title: Stable thermophilic anaerobic digestion of dissolved air flotation (DAF) sludge by co-digestion with swine manure.
abstract: Environmentally sound treatment of by-products in a value-adding process is an ongoing challenge in animal agriculture. The sludge produced as a result of the dissolved air flotation (DAF) wastewater treatment process in swine processing facilities is one such low-value residue. The objective of this study was to determine the fundamental performance parameters for thermophilic anaerobic digestion of DAF sludge. Testing in a semi-continuous stirred tank reactor and in batch reactors was conducted to determine the kinetics of degradation and biogas yield. Stable operation could not be achieved using pure DAF sludge as a substrate, possibly due to inhibition by long-chain fatty acids or to nutrient deficiencies. However, in a 1:1 ratio (w/w, dry basis) with swine manure, operation was both stable and productive. In the semi-continuous stirred reactor at 54.5 degrees Celsius, a hydraulic residence time of 10 days, and an organic loading rate of 4.68 gVS/day/L, the methane production rate was 2.19 L/L/day and the specific methane production rate was 0.47 L/gVS (fed). Maximum specific methanogenic activity (SMA) in batch testing was 0.15 mmoles CH(4) h(-1) gVS(-1) at a substrate concentration of 6.9 gVS L(-1). Higher substrate concentrations cause an initial lag in methane production, possibly due to long-chain fatty acid or nitrogen inhibition.
authors.affiliation: Novozymes North America, 77 Perrys Chapel Church Road, Franklinton, NC 27525, USA. kurt_creamer@ncsu.edu
authors.forename: K S
authors.initials: KS
authors.lastname: Creamer
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.forename: C M
authors.initials: CM
authors.lastname: Williams
authors.forename: J J
authors.initials: JJ
authors.lastname: Cheng
mesh_terms: D000388:Air; D000693:Anaerobiosis; D000818:Animals; D001673:Biodegradation, Environmental; D019149:Bioreactors / Q000382:microbiology; D052918:Environmental Restoration and Remediation / Q000379:methods*; D008372:Manure / Q000032:analysis*; D008697:Methane / Q000032:analysis; D012722:Sewage / Q000382:microbiology*; D012995:Solubility; D013552:Swine; D013696:Temperature
chemical_list: D008372:Manure; D012722:Sewage; D008697:Methane