Research On Nitrogen And Phosphorus Removal With Cyclic Activated Sludge Combined Biofilm System

Cyclic Activated Sludge combined Biofilm System(CASBS) process is developedbased on oxidation ditch、 SBR、OGO process.The process is a new technology,whichhas advantages of phostrip, Sequencing Batch Reactor and Membrane Bio-reactor, thusit removes nitrogen and phosphorus effectively, achieving good anti-shock loadingcapability and making running operation easily. It can be used to treat the wastewaterwith quality and quantity varies much more widely.The technology has beensuccessfully declared invention patents，and has been authorized. The research showsthat the biofilm and staggered aeration system in the combined process form aerobiczone and anoxic zone in loop reactor，but it has some deficiencies，such that the biofilmattached to semi-soft packing inside the system is easily too thick, and then increase theflow pattern of the reactor for sewage and activated sludge flow reactor block. Thisdissertation has studied the influence of fixed packing and suspended packingon flow rate、DO distribution and nitrogen and phosphorus removal in CASBS bycomparative methods. Also, the dissertation has studied the nitrogen and phosphorusremoval efficiency of CASBS with different fill rate in room and low temperature,andwith differernt plug-flow modes. The results of the research are showed as following.①The Two types of fixed packing and suspend packing affect on flow rate、DOdistribution and nitrogen and phosphorus removal in CASBS. The flow resistance infixed packing system is greater than that in suspended packing system. But the the filmformation property and DO distribution in fixed packing system is better than which inthe suspended packing system. The removal of nitrogen and phosphorus is better infixed packing system. When the concentrations of COD，NH3－N，TN and TP ininfluent are127to756mg/L，14.05to58.22mg/L，27.60to65.25mg/L and1.26to6.44mg/L and the average removal efficiencies of COD，NH3－N，TN and TP are94.2%、95.4%、79.4%、93.2%respectively, which meets the first level A criteriaspecified in the Discharge Standard of Pollutants for Municipal Waste water TreatmentPlant (GB18918-2002). Fixed packing system formed the conditions conducive to thesmooth progress of the SND, beneficially effect on improving the nitrogen andphosphorus removal of the system, relative to the suspension packing,fixed packingsuitable for CASBS process.②The fill rate could affect the removal efficiency of nitrogen and phosphorus of CASBS. In room temperatue, when fill rate are15%、25%、50%of CASBS,respectively, the average removal efficiency of chemical oxygen demand (COD) are92.4%,94.2%,94.7%, respectively; the average removal efficiency of NH3-N are91.6%,95.1%,94.7%, respectively; the average removal efficiency of total nitrogen (TN) are71.8%，79.4%,82.3%, respectively; the average removal efficiency of total phosphorus(TP) are89.8%,92.7%,92.4%, respectively. Fill rate on COD and TP removal is lessaffected;fill rate in CASBS increased, the nitrification and denitrificationcapacity of the system would be enhanced to strengthen nitrogen removal.At lowtemperatures (water temperature is lower than12℃), to enhance the fill rate inCASBS from25%to50%, the average removal efficiency of chemical oxygen demand(COD),NH3-N,total nitrogen (TN),total phosphorus (TP) are92.4%,91.6%,71.8%,89.8%respectively; The average removal rate is higer3.6,7.7,7.4,4.0percentage points respectively, than which with the fill rate of25%.③Two-way plug-flow is beneficial for the stability of the CASBS process. Nomatter plug flow in a clockwise or counterclockwise, the average removal efficienciesis or less, the average removal efficiency of chemical oxygen demand(COD),NH3-N,total nitrogen (TN),total phosphorus (TP) are about94%,95%,80%,93%respectively. Cis/anti-clockwiae altermating two-way plug-flow operation modecan delay the occurrence of this phenomenon, as compared to one-way plug flowmode,it canimprove the flow pattern of the rector, and reduce the sludege deposition inproduce, but also make packing biofilm can beuniform growth, to avoid due to push in asingle direction of flowshear stress, the side of the growth of thicker side of thin.Two-way plug-flow mode can reduce the number of regular cleaning of biofilm,and isbenefit of nitrogen and phosphorus removal in CASBS system.