| Pharmaceutical wastewater is a kind of industrial wastewater which is difficult to be treated,with complex components,high toxicity and other factors against biodegradation.For difficult removal of organic matters and ammonia nitrogen from pharmaceutical wastewater,the start-up and acclimation of advanced denitrification of pharmaceutical wastewater in actual process were investigated in this experiment using one set of SBR and two sets of SBBR with different fillers.The start-up and acclimation lasted for 99 days.Under the concentration of ammonia nitrogen in pharmaceutical wastewater of 200 mg/L ± 20 mg/L,the three reactors all achieved the removal rate of total nitrogen of more than 97% without any additional carbon sources.Under the C/N ratio of 3,the system could not achieve advanced denitrification.The denitrification efficiency could be improved by increasing the C/N ratio.After the C/N ratio was increased to 5,the three reactors all achieved advanced denitrification.Benefiting from massive biofilm on the fillers,the SBBR utilizing a fixed filling realized advanced denitrification after aeration,and the operation mode was determined as water inflow-agitation-aeration agitation-sedimentation-drainage.Due to a lot of nitrate nitrogen remaining in SBR and SBBR utilizing a fluidized filling after aeration,the operation mode was still water inflow-agitation-aeration-agitation-sedimentation-drainage.Additionally,during the reaction,the pH,DO,ORP,ammonia nitrogen,nitrite nitrogen,nitrate nitrogen and COD in typical cycle were monitored in real time,and the end points of nitrification and denitrification were indicated by ammonia valley and nitrate knee.After 99 days of experiment,the following conclusions are obtained:(1)The three reactors finally all achieved the advanced denitrification of pharmaceutical wastewater,with the total nitrogen removal rate higher than 97%,total nitrogen of SBR effluent lower than 1.9 mg/L,total nitrogen of SBBR utilizing a fluidized filling effluent lower than 1.5 mg/L,and total nitrogen of SBBR utilizing a fixed filling effluent lower than 0.8 mg/L.(2)The amount of denitrification in simultaneous nitrification and denitrification,the amount of denitrification in endogenous denitrification,the removal rate of total nitrogen and the total reaction period of the three reactors were compared.It was concluded that the removal of the simultaneous nitrification and denitrification under SBBR utilizing a fixed filling could reach 100%,which was much higher than that under SBBR utilizing a fluidized filling(60%)and SBR(25%).On the 64 th day,SBBR utilizing a fixed filling realized advanced denitrification,which was 8 days earlier than SBBR utilizing a fluidized filling(72 days)and 20 days earlier than SBR(84 days).In addition,the total reaction period of SBBR utilizing a fixed filling was finally stabilized at 6.1 h,which was 11.6 h earlier than SBBR utilizing a fluidized filling(15 h)and 15.6 h earlier than SBR(19 h).Comprehensive analysis demonstrates that adding fillers can improve denitrification efficiency,shorten reaction time and enhance the denitrification capacity of sludge.The effect of SBBR utilizing a fixed filling is better than that of square fillers.(3)SBBR had a significantly better performance in simultaneous nitrification and denitrification(SND)compared with SBR.However,it was found from real-time monitoring of the pH,DO and OBR during typical cycles that indicative points like ammonia valleys and nitrite knees still appeared in the system.This enables an accurate determination of the end-point of nitrification and denitrification,so that aeration can be timely stopped,unnecessary waste of resources can be avoided and denitrification efficiency of the system can be improved.(4)Changes in the three inorganic nitrogen species and COD within a typical cycle across the three groups of reactors were compared.The following conclusions are reached: the SBBR utilizing a fixed filling approach had the thickest and largest quantity of biofilms.Thus they had the best denitrification performance and were able to complete deep denitrification as soon as aeration was finished.The total nitrogen following aeration was lower than 0.2mg/L,and the time required to complete denitrification was the shortest(4.6h).In comparison,SBBR utilizing a fluidized filling approach had the poorest denitrification performance.Due to fewer biofilms within reactors,the remaining 22 mg/L nitrate nitrogen following aeration required post-mixing to be removed,resulting in a longer time(13h)to complete denitrification.SBRs had the poorest denitrification performance.No biofilms were found in the reactors.The remaining 37.5mg/L nitrate nitrogen following aeration required a long period of post-mixing to be removed,leading to the longest time(17.6h)to complete denitrification.As such,with reaction conditions being equal,the quantity of biofilms and the denitrification efficiency are positively proportional.This is mainly attributed to the fact that the microenvironment within biofilms are conducive to improving the SND performance of the system,thereby increasing the utilization rate of carbon sources within the system.(5)By comparing the denitriding effect of pharmaceutical wastewater in the sequence batch biofilm reactor(SBBR)of fiberfill under different conditions,results indicate that: 1)The nitrogen removal efficiency is obviously low at low temperature and the SND effect is weakened.The cycle time is prolonged to 8.5 hours at 20°C and 15mg/L of nitrate nitrogen is left after aeration.High temperature does not notably increase the nitrogen removal efficiency and the cycle time only is only declined to 4.5 hours at 30°C.2)Low dissolved oxygen(DO)apparently lowers the nitrogen removal efficiency and slacks the SND effect.The cycle time is extended to 9 hours when DO is 1mg/L and 12mg/L of nitrate nitrogen is left after aeration.High dissolved oxygen does not facilitate the nitrogen removal efficiency and only cuts the cycle time to 4.5 hours.3)The optimal ratio of carbon to nitrogen is 5:1,in which the cycle time becomes 6.1 hours and the total nitrogen is less than 0.2mg/L after aeration.When the ratio of carbon to nitrogen is 4.5:1,the cycle time is extended to 14 hours and 14mg/L of nitrate nitrogen is remained after aeration.When the ratio of carbon to nitrogen is 6:1,the cycle time is increased to 12 hours and the remaining nitrate nitrogen is 16mg/L after aeration. |
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