Study On Upgrading And Reconstruction Of Carrousel Oxidation Ditch With Internal Biological Nitrification Area

With the rapid development of modern society, the continuous expansion ofurbanizationlead to increase of urban water consumption and displacement, waterpollution and water shortage, which seriously restricts the development of socialeconomy.Water pollution is serious as a result of nitrogen and phosphorus emissions. Tocontrol the nitrogen and phosphorus emissions of sewage plants is meaningful forgovernance of water pollution.The oxidation ditch technology is widely used because of good processing capacity,simple process, convenient operation and management. As a form of activated sludgeprocess, the oxidation ditch technology has problem with sludge deposit, sludge bulkingand sludge emersion. Appling biofilm process in oxidation ditch can improve sludgesettleability, and inhibit sludge bulking problem effectively.This study developed aCarrousel oxidation ditch technology with internal biological nitrification areabycombining activated sludge process and biofilm process.The aim was to find reasonableoperating parameters and condition by comparing with the aeration at the bottom of theditch(16m3/h,22m3/h,28m3/h), the treatment loading of the diaphragm area filled withfiller(0.5m3/(m3h),0.67m3/(m3h),0.83m3/(m3h)), the returned sludge ratio(60%,80%,100%,120%) and aeration atthe diaphragm area filled with filler(12m3/h,16m3/h,20m3/h) on the removal of SS, COD, NH4+-N, TN.Then this study researched someindexs’variation along the direction of water flow in oxidation ditch and diaphragmareaand had a benefit analysis at last.①The results showed that when the influent was136m3/d, the hydraulic retentiontime of the reactor was7.1h, the aeration at the bottom of the ditch was22m3/h, thetreatment loading of the diaphragm area filled with filler was0.67m3/(m3h), thereturned sludge ratio was100%and the aeration at the bottom of the diaphragm areafilled with filler was16m3/h, the effluent of SS, CODcr, TN, NH4+-N, TP could reach8.2mg/L,29mg/L,12.45mg/L,1.35mg/L,1.16mg/Lwith removal efficiency of96.6%,86.9%,62.1%,95.8%,61.1%respectively..This paper mainly researched the ability ofbiological denitrification by transformation, so the reactor could supplementby chemicalphosphorus removalon the basis of biological phosphorus removal.②When the reactor was under the optimal operating conditions, sludge mixedmore evenly, DO had a little change in different depth and the whole ditch wasanaerobic-aerobic environment basically with the influence of the propeller and theaeration in the inlet side of the oxidation ditch. After the aerator, DO of upper andmiddle layerwas more than1.5mg/L, then falled down along the direction of water flowin oxidation ditch. This dissolved oxygen environment was beneficial to SND. Thesludge deposited by inclined plate sedimentation area was not mixed effectively, whichaffect the efficiency of dissolved oxygen mass transfer. In the diaphragm area filled withfiller, except the first area, DO in others was within the limits of2.0to4.0mg/L and theareas was aerobic environment basically. It was beneficial to cultivate nitrobacteriumand strengthen efficiencyof nitrification.③Under the optimal operating conditions,the removal rate of COD,NH4N, TNwas the largest in the anaerobic tank because of the large amount of nitrate carried byreturned sludge, the dilution effect by returned sludge, the adsorption effect of activatedsludge group, the denitrification effect and the PAOs. In the anaerobic tank, nitrateconcentration increased and nitrite concentration increased slightly. In the oxidationditch, the removal rate of COD,NH4N,TN was low and the concentration change ofCOD, TN,NH4N,NO3N,NO2Nwas not obvious. In the diaphragmarea,because of the concentration of COD,NH4Nof inletwas lowand most organicpollutant was nonbiodegradable organics, the removal rate of COD,NH4N,TN waslow. So it was known to us which nitrification potential of diaphragm area was notplayed out fully. In the secondary sedimentation tank, there was endogenousdenitrification, so the concentration of COD, TN of outletwasincreased and theconcentration ofNH4Nof outletwasdecreased conversely.④This study analyzed the feasibility of Carrousel oxidation ditch technology withinternal biological nitrification area still. The reactor has good environmental benefits;This technology could save the area and capital investment and it was applicative forthe areas Which were lack of land and capital. Carrousel oxidation ditch technologywith internal biological nitrification area belonged to low-cost upgrading andreconstruction technology.