Experimental Study On Microbial Grouting Materials Under Hydraulic Environment

Leakage problem has always been a key research topic in water conservancy projects.The traditional anti-seepage reinforcement methods used in water conservancy projects are mostly cement and chemical grouting.Cement slurry materials have high energy consumption,great pollution and great damage to the ecological environment,and cannot effectively deal with dense strata,while chemical slurry materials are mostly banned because of their toxicity.Therefore,it is necessary to develop a slurry with low energy consumption,low emission,good potable property,safety,stability and effective anti-seepage reinforcement effect.Microorganisms as a new type of grouting slurry material has experienced decades of scientific research,has made some achievement,urea hydrolysis mechanism where technology use in aerobic environment,more is not suitable for deep water conservancy project of oxygen,Therefore,it is necessary to study a new mechanism of action in order to be suitable for water environment,anoxic environment and deep tight formation to achieve the effect of seepage prevention and reinforcement.In this paper,the facultative anaerobic type aeromonas denitrificans are selected,and the calcium carbonate is induced by the mechanism of denitrification under the water environment and the anoxic environment to obtain a microorganism pulp material based on denitrification.The main research contents and results are as follows:(1)Study on cultivation of bacteria suitable for hydraulic environment.Selection of facultative anaerobically denitrifying Pseudomonas aeruginosa,water environment,anoxic conditions,the common medium experienced incubation period,exponential growth period,stable period and decline period after inoculation,among which the bacteria had the most vigorous vitality and showed exponential growth within 4-14h after inoculation.A new medium(nitrate beef extract peptone medium)was studied:peptone 10g/L.Beef paste 3g/L;Sodium chloride 5g/L;Potassium nitrate 1.5g/L;Potassium dihydrogen phosphate 0.6g/L;Magnesium heptahydrate 0.6g/L sulfate;When pH was 7.5 and 8.0,it was more favorable for the growth of the bacteria.Under the same culture conditions,strains could grow well in both aerobic and hypoxic environments,but the concentration of strains in the aerobic environment was 1.6 times of that in the absence of oxygen.(2)Factors influencing calcium carbonate deposition induced by pseudomonas denitrification in hydraulic environment.Under the condition of water environment and anoxia,the mineralization ability of microbial slurry was explored.C/N is one of the main influencing factors of microbial induced calcium carbonate deposition.When C/N is 2～3,it can promote the maximum calcium carbonate production induced by pseudomonas denitrification to 1.75g/100ml.The deposition effect within a certain range increased with the concentration of bacteria solution.When the concentration of bacteria solution reached 2.4,it was the optimal concentration.When the inoculation amount of bacterial liquid was 100ml,that is,the ratio between bacterial liquid and calcium salt solution was V:V=1:1,and the yield advantage was prominent.When the concentration of calcium ions is 0.15-0.20mol/L,the production of calcium carbonate is twice that of 0.1mol/L.When the addition amount of potassium dihydrogen phosphate is 0.6g/L,it is more conducive to the deposition of calcium carbonate.When PH is 6.2,it is more favorable for calcium carbonate precipitation than when PH is 7.2 and 8.2.(3)Indoor simulation of grouting effect of microbial pulp under hypoxia condition.In the water environment,the more the number of grouting under the anoxic condition,the higher the consumption rate of the calcium salt and the nitrogen source,the more the calcium carbonate is produced,so that the sand column can be better cemented;the step-by-step grouting method is better than the mixed grouting method,and the step-by-step grouting method can ensure that more strains are effectively adhered;The microbial pulp material is more suitable for dense formation with small particle clearance.The experimental results show that Pseudomonas aeruginosa can induce calcium carbonate deposition by denitrification under the condition of water environment and anoxia,and a microbial grouting material is obtained.Through the laboratory grouting simulation experiment,it is proved that the slurry material has a certain anti-seepage reinforcement effect on the formation with small particle gap,but the pulp material has a low yield of calcium carbonate,which leads to the poor uniformity of sand column cement,low strength and insufficient seepage prevention effect.The mineralization properties of slurry need to be further studied.