Study On The Treatment Of Micro-polluted Raw Water By Ultrafiltration/activated Carbon Filter Combined Process

With the continuous deterioration of raw water quality and the continuous improvement of drinking water sanitation standards in China,the traditional water treatment technology has obviously lagged behind,more and more new water treatment technology has been studied and used.It is found that the combined process of activated carbon filter and ultrafiltration after the sedimentation tank can greatly improve the effluent water quality than the single activated carbon treatment or ultrafiltration treatment.Ultrafiltration can reduce the turbidity of water very well,and activated carbon has strong adsorption performance,and has a good removal effect on organic matter and chroma in water.However,if activated carbon is placed in the front,it may lead to excessive activated carbon load and weaken the removal ability of activated carbon to organic matter.If activated carbon is placed after,organic matter pollution on the ultrafiltration membrane is bound to increase,and there may be carbon leakage.In thesis,the unit sequence of activated carbon and ultrafiltration process and some related parameters during process operation are studied.The submerged water from three water plants in Shandong province was used as test water samples.Two sets of ultrafiltration and activated carbon units with different sequences were operated for a long time.According to effluent quality,turbidity of backwash wastewater and pollution of activated carbon and ultrafiltration membrane,the appropriate unit combination process and corresponding process parameters were determined,and the engineering construction of actual water plant was guided.When the backwashing time is more than 8 min,the turbidity of backwashing wastewater is below 3 NTU in the optimization of operating parameters of activated carbon unit.In the treatment of low turbidity water and medium turbidity water,the backwashing cycle has little effect on the turbidity removal rate,which is about 85%and 91%,respectively.However,when the backwashing cycle is greater than 9 d,the removal rate of organic matter is significantly reduced.In the treatment of high turbidity water,when the backwashing cycle is greater than 6 d,the removal rate of turbidity and organic matter are significantly reduced.In the operation parameter optimization of ultrafiltration unit,when the lower yield water flow is 150 L·h^-1,that is,the membrane flux is 20.3 L/（m~2·h）,the effluent water quality of the two processes is better and the membrane pollution degree is the least.Ultrafiltration unit during backwash,each 1 h on a physical backwashing,separate water backwashing method,treatment of low water and water,when backwashing filter speed was 2 times and 2.5 times of normal filter speed,time of 180 s,TMP recovery rate of good effect,based on the principle of saving water,choose the backwashing filter speed is 2 times the normal speed,high water,When the backwash filter speed is 2.5 times of the normal filter speed and the time reaches 180 s,and the backwash filter speed is2 times of the normal filter speed and the time reaches 240 s,the TMP recovery rate reaches a good effect.Based on the principle of water saving and the principle of ensuring the safety of membrane components,the backwash filter speed is 2 times of the normal filter speed and the time reaches 240 s.Once every 6 d ultrafiltration membrane for chemical backwashing,backwashing reagents using sodium hypochlorite,when processing low water and water,soaking time from 1 h to 2.5 h,effect on the removal rate of organic matter in water is not obvious,but time after reaching 2 h,the turbidity removal rate to achieve better effect,when dealing with high water,soaking with the extension of time,The removal rate of turbidity is continuously improved,but the removal rate of organic matter is decreased.Considering comprehensively,the soaking time is 2.5 h.The equipment is operated under the condition of definite process parameters,and the treatment results of low turbidity water,medium turbidity water and high turbidity water are obtained through a cycle test.In the combined process of ultrafiltration and carbon filtration,the turbidity removal rates of the three water samples were 90.76%,95.15%and 98.20%,the removal rates of particles larger than 2μm were 93.39%,97.01%and 98.68%,and the removal rates of COD_Mnwere 45.06%,48.90%and 70.94%,respectively.TOC removal rates were36.85%,42.46%and 68.80%,respectively.In the combined process of"GAC+UF",the turbidity removal rates of the three water samples were 92.40%,96.03%and 98.65%,the removal rates of particles larger than 2μm were 96.03%,98.35%and 99.32%,the removal rates of COD_Mnwere 49.24%,52.20%and 70.74%,respectively.TOC removal rates were 41.41%,46.16%and 68.65%,respectively.The removal rate of UV₂₅₄is similar between the two processes.The transmembrane pressure difference of the combined process of"GAC+UF"is lower than that of"UF+GAC"for the same water sample.Although the iodine value of activated carbon of the combined process of"GAC+UF"decreases rapidly,it is still within the reasonable use range.When the combined process of ultrafiltration/activated carbon filter is used to treat micro-polluted raw water,the activated carbon filter is better before ultrafiltration.According to the test results,the combined process of"GAC+UF"was added to the expansion project of Yucheng Second Water Plant.After the construction,the turbidity removal rate reached 94.02%,increased by 20.36%compared with the original process,and the particle number>2μm removal rate reached 96.11%,increased by 27.99%compared with the original process.The removal rate of COD_Mnreached 50.34%,35.56%higher than that of the original process,and the removal rate of TOC reached 42.54%,21.02%higher than that of the original process.Over the course of 90 days of operation,the transmembrane differential pressure of the ultrafiltration membrane increased by 4.27KPa,with a small change that did not exceed the maximum pressure that the membrane assembly could withstand.The iodine value of activated carbon is stable at about 800 mg·g-1,which is within the applicable range.After adding the combined technology of"GAC+UF",the water quality and quantity are not only guaranteed,but also the engineering benefit is very significant.