Study On Activated Sludge Reduction By Ozonation And Feasibility Of Ozonated Sludge Recirculation

A large number of excess sludge poses a serious threat to theecological environment. Research on sludge reduction technologies playsan important role in wastewater treatemnt in our country, in whichozonation technology is an effective method for excess sludge reductionbased on the enhanced cryptic growth way.In this study, experimental research and theoretical analysis on sludgereduction by ozonation were conducted. The influence of different ozoneconcentration with31.82mg/L,34.03mg/L,36.76mg/L and dosage in arange of0.02-0.16gO₃/gSS on the sludge properties was evaluated and theresult showed that in ozone dosage range of0.04-0.12gO₃/gSS, with theincrease of ozone dosage,△MLSS and△MLVSS had significantelevations, in which△MLSS reached2042mg/L and2208mg/L with theozone concentration of34.03mg/L and36.76mg/L, respectively. However,VSS/SS decreased from0.75to around0.60. The variation of△SCODwas also obvious with the ozone dosage, and under each ozoneconcentration, values of SCOD were17.0,22.6and24.2times higher thanthe original ones with the same ozone dosage of0.12gO₃/gSS. Due toacetic acid mainly produced during the ozonation process, pH value of the sludge reduced from7.09to5.61.The mechanism of ozonation process was further explored throughadding hydroxyl radical scavenger. It was indicated from the comparativetests that under the neutral condition coupled with the ozone concentrationof34.03mg/L, direct oxidation by ozone and indirect reaction by hydroxylradical contributed to the increase of△SCOD by51.2%and48.8%,respectively. Meanwhile, the model of sludge reduction by ozone wasestablished and validated, which y=e^-1.840×Q^1.35×c^3.34, with ozonedosage and concentration as the independent variables, and△SCOD asdependent variable. The results showed that there was a good correlationbetween the test data and predicted data by this model with R²of0.9151,which could be applied to describe the sludge reduction process by ozonewell.The denitrification experiments with sludge supernatant by ozonationwere carried out and its feasibility of recirculation to the biologicaltreatment process was also discussed. It was found that43.02%of carbonsource from sludge supernatant by ozonation could be used fordenitrification, while the increase of NO₂^-concentration occurred at lowC/N ratio of7.1in this process. Furthermore, based on the analysis ofabove influencing factors in the sludge reduction process by ozone, thefeasibility of ozonated sludge recirculation to the biological treatmentsystem could be determined qualitatively through the recirculation index X, which was described as followed, X（X=SCOD×η/N×COD_N2）...