| The increasingly stringent in sewage discharge standard is generally the trend ofdevelopment in the world recently. It was impossible to meet land use, noise, especiallyits total nitrogen effluent limitations by conventional secondary bio-treatment.Biological aerated filter is a new sewage treatment technology developed in recentyears,which was characterized for the efficient removal of COD and SS, nitrificationand denitrificationand, low land usage, less investment in capital construction andoperation cost, convenient management and capacity of anti impact load etc. The actualcontradiction induced by land resources shortage, large sewage, high sewage dischargestandard can be solved by biological aerated filter process. There are few documentabout pre-denitrification aerated biofilter and its application is less in practice. The keytechnologies of this technology are pretreatment technology selection, the pretreatmentdegree of important indicators, the control on COD/NO3--N and reflux ratio ofdenitrification influent and biofilter material etc.According to problems Existing in practical engineering application and theoreticalresearch on pre-denitrification aerated biofilter, hydrolysis precipitation andpre-denitrification aerated biofilter combined process was put forward. Respectivelybased on the hydrolyzsis sedimentation tank, Denitrification biofilter （DN biofilter forshort）and Carbonization and nitrification biological aerated filter （CN biofilter forshort）, a comparatively extensive study and analize was made by lab and in field.Under stable operation condition, the average removal of SS, COD and TN was57.9%，45.9%and55.0%respectively with12～16.5℃and hydraulic loading of0.6m3/m2h. The change law of main pollutant consistence along longitudinal directionand the influence factors on hydrolyzsis sedimentation tank performance were studiedin lab. The result was height and concertration of suspended sludge layer in the tank isthe main determinants of pollutants removal rate. To sum up, the effluent of hydrolysisprecipitation can meet the qualification of pretreatment for pre-denitrification aeratedbiofilter.The test results of Air pump filtration and the adsorption test for sewage and sludgein the tank displayed, that the ammonia concentrations of interstitial water in sludgealways outclass that of influent. All above results demonstrated that NH4+-N removalmechanism is adsorption by the sludge in the tank, and has slight sorption for NO3--N,but it was been shown denification for NO2--N. Hydrolysis is happened in thesedimention but hydrolysis degrees were weaker. The contrast data of pretreatmenteffect under the same conditions of influent quality and operation, hydrolysissedimentation tank is vioursly higher than common sedimentation tank as pretreatmentprocess of denitrification biobiofilter. The average removal rate of TN and COD in DN biofilter is respectively37.4%and34.1%at hydraulic retention time of1.4h and the influent was consist of the CNbiofilter effluent at100%reflux and the effluent of sedimention. Most of COD isremoved because of interception of biofilter and DO consumption firstly, secondlybecause it was used as electron donor of denitrification. Denitrification of NO3--Nhappened at upper part of DN biofilter, and higher DO concentration at the entrance ofDN biofilter is the one of main reasons on low denitrification efficiency.The studies on the denitrification influence factors showed, that denitrificationefficiency increased with temperature raised. COD/NO3--N of14.0was taken as criticalvalue, but COD will be the main limiting factor less than that, and above that,it haslittle effect on denitrification larger than that. With hydraulic loading rising, the biofilteroxidation layer hight moved up, total removal rate of COD and NO3--N in DN biofiltershowed the downtrend. By comprehensive consideration, the reflux rate of130%isrelatively suitable.The oxidation layer hight of biofilter is availably reduced and dinitrification rate ofDN biofilter is raised when the CN effluent partially returned into the sedimental tank.Shunting ratio is1:1is relatively suitable considering decreasing COD consume andhydraulic loading shock in sedimental tank. Anammox is detected when DOconcertration in DN biofilter is zero and backwashing time of DN bioflter is prolonged.All indexes can meet the First Grade Standard of GB8978—1996during stablerunning. The influence of temperature, volume loading of NH4+-N and COD,hydraulic load were studied. The results showed that influence infactors had significanteffect on NH4+-N removal and had less effect on COD removal.Nitrification was strengthened by method of nitrifying bacteria occupying firstlyon the surface of biofilter material. The results showed that, it could improve thequantities of nitrifying bacteria in biofilter material and NH4+-N removal rate. But theenhancement degree of nitrification was still determinde by nutrient structure ofinfluent.By conventional microbial culture methods combined with scanning electronmicroscope, the biofilm pattern of CN biofilter and DN biofilter and dominantmicroorganism structure were studied. Activity recovery of microbial community,located at medium in denitrification biofilter （DN） and biological aerated filter （CN）,was studied by biological activity, biomass, and product of both under a mode andstrength of backwashing. The biomass of functional micro-flora was evaluated byMaximum Probable Number. All above results demonstrated was proved that pollutantbiodegrade maybe inevitable related to the corresponding activity and quantities offunctional micro-flora.On the basis of the hypothetical conditions and the micro-unit material balance,kinetic mathematical model of organic and NH4+-N removal in the organic competitive condition in CN biofilter were piecewise established under high middle and lowsubstrate concentration. Meanwhile, kinetic mathematical model of double substratesdenitrification was established, organic and NOx--N as substrate. |
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