title: Free nitrous acid (FNA)-based pretreatment enhances methane production from waste activated sludge.
abstract: Anaerobic digestion of waste activated sludge (WAS) is currently enjoying renewed interest due to the potential for methane production. However, methane production is often limited by the slow hydrolysis rate and/or poor methane potential of WAS. This study presents a novel pretreatment strategy based on free nitrous acid (FNA or HNO2) to enhance methane production from WAS. Pretreatment of WAS for 24 h at FNA concentrations up to 2.13 mg N/L substantially enhanced WAS solubilization, with the highest solubilization (0.16 mg chemical oxygen demand (COD)/mg volatile solids (VS), at 2.13 mg HNO2-N/L) being six times that without FNA pretreatment (0.025 mg COD/mg VS, at 0 mg HNO2-N/L). Biochemical methane potential tests demonstrated methane production increased with increased FNA concentration used in the pretreatment step. Model-based analysis indicated FNA pretreatment improved both hydrolysis rate and methane potential, with the highest improvement being approximately 50% (from 0.16 to 0.25 d(-1)) and 27% (from 201 to 255 L CH4/kg VS added), respectively, achieved at 1.78-2.13 mg HNO2-N/L. Further analysis indicated that increased hydrolysis rate and methane potential were related to an increase in rapidly biodegradable substrates, which increased with increased FNA dose, while the slowly biodegradable substrates remained relatively static.
authors.affiliation: Advanced Water Management Centre (AWMC), The University of Queensland , QLD 4072, Australia.
authors.forename: Qilin
authors.initials: Q
authors.lastname: Wang
authors.forename: Liu
authors.initials: L
authors.lastname: Ye
authors.forename: Guangming
authors.initials: G
authors.lastname: Jiang
authors.forename: Paul D
authors.initials: PD
authors.lastname: Jensen
authors.forename: Damien J
authors.initials: DJ
authors.lastname: Batstone
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Yuan
mesh_terms: D057919:Biological Oxygen Demand Analysis; D018533:Biomass; D003198:Computer Simulation; D016001:Confidence Intervals; D006868:Hydrolysis; D007700:Kinetics; D008697:Methane / Q000138:chemical synthesis*; D008962:Models, Theoretical; D009608:Nitrous Acid / Q000032:analysis*; D012722:Sewage / Q000737:chemistry*; D014866:Waste Products / Q000032:analysis*; D018508:Water Purification / Q000379:methods*
chemical_list: D012722:Sewage; D014866:Waste Products; D008697:Methane; D009608:Nitrous Acid