Variables Affecting Gas Production in Mesophilic Anaerobic Digestion

  • D. L. Hawkes

    Student thesis: Doctoral Thesis


    This dissertation presents the results of investigations into the factors which influence the net gas production in mesophilic anaerobic digesters. The major variables were examined during a six year period using equipment specially designed for the purpose. Continuous operation of these pilot plants over many months produced results which shoved a relationship "between gas yield and loading rate such that a lower loading rate produced a higher gas yield. A computer model demonstrated that the most significant parameters affecting net energy production were gas yield and the feed solids concentration.

    Further work involving the analysis of previously published results confirmed that there was a relationship between gas yield and loading rate and this was shown to be more complex than originally thought. The relationship postulated between gas yield, retention time and feed solids concentration is expressed as the LYES diagram. To obtain the maximum gas yield a digester needs to be operated with the highest solids feed but with the longest retention time possible to maintain a low loading rate. An increased retention time gives a larger and hence more costly digester. It is thus an optimisation exercise to find the best operating conditions to give either the maximum gas production possible or the minimum cost of the net energy produced which ever is required. The computer model developed can be used for this.

    It is suggested that anaerobic digestion has a potentially significant part to play as one of the alternative processes for utilising energy in the form of renewable photosynthetically produced biomass.
    Date of AwardFeb 1980
    Original languageEnglish
    Awarding Institution
    • Polytechnic of Wales

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