Roles of various mixed liquor constituents in membrane filtration of activated sludge

Abstract

The roles of various mixed liquor constituents in the membrane filtration of activated sludge were investigated. Bench-scale filtration tests with four mixed liquor fractions (whole mixed liquor, mixed liquor supernatant, filtrate I (<8.0 μm), and filtrate II (<0.45 μm) or the soluble fraction) were carried out at different permeate fluxes. It was found that due to its high contents of organic carbon compounds, macromolecules and small supra-dissolved particles, which were most likely to adsorb onto and/or clog in the membrane structure, the soluble fraction (<0.45 μm) of mixed liquor ranked first in terms of its contribution to the total mixed liquor fouling, followed by the colloidal fraction (0.45-8.0 μm) and the unsettleable microfloc fraction (>8.0 μm). In particular, the study revealed that large flocs were able to exert dual effects on membrane filtration. Depending on the hydrodynamic conditions, they could either act as membrane foulants causing fouling via particle deposition and cake formation, or serve as "moving filters" entrapping soluble and colloidal substances and thus alleviating the fouling. A "steric hindrance effect" mechanism was postulated to explain the positive effect of large sludge flocs on membrane filtration.

Production and Characterization of Foam in the Anoxic Zone of a Membrane‐Enhanced Biological Phosphorus Removal Process

“…The difference in foam accumulation in the CEBPR and the MEBPR was thought to be the result of the absence of a mechanism to transport floating material out of the MEBPR process, leading to an accumulation of floating material in the bioreactor. In addition, the use of vigorous coarse-bubble aeration in the MEBPR system resulted in a biomass with a smaller floc size distribution (Geng et al, 2009), which might be more easily separated by gas flotation in the anoxic zone. It also remains unclear whether the intermittent aeration used in the MEBPR contributed to mixedliquor backflow from the aerobic zone to the anoxic zone, possibly enhancing foam formation.…”

Effect of Worm Predation on Changes in Waste Activated Sludge Properties

“…The supernatant of the mixed liquor sample thereby represented the sum of SMP, colloids and unsettled microfloc fraction concentrations. Meanwhile, the filtration of the supernatant through a cellulose-acetate paper with a 0.45lm pore-size filter corresponded to SMP concentration (Geng et al, 2009). The remaining pellet was washed and re-suspended with saline water (0.9% NaCl solution).…”