Research On Control Strategy And Working Characteristics Of Internal-loop Granular Sludge Bed Shortcut Nitrifying Reactor

Shortcut nitrification of ammonia-containing wastewater can save energy, reduce cost, and has become one of the hotspots in the field of biological nitrogen removal from wastewater. Financially supported by the National Natural Science Foundation of China (No.3 0070017) and the Excellent Young Teacher Foundation of China Education Ministry, the research on control strategy and working characteristics of internal-loop granular sludge bed shortcut nitrifying reactor was carried out, and following achievements were obtained.1. The combined effects of operation parameters on performance of shortcut nitrification were tested for the first time. The optimum operation parameters were temperature 35癈, pH 8.0, dissolved oxygen concentration 1.0mg/L, ammonia-N concentration 4 mmol/L and hydraulic retention time (HRT) 16h. They exerted influences on performance of shortcut nitrification to different degree with an order of pH, temperature, dissolved oxygen concentration, ammonia-N concentration, HRT. Among them, pH, temperature and dissolved oxygen concentration were significant factors that attracted more attention.2. A control strategy named "priority+combination" for shortcut nitrification was suggested. Based on the control strategy, the significant factors (pH, temperature anddissolved oxygen concentration) were selected and controlled cooperatively. The detailed scheme was listed as follows.a. pH. pH was controlled around 8.0, and was prevented from large fluctuation.b. Temperature. Temperature was controlled between 32C and 35C.c. Dissolved oxygen concentration. Dissolved oxygen concentration was controlled between 1.0mg/L and 1.4 mg/L. In order to save energy, it could be controlled around the lower limit of 1.0-1.4 mg/L. In order to increase reaction rate, it could be controlled around the upper limit of 1.0-1.4 mg/L.According to the control strategy, the significant factors were controlled together. The results showed that NO2- /NOX- was raised from 79.2% to 94.5%, and the performance of shortcut nitrification was greatly optimized. So the control strategy can be applied to guide the operation of shortcut nitrification reactor.3. A strategy for quick start-up and stable operation of shortcut nitrification was suggested. According to the start-up strategy named "enrich+select", the shortcut nitrification reactor was successfully started up within 39 days. The start-up strategy was proved to work well and can be applied to guide the quick start-up of shortcut nitrification reactor. According to the stable operation strategy named "sludge granulation", the sludge concentration was increased, the sludge settlement was improved, and the reactor was kept under steady state with the fluctuation of ammonia removal rate and NO2-/NOx in effluent less than 4.11% and 5.72%, respectively, even though the hydraulic loading rate and volumetric nitrogen loading rate were raised to 221%. The stable operation strategy was proved to be good for the performance of shortcut nitrification reactor under steady state.4. The gas holdup and liquid flow velocity in the internal-loop granular sludge bed shortcut nitrifying reactor were determined. Based on hydrodynamic equilibrium, the model for gas holdup of the reactor was constructed as . Based on liquid continuity, the model for correlationship between gas holdup in riser and that indowncomer was constructed as . The model parameters were measured by experiment: . Based on the above models, the relationship between liquid superficial velocity in riser (Ulr) and aeration flux (Ugr) was constructed as Ulr= K (13.826 - 0.127 U0.871gr) , and the model parameters were measured by experiment: K -0.189.5. Two critical aeration fluxes (critical aeration flux for liquid loop and critical aeration flux for fluidization of granular sludge) were determined in the internal-loop granular sludge bed shortcut nitrifying reactor. According to the relationship between liquid superficial velocity in riser (Ulr) and aeration flux (Ugr), the criti...