Anaerobic digestion of swine manure: Inhibition by ammonia

Kaare Hvid Hansen, Irini Angelidaki, Birgitte Kiær Ahring

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    A stable anaerobic degradation of swine manure with ammonia concentration of 6 g-N/litre was obtained in continuously stirred tank reactors with a hydraulic retention time of 15 days, at Four different temperatures. Methane yields of 188, 141, 67 and 22 ml-CH4/g-VS were obtained at 37, 45, 55 and 60 degrees C, respectively. The yields were significantly lower than the potential biogas yield of the swine manure used (300 ml-CH4/g-VS). A free ammonia concentration of 1.1 g-N/litre or more was found to cause inhibition in batch cultures at pH 8.0 (reactor pH), and higher free ammonia concentrations resulted in a decreased apparent specific growth rate. Batch experiments with various mixtures of swine and cattle manure showed that the biogas process was inhibited when the swine-to-cattle manure ratio was higher than 25:75, corresponding to a free ammonia concentration of approximately 1.1 g-N/litre. Inhibition of the biogas process and, thereby, a reduction of the methane yield followed a four-stage pattern: below a threshold of 1.1 g-N/litre free ammonia, the process was uninhibited; over this concentration, inhibition occurred, forming first a phase with an initial inhibition, then a plateau and then an inhibition stage where the apparent specific growth rate decreased with increasing concentrations of free ammonia. (C) 1998 Elsevier Science Ltd. All rights reserved.
    Original languageEnglish
    JournalWater Research
    Issue number1
    Pages (from-to)5-12
    Publication statusPublished - 1998


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