrease in crude fiber content and an increase in the highest fine fiber content in the variation of adding 25% Pseudomonas taiwanensis bacteria.Meanwhile, the highest decrease in medium fiber content was found in the variation of 20% Pseudomonas taiwanensis bacteria addition.This occurred because the water content in the 14-day curing period decreased, so that the aeration process (the entry and exit of air) in the sample improved, increasing the metabolic activity of bacteria in breaking down peat fiber.From this, it can be concluded that the greater the percentage of Pseudomonas taiwanensis bacteria added, the longer the time needed to start the decomposition process.Previously, it has been explained that during the 7-day burial period, peat soil samples that were given the addition of bacteria in percentages of 10% and 15% had already experienced a significant decrease in crude fiber content and medium fiber content.This was because the water content in the peat soil samples with 5%, 10%, and 15% Pseudomonas taiwanensis bacteria was less than the peat soil samples with 20% and 25% Pseudomonas taiwanensis bacteria, so the aeration process went smoothly at the beginning.

Fiber size distribution of stabilized peat in the 28-days curing period
Figure 9 presents the fiber size distribution of stabilized peat during the 28-day curing period.During the 28-day curing period, it was found that the 5% addition of Pseudomonas taiwanensis bacteria decreased the highest crude fiber content.This has an impact on increasing the highest medium fiber content in the variation of adding 5% Pseudomonas taiwanensis bacteria.While the highest decrease in medium fiber content was found in the variation of adding 20% Pseudomonas taiwanensis bacteria.In addition, the highest increase in fine fiber content was found in the variation of adding 15% Pseudomonas taiwanensis bacteria.This is in line with the test results of fiber content in Figure 7, where in the 15% addition variation there was a decrease in the highest fiber content of 79.83%, from the initial fiber content value of 61.14% to 12.33%.However, a significant increase in the fine fiber content occurred in all samples, indicating that the decomposition process had reached its highest peak at 28 days and will continue.

Water content of stabilized peat
The results of testing the water content of the stabilized peat are shown in Figure 10.Based on Figure 10, it can be seen that during the 7-day curing period, there was an increase in the water content of the samples with 15%, 20%, and 25% Pseudomonas taiwanensis bacteria added.This is thought to be due to the addition of bacteria in the form of a solution or liquid so that the water content of the peat, which was already high, increased.This was also the case in [28] research, where during the 7-day curing period, there was an increase in the water content of peat soil samples added with a solution of decomposer bacteria (consortium).In addition, it was found that in the sample with a variation of 5% Pseudomonas taiwanensis bacteria added during the 28-day drying period, the highest water content decreased from 704.02% to 394.57%.However, all variations of bacteria addition in the 14-day and 28-day curing periods experienced a consistent decrease in water content.The reduction in water content in stabilized peat is due to the metabolic activities of bacteria that require H2O (water) [45].In addition, the stabilized peat no longer has micropores as a result of the decomposition of peat fibres, so water is easily evaporated.However, it is different from the results of [28] research, where the water content of stabilized peat did not change significantly even when it reached the 42-day curing period.It is known that in the results of this study, the water content experienced the highest decrease from 589.39% to 568.66% in the variation of adding 10% decomposer bacteria solution.This was influenced by the degree of decomposition of peat fiber obtained in the current study which was greater than in [28] study.

Acidity of stabilized peat
Measurement of the pH value of the stabilized peat was carried out periodically during the 7, 14 and 28 days of curing.The addition of Pseudomonas taiwanensis bacteria to the peat had an impact on increasing the pH value of the peat as shown in Figure 11.During the 7, 14 and 28 days, there was a significant increase in the pH value from the original value of to 6.5.This is caused by the release of carbon dioxide (CO 2 ) gas due to the decomposition process that occurs [46], thus reducing the acid content of the peat [28].In related research, the increase in pH value occurred as a result of the addition of a decomposer bacterial consortium solution [24,28,29,47,48].

Shear strength of stabilized peat
The shear cohesion values of the stabilized peat obtained from the direct shear test are shown in Figure 12.In this test, there were samples that could not be tested because the soil samples were so soft due to the very high moisture content.This phenomenon occurred in all samples at 7 days and 14 days, and some samples at 28 days (20% and 25%).Therefore, the samples that can be tested for shear strength are in the variation of 5%, 10% and 15% addition of Pseudomonas taiwanensis bacteria in the 28-day curing period.Based on Figure 12, it is known that the highest increase in the value of shear cohesion (c) is found in the variation of 15% addition in the 28-day curing period.However, in the variation of 5% and 10% addition in 28 days curing period, there is a significant increase in shear cohesion value.This increase in shear cohesion value is thought to be due to the decomposition of peat fibres so that the soil becomes denser [30].This is explained in Figure 13, where the shear angle obtained from the direct shear test results explains the soil density based on Table 3 [49].Based on this approach, it is known that the sample with the variation of adding 5% Pseudomonas taiwanensis bacteria in the 28-day soaking period has a shear angle of 46.62° and a shear cohesion value of 0.065 kg/cm 2 .This indicates that the soil sample in this variation is very dense.This can occur because the water content in the variation of 5% addition of Pseudomonas taiwanensis bacteria is the lowest when compared to other samples.While in the variation of the addition of 10% Pseudomonas taiwanensis bacteria, there was an increase in shear cohesion value of 187.34%, from 0.029 kg/cm 2 to 0.083 kg/cm 2 .Likewise, in the variation of adding 15% Pseudomonas taiwanensis bacteria in the 28-day curing period, where a shear angle of 37.71° and a cohesion value of 0.119 kg/cm2 were obtained.This makes it the addition variation with the highest percentage increase in shear cohesion value.This is because the fiber content in the 15% bacteria addition variation is the lowest compared to the 5% and 10% variations.In addition, from the magnitude of the shear angle, the sample with 15% Pseudomonas taiwanensis bacteria addition variation in the 28day curing period turned out to be rather dense.

Conclusion
Based on preliminary testing results, Palangkaraya fibrous peat was classified as "hemic peat with low ash content and highly acidic".The Palangkaraya fibrous peat had very poor mechanical properties with a shear strength of only 0.029 kg/cm2 and compressibility of 5.5 mm.After the biological stabilization process through bioaugmentation of Pseudomonas taiwanensis bacteria, the physical and mechanical properties of fibrous peat improved.This happened because Pseudomonas taiwanensis bacteria accelerated the decomposition process of peat fibres so that the peat was denser due to the reduction of macropores and micropores along with the decomposition of peat fibres.The stabilization results showed that the addition of 15% Pseudomonas taiwanensis bacteria in the 28-day holding period was the optimum variation to improve the physical properties and shear strength of fibrous peat.In the variation of adding 15% Pseudomonas taiwanensis bacteria with a 28-day holding period, there was a decrease in fiber content, from the initial fiber content of 61.14% to 12.33%.This very significant decrease in fiber content caused a significant increase in shear strength in the sample with the addition of 15% Pseudomonas taiwanensis bacteria in the 28-day curing period, from the initial cohesion value of 0.029 kg/cm2 to 0.119 kg/cm2.Therefore, it can be concluded that Pseudomonas taiwanensis bacteria can be used as an alternative to improve the geotechnical properties of fibrous peat.Moreover, the use of these Pseudomonas taiwanensis bacteria as stabilization materials does not damage the environment because there are no chemicals used that can cause groundwater contamination, so these bacteria are one of the environmentally friendly methods of stabilizing fibrous peat.
We would like to thank the P3M of Politeknik Negeri Bandung for funding this research with the applied research scheme with contract number: B/92.26/PL1.R7/PG.00.03/2023.

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Density test (content weight), with reference to ASTM D-7263; • Testing of ash content and organic content, with reference to SNI 13-6793-2002; • Testing fiber content and fiber size distribution, based on the reference Peat Testing Manual 1979; • Soil pH value testing, carried out using the iTuin brand digital soil pH meter, as can be seen in Figure 2a.The test was carried out by poking the pH meter into the soil sample at several points as shown in Figure 2b, then the values obtained were averaged; • Direct shear testing, based on ASTM D-3080; • Oedometer consolidation test, based on ASTM D698-12.

Fig. 2 .
Fig. 2. Instrument for testing the pH value of peat soil: (a) Digital soil pH meter (iTuin), (b) Soil pH value testing.

Fig. 4 .
Fig. 4. The process of mixing bacteria with peat soil.

Fig. 6 .
Fig. 6.Fiber content of stabilized peat from various addition of bacteria.

,Fig. 7 .
Fig. 7. Fiber size distribution of stabilized peat from various addition of bacteria in the 7-days curing period.

Fig. 8 .
Fig. 8. Fiber size distribution of stabilized peat from various addition of bacteria in the 14-days curing period.

Fig. 9 .
Fig. 9. Fiber size distribution of stabilized peat from various addition of bacteria in the 28-days curing period.

Fig. 10 .
Fig. 10.Water content of stabilized peat from various addition of bacteria.

Fig. 11 .
Fig. 11.pH level of stabilized peat from various addition of bacteria.

Fig. 13 .
Fig. 13.Shear angle of stabilized peat from various addition of bacteria.

Table 1 .
Variation of Sample

Table 2 .
Initial physical and engineering properties of Palangkaraya fibrous peat.