Study On Treatment Efficiency And Chemical Phosphorus Removal Of BAF In Treating Urban Sewage

The paper reviewed the biological aerated filter(BAF) technology and phosphorus removal technology from wastewater. Studied on the bio-film culturing of BAF; the optimal operating condition was determined by changing the air-water ratio, hydraulic loading and running time; studied on the treatment efficiency of BAF in municipal wastewater at the optimal operating condition; the phosphorus removal of BAF was studied and analyzed the phenomenon; the optimal coagulant and dosage was determined via static tests; application of the AHM in choosing phosphorus removal program of BAF, the influence on treatment efficiency and micro-organism of BAF by dosing coagulant was studied via chemical phosphorus removal experiment in BAF. The results show that:Its costed 20d to accomplish the forming bio-film under the condition of pH was 7.10⁷.53, temperature was 18.4²9.7℃. In this case, the removal rate of CODCr and NH₄⁺-N were over 80%, marked the bio-film was matured. When the air-water ratio varied from 1:1 to 5:1, the removal rates of SS,CODCr,NH₄⁺-N and TP firstly increased then decreased a little, when the air-water ratio was 3:1, the highest removal rates were 97.69%,86.76%,92.18%,31.04% respectively; when the hydraulic loading varied from 0.80m3/m2·h to 2.23m3/m2·h, the removal rates of SS,CODCr,NH₄⁺-N and TP decreased with the increase of hydraulic loading, when the hydraulic loading was 1.27m3/m2·h, the highest removal rates of SS,CODCr,NH₄⁺-N and TP were 97.69%,86.76%,92.18%,31.04% respectively; the water head loss of BAF was increased gradually with the increase of running time, and 5d later, the water head loss increased to 791mm, and then the removal rates of SS and CODCr were decreased. As a result, the optimal operating condition of BAF were concerned in this study, the air-water ratio, the hydraulic loading and the backwashing cycle were 3:1, 1.27m3/m2·h and 4⁵d, respectively.In the optimal operating condition, the removal effect of SS,CODCr and NH₄⁺-N were good, but removal rate of TP was only about 30%, from the analysis believes that the mechanism of filtration, microbe assimilation and some biological phosphate removal in BAF played a main role on phosphorus removal. If the concentration of TP in influent could be controlled at less than 1.48mg/L, the concentration of TP in effluent would be decreased under 0.5mg/L. If the concentration of TP in influent could be decreased under 1.5mg/L, the dosage of FeCl3·6H2O was the least among the coagulant, the least dosage was 60mg/L, and it is harmless for human bady. The use of PAM could improve the removal effect of TP by FeCl₃·6H₂O, and could reduce the sediment time effectively, the optimal dosage of PAM was 0.4mg/L. It applies AHM for analyzing phosphorus removal program of BAF, the results show that the weights of pre-dephosphorization, synchronization dephosphorization and post dephosphorization were 0.394,0.284,0.322, respectively. When use of pre-dephosphorization, the results show that the removal of pollutants by combined process had a good result; the removal rate of TP could be enhanced effectively by dosging FeCl₃·6H₂O in the No.2 reactor, and the backwashing cycle could be extended to 6 days; the biological activity and the biomass were reduced by 7.85% and 17.15% respectively in No.2 reactor, but it did not affect the treatment performance of BAF, the combined process is a feasible method of sewage treatment.