Research Of Simultaneous Nitrification And Dentirification Effect On Removal Of Nitrogen

As the water eutrophication becoming more and more serious, as well as the standards of nitrogen and phosphorus had been improved, It is necessary to develop a high-efficient, low energy required and simply operated technology to nutrient removal. SBBR (sequencing biofilm batch reactor) is a new wastewater biontreatment process researching at present. It is developing based at SBR and inherits SBR many merits, as well as developed the new characteristics.The prospect of the SBBR technical application has full vastitude for its good effects of nitrogen and phosphorus removal, the high automation, the simple running supervision, the low charge of the capital construction and saving the running charge. Popularized at the field of municipal sewage teatment, the technical will produce the good environment benefit and the social benefit. The character of simultaneous nitrification and denitrification of sequencing batch biofilm reactor(SBBR) under the condition of oxygen existing was studied. The paper discuss the mechanism of nitrogen removal by simultaneous nitrification and denitrification (SND) and study the various factors affecting SND in detail. In the paper, the biological reator is made of synthetic glass, Its main dimensions are: Diameter is 15cm, Height is 40cm, Volume is 7L, Working Volume is 6.2L, And the biological filler is tridimensional elastic packing. The raw wastewater is high concentration NH₄-N wastewater. The regular that the main factors such as DO, CODconcentration (or C/N ratio) affected SND had been researched. The result show that under the condition of dissolved oxygen value (DO) about 2mg/L the phenomena of simultaneous nitrification and denitrification is obvious and the denitrification effect is optimal. The removal of NH₄-N reached 90% and that of CODcr reached 94.6% in the meantime. According to the experimental result showing more than 50% TN removal, the study suggests aerobic denitrification, i.e., simultaneous nitrification and denitrification (SND), took place during the operation. When C/N is increased, the total nitrogen removal rate increases. when C/N is 4～8, total nitrogen removal could reach the highest rate of 66.8%. When C/N increases further, nitrogen removal rate has no obvious growing, and will result in nitrifying functionin incompletely.A complete aerobic denitrification function can take place when there are enough degradable organic carbon sources.The SBBR is advantageous to create anoxic condition, and biofilm can absorb and store carbon for good nitrification and denitrification. The efficiency of simultaneous nitrification and denitrification increased with increasing of thickness of the biofilm. SBBR possessed the capacity of simultaneous nitrification and denitrification in wider range of dissolved oxygen concentration; and when NH₃-N reduced to zero or minimum value, the time was suggested to be the end of simultaneous nitrification and denitrification. It is suggested that a subsequence for denitrification is added or influent amount is decreased for requirement of effluent quality. At optimum operating parameters, the TN removal efficiency could be achieved.Based on the previous research work, it is appropriate that using the Microscopic Environmental view and the Microorganism Theory to explain the mechanism of the SND in biofilm process: at the condition of low DO concentration, because of the DO concentration gradient which exists in biofilm, the biofilm could classify three party from outside to inside: layer of oxygen, layer of oxygen deficient, anaerobic layer. Beause the layer of oxygen deficient and the anaerobic layer are consist of some facultative bacteria or anaerobic bacteria such as denitrifying bacteria, it make the denitrification to be probable. In a word, the DO concentration gradient exists in biofilm is the critical factor of SND.It was concluded that SBBR was an effective technology for simultaneously removing nitrogen during control of small scale point polluting sources and further treatment of water.