Influence Of Organic Loading Rate On Sludge Characteristics In Modified A~2+OSA Process

The good nitrogen and phosphorus removals can be achieved in the modified A²+OSA process,which can simultaneously realize in-situ sludge reduction.Thus a depth-research of this process has great significance in sewage treatment field.Adjusting the the organic loading rate can be obtained through changing the sewage flow based on the optimal operational conditions from the previous study.The contaminates removals have been investigated in both of the modified A²+OSA process and modified A² O process under different organic loading rates;in-situ sludge reduction efficiency and mechanisms have been explored as well;the sludge characteristics of the two processes have been studied under different organic loading rates,the extracellular polymeric substances?EPS?content,compositions and the changing rules of the specific oxygen uptake rate?SOUR?being further comparatively analyzed.In this study,the inoculated sludge was taken from the pre-anoxic tank in the Carrousel oxidation ditch process from the west sewage treatment plant in Handan and domesticated in the two processes in the laboratory.After the completion of domestication,continous-running was started in both of the two process installations.In this current study,the average organic loading rates of 0.5184,0.6048 and 0.6912gCOD/?gMLSS·d?were achieved treating synthetic sewage by changing the influent flows?6 L/h,7 L/h,8 L/h?under the optimal operational conditions?the influent distribution ratio into the anaerobic and anoxic tanks of 5:5,the internal reflux of100% and external reflux of 250%?.Good contaminants(COD_cr,TN,TP,etc)removals could be gained in both of the two processes under three different organic loading rates.The highest contaminants removal could be obtained under the condition of the medium organic loading rate in the both of the two processes,while removal efficiencies of CODcr,TN and TP were 90.28%,98.56% and 96.75%respectively in the A²+OSA process,which were improved by 0.69%?0.7% and 2% of that in the modified A² O process.EPS content and compositions of the two processes have been studied,and the results showed that the distribution of the total amount of EPS from the modified A²+OSA process was EPS_OSA-tank > EPS_anoxic-tank> EPS_oxic-tank>EPS_{anaerobic-tank},whereas the distribution of the total amount of EPS from the modified A² O process was EPS_anoxic-tank> EPS_oxic-tank>EPS_{anaerobic-tank};the distribution of the total amount of EPS under the three organic loading rates was EPS_high-loading> EPS_{medium-loading} >EPS_low-loading,and EPS content presented a certain positive correlation with organic loading rate.From the research results of EPS compositions,the protein showed the highest content in the range of 50% to 60%,followed by polysacchairdes,humic acid and DNA.In-situ waste sludge reduction can be realized in the modified A²+OSA process,which exhibited better sludge reduction efficiency than that of modified A² O process.After one-month continous running,the average sludge yields from the two processes were 6.827 g/d and 12.31 g/d,with Yobs of the two processes being 0.0932gMLSS/gCOD and 0.1627 gMLSS/gCOD respectively.The sludge reduction rate of modified A²+OSA step-feeding process was 44.5%,which was 5.45% higher than that of the previous research.In addition,the research results of the SOUR values from the two processes showed that strongest respiration reactions could be achieved and SOUR_EN values in the modified A²+OSA process tanks were higher than those in the modified A² O process.