Investigation of the cocktail effect of sludge fractions in MBR fouling

Abstract

I dette speciale undersøges hvordan de forskellige komponenter i slam fra en membran- bioreaktor (MBR) påvirker hinanden under foulingprocessen der foregår under membran- filtrering. Dette gøres for at bekræfte hypotesen om at indholdet af ekstracellulære poly- meriske substanser (EPS) og kolloider reducerer fluxen gennem membranen, hvorimod flokke og pulveriseret aktivt kul (PAC) vil øge fluxen på grund af skuringseffekten. For at opnå en bekræftelse af dette er der foretaget MBR filtreringsexperimenter, med slam indeholdende forskellige koncentrationer af de tre slamfraktioner (EPS, kolloider og flokke), samt forsøg med slam og supernatant tilsat PAC. Fraktioneringen af slam er opnået ved centrifugering i 8min ved 3400g for at separere partiklerne, samt filtrering gennem en mixed cellulose ester membran for at separere colloiderne. Forsøgene udføres ved 1 times filtrering ved hvert af syv forskellige transmembrane tryk (TMP), med en times relaksationsfase mellem hver filtrering. Forsøgene er udført i en laboratorieskaleret MBR på Aalborg Universitet og MBR-slammet stammer fra Aalborg Vest renseanlæg samt Grundfos Biobooster-anlæg i Bjerringbro. Resultaterne af forsøgene bekræfter at EPS og kolloider reducerer fluxen gennem mem- branen, hvorimod forholdet C floc /(C colloid +C EPS ) forbedrer fluxen gennem membranen. Der var dog kun en begrænset positiv effekt af tilsætningen af PAC. Desuden kan det kon- kluderes at kagelaget der dannes på membranen er mere kompakt og kompressibelt ved øgede koncentrationer af EPS og kolloider, hvorimod et mindre kompakt og kompressibelt kagelag dannes ved et øget indhold af flokke.

In this thesis it is investigated how the di?erent components in sludge from a membrane bioreactor (MBR) affect each other during the fouling process that occurs during membrane filtration. This is done to confirm the hypothesis that the content of extracellular polymeric substances (EPS) and colloids reduces the flux through the membrane, whereas flocs and powdered activated carbon (PAC) increases the flux through the membrane because of the scouring effect. In order to obtain a confrmation of this, experiments have been performed by MBR filtration of sludge containing different concentrations of the three sludge fractions (EPS, colloids, and flocs), along with experiments with sludge and supernatant containing PAC. The fractionation of sludge is performed by centrifugation for 8min at 3400g in order to separate the flocs and filtration through a mixed cellulose membrane in order to separate the colloids. The experiments is performed by 1hour filtration at each of seven transmembrane pressures (TMPs), with 1hour relaxation phase between each ?ltration. The experiments is performed in a laboratory-scale MBR at Aalborg University and the MBR sludge is obtained from Aalborg vest wastewater treatment plant and Grundfos Biobooster facility in Bjerringbro. The results of the experiments confirm that EPS and colloids reduces the flux through the membrane, whereas the ratio C floc /(C colloid +C EPS ) increases the flux through the membrane. However, there was only a limited positive effect of the addition of PAC. Furthermore, it can be concluded that the cake layer that is formed on the membrane is more compact and compressible at increased concentrations of EPS and colloids, whereas a less compact and compressible cake layer is formed when the concentration of flocs is increased.

A master thesis from Aalborg University

Investigation of the cocktail effect of sludge fractions in MBR fouling

[Undersøgelse af cocktaileffekten i slamfraktionerne i MBR fouling]