Scholarly article on topic 'Evaluation of the Ability to Control Biological Precipitation to Improve Sandy Soils'

Evaluation of the Ability to Control Biological Precipitation to Improve Sandy Soils Academic research paper on "Materials engineering"

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{"Soil improvement" / "biological precipitation" / "urease activity" / "calcium carbonate sediment" / "precipitation control."}

Abstract of research paper on Materials engineering, author of scientific article — Farzin Kalantary, Mostafa Kahani

Abstract Biological soil improvement is a novel improvement technique in which chemical and biological processes leads to an improvement of physical and mechanical soil properties. Since this method is environmentally compatible and applicable to various soil types using different materials, it has turned into an efficient soil improvement method in numerous ground treatment projects. Microbiologically induced calcite precipitation (MICP) is one of the most well-known biological soil improvements method in which after the injecting bacterial suspension, reaction solution (cementation solution) into soil particles, calcium carbonate sediment is formed, and thereby soil properties are improved. In this paper, the ability to manage time and location when calcium carbonate sediments are biologically formed was investigated in sandy soil. The electrical conductivity method, unconfined compressive strength test and X-ray diffraction examinations were sequentially used to determine urease bacterial activity, measure the amount of the increased strength of treated soil and determine crystal type. The results showed good ability of this method to control time and location of biological precipitating. Furthermore, unconfined compressive strength of Caspian Sea coast sandy soil was increased up to 400kPa. The ability to manage time and location of biological precipitating indicates this method can be potentially used in different application such as mitigation of liquefaction, soil erosion control, immobilizing of pollutions in soil and other soil improvement projects.

Academic research paper on topic "Evaluation of the Ability to Control Biological Precipitation to Improve Sandy Soils"

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Procedia Earth and Planetary Science 15 (2015) 278 - 284

The World Multidisciplinary Earth Sciences Symposium, WMESS 2015

Evaluation of the Ability to Control Biological Precipitation to

Improve Sandy Soils

Farzin Kalantarya*, Mostafa Kahanib

aFaculty of Civil Engineering, K.N.Toosi University of Technology, Tehran, Iran bPhD Student of Civil Engineering, K.N.Toosi University of Technology, Tehran, Iran

Abstract

Biological soil improvement is a novel improvement technique in which chemical and biological processes leads to an improvement of physical and mechanical soil properties. Since this method is environmentally compatible and applicable to various soil types using different materials, it has turned into an efficient soil improvement method in numerous ground treatment projects. Microbiologically induced calcite precipitation (MICP) is one of the most well-known biological soil improvements method in which after the injecting bacterial suspension, reaction solution (cementation solution) into soil particles, calcium carbonate sediment is formed, and thereby soil properties are improved. In this paper, the ability to manage time and location when calcium carbonate sediments are biologically formed was investigated in sandy soil. The electrical conductivity method, unconfined compressive strength test and X-ray diffraction examinations were sequentially used to determine urease bacterial activity, measure the amount of the increased strength of treated soil and determine crystal type. The results showed good ability of this method to control time and location of biological precipitating. Furthermore, unconfined compressive strength of Caspian Sea coast sandy soil was increased up to 400 kPa. The ability to manage time and location of biological precipitating indicates this method can be potentially used in different application such as mitigation of liquefaction, soil erosion control, immobilizing of pollutions in soil and other soil improvement projects.

© 2015Published byElsevierB.V.Thisisanopenaccess article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibilty of the Organizing Commitee of WMESS 2015.

Keywords: Soil improvement; biological precipitation; urease activity; calcium carbonate sediment; precipitation control.

* Corresponding author. Tel.: +98 912 1069256; fax: +98(21)88779476. E-mail address: Fz_kalantary@kntu.ac.ir

1878-5220 © 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibilty of the Organizing Commitee of WMESS 2015. doi: 10.1016/j.proeps.2015.08.067

1. Introduction

Population and consequently civil projects have increased significantly in different countries during recent years. Therefore soil improvement is continuously in need due to the increase of civil infrastructure. According to the research in 2008, every year more than 40,000 soil improvement projects worth of more than 6 billion US dollars take place around the earth (DeJong et al., 2010). Available methods of soil improvement are often based on utilizing outside material (cement, chemical grout, geo-synthetics, strips and etc.) or mechanical energy (dynamic compaction, compaction piles, vibroflotation and etc.).

One of the most common soil improvement methods is injection of cement and chemical grout into the soil, but according to the reports all chemical grouts are poisonous and dangerous except Sodium Silicate (U.S. Army Corps of Engineers, Engineering Manual NO. EM 1110-1-3500, 1995; Karol, 2003). Some of the acrylamides (a substance used in chemical grouts) are neurotoxic material and have side effects for the neural tissues. The acrylamide poisoning has been reported when acrylamides have been used carelessly. Therefore, this product must be used with caution. In several countries there are restrictions for their use or its consumption is banned (Karol, 2003). Another problem for injection on in-situ ground improvement projects, especially when cement is used, is the depth of grout penetration. Since the injected material is filtered by soil particle, the penetration depth is low and this method is only effective to a radius of 1 to 2 meters depending on the injection pressure and the amount of injected material.

Microbiologically induced calcium carbonate precipitation method is one of the newest methods of ground improvement, in which calcium carbonate crystal was formed between soil particle using bacteria in order to improve soil properties. This procedure can stabilize the soil or other small particles (porous material) without disturbing the initial structure. In this method, penetration reduction and the cost of implementation are low. Moreover, it is environmentally compatible and a wide range of material and micro-organisms can be used in this method without harmful environmental consequences (Kahani et al., 2013).

Many studies have been carried out up to now on the capability of this method in different applications. MICP has been used to improve sandy soil properties (DeJong et al., 2006; Whiffin et al., 2007; Van Paassen, 2011; Kahani et al., 2013), removal and immobilization of soil pollution (Warren et al., 2001; Fujita et al., 2004; Fujita et al., 2010; Li et al., 2011), crack repair in concrete (Ramachandran et al., 2001; Abo-El-Enein et al., 2012; Abo-El-Enein et al., 2013), increasing brick strength by reducing water absorption (Sarda et al., 2009), distribution and fixation of bacterial activity in soil (Harkes et al., 2010) optimization of carbonate precipitation (Okwadha and Li, 2010). Moreover, many other researches are being carried out in the fields of Microbiology, Chemistry and Geotechnical engineering. Recently, some field trials of this method have been reported in Netherlands and in the US in order to gravel stabilization and heavy metals immobilization (co-precipitation) respectively (DeJong et al., 2013). According to the () results unconfined compressive strength of biological treated soil was increased up to 55 MPa (Yang and Cheng, 2013). Which indicates the ability of this method in soil improvement projects.

After considering different methods of biological precipitation in this study, the possibility of managing the biological precipitation for different functions was investigated.

2. Biochemical catabolic reactions

2.1. A review of biological precipitation methods

Biological soil improvement is often based on sediments containing calcium, magnesium, iron, manganese and aluminum sediments which precipitate between soil particles as carbonates, silicates, phosphates, sulfides and iron hydroxides (Ivanov and Chu, 2008). This paper was focused on microbial induced carbonate precipitation (MICP). One of the most attractive attribute of biological soil improvement method is the ability to use different microbial processes. Therefore different microorganisms and catabolic reactions can be used in order to form carbonate. Table 1 shows several chemical reactions, which can be produced carbonate sediments using bacteria.

As shown in Table 1, reaction material, mediated-bacteria and resulting governor conditions were different in each reaction. The choice of chemical reaction was made regarding different criteria such as reaction condition, reaction rate, material availability, sediment durability, etc. In situ biological carbonate precipitation by hydrolysis of urea was chosen for this study.

Table 1. Several chemical reactions which able to form carbonate and can be potentially used in biological soil improvement. (Ivanov and Chu, 2008; Dejong et al., 2010; Van Passen et al., 2010).

Conversion type Chemical reactions Aerobic/anaerobic conditions

Sulfate reduction Ca(CH3CÜ2)2 + 2CaSO4^2H2S+H2O+3CaCO3+CO2 Anaerobic

Urea hydrolysis CO(NH2)2+3H2O^2NH4++HCO-3+OH- Aerobic

Iron reduction CH3CO2" +8Fe(OH)3(soiid)+6HCO3"+7H+^8FeCO3(soiid)+20H2O Aerobic

Aerobic oxidation of calcium acetate Ca(C2H3O2)2+4O2^1CaCO3+3CO2+3H2O Aerobic

Nitrate reduction Ca(C2H3O2)2+1.6Ca(NO3)2^2.6CaCO3+1.6N2+1.4CO2 Anaerobic

2.2. Biological precipitation of calcium carbonate by hydrolyzing of urea

Urea hydrolysis is a chemical reaction in which urea reacts with water and produces ionic product. When this reaction was done in the presence of calcium ion (Ca2+), calcium carbonate sediment was formed.

urease

CO(NH2)2 + 2H20-> C03" + 2NHX

C^CO3(solid) (1)

In presence of Ca2+

When this reaction was done inside soil particle or porous material, after settling produced sediment, a coating and bridge was formed sequentially around and between the particles and increased particles linkage.

Hydrolyzing of urea (when there is no catalyzer) is a slow and lengthy process and in the presence of urease^, it is about 1014 times faster than the usual process (non-catalyzed reaction) (Benini et al., 1999). In this reaction, urease enzyme was discharged from a positive urease bacterium, and the reaction rate was accelerated by bacteria as a mediator agent. In other words, chemical reaction (catabolic reaction) and the time of sediment forming were controlled by biological activity (Kahani et al., 2013).

3. Materials and methods

Urea Hydrolysis is the dominant activity in the mentioned chemical reaction which has a great role in its performance and usage. If the speed of the reaction (hydrolysis) is controllable, it can be a regulating factor for improvement with various aims and goals. Ground improvement projects need () a flexible improvement method due to the different conditions and goals. To evaluate the possibility of controlling the speed of reaction, the bacteria activity was studied using two different culture media in different conditions. Conductivity method was used to measure the rate of bacteria activity and X-ray diffraction (XRD) experiment was used to identify the composition of the formed precipitate.

3.1. Microorganism

Since forming carbonate by hydrolysis of urea in the presence of urease enzyme was the chosen reaction, the microorganism must be able to discharge urease enzyme. Sporosarcina Pasteurift (PTCC=1645) was used as a urease positive bacterium. This bacterium exists in the soil naturally and can also be isolated from soil if needed.

t an enzyme that catalyses the hydrolysis of urea

^ this bacterium was obtained from the bacteria collection of the Iranian Research Organization for Science and Technology (IROST) in Iran

3.2. Electrical conductivity

Since the role of the bacteria was to supply the urease enzyme, the rate of urease enzyme activity was considered as the bacteria activity and it can be measured through the rate of urea hydrolysis. As () mentioned, urea hydrolysis consists of conversion of urea to ammonium and carbonate ions in the presence of water. To measure the urease enzyme activity, the rate of change in electrical conductivity was measured in time.

According to the proposed method by Whiffin (Whiffin, 2004) and Harkes (Harkes et al., 2010), by completely hydrolyzing anionic material of urea to ionic material under standard conditions, the rate of electrical conductivity distinctly increases. Accordingly, 1 ml bacterial suspension was added to 9 ml of 1.11 M urea solution and the change in electrical conductivity after 5 minutes in lab conditions was measured on the basis of mS/min. Finally, 1 mS/min is proportional to hydrolysis of 11 mM of urea per min.

3.3. Culture media

Initially, in this study 3 culture media with different compositions were used. One of the culture media was eliminated from the study after primary evaluation and lack of urease bacteria activity in spite of suitable growth in it, and the rest of the study was carried out on the other two. Table 2 shows the combination of the two culture media which showed urease activity.

Table 2. Composition of the used culture media.

Culture media YE-1 Caso-1

20 gr/l Yeast Extract 15 gr/l Peptone casein 10 gr/l NH4Cl 5 gr/l Pepton soymeal

10mM NiCl2 5 gr/l NaCl

- 20 gr/l Urea

8.0 8.5

3.4 Measuring the precipitation rate

To measure the rate of the precipitation, equal amount of bacterial suspension was combined with specified molarity of reaction substances in the mentioned culture media and they were left to precipitate. The formed precipitation was separated using centrifuge in specific time lapses (10 min, 20 min, 1, 2, 4, 8 and 24 hour), after that it was dried in the oven and the percentage by weight of formed sediment was calculated. Table 3 shows the used material.

Table 3. Detail of used material in measuring precipitation rate test.

Test No. Solution Type Culture media Reaction Solution

1 Caso-1 1 M

2 YE-1 1 M

3 Caso-1 2 M

4 YE-1 2 M

4. Results and Discussion

Table 4 shows the amount of urease activity of Sporosarcina Pasteurii bacterium in the mentioned culture media which was measured by conductivity method.

Table 4. Urease activity of Sporosarcina Pasteurii. Urease Culture Media

Composition

Caso-1 YE-1

42.6 mM 19 mM

Urease activity in a way indicates the speed of precipitation. In the equal amounts of reactants (urea and calcium chloride) the case which have more urease activity, hydrolyses specified amount of urea in less time. Therefore, in a specified time lapse, if reactants are continuously provided, more sediments are produced. In order to assess the effect of urease activity on the rate of precipitation, it was investigated directly. Figure 1 shows the sediment formation procedure of Sporosarcina Pasteurii in the two mentioned culture media in the presence of 1 M reactants solution.

Sediment _ Amount of formed sediment at time t (2)

Expectable sediment

Expected sediment: Total expected sediment at the end of reaction.

Fig. 1. The sediment formation procedure (1 M reactant solution).

As it is shown in figure 1, the difference in the urease bacteria activity in the two media leads to delay in the precipitation process. Using Caso-1 medium about 50% of the anticipated sediment formed during 1 hour which was nearly 1.5 times the amount formed using YE-1 medium in same time. YE-1 culture medium caused half an hour delay in the formation of calcium carbonate sediment. Figure 2 shows the sediment formation procedure of Sporosarcina Pasteurii in the above-mentioned culture media in the presence of 2 M reactant solution.

0.1 1 10

Fig. 2. The sediment formation procedure (2M reactant solution).

Regarding the results in Figure 2, despite the increase of initial material (urea) at the beginning of the reaction has an inhibitor role up to 4 hours; at the beginning, the weight was nearly equal to the same amount of formed

sediment in Figure 1. Increasing the amount of initial material () also leads to an increase in the end-time of the precipitation. It was observed that after 24 hours, unlike figure 1 about 90% of the sediment was formed and precipitation was still ongoing.

Moreover, due to low urease activity of bacteria in YE-1 medium in comparison to Caso-1 medium, the amount of formed sediment after 24 hour in YE-1 was also less than Caso-1.

In addition to the tested bacterium, other urease positive bacteria such as indigenous bacteria can () be implemented in the biological calcification. Arthrobacter Crystallopoietes isolated from the mountains of Eshtehard region in Alborz province) is an indigenous urease positive bacteria. Its bacterial activity in Caso-1 culture media was lower than Sporosarcina Pasteurii in the both mentioned culture media (about 0.5 mM urea/min), and therefore is more successful in precipitating calcium carbonate in deeper soil (result not shown here). Calcium Carbonate is polymorph and therefore consists of several crystal types or different shapes, which include: 1) calcite, 2) vaterite and 3) aragonite. According to the strength, calcite is in the first place, the second one is vaterite and aragonite is in the last place. Regarding appearance, calcite is in the form of rhomboidal and square, vaterite forms spherical and planar form and aragonite is needle-shaped (Van Paassen, 2009). According to the results of X-ray diffraction§ examinations and Scanning Electron Microscopy** (SEM) on the produced sediment samples (the sediment samples was ground before XRD examinations), the formed calcium carbonate sediments according to weight was calcite and vaterite respectively.

Finally, using biological precipitation, the unconfined compressive strength of poorly graded sandy soil^ was increased up to range 100-400 kPa after treatment. This amount of unconfined strength is in satisfied range for most of ground improvement projects such as mitigation of liquefaction risk (Port and Harbour Research Institute, 1997).

5. Conclusion

Since the viscosity of used materials in the biological improvement methods are very low, it has great potential on in situ improvement applications. Therefore, in comparison with cement grout injection (which is the most commonly used ground improvement method), it is possible to improve deeper soil if precipitation process is controlled.

In this study, the precipitation rate was investigated using two different culture media. The results showed the ability to control the precipitation rate using different culture media and different bacteria. In the cases when deep improvement is needed, like liquefiable soil, () it can be achieved by controlling the precipitation rate using delay conditions and/or proper bacteria. However, in many projects like stabilization of soil which suspected to erosion, the improvement aims are increasing shear strength of shallow soil, thus those culture media in which precipitation is formed more quickly like Caso-1 can be used.

Regarding the mentioned results, this method can be implemented for different ground improvement applications such as mitigation of liquefaction risk, fugitive dust control and etc. by different culture media or different bacteria.

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