Development Of Magnetic Biocarrier And Its Experimental Research In Wastewater Treatment

The biofilm process is a highly efficient technology in the wastewater treatment. Biocarrier is the key factor for this method, and its performance directly influences and restricts the efficiency of the process. In the experiment, a magnetic biocarrier was first developed in order to improve the result of biological nitrogen removal and sludge reduction for wastewater treatment, which was made up of pumice-a kind of natural porous mineral, magnet and retiform plastic ball. Then the biofilm reactor with the magnetic biocarrier was used to treat the wastewater.In order to develop the magnetic biocarrier, the physical performance of pumice was firstly studied, its microstructure was observed by SEM, and the adsorption experiment and the biofilm formation performance experiment were performed. Then the parallel test of biofilm reactor with magnetic biocarrier and the one with nonmagnetic biocarrier was employed to study the biofilm formation performance of magnetic biocarrier. The reactors were also used to treat the simulated wastewater in order to find out the optimal operating parameters. And then the domestic sewage and coking wastewater were treated by biofilm reactor with magnetic biocarrier. Finally, the degradation mechanism of pollutant in the reactor was studied. The main conclusions were gained as follows:(1) The natural pumice has rough surface, porous structure with average pore diameter of 15μm, porosity of 69.5～71.8%, water absorption of 58～61% and thicker pore walls of 1～2μm, which offers a nicer living condition for microbe.(2) Compared to the biofilm reactor with nonmagnetic biocarrier, the biofilm formation performance of the magnetic biocarrier was better, and the period of biofilm formation reduced from 8 days to 5 days, the removal rates of COD_Cr and NH₄⁺-N by the biofilm reactor with magnetic biocarrier were increased by 5% and 20% respectively.(3) The two biofilm reactors were employed to treat simulated wastewater by changing the operating parameters—DO, HRT, and magnetic field intensity. The treated effect is best under the conditions of the central magnetic field intensity of biocarrier 200Gs, DO 2.0～3.5mg/L and HRT 8h. The concentration of COD_Cr, NH₄⁺-N, TN and TP of effluent were about 30mg/L, 5mg/L and 20mg/L, and the removal rates were 90%, 80%, 50% and 20% respectively after the treatment. Compared to the biofilm reactor with nonmagnetic carrier, the activated sludge in the biofilm reactor with magnetic carrier was reduced from 231.76g to 163.25g, which showed that magnetic field could improve the efficiency of sludge reduction.(4) Under the condition of DO 2.0～3.5mg/L, HRT 5h, the removal rates of COD, NH₄⁺-N and TN were 90%, 90% and 50% respectively, with COD content of 10.25mg/L, NH₄⁺-N content of under 5mg/L, TN content of 15mg/L in the effluent of domestic sewage. The coking wastewater was treated under the condition of DO 2.0～3.5mg/L and HRT 5h, the removal rates of COD was 80% with the content of about 100mg/L, but the removal rates of NH₄⁺-N was very low.(5) The experimental result showed that the low magnetic field could stimulate the microbe activity, and it is helpful to nitrification and sludge reduction in wastewater treatment.