Study On Phosphorus Removal Efficiency Of Hybrid Biofilm-Oxidation Ditch Process

Currently, control of eutrophication and research on effective and economicalphosphorus and nitrogen removal from wastewater are deeply concerned in the field ofwastewater treatment all over the world. Although the traditional single activated sludgebiological phosphorus and nitrogen removal process is more mature, there are somedisadvantages, such as effective phosphorus removal and nitrogen removal could not bereached as a result of the different SRT and the competition for the carbon sourceamong between phosphate accumulating bacteria and denitrifying bacteria, and inengineering practice,the capability against impact load is poor and operating is notstable. In general, the application of traditional activated sludge method in wastewatertreatment engineering still exist deficiencies. The hybrid process of biologicalmembrane and activated sludge combines the advantages of two types of technology,improve the efficiency of phosphorus and nitrogen removal while strengthening thecapability against impact load.This paper is for the study of hybrid biofilm-oxidation ditch process, whichcombines biofilm process with improved Carrousel2000oxidation ditch process,adding suspended bio-carrier in anaerobic Tank and oxidation ditch. In this experiment,the phosphorus removal efficiency and the removal effects of COD、NH4+-N and TN indifferent conditions are studied, the optimal conditions are determined, the systemperformance under the optimal operating condition are verificated, and the phosphoursremoval mechanism of the hybrid technology system are analyzed.The three factors such as the adding ratio of carrier in oxidation ditch（10%、20%、30%）、anaerobic HRT（1.5h、2h、2.5h）and SRT（15d、20d、25d） are studied by orthogonalexperiments. The experimental results show that:The most significant factor affecting phosphorus removal efficiency is the addingratio of carrier, followed by anaerobic HRT, while the effect on phosphorus removalefficiency of SRT is not significant. When the adding ratio of carrier increased from10%to30%、anaerobic HRT extended from1.5h to2h、SRT extended from15d to25d, the removal rate of TP of the system increase firstly and decrease afterwards、decrease firstly and increase afterwards and keep increasing，respectively. The optimaloperating conditions of the system are obtained by selecting the optimal level of theoperation parameters: the adding ratio of carrier is30ï¼…,the anaerobic time、anoxidic time and oxidic time of the system is2h、2.2h and7.8h respectively, and SRT is25d.As the system return sludge ratio is50%, the mixture reflux ratio is250%,anaerobic stage DO <0.2mg/L, aerobic stage DO is0.6-1.2mg/L and MLSS is2500-3500mg/L, the stable operation results under the optimal conditions of the systemshow that the phosphorus removal efficiency of the system is good and stable. In themeantime,the influent TP is2.15mg/L-3.39mg/L, the effluent TP is0.49mg/L-0.82mg/L,the the removal rate of TP is75.62%-77.19%，while the removal rates of COD、NH4+-N、TN are80.26%-83.78%、89.79%-93.45%、63.03%-68.37%and the effluentCOD、NH4+-N、TN are25mg/L-mg/L、0.92mg/L-4.49mg/L、12.16mg/L-15.72mg/L,respectively. Under the optimal conditions, the effluent TP、COD、NH₄⁺-N、TN can meetthe requirements of the first Grade B standard of《the standard of pollution emissions inUrban sewage treatment plant》（GB18918-2002）.By the static phosphorus release experiment, the anaerobic phosphate release of thebiological membrane was observed, which verified the attached growth of phosphateaccumulating bacteria on the suspended carrier biofilm. On the analysis of the staticrelease phosphorus experimental results under different orthogonal conditions, it comesto the conclusion that the maximum rate of phosphorus release、effective phosphorusrelease quantity and the removal rate of TP is positively related.