| The Anaerobic Self-forming dynamic membrane bioreactor(AnSFDMBR)combines anaerobic biological treatment technology with dynamic membrane technology.By utilizing anaerobic dynamic membranes that are naturally deposited and adhered to a large pore size support material(e.g.,nylon mesh and non-woven fabric)at the beginning of filtration,the same solid-liquid separation results can be achieved as with micro/ultrafiltration membranes.With the advantages of both anaerobic biological treatment technology and dynamic membrane technology,AnSFDMBR has received increasing attention in recent years.The Anaerobic Self-forming dynamic membrane(AnSFDM)is the core component of the AnSFDMBR.In the early stages of operation,the membrane formation time and the membrane formation properties(i.e.formation resistance,stability resistance and fouling propensity)of the AnSFDM play a crucial role in the overall reactor operation.Operating parameters(e.g.,MLSS,stirring speed and flux)are important factors influencing the formation of AnSFDM.Current optimization studies used traditional single-factor experiments with factors,one at a time,which were inefficient and optimal conditions can only be chosen among the set experimental sites,and did not allow the interaction between parameters to be assessed.Response Surface Methodology(RSM)is an effective method for multivariate optimization,fitting regression equations between factor variables and response values within a given range of factors,significantly reducing the number of experiments and time costs,finding the best parameters for an experiment accurately and efficiently,and investigating the interaction between multiple factors.RSM was currently used in a wide range of fields including the chemical industry,food science and biology,but its application in membrane science is relatively rare and has not been applied to the study of dynamic membrane bioreactors.Therefore,this paper investigates the effects of MLSS,stirring speed and flux on the formation of AnSFDM through the Box-Behnken design method(BBD)of response surface methodology.A response surface quadratic model coding the independent variables and response indicators(formation time,formation resistance,stability resistance and fouling propensity)was fitted and the ANOVA showed that the model was reasonable and reliable.The main conclusions are as follows:(1)The response surface plots,contour plots and interaction plots of the three operating parameters of MLSS,stirring speed and flux were compared and analyzed to investigate the effects of different operating parameters and interactions between operating parameters on the formation time,formation resistance,stability resistance and fouling propensity of AnSFDM respectively.The results show that the three operating parameters have a significant effect on formation time,formation resistance,stability resistance and fouling propensity over a range of parameter levels.The influence on formation time is in the order of flux>MLSS>stirring speed;the influence on formation resistance,stability resistance and fouling propensity are in the order of MLSS>stirring speed>flux.It is worth noting that there are interactions between the three operating parameters.The interaction between MLSS and stirring speed has a significant effect on fouling propensity;the interaction between MLSS and flux has a significant effect on formation time;the interaction between stirring speed and flux has a significant effect on formation time and formation resistance.(2)Different operating conditions have important effects on the formation and initial rapid contamination of AnSFDM during the formation and initial contamination phases by influencing the composition and sludge properties of mixed liquor and AnSFDM.The higher sludge concentration increases the number of substances that can be used to form AnSFDM in the reactor and shortens the formation time,but it also causes a large amount of sludge deposition and an increase in the proportion of small hydrophobic particles in the mixed liquor,making the formed AnSFDM more resistant.The presence of shear force makes the formation time longer with higher stirring speed,while too high or too low stirring speed will cause the increase of formation resistance,stability resistance and fouling propensity.The higher the flux,the shorter the formation time,which is related to the higher drag force to deposit more sludge onto the membrane module per unit time.In addition,the higher flux leads to smaller hydrophobic particles and EPS trap in the initial contamination phase causing greater stability resistance and fouling propensity.(3)The operating parameters for the formation of AnSFDM were optimized and examined.The optimal formation conditions were obtained by considering four response values of formation time,formation resistance,stability resistance and fouling propensity:MLSS of 3600 mg/L,stirring speed of 240 rpm and flux of 150 LMH.The formation time was 87.58 min,formation resistance was 1.72 × 109 m-1,stability resistance was 9.21 × 109 m-1 and contamination tendency was 1.41 × 108 m-1min-1 under the optimal conditions.The relative errors between the model predictions and the experimental averages were 2.95%,8.14%,6.73%and 6.38%for the formation time,formation resistance,stability resistance and fouling propensity,respectively,when the model predictions were tested under these film formation conditions. |
PDF Full Text Request