title: The role of anaerobic sludge recycle in improving anaerobic digester performance.
abstract: Solids retention time (SRT) is a critical parameter for the performance of anaerobic digesters (AD) in wastewater treatment plants. AD SRT should increase when active biomass is input to the AD by recycling anaerobic sludge via the wastewater-treatment tanks, creating a hybrid aerobic/anaerobic system. When 85% of the flow through the AD was recycled in pilot-scale hybrid systems, the AD SRT increased by as much as 9-fold, compared to a parallel system without anaerobic-sludge recycle. Longer AD SRTs resulted in increased hydrolysis and methanogenesis in the AD: net solids yield decreased by 39-96% for overall and 23-94% in the AD alone, and AD methane yield increased 1.5- to 5.5-fold. Microbial community assays demonstrated higher, more consistent Archaea concentrations in all tanks in the wastewater-treatment system with anaerobic-sludge recycle. Thus, multiple lines of evidence support that AD-sludge recycle increased AD SRT, solids hydrolysis, and methane generation.
authors.affiliation: Swette Center for Environmental Biotechnology, The Biodesign Institute, Arizona State University, 1001 S McAllister Ave, PO Box 875701, Tempe, AZ 85287-5701, USA. aumny@asu.edu
authors.forename: Michelle N
authors.initials: MN
authors.lastname: Young
authors.forename: Rosa
authors.initials: R
authors.lastname: Krajmalnik-Brown
authors.forename: Wenjun
authors.initials: W
authors.lastname: Liu
authors.forename: Michael L
authors.initials: ML
authors.lastname: Doyle
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Rittmann
mesh_terms: D001421:Bacteria, Anaerobic / Q000502:physiology*; D019149:Bioreactors / Q000382:microbiology*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D010865:Pilot Projects; D012722:Sewage / Q000382:microbiology*
chemical_list: D012722:Sewage