Abstract
Dynamic membrane (DM) formation in dynamic membrane bioreactors plays an important role in achieving efficient solid-liquid separation. In order to study the contribution of extracellular polymeric substances (EPS) to DM formation in anaerobic dynamic membrane bioreactor (AnDMBR) processes, EPS extraction from and re-addition to bulk sludge were carried out in short-term filtration tests. DM formation behaviors could be well simulated by cake filtration model, and sludge with EPS re-addition showed the highest resistance coefficient, followed by sludge after EPS extraction. The DM layers exhibited a higher resistance and a lower porosity for the sludge sample after EPS extraction and for the sludge with EPS re-addition. Particle size of sludge flocs decreased after EPS extraction, and changed little with EPS re-addition, which was confirmed by interaction energy analysis. Further investigations by confocal laser scanning microscopy (CLSM) analysis and batch tests suggested that the removal of in-situ EPS stimulated release of soluble EPS, and re-added EPS were present as soluble EPS rather than bound EPS, which thus improved the formation of DM. The present work revealed the role of EPS in anaerobic DM formation, and could facilitate the operation of AnDMBR processes.
Highlights
Anaerobic treatment processes have been widely used for their unique ability to produce energy, generate good soil conditioners and destroy troublesome hazardous chemicals [1]
All the R2 values in the fitting results of cake filtration model were higher than 0.90, and regression analysis was significant at 0.05 level, demonstrating that all the dynamic membrane (DM) formation behaviors in our study can be simulated by cake filtration model on the mesh surface
Based on one-way analysis of variance (ANOVA), fouling resistances of AS0 and AS1 exhibited no notable differences at each trans-membrane pressure (TMP) (p = 0.832, 0.215 and 0.807 at 10, 20 and 30 kPa, respectively), indicating sludge after supernatant decantation had no obvious distinctions in DM formation
Summary
Anaerobic treatment processes have been widely used for their unique ability to produce energy, generate good soil conditioners and destroy troublesome hazardous chemicals [1]. With the aim for sustainable development in the future, anaerobic processes are expected to play a dominant role in wastewater treatment and sludge digestion. When anaerobic processes are combined with membrane technologies, solid-liquid separation efficiency will be improved. Dynamic membrane (DM) technology has been adopted as an alternative to traditional microfiltration/ultrafiltration (MF/UF) membranes in membrane bioreactor (MBR) processes as DM has several advantages such as lower membrane costs, lower fouling rate and higher filtration fluxes [2]. DMs, which are called as secondary membranes, can be formed.
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