Simultaneous denitrification and anaerobic digestion in granular bed baffled reactor (GRABBR)

M. I. Baloch, Joseph C. Akunna

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    3 Citations (Scopus)


    This study elucidates the characteristics of compartmentalised anaerobic system seeded with UASB granules, called GRAanular Bed Baffled Reactor (GRABBR), for combined denitrification and anaerobic digestion processes. The reactor was used for the treatment of glucose enriched synthetic wastewater with various nitrate concentrations. The study was carried out with a 10 litre working volume GRABBR divided into 5 equal compartments operating at organic loading rate (OLR) of 20 kg COD/m3.d with a hydraulic retention time (HRT) of 6 hours. At these conditions, phase separation (between acidogenesis and methanogenesis) was created in the system and then the effect of varying nitrate concentrations (50-200 mg/l NO3-N) in the acidogenic zone (i.e. first compartment) was studied. Due to its unique compartmentalised design, denitrification was the major pathway for nitrate reduction with no noticeable dissimilatory nitrate reduction to ammonia (DNRA). More than 84% of all added nitrates were removed in the acidogenic zone, showing that acidogens possess high denitrifying capabilities. The denitrification rate increased with increase in nitrate concentration, with maximum value estimated as 175 mg NO3-N/l.h at influent nitrate concentration of 200 mg/l NO3-N in the acidogenic zone. Although nitrate addition resulted in lower methane production, COD removal efficiencies improved by up to 8% when compared with the reactor performance before nitrate addition. Furthermore, the alkalinity produced during denitrification improved the stability of the system by controlling the decrease in pH resulting from acidogenesis. The system encouraged simultaneous denitrification and anaerobic digestion in a single unit by accommodating denitrifiers in the early compartments and allowing methanogenesis to flourish in the downstream compartments of the system, thus minimising inhibition to methane producing bacteria by nitrates.
    Original languageEnglish
    Title of host publication2002 Joint CSCE/EWRI of ASCE International Conference on Environmental Engineering
    Subtitle of host publicationan international perspective on environmental engineering
    EditorsWarren Stiver, Richard Gustav Zytner
    Place of PublicationGuelph
    PublisherSchool of Engineering, University of Guelph
    ISBN (Print)088955532X, 9780889555327
    Publication statusPublished - 2002
    EventJoint CSCE/ASCE International Conference on Environmental Engineering: An International Perspective on Environmental Engineering - Niagara Falls, Ontario, Canada
    Duration: 21 Jul 200224 Jul 2002


    ConferenceJoint CSCE/ASCE International Conference on Environmental Engineering


    • Anaerobic digestion
    • COD removal
    • Denitrification
    • Granular bed baffled reactor
    • Nitrate removal


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