Study On The Inhibition Of Microbial Agent On The Growth Of Legionella In Circulating Water System

During the operation of the industrial circulating cooling water system,as the cooling water continuously evaporates and dissipates,it leads to the accumulation of various organic substances and minerals in the water body,which creates favorable conditions for the growth of microorganisms.As a type of bacteria in the circulating cooling water system,Legionella has been detected in air-conditioning cooling water systems all over my country in recent years.When there are a large number of Legionella bacteria in circulating water,they can form a cross infection through aerosols and atomized air,which is very likely to cause the risk of regional outbreak of Legionnaires'disease.Therefore,effective control of Legionella in circulating water is of great significance to social health and safety.This article explores the nutrients and environmental factors required during the growth of Legionella,and derives the most unfavorable growth conditions by fitting its growth model.The microbial inoculant was selected as the control method to explore the inhibitory effect on Legionella under different nutritional conditions and inoculation ratios,and the inhibitory effect of the microbial inoculant on Legionella was verified during the operation of the circulating water simulation device,the result shows:(1)The most suitable carbon source,nitrogen source and amino acid for the growth of Legionella are succinic acid,peptone and cysteine;The optimum temperature,shaker speed and p H are 40?,180rpm and p H=7.5 and its growth is negatively correlated with hardness and alkalinity.The fitting model was established by response surface method,and the growth amount reached the lowest value when the temperature was30?,the p H was 6.0,the alkalinity was 331.13mg/L,and the hardness was 175.67mg/L.(2)Under the condition of poor nutrition(COD=100mg/L),the microbial agent has a significant inhibition on the growth of Legionella,and the time to enter the logarithmic phase is delayed from 12h to 20h under more nutrient conditions and the order of magnitude dropped from 10¹¹ to 10⁴;Under different inoculation ratio conditions,the time for the Legionella to enter the logarithmic phase is different.The 2:1 inoculation ratio enters the logarithmic phase at 24h,and the total number of Legionella during the stable phase is 10⁴;Through the establishment of Real-time PCR detection method for Legionella,quantitative detection of Legionella from the molecular biological point of view to verify the inhibitory effect of microbial agents on Legionella.(3)By constructing a simulated circulating water system,we explored the effects of microbial agent on the quality of circulating water and the inhibitory effect on Legionella;The results showed that the experimental group with added microbial inoculum at the end of the experiment compared with the control group,COD content decreased by 10mg/L,the p H value was stable at 6.92-6.97,and there was no significant difference in alkalinity and hardness.The number of Legionella in the experimental group decreased from 9.7×10³cfu/ml to 4.3×10³cfu/ml,the reduction rate was 55.67%,but the number of Legionella in the control group did not decline.Therefore,it shows that the microbial agent is feasible for the method of inhibiting Legionella in circulating water.The high-throughput sequencing technology was used to analyze the microbial community of the cooling water in the circulating water system.The results showed that the microbial agent would inhibit the growth of certain bacteria in the circulating water and significantly change the direction of the succession of the microbial community.