title: Effect of specific gas loading rate on thermophilic (55 degrees C) acidifying (pH 6) and sulfate reducing granular sludge reactors.
abstract: The effect of the specific gas loading rate on the acidifying, sulfate reducing and sulfur removal capacity of thermophilic (55 degrees C; pH 6.0) granular sludge bed reactors treating partly acidified wastewater was investigated. A comparison was made between a regular UASB reactor and a UASB reactor continuously sparged with N(2) at a specific gas loading rate of 30 m(3)m(-2)d(-1). Both UASB reactors (upflow velocity 1.0 mh(-1), hydraulic retention time about 5h) were fed a synthetic wastewater containing starch, sucrose, lactate, propionate and acetate and a low sulfate concentration (COD/SO(4)(2-) ratio of 10) at volumetric organic loading rates (OLR) ranging from 4.0 to 49.8 gCODl(-1) reactord(-1). Immediately after imposing an OLR of 25 gCODl(-1) reactord(-1), the acidification and sulfate reduction efficiency dropped to 80% and 30%, respectively, in the UASB reactor. Both efficiencies recovered slowly to 100% during the course of the experiment. In the N(2) sparged reactor, both the acidification and sulfate reduction efficiency remained 100% following the OLR increase to 25 gCODl(-1) reactord(-1). However, the sulfate reduction efficiency gradually decreased to about 20% at the end of the experiment. The biogas (CO(2) and CH(4)) production rate in the UASB was very low, i.e. <3l biogasl(-1) reactorday(-1), resulting in negligible amounts (<20%) of H(2)S stripped from the reactor liquid. The total H(2)S concentration of the N(2) sparged UASB reactor effluent was always below 25 mgl(-1), but incomplete sulfate reduction kept the maximal H(2)S stripping efficiency below 70%.
authors.affiliation: Sub-department of Environmental Technology, Agricultural University of Wageningen, Biotechnion, Bomenweg, 2, P.O. Box 8129, 6700 EV Wageningen, The Netherlands. piet.lens@algemeen.wu2.nl
authors.forename: P N L
authors.initials: PN
authors.lastname: Lens
authors.forename: R
authors.initials: R
authors.lastname: Klijn
authors.forename: J B
authors.initials: JB
authors.lastname: van Lier
authors.forename: G
authors.initials: G
authors.lastname: Lettinga
mesh_terms: D000393:Air Pollutants / Q000032:analysis; D019149:Bioreactors; D005740:Gases; D006862:Hydrogen Sulfide / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D008697:Methane / Q000032:analysis; D013455:Sulfur / Q000302:isolation & purification* / Q000378:metabolism; D016999:Sulfur-Reducing Bacteria / Q000502:physiology*; D013696:Temperature; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D000393:Air Pollutants; D005740:Gases; D013455:Sulfur; D008697:Methane; D006862:Hydrogen Sulfide