Effects of initiating anaerobic digestion of layer-hen poultry dung at sub-atmospheric pressure

Abstract

This study investigated the effects of initiating anaerobic digestion (AD) of dry layer-hen poultry dung at the sub-atmospheric pressure of -30 cmHg on biodegradation, biogasification, and biomethanation. The setup was performed as a batch process at an average ambient temperature of 29±2 0 C and a retention time of 15 days. Comparisons were made with two other experiments which were both begun at ambient atmospheric pressure; one was inoculated with digestate from a previous layer-hen dung AD, while the other was not inoculated. The bioreactors initiated at sub-atmospheric pressure, ambient atmospheric pressure without inoculum, and ambient atmospheric pressure with inoculum showed the following for biogas and biomethane yields respectively: 16. 6 cfu mL -1 for volatile solids and total viable count respectively. There was a slight difference in the volatile solids of the digestates of the three bioreactors after AD. The pH recorded for the feedstock slurry before AD was 7.9 at 30 o C, while after AD, the digestates from all the three bioreactors showed the same pH of 5.9 at 29 0 C. Statistical analysis using ANOVA showed no significant difference in biogas yields of the feedstock for the three bioreactors (A, B, C). ANOVA showed no significant difference for biomethane yields in the bioreactors initiated at sub-atmospheric pressure and for those initiated at ambient atmospheric pressure with inoculums. However, it showed significant difference in the bioreactor initiated at sub-atmospheric pressure and that initiated at ambient atmospheric pressure without inoculums, and significant difference in the two sets of bioreactors initiated at ambient atmospheric pressure (with and without inoculum). Initiating AD at reduced atmospheric pressure (-30 cmHg) and the addition of inoculum at ambient atmospheric pressure both increased biomethanation, by 20.31% and 15.80% respectively. The AD initiated at sub-atmospheric pressure yielded the least amount of carbon dioxide (a greenhouse gas), and improved biodegradation and biomethanation. The results also suggest that biomethane production is dependent on specific methanogenic growth. Analyzing the populations of methanogens isolated from the different bioreactors in relation to their biomethane yields suggests that Methanosarcina barkeri may have been largely responsible for the differences in biomethane yields. Efeitos do início da digestão anaeróbica da camada de esterco de aves à pressão sub-atmosférica RESUMOOs efeitos do início da digestão anaeróbica (DA) da camada de estrume seco de galinha à pressão sub-atmosférica de -30 cmHg na biodegradação, biogaseificação, e biometanização foram investigados. Foi realizado um processo em lote a uma temperatura ambiente média de 29 ± 2 0 C e um tempo de retenção de 15 dias. As comparações foram feitas com duas outras experiências; ambas foram iniciadas à pressão atmosférica ambiente, enquanto que uma foi previamente inoculada com digestores de uma camada de estrume de galinha AD, a outra sem inoculação. Os biorreatore...