A Study On The Impact Of The Actual Refinery Wastewater On The Activated Sludge Settling Ability By Quantitative Image Analysis

Oil-refining wastewater is featured with the high amount of discharge,the complexity of components and the difficulty to treat,which made it one of the most significant problems in water pollution control in the petrochemical industry.The oil substances in the wastewater have an impact on the biological treatment system,which often causes the reduced settling ability of sludge and also affects the effluent quality.Therefore,it is urgent to establish a method to quantitatively and quickly characterize the changes of sludge settling ability.The technology of quantitative image analysis(QIA)has the advantages of foresight,efficiency and automatio,which made a good prospect for its application in researching the settling ability of activated sludge.This study investigated the effect of typical oil substances under different concentrations on the settling ability of activated sludge.The macroscopic and microscopic settling ability parameters of activated sludge flocs were characterized respectively by the traditional settling test and the QIA analysis.The correlation among micro-parameters and between micro-and macro-parameters were analyzed.Relevant conclusions were verified with actual refining wastewater.The study results would provide technical support for the stable and efficient operation of biotreatment systems of refinery wastewater.The effects of typical oil substances cyclohexane,2,2,4-trimethylpentane and hexadecane on the settling ability of activated sludge were investigated by both traditional settling tests and quantitative image analysis.It was found that when the concentration of oil substances was low,the settling volume of activated sludge increased,and the settling velocity increased;when the concentration of oil substances was high,the activated sludge floated and lost,and the settling velocity and suspended solids of the sludge decreased.The turning of the two phenomena occurred when the concentration of the oil substances was in the range of 0.5-2 g/L.Under the influence of actual oil refining wastewater,the activated sludge also showed an transformation from volume increasing to sludge floating,and the turning point was 0.5 g/L.According to the changing rules of the microcosmic parameters influenced by the oil substances and the correlation among the parameters,the microcosmic parameters could be classified into size,regularity and density groups.Once the oil substances concentration exceeded the turning point,with the increasing of concentration,theparameters of size class declined.The correlations of perimeter and convexity with the macroscopic settling parameters were very significant.The parameter hole rate in the regularity group showed a monotonous decreasing trend,and smaller hole rate meant more oil existed.It is for the reason that the extrusion of interstitial water is hindered with the increase of the oil substances in the hole,and the reduction rate of the inner hole is inferior to that of the whole flocs.This can even trigger the amplification of the inner hole,and then the convexity and the hole rate could also decrease.Meanwhile,The parameter fractal dimension in the regularity group presented a monotonous upward trend: the larger the fractal dimension was,the more serious the loss would be.This can be attributed to the tendency of reducing the superficial area which is caused by the oil substance covering the floc.Its shape tends to be spheroid,which is more like a circle in the perspective of two dimensions.The changing mechanism for the microcosmic parameters of activated sludge caused by oil substances was essentially different from other factors mentioned in previous researches,and deserved further study.Influenced by the actual refinery wastewater,the microscopic parameters of the activated sludge flocs showed the same classification characteristics,changing rules and correlation relationships as those under influence of the single oil substances.This study provided useful tools for the prediction of settling ability changes of activated sludge and sludge loss caused by the refinery wastewater.It also provided technical support for the on-line monitoring and early warning of sludge performances with low cost and high efficiency.