A Pilot-scale Study On Phosphate Removal Characteristics And Operation Control Of BICT Process

The single-sludge suspended-growth system, as most widely applied biological nitrogen and phosphorus removal process, has met certain problems whit respect to 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 to an independent biofilm reactor, separating autotrophic and heterotrophic microorganisms into two different growth phases. This process has shortened the SRT of the system, improved the effect of phosphorus removal and enhanced operation stability and reliability, having no effect on the nitrogen removal.The pilot-scale experiment of BICT biological process is in the wastewater treatment plant of Suzhou New District using domestic wastewater, discussing COD, nitrogen and phosphorus removal in the process under different operation control conditions. Focusing on phosphate removal characteristics and efficiency, it's 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, such as SRT, operation modes, C/P, sludge transference and so on. It's analyzed 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 has good effect on the COD, nitrogen and phosphorus removal. 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%. The effluent PO43-concentration reaches the first class standard of GB8978-1997(<0.5 mg/L).SRT has very effect on the phosphorus removal in the BICT process. When the SRT decreases from 15d to 5d, the removal efficiency of PO₄^3- increases from 60% to 90%. The independent nitrification is provided in the the BICT process, shortening the SRT in the main reactor, promoting the ability of phosphorus removal in the process.The HRT of biological selector also influences the phosphorus removal in the BICT process badly. When the HRT is 60min, it meets the demand of releasing phosphorus.The C/P rate in the influent has effect on the phosphorus removal. When C/P rate is between 75～140, phosphorus removal of BICT process is effective.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.