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Seepage control in sand using bioslurry
Construction and Building Materials 212 (2019) 342–349
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Seepage control in sand using bioslurry Yang Yang a, Jian Chu a,⇑, Yang Xiao b, Hanlong Liu b, Liang Cheng c a
School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore School of Civil Engineering, Chongqing University, Chongqing 400045, China c School of Environmental and Safety Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang, Jiangsu Province 212013, China b
h i g h l i g h t s The bioslurry contains high urease active bacteria cells and allows further MICP treatment. Permeability reduction of bioslurry was comparable to a well compacted clay liner. The biocemented bioslurry layer is less affected by the wet-drying processes. Cracks of bioslurry can be repaired using the same MICP method.
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Article history: Received 23 October 2018 Received in revised form 25 March 2019 Accepted 28 March 2019
Keywords: Bioslurry Biocementation Microbially induced carbonate precipitation (MICP) Water barrier layer Permeability
a b s t r a c t This paper presents a new method for seepage control in sand using bioslurry, a suspension of CaCO3 crystals formed using a microbial calcium carbonate precipitation process (MICP). The bioslurry can be permeated through sand or deposit on top of a sand layer. The bioslurry contains high urease active bacteria cells and allows further MICP treatment when introducing cementation solution. In this way, the permeability of the bioslurry layer or bioslurry permeated sand layer could be further reduced to the order of 109 m/s through another 2–3 numbers of MICP treatment using a cementation solution with an optimum concentration of 1.6 M. Such a low permeability is hardly achievable using the conventional MICP method which would require many more numbers of treatment to reduce the permeability of sand to be below 107 m/s. Therefore, the proposed bioslurry method is not only more effective, but also more efficient. The water barrier layer formed using the proposed method is much less affected by wet and dry or temperature change cycles than compacted clay liners. It also allow cracks in the water barrier layer to be repaired if required. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction Seepage control is a common construction process for many infrastructure projects such as reservoirs, earth dams, tunnels and other underground constructions. Seepage leads to the largest single loss of water for aquacultural pond which may also diminish the nutrients content in the pond in addition to the water loss [1– 3]. High seepage rate may also lead to leaking of harmful substances from waste to water and result in groundwater pollution. For example, Kvenvolden et al. (2003) [4] has shown that 47% of the crude oil entering into the marine environment is through natural seepage and the estimated amount of crude-oil leakage is 600,000 metric tons per year. To date, various solutions, such as polymers, water-swellable colloidal clays, and chemical cement ⇑ Corresponding author. E-mail addresses: [email protected] (Y. Yang), [email protected] (J. Chu), [email protected] (L. Cheng). https://doi.org/10.1016/j.conbuildmat.2019.03.313 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.
grout, have been applied to the surface of soil to provide a waterproofing liner to prevent the penetration of water or toxic chemicals into the soil [5,6]. Cement grout is the most common method adopted for seepage control in porous soils. However, production of cement requires high energy consumption and generates substantial amount of CO2 (0.95 t CO2/t Portland Cement) [7,8]. Biocement is a new material that requires less energy to make and is more environmentally friendly. Biocement is formed in the pores of soil at an ambient temperature through a microbially induced carbonate precipitation (MICP) process. The precipitates act as a bonding material to increase the shear strength of soil or as a pore-filling material to reduce the permeability of soil [9– 12]. Studies have been carried out to use biocement for soil erosion control, slope protection, mitigation of internal erosion or liquefaction, reducing fluid flow in soil and sealing the leakage of construction landfill [5,10,13–15].
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The MICP process adopted in this study utilized urease-positive bacteria to hydrolyze urea to produce calcium carbonate crystals in the presence of calcium ions [11,16–20] as illustrated by:
COðNH2 Þ2 þ 2H2 O ! 2NHþ4 þ CO2
ð1Þ
Ca2þ þ CO2 3 ! CaCO3 ð#Þ
ð2Þ
Using a biotreated layer formed in sand through a specially designed MICP process, the permeability of sand can be reduced from the order of 104 m/s–107 m/s [18,21,22]. However, this can only be achieved through a number times of treatment. This is not efficient for construction. Furthermore, it appears difficult to reduce the permeability to be lower than 107 m/s [6,11,23]. To overcome the difficulties with multiple treatment, the bioslurry method is adopted in this study. Bioslurry consists of calcium carbonate crystals with highly urease active bacterial cells. The calcium carbonate crystals are formed in water by mixing calcium chloride and urea with bacterial culture. The calcium carbonate crystals so produced contain bacterial cells which can still activate the MICP process to produce more CaCO3 with the presence of urea and Ca2+ ions [6]. To form a water barrier in a sand layer using bioslurry method, the bioslurry is either placed on to the sand layer or permeate into sand layer followed by one to three times of MICP treatment of the bioslurry layer by injecting cementation solution. The detailed procedure will be further explained later. In the past, compacted clay liners or geosynthetic clay liners have been used to form hydraulic barriers for landfills [24]. However, clay liner may shrink and crack. The biocemented layer contains calcium carbonate and thus is less affected by shrink caused by wet and dry or temperature change cycles. The durability of a water barrier layer formed using the bioslurry method was also studied under wet-dry cycles. Several parameters related to the permeability reduction of sand using the bioslurry method were also examined and discussed. These included the chemical conversion efficiency of cementation solution, the thickness of the sand layer above the bioslurry layer, the calcium carbonate content, and treatment times. An experiment to repair a crack formed by impact load was also carried out to verify the ability of the new method to allow repair of cracks formed in the water barrier layer. 2. Materials and methods 2.1. Urease producing bacteria and cementation solution Urease producing bacteria used in this study was isolated from activated sludge obtained from local wastewater treatment plant and identified by 16S rDNA sequence analysis, known as Bacillus Sporosarcina pasteurii, which was then cultivated under aerobic sterile conditions. The growth medium comprises 10 g/L ammonia chloride, 20 g/L yeast extract, 0.01 g/L nickel chloride and initial pH was set at 9. The bacterial cultivation was conducted at 28 °C on an orbital shaker at shaking rate of 200 rpm. Bacteria culture was then harvested after 48 h of the cultivation and stored at 4 °C. The optical density (OD600) of the harvested bacterial culture varied from 2 to 3, and the urease activity was measured by conductivity meter and adjusted to approximately 10 U/ml (1 U = 1 mmol urea hydrolyzed per minute) prior to use [18,25]. 2.2. Bioslurry preparation Following the work by Cheng and Shahin (2016) [6], bioslurry was prepared by adding 44.4 g calcium chloride and 24 g urea into 1 L of the raw bacteria culture, followed by stirring at a speed of 200 rpm for 24 h (Fig. 1). The calcium carbonate crystals with imbedded highly active ureolytic bacteria were then produced. After complete settle-
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ment, the clean supernatant was disposed and the settled crystals [6] were collected and stored in a refrigerator prior to use. The solid content of the collected bioslurry was about 25 ± 3% (w/w). 2.3. Effect of cementation solution concentration on chemical conversion efficiency The effect of cementation solution concentration on the chemical convention efficiency of bioslurry was investigated as follows: 1) five centrifuge tubes were filled with 4 g (25% solid content, urease activity = 48 U/ml/g) of bioslurry respectively, and centrifuged at a speed of 3000 rpm for 12 min; 2) After removing the supernatant, 20 ml of different concentrations of cementation solution (equimolar of CaCl2 and Urea) ranging from 1 to 2 M were added to the centrifuge tubes. 3) the centrifuge tubes were shaken continuously at a speed of 200 rpm and the calcium concentration of the cementation solution was measured after 24 h, 48 h and 72 h according to the standard method 2340C with ethylene diamine tetraacetate dehydrate (EDTA) titration [18]. All tests were conducted in duplicate. 2.4. Column tests Transparent acrylic columns (50 mm inner diameter and 100 mm in length) were utilized for the formation of waterproofing layer using bioslurry. The column was filled with multiple layers of materials (Fig. 2): 1) The bottom layer was filled with 150 g dry Ottawa sand with a mean grain size of D50 = 0.4 mm; 2) The middle layer was formed by spraying 4 g homogenized solid bioslurry (25% solid content, urease activity = 48 U/ml/g) onto the top surface of the bottom sand layer to form a 2–3 mm thick slurry layer; and 3) The top layer was formed by placing 100 g dry Ottawa sand on the top of bioslurry layer. The top sand layer had a porosity 0.35 or a void volume of 20 cm3. Fitting cap with a drainage outlet at the bottom was also designed to match each column and facilitate the permeability test. The sand columns were treated using four different concentrations of cementation solution of 1.0 M, 1.3 M, 1.6 M and 1.8 M respectively. For each type of solution, three tests with treatment of one, two and three times were conducted respectively. In total, 12 tests were carried out. For the first treatment, 40 ml of cementation solution was poured onto the surface of the top sand layer. For the 2nd and 3rd treatment, 20 ml of the cementation solution was added. Each treatment was applied for 24 h at room temperature (25 ± 1 °C). After the treatments were completed, the sand columns were subjected to permeability test. To evaluate the effect of the top sand layer on permeability reduction, another three tests without the top sand layer were carried out using cementation solution of 1.6 M by following the same procedure as stated above. The effect of the thickness of the top sand layer were also evaluated. Three columns with different thickness of top sand layer of 1.5 cm (50 g sand with void volume of 10 cm3), 3 cm (100 g sand with void volume of 20 cm3) and 6 cm (200 g sand with void volume of 40 cm3) were treated 3 times using cementation solution of 1.6 M. After treatment the permeability of each column was measured. To develop a method to heal cracks of bioslurry based water barrier layer, a bioslurry sample with cracks was prepared as follow. A sand column was prepared as described in Section 2.4. The sand in the column was treated once using 20 ml cementation solution with a concentration of 1.6 M. After this, the top layer of sand was removed and cracks were then created by dropping a ball onto the water barrier layer. To heal the cracks, a 100 g clean and dry Ottawa sand was added on top of cracked bioslurry liner. Then, repeated treatment (3 times) of 20 ml of cementation solution (1.6 M) was applied. The permeability of the sand column was measured after each treatment.
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Fig. 1. Bioslurry during Reaction (A) and Settled Bioslurry (B).
Fig. 2. Schematic Set Up of Sand Column.
2.5. CaCO3 content determination and microstructure analysis After the permeability test, all samples treated by 1.6M of cementation solution were taken from the bioslurry layer to determine the CaCO3 content. The sample was rinsed with tap water and oven dried at 105 °C for 24 h prior to weight measurement. The calcium carbonate content of the sample was determined by weight difference of bioslurry before (4 g) and after treatment. For each test, CaCO3 were measured at least three times so as to achieve an average value and minimize the error. Laboratory determination of the permeability of the treated sand columns were conducted using a falling-head method in accordance with ASTM D5084. All permeability measurements
were carried out twice and the average values were reported. Scanning Electron Microscopy tests were also carried out for samples from the bioslurry based waterproofing layer. The sample was rinsed with tap water and oven dried at 105 °C for 24 h prior to the SEM using a SEM analyzer (Zeiss EV050, UK).
3. Results 3.1. Effect of concentration of cementation solution In this study, the effect of concentration of cementation solution on the chemical conversion efficiency using bioslurry method was
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tested. The results of calcium consumption versus the initial calcium concentration of the solution are presented in Fig. 3. It can be seen that the calcium consumption increased with the increase in the calcium concentration up to 1.6 M, following by a gradual decrease with the increase in the calcium concentration. This was probably due to the toxic effect of the high concentration of calcium ions to the urease producing bacteria [26]. The maximum calcium consumption was about 1.44 M in 72 h for an initial concentration of calcium of 1.6 M with the maximum precipitation rate of 1.03 mol/L/day. Therefore, 1.6 M was taken as the optimum concentration of cementation solution for the CaCO3 production of bioslurry. The permeability obtained for the treated columns is plotted versus the concentration of the cementation solution in Fig. 4. The reduction in permeability is dependent on the concentration of cementation solution as well as the number of treatments applied. As shown in Fig. 4, the reduction in permeability is significant even with one treatment. The 2nd and 3rd treatment would lead to further reduction in permeability. It can also be seen from
Fig. 4 that the lowest permeability of 3.6 109 m/s was obtained for samples treated 3 times using 1.6 M cementation solution. Thus, the optimum concentration of cementation solution is 1.6 M as it resulted in lowest permeability, which is consistent with the results shown in Fig. 3. In the previous studies, the lowest permeability reduction by a MICP method is normally to an order of 107 m/s through many number of treatment, unless it is a layer of CaCO3 crust [16– 18,21]. The permeability versus CaCO3 content obtained in this study for the bioslurry treated layer is shown in Fig. 5. The number of treatment is also indicated in Fig. 5. It can be seen that the permeability reduction is dependent on the precipitated CaCO3 content as established by previous studies [9,16,21]. According to Fig. 5, the permeability can be lower than 107 m/s after the first treatment, and a permeability lower than 108 m/s can also be achieved after the 2nd and 3rd treatment. If the conventional MICP method is used, it will require many numbers of treatment to reduce the permeability of sand to this level [16–18,21]. This would be hardly feasible using the conventional method. Thus
1.8 24 Hours
Calcium Consumption (M)
1.6
48 Hours
72 Hours
1.4 1.2 1 0.8 0.6 0.4 0.2 0 1
1.3 1.6 1.8 Initial Concentration of Calcium Content (M)
2
Fig. 3. Calcium Consumption vs. Concentration of Initial Cementation Solution.
Before Treatment
One Treatment
1.0 M
1.3 M
Two Treatments
Three Treatments
1.6 M
1.0E+00
Permeability (m/s)
1.0E-01 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08 1.0E-09 Concentration of Cementation Solution Fig. 4. Permeability of Bioslurry Based Water Barrier.
1.8 M
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Bbefore Treatment
First Treatment
0
2
4
Second Treatment 6
Third Treatment 8
10
Permeability (m/s)
1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08 1.0E-09
CaCO3 Content (g) Fig. 5. CaCO3 Content vs. Permeability Reduction with 1.6 M of CS Treatment.
the proposed method of injection using bioslurry followed by one or two more MICP treatment in the bioslurry layer is much more efficient than the conventional MICP method. Furthermore, a permeability reduction to be an order of 108 or 109 m/s becomes achievable. Therefore the proposed bioslurry method is a more efficient method than the conventional MICP method for seepage control. The effect of the thickness of the top sand layer on the permeability reduction of the bioslurry treated water barrier layer was also studied by comparing the permeability of the water barrier layer formed using 1.5, 3 and 6 cm sand layers, respectively, given the other conditions the same. The results are shown in Fig. 6. It can be seen that a sand layer of at least 3 cm thick is required to reduce permeability from the initial level of 104 m/s to a level lower than 108 m/s. If the thickness of the sand layer is less than 3 cm or without a sand layer, the reduction in permeability could only reach 105 or 106 m/s. The function of the sand layer on top is like a distribution regulator for the cementation solution to be permeated into the bioslurry layer. The time taken for the cementation solution to flow and diffuse through the sand layer creates a longer time interval for the solution to enter the bioslurry layer and thus prolong the MICP process [11,27]. In this way, more CaCO3 could be produced in the bioslurry layer and reduce more pores in the bioslurry layer. Without the top sand layer, the cementation solution flowed through bioslurry layer rapidly, which was
Before Treatment
One Treatment
0 cm
1.5 cm
too fast to enable sufficient calcium carbonate precipitation. The 1.5 cm thick sand layer might be too thin to provide sufficient among of time delay for MICP reaction. The difference in the permeability reduction for a sand layer thickness of 3 and 6 cm is small. It probably implies that a 3 cm thick layer might be sufficient to allow sufficient CaCO3 to be precipitated to form a water barrier layer with a permeability of 10-8 m/s or lower. 3.2. Durability of bioslurry based water barrier It is well known that a clay liner may undergo irreversible shrinkage upon desiccation at a relatively arid site [24] and result in cracking and increase in permeability. Thus the durability of the proposed bioslurry liner was examined under wet-dry cycles. To examine the durability of bioslurry based water barrier layer, one sample was subjected to 4 cycles of wet and dry process. Permeability tests were carried out after each cycle and the results are shown in Fig. 7. It can be seen that no permeability change was detected during the four cycles of the wet and dry process. This is because bioslurry based water barrier layer was composed mainly of inorganic mineral of calcium carbonate which does not shrink with the reduction in water content. The precipitated calcium carbonate could bond the loose bioslurry crystals all together, forming a dense and firm crust, but there is no connection between clay particles [9,10]. Therefore, the wet and dry process has little
Two Treatments
3.0 cm
1.0E+00
Permeability (m/s)
1.0E-01 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08 1.0E-09
Thickness of Top Sand Layer Fig. 6. Effect of the Thickness of the Top Sand Layer.
Three Treatments
6.0 cm
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Before treatment
After theatment
1
2
3
4
1.0E+00 1.0E-01
Permeability (m/s)
1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08 1.0E-09
Desiccation Cycles Fig. 7. Durability Test of Bioslurry Induced Water Barrier.
effect on bioslurry based water barrier layer. For the same reason, temperature change will also have little effect on the permeability of bioslurry based water barrier layer as permeability remain unaffected under drying process. On the other hand, calcium carbonate is brittle and thus bioslurry based water barrier layer can crack easily under bending. Therefore, this method will not be suitable to conditions where large bending will take place in the water bearing layer unless the cracks can be repaired easily. For this reason, a study on the healing of cracks developed in bioslurry based water barrier layer was also carried out and the results will be discussed in the next section.
of bioslurry based water barrier was recovered to the level of 108 m/s after 3 treatments. This is due to the crack of bioslurry layer was gradually filled with the newly induced calcite crystals which sealed the cracks and recovered the permeability. Therefore, the effect of the cracks on permeability can be mitigated through repair by supplying cementation solution when the bacteria cells carried by bioslurry particles are still active. When the bacteria cells are inactive after a long-term of operation, the crack can also be healed through a MICP process by adding new bacteria cells besides cementation solution [28,29]. 3.4. Microscopic observations of bioslurry and CaCO3 induced in bioslurry
3.3. Healing of cracked bioslurry water barrier The permeability of the treated sand column increased from 7.6 108 m/s to 1.8 105 m/s after the cracks were formed. A significant reduction in the permeability was also observed after each treatment as shown in Fig. 8. Eventually, the permeability
Before Treatment
After Treatment
The microstructures of both bioslurry and the MICP treated bioslurry were examined using SEM. The SEM images of bioslurry sample at 3 different magnifications (250, 500 and 1000) are shown in Fig. 9. It can be seen that the crystals is mainly spherical shape with particle size around 0.2–5 lm (Fig. 9b). The crystals
After Cracking
1
1.0E+00
Permeability (m/s)
1.0E-01 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08
Healing Treatments Fig. 8. Healing Test of Bioslurry Induced Water Barrier.
2
3
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form small clusters of 10–20 lm in size. However, the clusters are loosely packed with little or only weak bonding among the clusters. This explains why the permeability of bioslurry layer itself is high in permeability (in the order of 105 m/s). The SEM images of bioslurry based water barrier layer, that is, bioslurry layer with more CaCO3 crystals precipitated as the subsequent MICP process are shown in Fig. 10 also in 3 different magnifications. The crystals are mainly rhombohedral shaped which are similar to the crystal shape precipitated by ureolytic bacteria
[6,12,30]. The rhombohedral shaped crystals with various sizes from 5 to 15 lm have filled in the pores of the spherical shaped CaCO3 particles of bioslurry and are also bonded together or likely between the two types of crystals to form a densely packed matrix as shown in Fig. 9a. Comparing Fig. 9b & c and Fig. 10b & c, it can be seen that the pores among the calcium carbonate crystals are much reduced. This explains why the permeability of the biocemented bioslurry layer is much lower (in the order of 108 m/s) compared with uncemented bioslurry.
Fig. 9. Pure Biolsurry Power Induced from 400 mmol/L Cementation Solution.
Fig. 10. Bioslurry Induced Rhombohedral Shape Calcite Crystals.
Y. Yang et al. / Construction and Building Materials 212 (2019) 342–349
4. Conclusions This study presented a novel approach for seepage control based on microbially induced carbonate precipitation (MICP) using urease active bislurry as catalyzer to induce water barrier. With the effect of top sand layer, sustainable MICP process was achieved through diffusion of cementation solution. Due to the massive precipitated crystals at the gaps between CaCO3 grains, bioslurry liner was formed and resulted in a reduction of the permeability from 4.1 104 m/s to 4.3 109 m/s in average after 3 flushes of cementation solution at optimal concentration of 1.6 M. Although the water barrier induced using bioslurry was as thin as 2–3 mm, the permeability reduction was comparable with that achieved by a thick and well compacted clay liner. Furthermore, the biocemented bioslurry layer is less affected by the wet-drying processes as it does not shrink or crack under a change in temperature. Even when cracks have developed in the water barrier layer, the cracks can be repaired using the same MICP method. Thus, the proposed method has the potential to be applied for construction of agricultural drains, aquacultural ponds, or water cutoff barriers. Conflict of interest None. Acknowledgements The authors would like to acknowledge gratefully that the study presented in this paper was supported partially by Grant No MOE2015-T2-2-142 provided by the Ministry of Education, Singapore and the Centre for Usable Space, Nanyang Technological University, Singapore. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.conbuildmat.2019.03.313. References [1] D. Teichert-Coddington, N. Stone, R. Phelps, Hydrology of fish culture ponds in Gualaca Panama, Aquacult. Eng. 7 (5) (1988) 309–320. [2] C.A. Boyd, C.E. Boyd, D. Rouse, Potassium budget for inland, saline water shrimp ponds in Alabama, Aquacult. Eng. 36 (1) (2007) 45–50. [3] M. Jayanthi, P.N. Rekha, M. Muralidhar, B. Gupta, Seepage reduction in brackishwater ponds with different materials, Ecol. Environ. Conserv. 10 (3) (2004) 257–260. [4] K. Kvenvolden, C. Cooper, Natural seepage of crude oil into the marine environment, Geo-Mar. Lett. 23 (3–4) (2003) 140–146. [5] J. DeJong, K. Soga, E. Kavazanjian, S. Burns, L. Van Paassen, A. Al Qabany, A. Aydilek, S. Bang, M. Burbank, L.F. Caslake, Biogeochemical processes and geotechnical applications: progress, opportunities and challenges, Geotechnique 63 (4) (2013) 287.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Seepage control in sand using bioslurry Yang Yang a, Jian Chu a,⇑, Yang Xiao b, Hanlong Liu b, Liang Cheng c a
School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore School of Civil Engineering, Chongqing University, Chongqing 400045, China c School of Environmental and Safety Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang, Jiangsu Province 212013, China b
h i g h l i g h t s The bioslurry contains high urease active bacteria cells and allows further MICP treatment. Permeability reduction of bioslurry was comparable to a well compacted clay liner. The biocemented bioslurry layer is less affected by the wet-drying processes. Cracks of bioslurry can be repaired using the same MICP method.
a r t i c l e
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Article history: Received 23 October 2018 Received in revised form 25 March 2019 Accepted 28 March 2019
Keywords: Bioslurry Biocementation Microbially induced carbonate precipitation (MICP) Water barrier layer Permeability
a b s t r a c t This paper presents a new method for seepage control in sand using bioslurry, a suspension of CaCO3 crystals formed using a microbial calcium carbonate precipitation process (MICP). The bioslurry can be permeated through sand or deposit on top of a sand layer. The bioslurry contains high urease active bacteria cells and allows further MICP treatment when introducing cementation solution. In this way, the permeability of the bioslurry layer or bioslurry permeated sand layer could be further reduced to the order of 109 m/s through another 2–3 numbers of MICP treatment using a cementation solution with an optimum concentration of 1.6 M. Such a low permeability is hardly achievable using the conventional MICP method which would require many more numbers of treatment to reduce the permeability of sand to be below 107 m/s. Therefore, the proposed bioslurry method is not only more effective, but also more efficient. The water barrier layer formed using the proposed method is much less affected by wet and dry or temperature change cycles than compacted clay liners. It also allow cracks in the water barrier layer to be repaired if required. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction Seepage control is a common construction process for many infrastructure projects such as reservoirs, earth dams, tunnels and other underground constructions. Seepage leads to the largest single loss of water for aquacultural pond which may also diminish the nutrients content in the pond in addition to the water loss [1– 3]. High seepage rate may also lead to leaking of harmful substances from waste to water and result in groundwater pollution. For example, Kvenvolden et al. (2003) [4] has shown that 47% of the crude oil entering into the marine environment is through natural seepage and the estimated amount of crude-oil leakage is 600,000 metric tons per year. To date, various solutions, such as polymers, water-swellable colloidal clays, and chemical cement ⇑ Corresponding author. E-mail addresses: [email protected] (Y. Yang), [email protected] (J. Chu), [email protected] (L. Cheng). https://doi.org/10.1016/j.conbuildmat.2019.03.313 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.
grout, have been applied to the surface of soil to provide a waterproofing liner to prevent the penetration of water or toxic chemicals into the soil [5,6]. Cement grout is the most common method adopted for seepage control in porous soils. However, production of cement requires high energy consumption and generates substantial amount of CO2 (0.95 t CO2/t Portland Cement) [7,8]. Biocement is a new material that requires less energy to make and is more environmentally friendly. Biocement is formed in the pores of soil at an ambient temperature through a microbially induced carbonate precipitation (MICP) process. The precipitates act as a bonding material to increase the shear strength of soil or as a pore-filling material to reduce the permeability of soil [9– 12]. Studies have been carried out to use biocement for soil erosion control, slope protection, mitigation of internal erosion or liquefaction, reducing fluid flow in soil and sealing the leakage of construction landfill [5,10,13–15].
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The MICP process adopted in this study utilized urease-positive bacteria to hydrolyze urea to produce calcium carbonate crystals in the presence of calcium ions [11,16–20] as illustrated by:
COðNH2 Þ2 þ 2H2 O ! 2NHþ4 þ CO2
ð1Þ
Ca2þ þ CO2 3 ! CaCO3 ð#Þ
ð2Þ
Using a biotreated layer formed in sand through a specially designed MICP process, the permeability of sand can be reduced from the order of 104 m/s–107 m/s [18,21,22]. However, this can only be achieved through a number times of treatment. This is not efficient for construction. Furthermore, it appears difficult to reduce the permeability to be lower than 107 m/s [6,11,23]. To overcome the difficulties with multiple treatment, the bioslurry method is adopted in this study. Bioslurry consists of calcium carbonate crystals with highly urease active bacterial cells. The calcium carbonate crystals are formed in water by mixing calcium chloride and urea with bacterial culture. The calcium carbonate crystals so produced contain bacterial cells which can still activate the MICP process to produce more CaCO3 with the presence of urea and Ca2+ ions [6]. To form a water barrier in a sand layer using bioslurry method, the bioslurry is either placed on to the sand layer or permeate into sand layer followed by one to three times of MICP treatment of the bioslurry layer by injecting cementation solution. The detailed procedure will be further explained later. In the past, compacted clay liners or geosynthetic clay liners have been used to form hydraulic barriers for landfills [24]. However, clay liner may shrink and crack. The biocemented layer contains calcium carbonate and thus is less affected by shrink caused by wet and dry or temperature change cycles. The durability of a water barrier layer formed using the bioslurry method was also studied under wet-dry cycles. Several parameters related to the permeability reduction of sand using the bioslurry method were also examined and discussed. These included the chemical conversion efficiency of cementation solution, the thickness of the sand layer above the bioslurry layer, the calcium carbonate content, and treatment times. An experiment to repair a crack formed by impact load was also carried out to verify the ability of the new method to allow repair of cracks formed in the water barrier layer. 2. Materials and methods 2.1. Urease producing bacteria and cementation solution Urease producing bacteria used in this study was isolated from activated sludge obtained from local wastewater treatment plant and identified by 16S rDNA sequence analysis, known as Bacillus Sporosarcina pasteurii, which was then cultivated under aerobic sterile conditions. The growth medium comprises 10 g/L ammonia chloride, 20 g/L yeast extract, 0.01 g/L nickel chloride and initial pH was set at 9. The bacterial cultivation was conducted at 28 °C on an orbital shaker at shaking rate of 200 rpm. Bacteria culture was then harvested after 48 h of the cultivation and stored at 4 °C. The optical density (OD600) of the harvested bacterial culture varied from 2 to 3, and the urease activity was measured by conductivity meter and adjusted to approximately 10 U/ml (1 U = 1 mmol urea hydrolyzed per minute) prior to use [18,25]. 2.2. Bioslurry preparation Following the work by Cheng and Shahin (2016) [6], bioslurry was prepared by adding 44.4 g calcium chloride and 24 g urea into 1 L of the raw bacteria culture, followed by stirring at a speed of 200 rpm for 24 h (Fig. 1). The calcium carbonate crystals with imbedded highly active ureolytic bacteria were then produced. After complete settle-
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ment, the clean supernatant was disposed and the settled crystals [6] were collected and stored in a refrigerator prior to use. The solid content of the collected bioslurry was about 25 ± 3% (w/w). 2.3. Effect of cementation solution concentration on chemical conversion efficiency The effect of cementation solution concentration on the chemical convention efficiency of bioslurry was investigated as follows: 1) five centrifuge tubes were filled with 4 g (25% solid content, urease activity = 48 U/ml/g) of bioslurry respectively, and centrifuged at a speed of 3000 rpm for 12 min; 2) After removing the supernatant, 20 ml of different concentrations of cementation solution (equimolar of CaCl2 and Urea) ranging from 1 to 2 M were added to the centrifuge tubes. 3) the centrifuge tubes were shaken continuously at a speed of 200 rpm and the calcium concentration of the cementation solution was measured after 24 h, 48 h and 72 h according to the standard method 2340C with ethylene diamine tetraacetate dehydrate (EDTA) titration [18]. All tests were conducted in duplicate. 2.4. Column tests Transparent acrylic columns (50 mm inner diameter and 100 mm in length) were utilized for the formation of waterproofing layer using bioslurry. The column was filled with multiple layers of materials (Fig. 2): 1) The bottom layer was filled with 150 g dry Ottawa sand with a mean grain size of D50 = 0.4 mm; 2) The middle layer was formed by spraying 4 g homogenized solid bioslurry (25% solid content, urease activity = 48 U/ml/g) onto the top surface of the bottom sand layer to form a 2–3 mm thick slurry layer; and 3) The top layer was formed by placing 100 g dry Ottawa sand on the top of bioslurry layer. The top sand layer had a porosity 0.35 or a void volume of 20 cm3. Fitting cap with a drainage outlet at the bottom was also designed to match each column and facilitate the permeability test. The sand columns were treated using four different concentrations of cementation solution of 1.0 M, 1.3 M, 1.6 M and 1.8 M respectively. For each type of solution, three tests with treatment of one, two and three times were conducted respectively. In total, 12 tests were carried out. For the first treatment, 40 ml of cementation solution was poured onto the surface of the top sand layer. For the 2nd and 3rd treatment, 20 ml of the cementation solution was added. Each treatment was applied for 24 h at room temperature (25 ± 1 °C). After the treatments were completed, the sand columns were subjected to permeability test. To evaluate the effect of the top sand layer on permeability reduction, another three tests without the top sand layer were carried out using cementation solution of 1.6 M by following the same procedure as stated above. The effect of the thickness of the top sand layer were also evaluated. Three columns with different thickness of top sand layer of 1.5 cm (50 g sand with void volume of 10 cm3), 3 cm (100 g sand with void volume of 20 cm3) and 6 cm (200 g sand with void volume of 40 cm3) were treated 3 times using cementation solution of 1.6 M. After treatment the permeability of each column was measured. To develop a method to heal cracks of bioslurry based water barrier layer, a bioslurry sample with cracks was prepared as follow. A sand column was prepared as described in Section 2.4. The sand in the column was treated once using 20 ml cementation solution with a concentration of 1.6 M. After this, the top layer of sand was removed and cracks were then created by dropping a ball onto the water barrier layer. To heal the cracks, a 100 g clean and dry Ottawa sand was added on top of cracked bioslurry liner. Then, repeated treatment (3 times) of 20 ml of cementation solution (1.6 M) was applied. The permeability of the sand column was measured after each treatment.
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Fig. 1. Bioslurry during Reaction (A) and Settled Bioslurry (B).
Fig. 2. Schematic Set Up of Sand Column.
2.5. CaCO3 content determination and microstructure analysis After the permeability test, all samples treated by 1.6M of cementation solution were taken from the bioslurry layer to determine the CaCO3 content. The sample was rinsed with tap water and oven dried at 105 °C for 24 h prior to weight measurement. The calcium carbonate content of the sample was determined by weight difference of bioslurry before (4 g) and after treatment. For each test, CaCO3 were measured at least three times so as to achieve an average value and minimize the error. Laboratory determination of the permeability of the treated sand columns were conducted using a falling-head method in accordance with ASTM D5084. All permeability measurements
were carried out twice and the average values were reported. Scanning Electron Microscopy tests were also carried out for samples from the bioslurry based waterproofing layer. The sample was rinsed with tap water and oven dried at 105 °C for 24 h prior to the SEM using a SEM analyzer (Zeiss EV050, UK).
3. Results 3.1. Effect of concentration of cementation solution In this study, the effect of concentration of cementation solution on the chemical conversion efficiency using bioslurry method was
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tested. The results of calcium consumption versus the initial calcium concentration of the solution are presented in Fig. 3. It can be seen that the calcium consumption increased with the increase in the calcium concentration up to 1.6 M, following by a gradual decrease with the increase in the calcium concentration. This was probably due to the toxic effect of the high concentration of calcium ions to the urease producing bacteria [26]. The maximum calcium consumption was about 1.44 M in 72 h for an initial concentration of calcium of 1.6 M with the maximum precipitation rate of 1.03 mol/L/day. Therefore, 1.6 M was taken as the optimum concentration of cementation solution for the CaCO3 production of bioslurry. The permeability obtained for the treated columns is plotted versus the concentration of the cementation solution in Fig. 4. The reduction in permeability is dependent on the concentration of cementation solution as well as the number of treatments applied. As shown in Fig. 4, the reduction in permeability is significant even with one treatment. The 2nd and 3rd treatment would lead to further reduction in permeability. It can also be seen from
Fig. 4 that the lowest permeability of 3.6 109 m/s was obtained for samples treated 3 times using 1.6 M cementation solution. Thus, the optimum concentration of cementation solution is 1.6 M as it resulted in lowest permeability, which is consistent with the results shown in Fig. 3. In the previous studies, the lowest permeability reduction by a MICP method is normally to an order of 107 m/s through many number of treatment, unless it is a layer of CaCO3 crust [16– 18,21]. The permeability versus CaCO3 content obtained in this study for the bioslurry treated layer is shown in Fig. 5. The number of treatment is also indicated in Fig. 5. It can be seen that the permeability reduction is dependent on the precipitated CaCO3 content as established by previous studies [9,16,21]. According to Fig. 5, the permeability can be lower than 107 m/s after the first treatment, and a permeability lower than 108 m/s can also be achieved after the 2nd and 3rd treatment. If the conventional MICP method is used, it will require many numbers of treatment to reduce the permeability of sand to this level [16–18,21]. This would be hardly feasible using the conventional method. Thus
1.8 24 Hours
Calcium Consumption (M)
1.6
48 Hours
72 Hours
1.4 1.2 1 0.8 0.6 0.4 0.2 0 1
1.3 1.6 1.8 Initial Concentration of Calcium Content (M)
2
Fig. 3. Calcium Consumption vs. Concentration of Initial Cementation Solution.
Before Treatment
One Treatment
1.0 M
1.3 M
Two Treatments
Three Treatments
1.6 M
1.0E+00
Permeability (m/s)
1.0E-01 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08 1.0E-09 Concentration of Cementation Solution Fig. 4. Permeability of Bioslurry Based Water Barrier.
1.8 M
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Bbefore Treatment
First Treatment
0
2
4
Second Treatment 6
Third Treatment 8
10
Permeability (m/s)
1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08 1.0E-09
CaCO3 Content (g) Fig. 5. CaCO3 Content vs. Permeability Reduction with 1.6 M of CS Treatment.
the proposed method of injection using bioslurry followed by one or two more MICP treatment in the bioslurry layer is much more efficient than the conventional MICP method. Furthermore, a permeability reduction to be an order of 108 or 109 m/s becomes achievable. Therefore the proposed bioslurry method is a more efficient method than the conventional MICP method for seepage control. The effect of the thickness of the top sand layer on the permeability reduction of the bioslurry treated water barrier layer was also studied by comparing the permeability of the water barrier layer formed using 1.5, 3 and 6 cm sand layers, respectively, given the other conditions the same. The results are shown in Fig. 6. It can be seen that a sand layer of at least 3 cm thick is required to reduce permeability from the initial level of 104 m/s to a level lower than 108 m/s. If the thickness of the sand layer is less than 3 cm or without a sand layer, the reduction in permeability could only reach 105 or 106 m/s. The function of the sand layer on top is like a distribution regulator for the cementation solution to be permeated into the bioslurry layer. The time taken for the cementation solution to flow and diffuse through the sand layer creates a longer time interval for the solution to enter the bioslurry layer and thus prolong the MICP process [11,27]. In this way, more CaCO3 could be produced in the bioslurry layer and reduce more pores in the bioslurry layer. Without the top sand layer, the cementation solution flowed through bioslurry layer rapidly, which was
Before Treatment
One Treatment
0 cm
1.5 cm
too fast to enable sufficient calcium carbonate precipitation. The 1.5 cm thick sand layer might be too thin to provide sufficient among of time delay for MICP reaction. The difference in the permeability reduction for a sand layer thickness of 3 and 6 cm is small. It probably implies that a 3 cm thick layer might be sufficient to allow sufficient CaCO3 to be precipitated to form a water barrier layer with a permeability of 10-8 m/s or lower. 3.2. Durability of bioslurry based water barrier It is well known that a clay liner may undergo irreversible shrinkage upon desiccation at a relatively arid site [24] and result in cracking and increase in permeability. Thus the durability of the proposed bioslurry liner was examined under wet-dry cycles. To examine the durability of bioslurry based water barrier layer, one sample was subjected to 4 cycles of wet and dry process. Permeability tests were carried out after each cycle and the results are shown in Fig. 7. It can be seen that no permeability change was detected during the four cycles of the wet and dry process. This is because bioslurry based water barrier layer was composed mainly of inorganic mineral of calcium carbonate which does not shrink with the reduction in water content. The precipitated calcium carbonate could bond the loose bioslurry crystals all together, forming a dense and firm crust, but there is no connection between clay particles [9,10]. Therefore, the wet and dry process has little
Two Treatments
3.0 cm
1.0E+00
Permeability (m/s)
1.0E-01 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08 1.0E-09
Thickness of Top Sand Layer Fig. 6. Effect of the Thickness of the Top Sand Layer.
Three Treatments
6.0 cm
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Before treatment
After theatment
1
2
3
4
1.0E+00 1.0E-01
Permeability (m/s)
1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08 1.0E-09
Desiccation Cycles Fig. 7. Durability Test of Bioslurry Induced Water Barrier.
effect on bioslurry based water barrier layer. For the same reason, temperature change will also have little effect on the permeability of bioslurry based water barrier layer as permeability remain unaffected under drying process. On the other hand, calcium carbonate is brittle and thus bioslurry based water barrier layer can crack easily under bending. Therefore, this method will not be suitable to conditions where large bending will take place in the water bearing layer unless the cracks can be repaired easily. For this reason, a study on the healing of cracks developed in bioslurry based water barrier layer was also carried out and the results will be discussed in the next section.
of bioslurry based water barrier was recovered to the level of 108 m/s after 3 treatments. This is due to the crack of bioslurry layer was gradually filled with the newly induced calcite crystals which sealed the cracks and recovered the permeability. Therefore, the effect of the cracks on permeability can be mitigated through repair by supplying cementation solution when the bacteria cells carried by bioslurry particles are still active. When the bacteria cells are inactive after a long-term of operation, the crack can also be healed through a MICP process by adding new bacteria cells besides cementation solution [28,29]. 3.4. Microscopic observations of bioslurry and CaCO3 induced in bioslurry
3.3. Healing of cracked bioslurry water barrier The permeability of the treated sand column increased from 7.6 108 m/s to 1.8 105 m/s after the cracks were formed. A significant reduction in the permeability was also observed after each treatment as shown in Fig. 8. Eventually, the permeability
Before Treatment
After Treatment
The microstructures of both bioslurry and the MICP treated bioslurry were examined using SEM. The SEM images of bioslurry sample at 3 different magnifications (250, 500 and 1000) are shown in Fig. 9. It can be seen that the crystals is mainly spherical shape with particle size around 0.2–5 lm (Fig. 9b). The crystals
After Cracking
1
1.0E+00
Permeability (m/s)
1.0E-01 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08
Healing Treatments Fig. 8. Healing Test of Bioslurry Induced Water Barrier.
2
3
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form small clusters of 10–20 lm in size. However, the clusters are loosely packed with little or only weak bonding among the clusters. This explains why the permeability of bioslurry layer itself is high in permeability (in the order of 105 m/s). The SEM images of bioslurry based water barrier layer, that is, bioslurry layer with more CaCO3 crystals precipitated as the subsequent MICP process are shown in Fig. 10 also in 3 different magnifications. The crystals are mainly rhombohedral shaped which are similar to the crystal shape precipitated by ureolytic bacteria
[6,12,30]. The rhombohedral shaped crystals with various sizes from 5 to 15 lm have filled in the pores of the spherical shaped CaCO3 particles of bioslurry and are also bonded together or likely between the two types of crystals to form a densely packed matrix as shown in Fig. 9a. Comparing Fig. 9b & c and Fig. 10b & c, it can be seen that the pores among the calcium carbonate crystals are much reduced. This explains why the permeability of the biocemented bioslurry layer is much lower (in the order of 108 m/s) compared with uncemented bioslurry.
Fig. 9. Pure Biolsurry Power Induced from 400 mmol/L Cementation Solution.
Fig. 10. Bioslurry Induced Rhombohedral Shape Calcite Crystals.
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4. Conclusions This study presented a novel approach for seepage control based on microbially induced carbonate precipitation (MICP) using urease active bislurry as catalyzer to induce water barrier. With the effect of top sand layer, sustainable MICP process was achieved through diffusion of cementation solution. Due to the massive precipitated crystals at the gaps between CaCO3 grains, bioslurry liner was formed and resulted in a reduction of the permeability from 4.1 104 m/s to 4.3 109 m/s in average after 3 flushes of cementation solution at optimal concentration of 1.6 M. Although the water barrier induced using bioslurry was as thin as 2–3 mm, the permeability reduction was comparable with that achieved by a thick and well compacted clay liner. Furthermore, the biocemented bioslurry layer is less affected by the wet-drying processes as it does not shrink or crack under a change in temperature. Even when cracks have developed in the water barrier layer, the cracks can be repaired using the same MICP method. Thus, the proposed method has the potential to be applied for construction of agricultural drains, aquacultural ponds, or water cutoff barriers. Conflict of interest None. Acknowledgements The authors would like to acknowledge gratefully that the study presented in this paper was supported partially by Grant No MOE2015-T2-2-142 provided by the Ministry of Education, Singapore and the Centre for Usable Space, Nanyang Technological University, Singapore. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.conbuildmat.2019.03.313. References [1] D. Teichert-Coddington, N. Stone, R. Phelps, Hydrology of fish culture ponds in Gualaca Panama, Aquacult. Eng. 7 (5) (1988) 309–320. [2] C.A. Boyd, C.E. Boyd, D. Rouse, Potassium budget for inland, saline water shrimp ponds in Alabama, Aquacult. Eng. 36 (1) (2007) 45–50. [3] M. Jayanthi, P.N. Rekha, M. Muralidhar, B. Gupta, Seepage reduction in brackishwater ponds with different materials, Ecol. Environ. Conserv. 10 (3) (2004) 257–260. [4] K. Kvenvolden, C. Cooper, Natural seepage of crude oil into the marine environment, Geo-Mar. Lett. 23 (3–4) (2003) 140–146. [5] J. DeJong, K. Soga, E. Kavazanjian, S. Burns, L. Van Paassen, A. Al Qabany, A. Aydilek, S. Bang, M. Burbank, L.F. Caslake, Biogeochemical processes and geotechnical applications: progress, opportunities and challenges, Geotechnique 63 (4) (2013) 287.
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