Study On The Characteristics And Applications Of A Sequential Batch Bi-external Recycling Biological Fluidized Bed

In this thesis, a new equipment called a Sequential Batch Bi-extemal Recycling Biological Fluidized Bed (SBBRBFB) is designed to treat the highly polluted, toxic industrial wastewater which is hard to bio-degrade. The BRBFB is designed on the basis of techno-peculiarity of biological fluidized bed and the reasonable combination of anaerobic-aerobic courses. The BRBFB process has some innovations, which include:●It is a new type of sequencing batch biofilm reactor(SBBR), which combines both the advantages of sequencing batch reactor technology and those of the biological fluidized bed technology. The shortages of liability of being blocked and low efficiency of treatment for packed bed sequencing batch biofilm reactor are overcome in this new system.●Several different processes involving anaerobic treatment, aerobic treatment and settlement can be easily realized in this fluidized bed reactor because this system can be switched easily from solid-liquid fluidized bed recycling by hydrodynamic jet to gas-solid-liquid recycling by airlift in different process stages.●The wastewater in this fluidized bed can be well dealt by various combination of anaerobic/aerobic course including sequencing, alternate, local concurrent mode, so the large molecules like dye which are difficult to dissolve and degrade can be absorbed and decomposed more effectively.●This new system can be started up and fluidized easily and has higher biodegradation ability since the fine light activated carbon particles are adopted as carrier of the microorganism, and the recycling jet is taken to start up and fluidize the liquid-solid two phase fluid.●The microorganisms in this reactor exist and develop in both suspended and attached manners and are domesticated by sequential anaerobic/aerobic process. Therefore the system has rich microorganism, good adjustability and degradation ability to many types of waste water.●An idle period devised rationally makes the hydrolyzation- acidification and denitration more completely. The idle time can also help to reduce the residual sludge, and help the carriers and the within biofilm reproduce.●Finally, an automatic control box, which can provide manifold modes of process according to the different calling for sequencing batch, is introduced, and therefore, in some way; the targets of automation, high efficiency and no secondary pollution of waste water treatment are realized in this new system.The primary investigation of the new system shows that: the gat-liquid-solid fluidized bed possesses a good ability to absorb oxygen. The total coefficient for transferring oxygen is K_La(20℃)=10.78h^-1, and the Oxygen utilization is high (E_A=18.9%). The microorganisms can adapt for the change of environment of dissolving oxygen from anaerobic to aerobic course. The amount of rich microorganism is appropriate and the ratios of suspended microorganism to attached ones are 21% and 28% in anaerobic and aerobic processes respectively. Besides, the thick of the biofilm are 124μm and 146μm in anaerobic and aerobic processes respectively which are appropriate for biologic treatment.The fluid dynamics in the fluidized bed have also been investigated in detail both numerically and experimentally. First, the characteristics of the velocity fields in the main bed and the auxiliary bed were measured in solid-liquid fluidized phase by the particle image velocimetry (PIV). The Reynolds averaged velocities and vorticity in the main bed and the auxiliary bed were shown and analyzed. It is shown that axial velocity component is asymmetric with respect to the X direction(V_Z-r_x/R) and the excursion to the outside wall (+ r_x/R) of the maximal value is clearly seen, whereas the distribution of the axial velocity in the Y (V_Z-r_y/R) direction is symmetric and the maximal speed is located in the centre (r_y/R=0). On the other hand, the vorticities in the main bed and the auxiliary bed are both uniformly distributed so that the turbulent shear stresses around the carriers are not too strong to destroy the biofilms, and this accounts for the validity of the design of the reactor. The vorticities in the main bed and the auxiliary bed are between (35-45)s^-1 and (10-20)s^-1 respectively under the situation of optimal flux of recycling (1.4m³/L). Second, a Reynold-stress model (RSM) was used to simulate the three dimensional velocities in the main and auxiliary beds. By comparison to the experiments, it is indicated that the numerical results by RSM model agree well with experiments under any flux of recycling. The distribution of pressure and turbulence intensity were also obtained and analyzed. The numerical method used in this thesis can be used to evaluate the performance of the reactor, and to shed new light on the design of such equipment.Finally, the new system was used to treat a model waste water from a dyeing plant. The effects of the removal of COD_Cr and NH₃-N were investigated in both anaerobic and aerobic phases. It is found that the most appropriate fluxes of recycling and aeration are 1.4m³/h and 0.17m/min respectively. By the comparison of five different treatment courses, the optimization of the combined operation of the system is determined to be a 12-hour cycle including an inflow process and anaerobic digestion process (4 hr), an aerobic aeration process (4 hr), a settlement process (2 hr), and a recess process including effluent discharge process (2hr). After this optimal treatment, 90% of COD_Cr is removed for a higher concentration water (COD_Cr 1000-1200mg/L), and 82% of COD_Cr is removed for a lower concentration water (COD_Cr 400-600mg/L). The removal rate of NH₃-N is higher than 60%, and nearly 100% color is removed. These results indicate that wastewater containing dying wastewater can be well treated using SBBRBFB with proper choice of courses. Meanwhile, some other performance parameters under the optimization condition were also examined. These examinations show that the values of DO and pH in the reactor are periodic and can meet the requirement of biochemistry treatment, and the sludge in the reactor is changed from the maximum in the end of aerobic process to the minimal quantity in the end of idle process, which meet the requirement of microorganism quantity for treatment. The final residual sludge is reduced to a low level. The temperature is between 18-30℃, and the organic load is between 1.4-5.4 kgCOD/m³Â·d. The discharge standards can be usually met after 30 periods of running. These results further indicate that SBBRBFB and the operating strategies are well designed and working well for treating dye waste water.