Monitoring of the bacterial communities of aerobic granular sludge during a change of wastewater type

The impact of fermentable and hydrolyzable compounds on already formed AGS was assessed by changing the composition of the influent from simple wastewater containing volatile fatty acids to complex monomeric wastewater containing amino acids and glucose, and then to complex polymeric wastewater containing starch and peptone. The reversibility of the observed changes was assessed by changing the composition of the wastewater from complex monomeric back to simple. The introduction of fermentable compounds in the influent changed dramatically the bacterial community but left the settling properties and nutrient removal performance unchanged, whereas the introduction of polymeric compounds induced small changes in the bacterial community but altered the settling properties and denitrification efficiency. The changes induced by the wastewater transition were only partly reversed. Seven distinct stables states of the bacterial community were detected during the 921 days of experiment, four of them observed with the complex monomeric wastewater. The transitions between these states were not only causes by wastewater changes but also by operation failures and other incidences. However, the nutrient removal performance and settling properties of the AGS were globally maintained due to the functional redundancy of its bacterial community.