Comprehensive Evaluation Of Sludge Granulation Process Based On Image Analysis And Fuzzy Mathematics

Aerobic granular sludge has been widely used in the field of water treatment due to its advantages of dense structure,good settlement performance and strong impact load resistance.However,the formation and stability of aerobic granular sludge are affected by many factors,such as poor operation stability,which limit its further application in engineering.In this paper,by running the reactor with different influent organic concentration,combined with quantitative image analysis technology,the change of sludge macro structure,micro morphology and sedimentation performance during granulation process was monitored.A partial least-squares regression model was established,which took the microscopic morphological parameters of sludge as the independent variable and the macroscopic sedimentation parameters as the dependent variable.A comprehensive evaluation system of aerobic sludge granulation process was established based on fuzzy mathematics theory and sludge granulation experimental data.The main research results are as follows:（1）Two groups of reactors with different influent organic matter concentration wereset to cultivate aerobic granular sludge,and mature granular sludge with average particle size of 708.46μm and 884.43μm were formed on the 53rd day,respectively.The increase of influent organic matter concentration promoted the increase of particle size of formed granular sludge.At the same time,higher influent organic matter concentration tend to enrich more biomass,and sludge concentration was stable at about 4 g/L.In terms of extracellular polymeric substance,the increase of influent organic matter concentration promoted sludge to secrete more polysaccharide,and the hydrophilicity of sludge was improved.The absolute value of Zeta potential of mature granular sludge was relatively high,and the flocculation capacity was relatively weak.（2）Based on the operation of the macro reactor,the micro-morphology of sludge in the granulation process was observed and analyzed.The results showed that with the granulation process,the sludge structure gradually tended to be dense,the shape tended to be round,and the boundary became smooth and regular.The partial least squares regression prediction equation was established with the equivalent diameter,roundness,aspect ratio,density,shape factor and fractal dimension as independent variables,and the macroscopic sedimentation performance parameters SVI₅,SVI₅/SVI₃₀,specific gravity and sedimentation velocity as dependent variables.The predicted values of each dependent variable had a good fitting relationship with the measured values.R² was 0.968,0.9801,0.9999 and 0.9881,respectively,indicating that microscopic morphological parameters can be used to reasonably predict the macroscopic subsidence.Fractal dimension played the most important role in the prediction results of SVI₅ and SVI₅/SVI₃₀.In the prediction equation for specific gravity,compactness had the greatest influence on the results,and roundness and compactness had the greatest influence on the regression prediction of settlement velocity.（3）Based on the experimental data from the operation of sludge granulation macro reactor and micromorphological analysis mentioned above,a comprehensive evaluation system of aerobic sludge granulation process was established with R1 as the experimental group and R2 as the verification group,taking multiple property parameters of sludge in the granulation process as evaluation indexes.The granulation process can be divided into flocs,initial granulation,rapid granulation and complete granulation.The weight coefficients of each evaluation index were calculated,and the roundness and length-diameter ratio had the greatest influence on the comprehensive evaluation results.The calculation results of the model were compared with the actual variation trend of each parameter in R2,and the evaluation model of the comprehensive evaluation system was reasonable.