Study On Model Extracelluar Polymeric Substances In Membrane Bio-reactors

In this paper, the preparation of hollow fiber membrane, the study of supernatantof sludge and the model extracellular polymeric substances (EPS) were studied. Theseresults will provide theoretical basis to further study on membrane fouling in MBRand choose of membrane filtration pollutants. This study has important theory valueand practicality value.Firstly, the hollow fiber membrane was prepared by phase inversion method withchemical reaction. The effect of casting solution content on membrane structure wasinvestigated. Results show that:(1) when solid content is16wt%with citric acid aschemical inducers, the optimal membranes which the pure water flux and BSArejection were higher were obtained;(2) the chemical reaction effect was differencefor different content of PVDF hollow fiber membrane, and the membrane with fingerpore distribution was better for18wt%PVDF content.Secondly, the activated sludge supernatant of MBR was filtrated in dead-endmode. The operating conditions and process conditions were quantitative analyzed bymultivariate linear regression method. Results show that:(1) Transmembrane pressureand pH had significant effects on membrane flux, while temperature has little effect.The relative influence sequence on flux was: transmembrane pressure (50.71%), pH(45.08%), and temperature (4.21%).(2) The sludge concentration, temperature,dissolved oxygen, sludge retention time and hydraulic retention time and pH on waterquality index were larger. The relative influence sequence on TOC was: the sludgeconcentration (49.36%), pH (32.52%), hydraulic retention time (9.87%), sludgeretention time (4.60%), dissolved oxygen (2.21%) and temperature (1.44%). Therelative influence sequence on NH3-N was: the sludge concentration (61.39%), pH(21.38%), hydraulic retention time (8.82%), sludge retention time (3.51%),temperature (4.11%) and dissolved oxygen (0.79%).(3) Extracellular polymericsubstances (EPS) are the major component causing membrane fouling.Finally, the deviations of filterability were investigated between the actual EPSand the model EPS. A series of binary and ternary model EPS solutions were prepared by using sodium alginate (SA), bovine serum albumin (BSA) and humic acid (HA)based on the composition of actual EPS. Using orthogonal method and multivariatelinear regression method, filterability (cumulative filtrate volume, specific cakeresistance and observed rejection) of the model EPS were studied. Results showedthat:(1) Comparing with the binary mixtures, the filterability of ternary mixtures wasmore similar to that of actual EPS solution.(2) Sodium alginate had a moresignificant impact on the flux of the membrane and its presence was a necessarycondition to model actual EPS solution.(3) The cake filtration mechanismpredominates in all filtration runs. When the mechanism curve of model solution wasclose to parallel with actual EPS solution, the deviation was smaller on the targetfactor.(4) A ternary mixture was found to model the filterability of actual EPSsolution, i.e. SA/BSA/HA=251.8/280.8/11.4mg L-1. The verification test showedthat its deviations were13%,2.5%and22%on CFV, αcand R respectively. So, itcould be used to model actual EPS.