A Study On Municipal Sewage Treating Characteristic And Operational Control Of BICT Process

The single-sludge suspended-growth system, as most widely applied biological nitrogen and phosphorus removal process, has met certain problems which respect to the low treatment efficiency and stability, due to the same mixed-culture microorganism in the system. The BICT(Bi-Cyclic Two-Phase) biological process is proposed to effectively resolve these problems. It based on a SBR process, adding an independent biofilm reactor, separating autotrophic and heterotrophic microorganisms into two different growth phases. This process has shortened the SRT, improved the effect of phosphorus removal and enhanced operational stability and reliability, while having no effect on the nitrogen removal.The pilot-scale experiment of BICT biological process located in the wastewater treatment plant of Suzhou New District was using domestic wastewater. The removing of COD, nitrogen and phosphorus in the process under different operational control conditions were discussed. It focused on phosphate removal characteristics and efficiency, further discussed rules of phosphate release in the selector, the influence and operation control of phosphate removal in the main reactors under different operation conditions.It analysed the main principle of phosphate removal in BICT biological process according to the experimental results. The experimental results as follows:The BICT(Bi-Cyclic Two-Phase) biological process both has good effect on the COD, nitrogen and phosphorus removal at average 15℃and 25℃. Under the controlled conditions: filling/aeration(30min), anoxic stirring(60min), re-aeration(60min), sedimentation/decanting(60min), recycling rate of clarified overflow is 150%. The average removal rate of COD is up to 80%. The removal efficiency of TN can reach 85%. The removal efficiency of TP is over 90%.It is found that the operational pattern of main reactor, recycling rate of clarified overflow and SRT have little effect on COD removal ,but the first two factors has a big influence on nitrogen removal and the latter one has an important effect on phosphorus removal by means of range analysis under the optimal operational conditions.The everage pecent conversions of COD at different stages got through materiel balancing calculations were as followings: front aeration stage 62.25%,the front 30 minutes of anoxic stirring stage 28.32%(with inlet),the later 30 minutes of anoxic stirring stage 6.43%(without inlet);nitration rate was 75.22% at front aeration stage while it was 24.78% at re-aeration;the average denitrification rates of nitrate in the main reactor at the 30-60min of anoxic stirring stage was 57.22% while it was 42.78% at the 60-90min;about 86.22% of phosphorus was absorpted at front aeration stage,and there was 13.78% denitrification phosphorus removal in the main reactor at anoxic condition,which was a small scal in the whole phosphorus removal.The sludge can be transferred in the BICT process, which can obtain the high nutrition degradation rate due to the great MLSS in the reacted stage. It also improves sedimentation and separation of sludge in the main reactor, increasing the filling rate, enhancing the capacity of treatment in the process.The test and the results indicated that the returned flow ratio had little effect on the phosphorus removal of BICT at the operation condition,but it affected nitrogen removal heavily.