What is AEROBIC GRANULATION? What does AEROBIC GRANULATION mean? AEROBIC GRANULATION meaning – AEROBIC GRANULATION definition – AEROBIC GRANULATION explanation.
Source: Wikipedia.org article, adapted under license.
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The biological treatment of wastewater in the sewage treatment plant is often accomplished using conventional activated sludge systems. These systems generally require large surface areas for treatment and biomass separation units due to the generally poor settling properties of the sludge. In recent years, new technologies have been developed to improve settlability. The use of aerobic granular sludge technology is one of them.
Proponents of aerobic granular sludge technology claim “it will play an important role as an innovative technology alternative to the present activated sludge process in industrial and municipal wastewater treatment in the near future” and that it “can be readily established and profitably used in activated sludge plants”. However in 2011 it was characterised as “not yet established as a large-scale application … with limited and unpublished full-scale applications for municipal wastewater treatment.”
The following definition differentiates an aerobic granule from a simple floc with relatively good settling properties and came out of discussions which took place at the “1st IWA-Workshop Aerobic Granular Sludge” in Munich (2004):
“Granules making up aerobic granular activated sludge are to be understood as aggregates of microbial origin, which do not coagulate under reduced hydrodynamic shear, and which settle significantly faster than activated sludge flocs”(de Kreuk et al. 2005)”
Granular sludge biomass is developed in sequencing batch reactors (SBR) and without carrier materials. These systems fulfil most of the requirements for their formation as:
Feast – Famine regime: short feeding periods must be selected to create feast and famine periods (Beun et al. 1999), characterized by the presence or absence of organic matter in the liquid media, respectively. With this feeding strategy the selection of the appropriate micro-organisms to form granules is achieved. When the substrate concentration in the bulk liquid is high, the granule-former organisms can store the organic matter in form of poly-ß-hydroxybutyrate to be consumed in the famine period, giving an advantage over filamentous organisms. When an anaerobic feeding is applied this factor is enhanced, minimising the importance of short settling time and higher hydrodynamic forces.
Short settling time: This hydraulic selection pressure on the microbial community allows the retention granular biomass inside the reactor while flocculent biomass is washed-out. (Qin et al. 2004)
Hydrodynamic shear force : Evidences show that the application of high shear forces favours the formation of aerobic granules and the physical granule integrity. It was found that aerobic granules could be formed only above a threshold shear force value in terms of superficial upflow air velocity above 1.2 cm/s in a column SBR, and more regular, rounder, and more compact aerobic granules were developed at high hydrodynamic shear forces (Tay et al., 2001 ).
Granular activated sludge is also developed in flow-through reactors using the Hybrid Activated Sludge (HYBACS®) process, comprising an attached-growth reactor with short retention time upstream of a suspended growth reactor. The attached bacteria in the first reactor, known as a SMART unit, are exposed to a constant high COD, triggering the expression of high concentrations of hydrolytic enzymes in the EPS layer around the bacteria (citation needed). The accelerated hydrolysis liberates soluble readily-degradable COD which promotes the formation of granular activated sludge….