Study On Shortcut Nitrification-Denitrification Under Different Aeration Methods

The water quality of municipal wastewater in China has the characteristics ofshortage of organic carbon source and excess of nitrogen, which is difficulty to meetdischarge standard by conventional biological nutrient removal technology. So, theshortcut nitrification-denitrification process was researched in this paper to deal withthe aritificially low C/N ratio municipal wastewater. It was investigated the effects ofdifferent aeration flows on characteristics of biofilm and the correlative performanceof shortcut nitrification process. Then, the aeration control mechanism of shortcutnitrification was discussed from the view of the effect of oxygen on characteristics ofshortcut nitrification biofilm. Based on the research results above, we proposed and provedan improved aeration mode of Multi-section Declined Aeration for the shortcut nitrificationfor the purposes of optimizing oxygenation efficiency, improving the effect of shortcutnitrification and reducing the aeration energy consumption.A laboratory-scale sequencing batch biofilm reactor （SBBR） was used to realizeshortcut nitrification-denitrification process under the aerationsof7.2L·h^-1,12.0L·h^-1and15.6L·h^-1(corresponding average dissolved oxygen concentration （DO） around0.5mg·L^-1,0.8mg·L^-1and1.2mg·L^-1) in28～30℃and pH7～8.5. And the experimentalresults showed below.1) It was benefit for the transformation of ammonia rapidly and produce largeamounts of nitrite and nitrate when DO concentration declined, while the nitriteaccumulation rate （NAR） was droped. On the contrary, the nitrite oxidation processwas restrained when DO concentration declined, which rose NAR. But if the DOconcentration was too low, the ammonium oxidation rate would drop.2) DO concentration had significant effects to microbial community structure and activityof biofilm. Along with the decrease of DO concentration, the biomass and total viablebacteria counts of biofilm in SBBR declined, and the amounts of heterotrophy andnitrite-oxidizing bacteria （NOB） gradually decreased in the meantime, the ammonia-oxidizingbacteria （AOB） became the dominant population in the system. At the same time, thebiological activity of total microbial, AOB and NOB declined, but the rate of biologicalactivity of AOB/NOB increased.3) In the early aeration, the DO was mainly used to degrade the organic matter inwastewater by heterotrophy, then it was used to the ammonium oxidation process by AOB and the nitrite oxidation process by NOB. The generation of nitrate could be suppressed effectivelyand high NAR could be abtained when the DO was under0.7mg·L^-1.According to the above conclusions, we proposed an improved aeration mode ofMulti-section Declined Aeration for the shortcut nitrification, and then we proved it. Theresults showed below.1) In the initial stage of aeration, high aeration (15.6L·h^-1) was effectively supplied toenhance COD degradation, promote the increase rate of DO concentration and ammoniumoxidation, whose average conversion rate of ammonia increased about two-thirds than middleaeration (12.0L·h^-1). Thereafter, the aeration flow was switched down (7.2L·h^-1) to maintainlow DO concentration circumstance, restrain nitrite oxidation process and promote NAR toalmost100%and nitrogen removal by simultaneous nitrification and denitrification （SND）.2) compare with the middle aeration (12.0L·h^-1) which owned the approximate treatment,it was effectively to use the Three-section Declined Aeration in SBBR shortcut nitrification-denitrification system for the purposes of optimizing oxygenation efficiency, improving theeffect of shortcut nitrification and reducing the aeration energy consumption. On the premisethat aeration was decreased about6.4%, NH₄⁺-N removal rate and TN removal rate wereincreased about10%and2%respectively, and the NAR was increased about8～10%because of the3.1mg·L^-1increment of NO₂^--N and decrement of NO₃^--N in the Three-section Declined Aeration.