| Along with water environment protection requirements of three gorges reservoirarea increase, the wastewater treatment plants which in this place face upgradingthemselves to make the effluent be superior to the first level B criteria of urbanwastewater treatment plant emissions standards (GB18918-2002), even reach the firstlevel A criteria. But it’s difficult to ensure the total nitrogen of effluent reach thestandards. How to make the total nitrogen of effluent reach the standards without addingcarbon source in existing wastewater treatment plants, which is a problem has not yetbeen solved.In the three gorges reservoir area, the technology of wastewater treatment plants ismultiform oxidation ditch. Study on Carrousel2000oxidation ditch for biologicaldenitrification by adding suspended filler without adding carbon source.In the condition of return sludge ratio was50%, the mixture reflux ratio was250%,the packing cast ratio (10%,20%,30%), hydraulic retention time (7.5h,10h,12.5h),sludge retention time (15d,20d,25d) and aeration (40L/h,60L/h,80L/h) werechosen as the test parameters of orthogonal test, nine tests have been done. Someconclusions were obtained through variance analysis of orthogonal test: the order thatinfluential factors on concentration of COD in effluent was aeration>hydraulicretention time>packing cast ratio> sludge retention time; the order that influentialfactors on concentration of ammonia in effluent was hydraulic retentiontime>aeration>packing cast ratio>sludge retention time; the order that influentialfactors on concentration of nitrogen was packing cast ratio> aeration>hydraulicretention time>sludge retention time. After a comprehensive comparison, the optimalcondition was chosen: packing cast ratio was30%, aeration was80L/h, hydraulicretention time was10h, sludge retention time was25d.According to results of orthogonal test and experience, and simultaneousnitrification and denitrification has been usually observed in low concentration ofdissolved oxygen that was considered, the optimal aeration condition of80L/h waschosen as a benchmark decrease progressively. Then80L/h,65L/h,50L/h aerationwere selected to observe the influence of aeration for SND and the removal of ammonianitrogen and total nitrogen. The test results showed that, when the aeration was80L/h,the average concentration of ammonia and total nitrogen in effluent were respectively 0.94mg/L and12.07mg/L, the average removal rate were respectively97.07%and69.23%, and SND/TN was11.82%; When the aeration was65L/h, the averageconcentration of ammonia and total nitrogen in effluent were respectively4.43mg/L,10.14mg/L, average removal rate were respectively86.18%,74.15%, and SND/TN was14.92%; when the aeration was50L/h, the average concentration of ammonia and totalnitrogen in effluent were respectively7.69mg/L and13.84mg/L, the average removalrate were respectively76.51%and62.25%, and SND/TN was20.51%. It means thatwhen the aeration was65L/h, the TN removal of system was best and effect of SNDwas preferable, and the low concentration of DO was beneficial for SND. The resultsshowed that the total nitrogen of the Carrousel oxidation ditch effluent can achieve thefirst level A criteria through adding suspended filler.The fixation of diatoms attached to the biofilm was observed by using scanningelectron microscopy in this study. The results provided a viable way of immobilizedalgae to purify sewage containing nitrogen and phosphorus.The results of this study provided a feasible approach to enhance the ability ofoxidation ditch on biological removal of nitrogen and provide technical and theoreticalsupport for total nitrogen in effluent of sewage plant which use oxidation ditch processas the main treatment step to meet the raised standards. |
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