Factors Influencing the Production of Methane during the Anaerobic Digestion of Poultry Wastes

  • Andrew Webb

    Student thesis: Doctoral Thesis


    The semi-continuous digestion of poultry litter and manure was carried out in 51 digesters at 35°C to determine the potential of each waste for methane production, and to investigate the relationships between gas yield (GY) and loading rate (LR). GY's obtained were 0.327 m3 kg VS added-1 for litter and 0.397 m kg VS added-1 for manure. During the digestion of litter, GY increased both with increasing retention time (RT) and influent concentration. For manure GY increased with influent concentration up to 2.6 - 4.1% VS after which further increases caused reductions in GY due to ammonia inhibition which reached 4274 mgl of NH4 + - N.

    The effects of raised concentrations of NH4 + - N on manure batch digesters seeded with sludge adapted to different levels of NH4 - N was investigated by shock loading NH4C1 or NH4 HCO3. High adapted seed was more tolerant of NH4C1 than low adapted seed whereas the opposite was true for NH4 HCO3 which at low levels had a stimulatory effect on low adapted seed.

    Long term effects of raised NH4 + -N concentrations were examined by adding NH4Cl to semi-continuously fed manure digesters. Increasing NH4 concentrations to 3062 mgl-1 and 4324 mgl-1 reduced GY's to 88% and 73°^ of control levels respectively. After periods of up to 22 weeks exposure to these concentrations GY's failed to regain untreated values indicating that complete adaptation had not occurred.

    The potential for digestion of poultry wastes at high solids concentrations (up to 27% TS) was tested in a packed bed type digester. Successful hydrolysis and acidogenesis occurred but methanogenesis was inhibited by NH4 + - N concentrations of up to 13,314 mgl -1. Replacing the liquor allowed intiation of Methane production during the digestion of manure but not litter.

    A study of Monod growth kinetics revealed that the increase in GY obtained with increasing influent concentration was due to the dependence of digester effluent concentration on RT but not influent concentration. Models were developed to describe the uninhibited digestion of litter and the inhibited digestion of manure.
    Date of AwardJan 1984
    Original languageEnglish
    Awarding Institution
    • Polytechnic of Wales

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