| The scaling of circulating cooling water systems causes problems such as reduced heat transfer efficiency to metal walls and clogging of pipes,while low carbon sources and high alkalinity loads in concentrated circulating cooling water provide conditions for the growth of Nitrobacter spp.The experiments were carried out to improve the removal efficiency of alkalinity in the simulated circulating cooling water and total nitrogen in the concentrated tailwater,and then to study the long-term stability of the enriched Nitrobacter spp.activated sludge on alkalinity in the actual circulating cooling water and the enriched denitrifying activated sludge on total nitrogen in the concentrated tailwater.The experimental conclusions were as follows:(1)The pre-experiment verified that the nitrifying bacteria genus has strong adaptability to circulating cooling water and has the effect of removing alkalinity in water.The self-tamed activated sludge concentration decreased from 6000 mg/L to 1500 mg/L,the colour changed from yellow-brown to yellow-brown and the nitrification rate increased about 5 times.(2)When the COD,ammonia nitrogen and phosphorus concentrations of the sequencing batch reactor were 60 mg/L,55 mg/L and 1.8±0.3 mg/L respectively,T=25 ℃,pH=9.0,MLSS=1250±50 mg/L and HRT=4 h,the ammonia nitrogen content of the simulated circulating cooling water effluent was less than 0.2 mg/L and the removal rate reached 99.64 %,and the alkalinity decreased from 10 to 10.5 mmol/L to less than 0.5 mmol/L,COD concentration decreased from 60 mg/L to 4.0-5.0 mg/L,with removal rates of 95 % and 91.7 %,respectively,and p H of the effluent decreased to 7.02-7.36 at this time;the ammonia nitrogen content of the circulating cooling water effluent was maintained at 0.3-0.6 mg/L,with removal rate of 98.91 %,and alkalinity decreased from 10.7 mmol/L to 1.35-1.8 mmol/L,COD concentration from 80-90 mg/L to 30.0-35.0 mg/L,the removal rate reached 84 % and65 % respectively,and the p H of the effluent dropped to 8.23-8.36.(3)Enriched denitrifying bacteria genus sludge concentration was reduced from 4000mg/L to 3000 mg/L,and nitrogen removal efficiency was improved.When the sequencing batch reactor was operated at T=30 ℃,COD concentration was 150 mg/L(sodium acetate as carbon source)and HRT=6 h,the COD of the simulated concentrated tailwater effluent was reduced to 34.9～38.4 mg/L and TN was reduced from 95 mg/L to 55.76～60.85 mg/L in the influent,and the removal rates reached 74.4 % and 35.94 % respectively,at which time the effluent p H was The COD of the concentrated tailwater was reduced to 46.1～50.1 mg/L and the TN was reduced from 95 mg/L to 59.05～65.67 mg/L,with removal rates of 66.7 % and 30.87 %,respectively,and the p H of the effluent was 8.38～8.58,with the total nitrogen content meeting the discharge requirements.(4)The relative abundance of Nitrospirota in the enriched nitrifying sludge increased by about 48.52 % compared to the original activated sludge,while the relative abundance of Actinobacteriota increased from 16.77 % to 39.10 % due to low carbon source loading.The relative abundance of Chloroflexi and Patescibacteria as denitrifying functional bacteria increased from 14.90 % and 2.51 % to 18.82 % and 12.18 % respectively.(5)The relative abundance of Micropruina increased from 0.053 % to 21.90 %,Pseudactinotalea increased from 0 % to 13.32 %,Nitrospira increased from 3.39 % to 5.04 %,and The relative abundance of Methylotenera decreased from 14.71 % to 0 %;the relative abundance of denitrifying enriched bacteria in the activated sludge genus Norank＿f＿norank＿o＿Saccharimonadales increased from 1.32 % to 9.11 % and unclassified＿f＿Comamonadaceae increased from 1.32 % to 9.11 %.Comamonadaceae increased from 2.34 % to 8.52 %,both of which are involved in denitrification processes.The biochemical treatment technology was used to reduce the alkalinity in the actual circulating cooling water and the TN content in the concentrated tailwater,effectively avoiding the high cost of the physical method and the secondary pollution of the chemical method,ensuring that the alkalinity of the actual circulating cooling water system and the total nitrogen content of the concentrated tailwater were below 2 mmol/L and 70 mg/L respectively,meeting the requirements of the actual circulating cooling water system to operate under low alkalinity conditions and discharge. |
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