Fouling with aerobic granule membrane bioreactor.

Aerobic granulation (AG) and membrane bioreactor (MBR) are two promising, novel environmental biotechnological processes that draw interest of researchers working in the area of biological wastewater treatment. Membrane fouling in the combined aerobic granular membrane bioreactor (AGMBR) process and the conventional MBR process was investigated in this work. The irreversible fouling on hollow-fibre membranes in both reactors were observed with the multiple staining and confocal laser scanning microscope technique. Following physical and chemical washing, the external fouling layers were mostly removed. However, the biofilms built up in the interior surface of membrane remained and contributed to the irreversible fouling resistance. AGMBR retained most cells with granules, thereby reducing their penetration through membrane and thus the chance to form internal fouling layer. The internal biofilm layer was principally composed of live cells embedded in a matrix of proteins and polysaccharides, with that on AGMBR denser and thicker than that on MBR. Prevention of development of internal biofilm is essential to reduce irreversible fouling of AGMBR and MBR membranes.

Harvesting of Scenedesmus obliquus FSP-3 using dispersed ozone flotation.

The Scenedesmus obliquus FSP-3, a species with excellent potential for CO(2) capture and lipid production, was harvested using dispersed ozone flotation. While air aeration does not, ozone produces effective solid-liquid separation through flotation. Ozone dose applied for sufficient algal flotation is similar to those used in practical drinking waterworks. The algae removal rate, surface charge, and hydrophobicity of algal cells, and fluorescence characteristics and proteins and polysaccharides contents of algogenic organic matter (AOM) were determined during ozonation. Proteins released from tightly bound AOM are essential to modifying the hydrophobicity of bubble surfaces for easy cell attachment and to forming a top froth layer for collecting floating cells. Humic substances in the suspension scavenge dosed ozone that adversely affects ozone flotation efficiency of algal cells.

Dispersed ozone flotation of Chlorella vulgaris.

Flotation separation of Chlorella vulgaris, a species with excellent potential for CO(2) capture and lipid production, was studied using dispersed ozone gas. Pure oxygen aeration did not yield flotation. Conversely, applying ozone effectively separation algae from broth through flotation. The ozone dose applied for sufficient algal flotation is <0.05 mg/g biomass, much lower than those used in practical drinking waterworks (0.1-0.3 mg/g suspended solids). Main products, lipid C16:0, was effectively collected in the flotage phase. The algae removal rate, surface charge, and hydrophobicity of algal cells, and proteins and polysaccharides contents of algogenic organic matter (AOM) were determined. Certain quantities of proteins were present in the cultivated algal suspension, hence, minimal quantity of ozone was required to release intracellular proteins as surfactants to lead to effective flotation.

Stable aerobic granules for continuous-flow reactors: Precipitating calcium and iron salts in granular interiors.

Aerobic sludge granules are compact, strong microbial aggregates that have excellent settling ability and capability to efficiently treat high-strength and toxic wastewaters. The aerobic granules cultivated with low ammonium and phosphates lost structural stability within 3 days in continuous-flow reactors. Conversely, stable aerobic granules were cultivated in substrate with high levels of ammonium salts that could stably exist for 216 days in continuous-flow reactors with or without submerged membrane. The scanning electron microscopy, energy dispersive spectroscopy microanalysis and the confocal laser scanning microscopy imaging detected large amounts of calcium and iron precipitates in granule interiors. The Visual MINTEQ version 2.61 calculation showed that the phosphates and hydroxides were the main species in the precipitate.

Strains of internal biofilm in aerobic granular membrane bioreactors.

This study isolated strains in suspended liquor, the surface fouling layer, and biofilm inside hollow-fiber membranes of a membrane bioreactor (MBR); analyzed their distributions, sizes, surface charges, and growth behaviors; and determined the quantities of extracellular polymeric substances (EPS) secreted by these strains under different organic loadings. Three strains, which may penetrate the microfiltration membranes, were close relatives of the Ralstonia mannitolilytica strain SDV (GenBank Accession No. GU451066), Arthrobacter sp. BJQ-2 (GenBank Accession No. GU451067), and Actinobacterium DS3 (GenBank Accession No. GU451068). Among these three strains, only Arthrobacter sp. developed an internal biofilm. The relatively short length of Arthrobacter sp. minimizes resistance to cells moving through the membrane matrix, thereby enhancing its ability to build a biofilm in the interior surface of membranes.

Influence of internal biofilm growth on residual permeability loss in aerobic granular membrane bioreactors.

Membrane fouling results in flux decline or transmembrane pressure drop increase during membrane bioreactor (MBR) operation. Physical and chemical cleanings are essential to keep an MBR operating at an appropriate membrane flux. Considerable residual membrane permeability loss that cannot be removed by conventional cleaning requires membrane replacement. This study demonstrates that an internal biofilm can develop inside a hollow-fiber membrane and can probably account for up to 58.9 and 81.3% of total membrane resistance for aerobic granular MBR operated in sequencing batch reactor (SBR) mode or continuous-fed mode, respectively. The Arthrobacter sp. (accession no. AM900505 in GenBank) corresponded to internal biofilm development by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis and the agar-plating technique. This study also identifies a single strain, Arthrobacter sp., generates the internal biofilm. The Arthrobacter sp. is a rod-shaped bacterium with a size close to that of membrane pores, and can secrete excess bound proteins, hence can penetrate and attach itself inside the membrane and grow. Internal biofilm growth could contribute significantly to membrane resistance during long-term MBR operation.

Biodiversity in aerobic granule membrane bioreactor at high organic loading rates.

The aerobic granular sludge process and the membrane bioreactor process are promising, novel environmental bioprocesses for the reclamation of industrial and municipal wastewaters. They are practical and have attracted much research interest. The combination of these two processes in the aerobic granular membrane bioreactor (AGMBR), yields reclaimed water of high quality in a compact reactor. Information on the microbial community in an AGMBR operated at a high organic loading rate is lacking. This study elucidates the microbial dynamics in acetate-fed AGMBR operated in sequencing batch reactor mode. The structure of the microbial community revealed by denaturing gradient gel electrophoresis, demonstrates the dominance of the denitrifying microbial community, which is affiliated with members of the families Comamonadaceae and Alcaligenaceae, of the class Betaproteobacteria. The role of the predominant strains in the AGMBR is discussed.

Enhanced aerobic granulation with extracellular polymeric substances (EPS)-free pellets.

Extracellular polymeric substances (EPSs) were secreted by cells after they agglomerated into a compact aggregate. This study shows that the EPS initially embedded in seed sludge before granulation may sterically slow subsequent microbe-microbe contact, thereby delaying aerobic granulation. Three identical bioreactors were used in this study using glucose as the sole carbon and energy source. Reactor 1 (R1) was seeded with EPS-free pellets and operated in sequencing batch reactor (SBR) mode. Reactor 2 (R2) was seeded with the original sludge flocs and operated in SBR mode. Reactor 3 (R3) was seeded with EPS-free pellets and operated in continuously stirred tank reactor (CSTR) mode. Granulation occurred in R1 earlier than in R2; the granules that formed in R1 were larger and more compact than those in R2 at the same cultivation time. The few mature granules in R3 suggest that aerobic granulation can occur in a CSTR when a reactor is seeded with EPS-free pellets.