Abstract
Fouling is a major challenge for the economic feasibility and applicability of membrane bioreactors. Several strategies have been proposed for fouling control, and among them, addition of flux enhancers (FE) have shown promising results. Previous research revealed a high variability of the required optimal dosage of FE for different types of sludge; however, studies analysing the causes for such variability are lacking. Therefore, this research examines the effect of sludge characteristics on the optimal FE dosage required for sludge filterability improvement (Dopt). We applied the cationic polymer Adifloc KD451 as FE, and determined Dopt with short-term cross-flow filtration tests. Sludge samples were obtained from five different pilot and full-scale anaerobic membrane bioreactors (AnMBRs) treating municipal or industrial wastewater. Results showed that Dopt was significantly correlated with colloidal organic matter concentration, sludge filterability, capillary suction time, and concentration of soluble polysaccharides. Furthermore, we derived empirical models to predict Dopt based on the significantly correlated sludge characteristics as input variables. This research identifies the factors affecting the required dosage of FE for different sludges and provides guidelines for safe continuous dosing of FE in AnMBR for fouling control.
Highlights
Anaerobic membrane bioreactor (AnMBR) technology is increasingly researched for wastewater treatment in a circular economy solution to recover nutrients and to produce reclaimed water and biogas
The time lapses between collection and testing for LiqOFMSW, Food2, Food2-II, Food3 and Food3-II were sufficiently long to assume that sludge characteristics might have changed due to physicochemical and biochemical processes taking place during transportation and stor age, such as degradation of substrates
LiqOFMSW was noticeably different from other sludges, that is: it had considerably higher ΔR20(1.5,60), capillary suction time (CST), colloidal COD (cCOD), soluble COD (sCOD), NH4–N, con ductivity, Soluble microbial products (SMP)-HS and SMP were characterised as polysaccharides (SMP-PS)
Summary
Anaerobic membrane bioreactor (AnMBR) technology is increasingly researched for wastewater treatment in a circular economy solution to recover nutrients and to produce reclaimed water and biogas. Never theless, membrane fouling is recognised as the major challenge limiting the economic feasibility and applicability of AnMBRs. Researchers extensively studied the causes and mitigation of membrane fouling in both aerobic and anaerobic membrane bioreactors [1,2,3,4]. Optimisation of operational variables is suitable when the sludge has good or moderate filtration quality, it may not be adequate or sufficient when fouling is caused by a sludge with poor filterability [5]. Mostly applied high shear stress near the membrane surface to mitigate fouling [6]. High shear stress promotes the production of extracellular polymeric sub stances, floc breakage and detachment of soluble and colloidal material [1]. Reports have shown that soluble and colloidal organic matter plays an important role in fouling due to the promotion of gel and cake layer formation, pore-blocking and adsorption into the membrane pores [1,7, 8]
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