TY - JOUR
T1 - Structural extracellular polymeric substances determine the difference in digestibility between waste activated sludge and aerobic granules
AU - Guo, Hongxiao
AU - Felz, Simon
AU - Lin, Yuemei
AU - van Lier, Jules B.
AU - de Kreuk, Merle
PY - 2020
Y1 - 2020
N2 - Aerobic granular sludge (AGS) technology is an alternative to conventional activated sludge to reduce the process footprint and energy consumption. Strategies for the efficient management of its produced biomass, that is grown in a granular morphology as well, need further development. Anaerobic digestion (AD) is commonly applied in waste activated sludge (WAS) treatment and is a potential option also for produced AGS treatment. In earlier studies, the biochemical methane potential of AGS was found lower than that of WAS both grown in full-scale municipal wastewater treatment systems. In order to understand this difference, this study aimed to investigate the anaerobic conversion of structural extracellular polymeric substances (SEPS), which is a type of gel-forming biopolymer, being responsible for the aggregation of sludge. Using WAS and AGS as substrates, a comparative AD batch experiment was performed for 44 days during which the SEPS fraction was extracted from both types of sludge. The changes in the SEPS chemical composition was analysed by Fourier transformed infrared spectroscopy and three-dimensional excitation and emission matrix analysis. In addition, the mechanical strength of hydrogels of extracted polymers cross-linked with Ca2+ ions was investigated by dynamic mechanical analysis. Results showed that the amount of SEPS was reduced by 26% in AGS (SEPSAGS) and by 41% in WAS (SEPSWAS), respectively. Polysaccharides and, to a lesser extent, the proteins in the SEPSAGS were more refractory compared to those in SEPSWAS. This resulted in a lower loss of the gel stiffness of SEPSAGS than that of SEPSWAS during the AD process. Moreover, the release of SEPS from tightly bound EPS to loosely bound EPS were observed in both types of sludge, but that in AGS exhibited a lower transition rate. The observed properties explain the distinct differences in anaerobic biodegradability, the slower decomposition of the sludge structure, as well as the better dewaterability of AGS as compared to WAS after the AD process.
AB - Aerobic granular sludge (AGS) technology is an alternative to conventional activated sludge to reduce the process footprint and energy consumption. Strategies for the efficient management of its produced biomass, that is grown in a granular morphology as well, need further development. Anaerobic digestion (AD) is commonly applied in waste activated sludge (WAS) treatment and is a potential option also for produced AGS treatment. In earlier studies, the biochemical methane potential of AGS was found lower than that of WAS both grown in full-scale municipal wastewater treatment systems. In order to understand this difference, this study aimed to investigate the anaerobic conversion of structural extracellular polymeric substances (SEPS), which is a type of gel-forming biopolymer, being responsible for the aggregation of sludge. Using WAS and AGS as substrates, a comparative AD batch experiment was performed for 44 days during which the SEPS fraction was extracted from both types of sludge. The changes in the SEPS chemical composition was analysed by Fourier transformed infrared spectroscopy and three-dimensional excitation and emission matrix analysis. In addition, the mechanical strength of hydrogels of extracted polymers cross-linked with Ca2+ ions was investigated by dynamic mechanical analysis. Results showed that the amount of SEPS was reduced by 26% in AGS (SEPSAGS) and by 41% in WAS (SEPSWAS), respectively. Polysaccharides and, to a lesser extent, the proteins in the SEPSAGS were more refractory compared to those in SEPSWAS. This resulted in a lower loss of the gel stiffness of SEPSAGS than that of SEPSWAS during the AD process. Moreover, the release of SEPS from tightly bound EPS to loosely bound EPS were observed in both types of sludge, but that in AGS exhibited a lower transition rate. The observed properties explain the distinct differences in anaerobic biodegradability, the slower decomposition of the sludge structure, as well as the better dewaterability of AGS as compared to WAS after the AD process.
KW - Anaerobic digestion
KW - Full-scale Nereda® municipal wastewater treatment system
KW - Gel-forming property
KW - Structural extracellular polymeric substances
KW - Waste aerobic granular sludge
UR - http://www.scopus.com/inward/record.url?scp=85085567020&partnerID=8YFLogxK
U2 - 10.1016/j.watres.2020.115924
DO - 10.1016/j.watres.2020.115924
M3 - Article
SN - 0043-1354
VL - 181
JO - Water Research
JF - Water Research
M1 - 115924
ER -
