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The effects of C/N on removal rate of COD and NH 3-N of a continuous running hybrid biological reactor were discussed. The results showed that the removal rates of COD and NH 3-N were both more than 90% in the normal condition. The bio-film played a key role in removing the COD and NH 3-N in hybrid biological reactor. The sludge bulking occurred when C/N is around 30. The extremely high nitrification efficiency could be an early warning of the sludge bulking and the precursor time might be one or several days. Till now, the most commonly adopted biological wastewater treatment methods are activated sludge process and bio-film process which both have good effects on the cleaning of wastewater. But activated sludge process does have many problems such as sludge bulking, sludge floatation, sludge washout and low adaptability for impact loads. On the other hand, the stuffed media surface is limited and which means limited volume load of bio-film reactor. Therefore, the hybrid biological reactor has become a new wastewater treatment method which has been studied more and more in recent years. It is an integration of activated sludge process and bio-film process. The characteristic is adding media into activated sludge aeration tank as carriers for microbes to grow on or attach on. The coexistence of bio-film and activated sludge improves the treatment efficiency and reliability. Compared with traditional activated sludge process, hybrid biological reactor has following advantages: (1) Hybrid biological system can accumulate more biomass than activated sludge system therefore has more efficient organic matter removal ability. (2) Filamentous bacteria are prone to attach on media which results in better settleability of activated sludge. This can prevent sludge bulking and improve the stability of running. (3) Because nitrifying bacteria attach on media and are resistant to be washed out, the nitrification efficiency will not be affected by the SRT and ultimately the denitrification ability is enhanced. These studies show that the hybrid biological reactor is an effective way to improve the organic matter removal ability. An experiment was carried out in order to investigate the effect of organic matter concentration on the organic matter degradability of the hybrid biological system. In this experiment, the removal efficiencies of COD and NH 3-N in hybrid biological reactor were studied by increasing organic matter concentration under continuous flow meanwhile limiting the NH 3-N concentration of the influent in a certain range. Materials and Methods Equipments. The hybrid biological reactor is a cylindrical column with a height of 2.0 m, diameter of 200 mm and effective volume of 45 L. The scheme of the reactor is shown in Figure 1. It is filled with QTL-80S suspended spherical media and the filling ratio is 35%. Parameters of the media are listed in Table 1.

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