Study On Nitrogen Removal For The Printing And Dyeing Wastewater By Anoxic/Oxic Moving Bed Biofilm Reactor Combined Process

The printing and dyeing wastewater had the characteristics of the changeable quality of water,high chromaticity,ingredient complex and poor biochemical,which belonged to one of the difficult industrial waste water.Since 2013,the implementation of the new standard of the textile dyeing and finishing industrial water pollutant discharge standard(GB4287-2012)put forward the more strict denitrification requirements for the printing and dyeing wastewater,where ammonia nitrogen direct emission limit was of 10 mg/L and total nitrogen direct emission limit was of 15 mg/L in table 2.The printing and dyeing enterprises containing a printing process used a large number of carbamide additives in the production process,making the printing and dyeing wastewater of high ammonia nitrogen and total nitrogen.At the same time,due to the low C/N ratio of the wastewater,the traditional biological denitrification process had poor denitrification efficiency to this watsewater.This research adopted the anoxic/oxic moving bed biofilm reactor(MBBR)to the nitrogen removal for the printing and dyeing wastewater,which could make full use of the carbon in the water source and achieve the simultaneous nitrification-denitrification of the aerobic MBBR to enhance nitrogen removal.The anoxic/oxic moving bed biofilm reactor was using the method of the aerobic precoating treatment and fast sludge discharge together for biofilm cultivation.Anoxic and oxic zone filler filling rates were 50%,30%,respectively,and the reactor started up successfully after 31 days,and COD,NH4 +-N,TN removal rate achieved steady at 74.4%,92.0%,58.1%,respectively.The high proportion of the amount of biofilm makes up for the insufficient total biomass caused by the low filling rate.The reactor had stronger ability of simultaneous nitrification and denitrification because of the aerobic biofilm thickness,andWith the hydraulic retention time shorten,the removal rate of COD,NH4 +-N,TN of the reactor presented the downward trend.So as to maintain the high efficient nitrification and denitrification,the total hydraulic retention time should be controlled in more than 12 h.Under the different nitrate recycling ratio,the reactor also had high removal rate of COD and NH4 +-N.Increasing the nitrate recycling ratio is beneficial to increase the TN removal and the nitrate recycling ratio of 200% was the best.When the temperature changed,there was no significant impact on removal rate of COD.But NH4 +-N,TN removal rate were presented obviously decreasing trend as the temperature decreased.The COD/TN greatly influenced the denitrification rate of the reactor,and when the COD/TN was 10.7,TN removal rate was the best.The optimal DO concentration in the aerobic zone was 1.0~1.5 mg/L,where simultaneous nitrification and denitrification were the best.Under the condition of the hydraulic retention time of 12 h,nitrate recycling ratio of 200%,after adjusting DO concentration to the different level in the three aerobic MBBR(1.0-1.5,2.0-2.5,3.0-3.5 mg/L),the denitrification potential of the reactor was further digging.NH4 +-N,TN average concentration of the efflluent were of 2.6 and 11.2 mg/L,the average removal rate were of 93.0% and 76.3%,respectively,which met the table 2 direct emissions standards in the textile dyeing and finishing of industrial water pollutant discharge standard(GB 4287-2012).The anoxic MBBR denitrification rate and the aerobic MBBR denitrification rate of simultaneous nitrification-denitrification(SND)and excess sludge discharge denitrification rate were 40.7%,32.5%,3.1%,respectively,where SND in the aerobic MBBR strengthened the TN removal rate largely.During stable operation,the biomass decreased gradually along the reactor,and the microbes mainly existed in the form of biofilm.The nitrification activity of the aerobic biofilm rised gradually along the reactor,and the high nitrification activity of aerobic 3 biofilm ensures high efficiency nitrification of the reactor.All the aerobic biofilm had denitrifying activity,thus achieving simultaneous nitrification and denitrification to enhanced nitrogen removal.