Characteristics Of A Modified A~2/O Process

Many problems exist in the traditional A2/O process that could remove phosphorusand nitrogen simultaneously by biological, such as the contradiction of PAO andnitrifying bacteria for the sludge age and compete of PAO and denitrifying bacteria forthe limited source, which results in that high removal for phosphorus and nitrogensimultaneously hardly was realized in the process. The modified A2/O process, whichused an additional biological selector and cultivated aerobic granular sludge to enhanceaerobic simultaneous nitrification and denitrification in the aerobic tank, in order toenhance the nutriment with the low carbon source and short SRT, and reduce the runexpense.This research studied culture of granular sludge, effect of nutriment removal in thedifferent SRT of the modified A2/O process, and enhancement effect of simultaneousnitrification and denitrification. The results showed that:(1) Through the additional biological selector in the aerob ic tank, the granularsludge could be cultivated. Observed sludge by microscope: round appearance, smoothsurface, clear boundary, the average SVI was39.3mL/g, particle size in the range of0.3~2.5mm, settling velocity>20m/h.(2) Modified A2/O process could be effective removed simultaneous nitrogen andphosphorus at low carbon source and low SRT. When the SRT was10d, influent CODwas300mg/L, the system C/N was less than8, the average effluent concentration ofCOD, NH3-N, TN, TP was31.2,0.8,9.2,1.2mg/L, except just TP close to the standardB, the others could reach requirements of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB18918-2002) Standard A, When SRT was10d, the new A2/O process for TN, TP removal efficiency compared to traditional A2/Oprocess, the average removal rate increased by19.5%and19.0%.(3) The effect of SND could be enhanced in the aerobic tank by the modified A2/O.When the system was in a shorter SRT, the removal percentage of TN is greater in themodified A2/O process aerobic tank than the traditional. By material balance, when SRTwas30d,20d and10d, the modified A2/O process, in aerobic tank, TN removal ratiowere6.2%,19.8%and22.8%, while the traditional A2/O process only6.7%,7.6%and7.8%.(4) Separation of SRT of nitrifying bacteria and PAO could be realized. When SRTwas10d, the traditional A2/O process had been unable to ensure the effect of nitrogenand phosphorus removal. Due to the biological selector in the modified A2/O, a certainamount of granules sludge stay in the aerobic tank in a long time to meet the growth ofnitrifying bacteria, so nitrogen and phosphorus removal efficiency can be guaranteed.