Analysis Of Microbial Community In Circulting Water System Of Coal Power Plant During Reagent Conversion

There are many problems occur in the circulating cooling water system of a coal power plant,such as orrosion and scale formation,caused by evaporation of cooling water,which leads to the increase of salt ions,alkalinity and COD concentration.The use of phosphorus corrosion and scale inhibitor not only introduce phosphorus which leads excessive phosphorus emission,but has no effect on COD removal,and it is unable to meet the increasingly strict wastewater discharge standard.Based on the principles of biological competitive exclusion and low nutrient limitation,a microbial mixed agent was constructed with the main functions of COD degradation,acid secretion and biological flocculant.The effect of this bio-corrosion and scale inhibitor and ability and mechanism of its pollutant degradation were studied.The dynamic simulation experiment of circulating cooling water was carried out,and water quality of the two groups were monitored while taking no biological agent as a control.At the same time,the corrosion and scaling of the system were studied by carbon steel coupons and heat exchange tubes.The agent was applied to a circulating water system of a coal power plant in Tianjin to replace chemical agent.Within 20 days of the transition period,Water quality was monitored.Heat transfer end difference and thermal resistance of the condenser and structural water preference index Puckorius Index?PSI?were monitored to monitor system fouling.The corrosion of the system ware monitored by carbon steel tubes and copper alloy tubes.And microbial community structure in the system were monitored.Compared with the control group in the dynamic simulation experiment,circulating water turbidity of the experimental group decreased from 17.28 NTU to 13.44 NTU,and CODcr decreased from 32.52 mg/L to 21.34 mg/L,and total phosphorus decreased from0.46 mg/L to 0.40 mg/L.Carbon steel coupon corrosion rate was 0.0585 mm/a lower than control group 0.1375 mm/a,and carbon steel heat exchange tube corrosion rate was 0.070mm/a lower than control group 0.210 mm/a.At the same,heat exchange tube fouling deposition decreased from 39.936 mg/?cm²·month?to 11.225 mg/?cm²·month?,indicating that the biological agent has good corrosion and scale inhibition ability and pollutant degradation ability.Compared with chemical method in the conversion stage of corrosion and scale inhibitor of circulating water system in coal power plant,turbidity of circulating water decreased from 19.44 NTU to 9.60 NTU,and CODcr decreased from 71.55 mg/L to 45.47mg/L,and the concentration multiple increased by 1.27 times.The concentration of Cl^-,SO₄^2-and calcium hardness were not significantly different from the previous stage.Total phosphorus decreased from 2.35 mg/L to 0.38 mg/L,and the corrosion rate of carbon steel tube was 0.955 mm/a less than the chemical period of 1.189 mm/a.Corrosion rate of the alloy tube was 0.030 mm/a,which was less than the chemical period of 0.045mm/a.PSI index of the circulating water was 6.68,which was lower than the chemical method of 6.87.All of these indicate that the biologi agent has better corrosion and scale inhibition effection than chemical agent,and the effect of reducing pollutants,increasing the concentration multiple and reducing phosphorus emissions are better.After the addition of biological agent,the relative abundance of corrosion-related,such as Flavobacterium,Sediminibacterium,Pedomicrobium,Hyphomicrobium and Hydrogenophaga in the suspended microbial community in circulating water wre greatly reduced,and relative abundance of the contaminating and degrading microorganisms CL500-3,SM1A02,CL500-29_marine_group were increased.Fiber-ball-attached microbial Hyphomicrobium,CL500-3,SM1A02,Rhodobacter,Mesorhizobium and Rhodobacter could enhance the ability to remove pollutants from circulating water.in the sediment The decreace of relative abundance of anaerobic bacteria such as Anaerolineaceae and Rhodopseudomonas could help reduce corrosion for the system.In summary,the addition of bio-corrosion and scale inhibitors can not only reduce the relative abundance of corrosive microorganisms in the circulating water system,but also improve the corrosion and scale inhibition ability than that of chemical agent.The agent can increase the number of microbial populations to increasing pollution,which improve the ability to remove pollutants.and increase the concentration of circulating water,and reduce phosphorus emissions.It is reliable alternative for chemical corrosion and scale inhibitor in circulating water system of coal power plants.