Experimental Study On The Filtration Performance Of Ordinary Fast Filtration Tank In Shuanggang Water Plant In Nanchang City

In response to the problems of single backwashing process,poor flushing effect,short filtration cycle and high production energy cost in the old water plant,this study was based on Nanchang Shuanggang water plant,relying on the pilot plant in the water plant,using orthogonal test to optimize the backwashing process parameters and evaluate the effect of different backwashing methods.On this basis,the filtration performance of the backwashing filter was studied in depth.Finally,an economic analysis of the optimized backwashing process was conducted.The main research results are as follows.（1）The overall raw water quality of Shuanggang water plant is good,and the turbidity,COD_Mn,UV₂₅₄and ammonia nitrogen content are low after mixing-sedimentation-filtration,and the operation is smooth.However,the backwashing effect is poor,the head loss of clean filter layer after flushing reaches 38.5cm,the turbidity of wastewater at the end of backwashing reaches 16.9NTU,the time to reach the standard of primary filter water is4.26min,and mud balls and mud blankets appear in the filter media after long-term operation.And the actual filtration speed of Shuanggang water plant is much higher than the design filtration speed,resulting in a shorter filtration cycle,especially in the dry water period,resulting in more frequent backwashing and increased production energy costs.（2）In the combined gas-water backwashing,the main influencing factor of the initial head loss of the filter layer is the combined gas-water flushing intensity,the main influencing factor of the turbidity of the wastewater at the end of the backwashing is the water flushing intensity,the main influencing factor of the time to reach the standard of the initial filter water is the water flushing time,and the total cost of backwashing energy consumption is the gas-water flushing time at the same time;the best parameters optimized by backwashing are:a)first gas flushing stage.Gas flushing intensity 15L/（m²-s）,gas flushing time 1min;b)gas-water simultaneous flushing stage.Air flushing intensity 15L/（m²-s）,water flushing intensity 4L/（m²-s）,flushing time 2min;c)Post water flushing stage.Water flushing intensity8L/（m²-s）,flushing time 6min.（3）Compared with single water backwashing,after using air-water backwashing,the initial head loss of the filter layer was reduced by 5.1cm,7.4cm,6.2cm,5cm and 6.5cm at the filtration speed of 6.6m/h,7.7m/h,8.8m/h,9.9m/h and 11m/h,respectively,and the turbidity removal rate of the filter tank was increased by 4.5%,1.8%,5.2%,2.2%and 2.9%,and the filtration cycles were extended by 1h,0.72h,0.63h,0.3h,and 0.15h,respectively.（4）After air-water backwashing,the equation of semi-empirical calculation of the initial head loss of the filter layer and the equation of the growth of head loss versus time during filtration was obtained;when the turbidity of the water to be filtered was between 1.8 and 5.0NTU and the filtration speed was between 6.6m/h and 11 m/h,the turbidity removal rate of the surface layer of 30 cm filter media was 61.9%～68.2%,and the turbidity removal rate at the surface layer to 60 cm filter media reached 80.9%～85.9%,playing a major role in pollution interception.（5）Shuanggang water plant under the current conditions,the use of air-water backwashing,filter speed=8.8m/h,the filtration cycle of 10 hours 50 minutes,the highest water production rate of 95.3%,the comprehensive evaluation index F and JP value of the lowest,respectively,1.68×10^-3,1.95,the best overall filtration performance,the annual power and water consumption costs can be reduced by 48,500 yuan.