Intermittent Aeration Investigation On Denitrification And Control Strategy In A Pilot-scale Oxidation Ditch Process

With the increasing requirements of water environmental protection in the ThreeGorges, all the wastewater treatment plant in Three Gorges were facing the task offunction ascension and transformation in order to make the effluent better than the“Urban Sewage Treatment Plant Pollutants Emission Standards” level1B standard.This paper is carried out the function ascension and transformation with low cost inThree Gorges, as the object of wastewater treatment plants of oxidation ditch process inChangshou, Chongqing to research. It is purposed on technical reformation of the urbansewage treatment plants in the Three Gorges reservoir area.This thesis is mainly investigated on aeration problem of the oxidation ditchprocess. By the means of researching the intermittent aeration in the oxidation ditch, itprobe into the rule of biodenitrification and the change rule of nitrogen indexes, in orderto determine the optimal aeration equipment startup and stop time. In addition, itdiscussed the relative rule of biodenitrification in the joint aeration process. In theprecise aeration control research, it probed into the ORP as the control parameter ofsimultaneous nitrification and denitrification in the oxidation ditch process. Additionally,this paper had studied the correlation relationship of ORP and NH4+-N/NO3--N, and putforward the accurate dissolved oxygen control process for intermittent aeration.The results demonstrated that different aeration-intermission time causeddiscrepant range of TN effluent concentration, which was attributed to different timeratio of aeration to intermission; excessive aeration would lead to that cells carbonsource was consumed so much that denitrification could not go smoothly due to lack ofelectron donor; but that intermission time last too long would resulted in NH4+-Nexcessive accumulation above standard. It had been showed that in the pattern ofaeration1.5h-intermission2h, the effluent concentration of TN and NH4+-N could wellmeet the first-grade B emission standard.Joint aeration was to change startup and shop time of the diffused air aerationequipment in order to discuss the denitrification discipline of the pour umbrella aerationand aeration blowing system. It demonstrated that the rotating speed of pour umbrellaaeration system is the key parameter to define the dissolved oxygen environment. And itdetermined the denitrification effect from overall. When only the pour umbrella couldsupply enough dissolved oxygen which was needed by the biological reaction, the time length of aeration blowing system startup and stop only played an insignificant role toDO environment of biological system. Consequently, at this time the aeration blowingsystem put an inappreciable impact on the biological denitrification.The study on accurate aeration control for the oxidation ditch process wasproceeded, and it came to a conclusion that ORP could used for control parameter forsimultaneous nitrification and denitrificaion in the OD. ORP could reflect the processand degree of SND. When ORP was in-22mV below, nitrification was not sufficientlyhappened, and more than71%of total inorganic nitrogen (TIN) in effluent was NH4+-N.Moreover, when ORP was in29mV above, more than89%of TIN in effluent wasNOx-N. Furthermore, when ORP was between-13mV and18mV, both the NH4+-N andNOx-N were relatively low, at this time the SND efficiency was quite above the average.The results revealed that ORP and the logarithm of the ratio of NH4+-N to NO3--Nwas good linear correlation. And the comparison expression was lg（NH4+-N/NOx-N）=-0.017x-0.095， of which correlation coefficient was0.987. Utilizing the aboverelationship combining NH4+-N online sensor, the intermittent aeration control processwas advanced.Consequently, the investigation results of this paper on intermittent aerationdenitrification and accurate dissolved oxygen control process had some importantpractical significance, which was for aeration transforming and operation optimizing tosewage treatment plants. On the other side, it could supply theoretical basis andtechnical guidance to carry out low-cost upgrading in the Three Gorges.