The mineralization process of microbial-induced calcium carbonate precipitation(MICP)is influenced by many factors,and the uniformity of the calcium carbonate precipitation has become the main focus and challenge for ...The mineralization process of microbial-induced calcium carbonate precipitation(MICP)is influenced by many factors,and the uniformity of the calcium carbonate precipitation has become the main focus and challenge for MICP technology.In this study,the uniformity of the saturated calcareous sand treated with MICP was in-vestigated through one-dimensional calcareous sand column tests and model tests.The coefficient of variation was employed in one-dimensional sand column tests to investigate the impact of injection rate,cementation solution concentration,and number of injection cycles on the uniformity of the MICP treatment.Additionally,model tests were conducted to investigate the impact of injection pressure and methods on the treatment range and uniformity under three-dimensional seepage conditions.Test results demonstrate that the reinforcement strength and uniformity are significantly influenced by the injection rate of the cementation solution,with a rate of 3 mL/min,yielding a favorable treatment effect.Excessive concentration of the cementation solution can lead to significant non-uniformity and a reduction in the compressive strength of MICP-treated samples.Conversely,excessively low concentrations may result in decreased bonding efficiency.Among the four considered con-centrations,0.5 mol/L and 1 mol/L exhibit superior reinforcing effects.The morphological development of calcareous sandy foundation reinforcement is associated with the spatial distribution pattern of the bacterial solution,exhibiting a relatively larger reinforcement area in proximity to the lower region of the model and a gradually decreasing range towards the upper part.Under three-dimensional seepage conditions,in addition to the non-uniform radial cementation along the injection pipe,there is also vertical heterogeneity of cementation along the length of the injection pipe due to gravitational effects,resulting in preferential deposition of calcium carbonate at the lower section,The application of injection pressure and a double-pipe circulation injection method can mitigate the accumulation of bacterial solution and cementation solution at the bottom,thereby improving the reinforcement range and uniformity.展开更多
Microbially induced carbonate precipitation(MICP)is an eco-friendly soil improvement technique.However,this method still has some drawbacks,such as low conversion efficiency of CaCO_(3) crystallization,insufficient st...Microbially induced carbonate precipitation(MICP)is an eco-friendly soil improvement technique.However,this method still has some drawbacks,such as low conversion efficiency of CaCO_(3) crystallization,insufficient strength for certain applications,and requiring multiple treatments.Previous studies have re-ported that sticky rice can regulate CaCO_(3) crystals(i.e.,chemical CaCO_(3))in the sticky rice-lime mortar,showing potential for improving the bio-cementation.Therefore,this study explored the possibility of using sticky rice to enhance the biocementation effect.Tests were carried out to assess the strength and perme-ability of bio-cemented sand with the inclusion of sticky rice.The results indicated that sticky rice may regulate the type and size of bio-CaCO_(3) crystals,and the use of an appropriate amount of sticky rice as additive could increase the strength of sand columns by regulating CaCO_(3) crystallization.Polyhedral calcites may be more favourable for the increasing strength than some vaterites with a hollow spherical structure.The combination of MICP and sticky rice can significantly decrease the coefficient of permeability to a value that was much lower than that by using sticky rice and MICP alone.Bio-CaCO_(3) immobilized the sticky rice on one end on sand particles,and the reticulated structure of sticky rice divided large pores into small pores,which may be the important cause of the decrease in permeability coefficient.Finally,this study proposed that the MICP with the sticky rice as an additive may enhance the MICP effect and prevent the surface erosion of coarse-grained sand slopes.展开更多
A laboratory-scale study with a sand column was designed to simulate trichloroethylene（TCE） pollution in the aquifer environment with three-section controlled-release potassium permanganate（CRP） barriers.The main ...A laboratory-scale study with a sand column was designed to simulate trichloroethylene（TCE） pollution in the aquifer environment with three-section controlled-release potassium permanganate（CRP） barriers.The main objective of this study was to evaluate the feasibility of CRP barriers in remediation of TCE in aquifers in a long-term and controlled manner.CRP particles with a 1：3 molar ratio of KMnO 4 to stearic acid showed the best controlled-release properties in pure water,and the theoretical release time was 138.5 days.The results of TCE removal in the test column indicated that complete removal efficiency of TCE in a sand column by three-section CRP barriers could be reached within 15 days.The molar ratio of KMnO 4 to TCE in the three-section CRP barriers was 16：1,which was much lower than 82：1 as required when KMnO 4 solution is used directly to achieve complete destruction of TCE.This result revealed that the efficiency of CRP for remediation of TCE was highly improved after encapsulation.展开更多
基金support of Natural Science Foundation of China(Grant No.52108324,No.52008207,and No.52108298)for conducting this study.
文摘The mineralization process of microbial-induced calcium carbonate precipitation(MICP)is influenced by many factors,and the uniformity of the calcium carbonate precipitation has become the main focus and challenge for MICP technology.In this study,the uniformity of the saturated calcareous sand treated with MICP was in-vestigated through one-dimensional calcareous sand column tests and model tests.The coefficient of variation was employed in one-dimensional sand column tests to investigate the impact of injection rate,cementation solution concentration,and number of injection cycles on the uniformity of the MICP treatment.Additionally,model tests were conducted to investigate the impact of injection pressure and methods on the treatment range and uniformity under three-dimensional seepage conditions.Test results demonstrate that the reinforcement strength and uniformity are significantly influenced by the injection rate of the cementation solution,with a rate of 3 mL/min,yielding a favorable treatment effect.Excessive concentration of the cementation solution can lead to significant non-uniformity and a reduction in the compressive strength of MICP-treated samples.Conversely,excessively low concentrations may result in decreased bonding efficiency.Among the four considered con-centrations,0.5 mol/L and 1 mol/L exhibit superior reinforcing effects.The morphological development of calcareous sandy foundation reinforcement is associated with the spatial distribution pattern of the bacterial solution,exhibiting a relatively larger reinforcement area in proximity to the lower region of the model and a gradually decreasing range towards the upper part.Under three-dimensional seepage conditions,in addition to the non-uniform radial cementation along the injection pipe,there is also vertical heterogeneity of cementation along the length of the injection pipe due to gravitational effects,resulting in preferential deposition of calcium carbonate at the lower section,The application of injection pressure and a double-pipe circulation injection method can mitigate the accumulation of bacterial solution and cementation solution at the bottom,thereby improving the reinforcement range and uniformity.
基金supported by the State Scholarship Fund from the China Scholarship Council(CSC)No.202006180076.
文摘Microbially induced carbonate precipitation(MICP)is an eco-friendly soil improvement technique.However,this method still has some drawbacks,such as low conversion efficiency of CaCO_(3) crystallization,insufficient strength for certain applications,and requiring multiple treatments.Previous studies have re-ported that sticky rice can regulate CaCO_(3) crystals(i.e.,chemical CaCO_(3))in the sticky rice-lime mortar,showing potential for improving the bio-cementation.Therefore,this study explored the possibility of using sticky rice to enhance the biocementation effect.Tests were carried out to assess the strength and perme-ability of bio-cemented sand with the inclusion of sticky rice.The results indicated that sticky rice may regulate the type and size of bio-CaCO_(3) crystals,and the use of an appropriate amount of sticky rice as additive could increase the strength of sand columns by regulating CaCO_(3) crystallization.Polyhedral calcites may be more favourable for the increasing strength than some vaterites with a hollow spherical structure.The combination of MICP and sticky rice can significantly decrease the coefficient of permeability to a value that was much lower than that by using sticky rice and MICP alone.Bio-CaCO_(3) immobilized the sticky rice on one end on sand particles,and the reticulated structure of sticky rice divided large pores into small pores,which may be the important cause of the decrease in permeability coefficient.Finally,this study proposed that the MICP with the sticky rice as an additive may enhance the MICP effect and prevent the surface erosion of coarse-grained sand slopes.
基金supported by the National Natural Science Foundation of China (No. 50978059,51178117)the Program for New Century Excellent Talents in University(No. NCET-11-0853)
文摘A laboratory-scale study with a sand column was designed to simulate trichloroethylene（TCE） pollution in the aquifer environment with three-section controlled-release potassium permanganate（CRP） barriers.The main objective of this study was to evaluate the feasibility of CRP barriers in remediation of TCE in aquifers in a long-term and controlled manner.CRP particles with a 1：3 molar ratio of KMnO 4 to stearic acid showed the best controlled-release properties in pure water,and the theoretical release time was 138.5 days.The results of TCE removal in the test column indicated that complete removal efficiency of TCE in a sand column by three-section CRP barriers could be reached within 15 days.The molar ratio of KMnO 4 to TCE in the three-section CRP barriers was 16：1,which was much lower than 82：1 as required when KMnO 4 solution is used directly to achieve complete destruction of TCE.This result revealed that the efficiency of CRP for remediation of TCE was highly improved after encapsulation.
