title: Aerobic/anoxic post-treatment of anaerobically digested sewage sludge as an alternative to biological nitrogen removal from reject water.
abstract: Stabilisation and biological nitrogen removal (BNR) of anaerobically digested sewage sludge were studied in a post-aeration reactor at pilot scale working under alternating anoxic-aerobic conditions. Digested sludge came from a two-stage anaerobic digestion (thermophilic + mesophilic). The best post-aerator performance was achieved when working at an HRT of 10 days (4 days aerobic; dissolved oxygen of 1.8 mg L(-1)) and VS content in the feed no lower than 6.7 g L(-1). Free ammonia concentration values in the effluent above 1.5 mg N L(-1) (around 150 mg NH4 (+)-N L(-1) at pH 7) were necessary to promote the BNR over nitrite. Removal efficiencies up to 80 % NH4 (+)-N, 50-55 % total nitrogen and 15-20 % VS were recorded in this study, with no external addition of chemicals. A nitrogen mass balance revealed that the high percent of NH4 (+)-N assimilated in heterotrophic growth was counteracted with that released in ammonification and fermentation, leading to a NH4 (+)-N removal mainly related to biological nitritation/denitritation.
authors.affiliation: Environmental Engineering Unit, CEIT and Tecnun (University of Navarra), Manuel de Lardizabal 15, 20018, San Sebastián, Spain, mmorras@ceit.es.
authors.forename: Mikel
authors.initials: M
authors.lastname: Morras
authors.forename: J
authors.initials: J
authors.lastname: Dosta
authors.forename: J L
authors.initials: JL
authors.lastname: García-Heras
mesh_terms: D000332:Aerobiosis; D000641:Ammonia / Q000737:chemistry; D064751:Ammonium Compounds / Q000737:chemistry; D000693:Anaerobiosis; D018533:Biomass; D019149:Bioreactors; D058440:Denitrification; D005285:Fermentation; D009573:Nitrites / Q000737:chemistry; D009584:Nitrogen / Q000032:analysis*; D010100:Oxygen / Q000737:chemistry*; D012722:Sewage / Q000737:chemistry*; D014865:Waste Disposal, Fluid; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification
chemical_list: D064751:Ammonium Compounds; D009573:Nitrites; D012722:Sewage; D014874:Water Pollutants, Chemical; D000641:Ammonia; D009584:Nitrogen; D010100:Oxygen