Integrated removal of nitrate and carbon in an upflow anaerobic sludge blanket (UASB) reactor: Operating performance

H.V. Hendriksen, Birgitte Kiær Ahring

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    Abstract

    Denitrification and methanogenesis of a synthetic wastewater containing volatile fatty acids and nitrate were obtained in a single-stage process using an upflow anaerobic sludge blanket (UASB) reactor. The reactor was initially inoculated with methanogenic granular sludge and was gradually adapted to nitrate by increasing the nitrate concentration in the influent. Excess carbon not utilized for denitrification was converted to methane. During steady-state at a loading of 336 mg NO3-N/l/d (24 mmol NO3/l/d) and 6600 mg COD/l/d more than 99% removal of both nitrate and carbon was achieved. Batch experiments with biomass from the reactor showed that approximately 90% of the added nitrate was recovered as nitrogen gas indicating that true denitrification occurred. This was further verified from mass balances over the reactor. The granules changed appearance during the first 5 months of operation being fluffy and buoyant, probably reflecting changes in the microbial composition induced by the presence of nitrate. However, during the next two months more dense granules with good settling abilities gradually established in the system making this kind of combined process feasible in a UASB reactor. Characterization of the produced granules showed that while the mean diameter and density was comparable to granules from purely methanogenic systems, although the strength was lower.

    Denitrification and methanogenesis of a synthetic wastewater containing volatile fatty acids and nitrate were obtained in a single-stage process using an upflow anaerobic sludge blanket (UASB) reactor. The reactor was initially inoculated with methanogenic granular sludge and was gradually adapted to nitrate by increasing the nitrate concentration in the influent. Excess carbon not utilized for denitrification was converted to methane. During steady-state at a loading of 336 mg NO3-N/l/d (24 mmol NO3/l/d) and 6600 mg COD/l/d more than 99% removal of both nitrate and carbon was achieved. Batch experiments with biomass from the reactor showed that approximately 90% of the added nitrate was recovered as nitrogen gas indicating that true dentrification occurred. This was further verified from mass balances over the reactor. The granules changed appearance during the first 5 months of operation being fluffy and buoyant, probably reflecting changes in the microbial composition induced by the presence of nitrate. However, during the next two months more dense granules with good settling abilities gradually established in the system making this kind of combined process feasible in a UASB reactor. Characterization of the produced granules showed that while the mean diameter and density was comparable to granules from purely methanogenic systems, although the strength was lower.
    Original languageEnglish
    JournalWater Research
    Volume30
    Issue number6
    Pages (from-to)1451-1458
    ISSN0043-1354
    DOIs
    Publication statusPublished - 1996

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