text: The development of biomass in the form of aerobic granules is being studied for its application in the removal of  organic matter, nitrogen and phosphorus compounds from wastewater.
  Aerobic granules in an aerobic SBR present several advantages compared to conventional activated sludge process such as:
  : Stability and flexibility: the SBR system can be adapted to fluctuating conditions with the ability to withstand shock and toxic loadings
  : Low energy requirements: the aerobic granular sludge process has a higher aeration efficiency due to operation at increased height, while there are neither return sludge or nitrate recycle streams nor mixing and propulsion requirements
  : Reduced footprint: The increase in biomass concentration that is possible because of the high settling velocity of the aerobic sludge granules and the absence of a final settler result in a significant reduction in the required footprint.
  : Good biomass retention: higher biomass concentrations inside the reactor can be achieved, and higher substrate loading rates can be treated.
  : Presence of aerobic and anoxic zones inside the granules: to perform simultaneously different biological processes in the same system (Beun et al. 1999  )
  : Reduced investment and operational costs: the cost of running a wastewater treatment plant working with aerobic granular sludge can be reduced by at least 20% and space requirements can be reduced by as much as 75% (de Kreuk et al., 2004).
  The HYBACS process has the additional benefit of being a flow-through process, thus avoiding the complexities of SBR systems. It is also readily applied to the upgrading of existing flow-through activated sludge processes, by installing the attached growth reactors upstream of the aeration tank. Upgrading to granular activated sludge process enables the capacity of an existing wastewater treatment plant to be doubled.