Improving anaerobic sewage sludge digestion by implementation of a hyper-thermophilic prehydrolysis step

Jingquan Lu, Hariklia N. Gavala, Ioannis V. Skiadas, Zuzana Mladenovska, Birgitte Kiær Ahring

    Research output: Contribution to journalJournal articlepeer-review


    The present study focuses on a two-step process for treatment and stabilisation of primary sludge. The process consists of a hyperthermophilic hydrolysis step operated at 70 degrees C and a hydraulic retention time (HRT) of 2 clays followed by a thermophilic (55 degrees C) anaerobic digestion step at a HRT of 13 days. A one-step anaerobic digester operated at 55 degrees C and 15 days HRT Was used as a reference process. The two-step process was characterized by a 12% higher organic suspended solids removal efficiency and better pathogen reduction effect than the conventional one-step digestion. The microbial community of the digester fed with pre-treated sludge was characterised by it higher activity compared to that of the digester treating raw sludge. Moreover, the pre-treatment of the primary sludge resulted up to 48% increase of the methane potential (20.09 and 13.56 mmol CH4 g(-)VS(-1) with and Without pre-treatment respectively) and up to 115% increase of the methane production rate. Finally it was shown that the extra energy requirements for the operation of a pre-treatment step would be covered by the energy Produced from the extra methane production and in addition there would be it significant energy Surplus of 2.17 kJ d(-1) For the system tested.
    Original languageEnglish
    JournalJournal of Environmental Management
    Issue number4
    Pages (from-to)881-889
    Publication statusPublished - 2008


    • thermal
    • two-step process
    • sludge
    • primary
    • anaerobic digestion
    • thermophilic
    • microbial activity
    • pre-treatment


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