Microbial Population Dynamics during Anaerobic Digestion of Guinea Grass (Panicum maximum)

Ogbonna C. B.^1, , Ibiene A. A.¹ and Stanley H. O.¹

¹Department of Microbiology, Faculty of Biological Science, College of Natural and Applied Sciences, University of Port Harcourt, P.M.B. 5323 Port Harcourt, Nigeria

Cite this paper:
Ogbonna C. B., Ibiene A. A. and Stanley H. O.. Microbial Population Dynamics during Anaerobic Digestion of Guinea Grass (Panicum maximum). Journal of Applied & Environmental Microbiology. 2014; 2(6):294-302. doi: 10.12691/jaem-2-6-5

Abstract

The effect of rumen fluid on microbial population dynamics during anaerobic digestion of Guinea grass (Panicum maximum) at ambient condition with respect to time was investigated. A one stage batch-typemesophilic anaerobic digestion system was configured using rumen fluid (RF) as inoculums (AD_RF) and a low solid loading of approximately 7.0% total solid (TS). Physicochemical parameters such as process temperature (PTM_RF), process pH_RF, chemical oxygen demand (COD_RF) and volatile fatty acid (VFA_RF) were monitored with time. Selected indicator microbial populations were monitored by standard cultural enumerations based on metabolic capacity and oxygen sensitivity with respect to time. Furthermore, their respective growth rates and population proportions were determined. Result showed that the average PTM_RF increased from 27.5°C to 35.2°C while average process pH_RF ranged from 6.5 to 7.9 with time, respectively. The COD_RF decreased from 11,250.60 mg/L to 2,865.20 mg/L, while VFA_RF ranged from 1,080.00 mg/L to 4,800.33 mg/L with time, respectively. In terms of metabolic capacity, the populations of cellulolytic bacteria (ACB_RF), lactose fermenting bacteria (LFB_RF) and glucose fermenting bacteria (GFB_RF) ranged from 3.6 x 10⁴ MPN/ml to 2.9 x 10⁵ MPN/ml, 3.4 x 10⁴ MPN/ml to 2.9 x 10⁵ MPN/ml and 4.4 x 10⁴ MPN/ml to 4.6 x 10⁵ MPN/ml respectively with time. The populations of propionate oxidizing bacteria (POB_RF), ethanol oxidizing bacteria (EOB_RF) and acetate oxidizing methanogens (AOM_RF) ranged from 2.9 x 10⁴ MPN/ml to 2.4 x 10⁵ MPN/ml, 2.7 x 10⁴ MPN/ml to 2.1 x 10⁵ MPN/ml and 1.4 x 10⁴ MPN/ml to 2.1 x 10⁵ MPN/ml respectively with time. In terms of O₂-sensitivity, the populations of obligate anaerobic bacteria (OAB_RF) and facultative aerobic and anaerobic bacteria (FAAB_RF) ranged from 2.12 x 10⁵ CFU/ml to 4.53 x 10⁶ CFU/ml and 4.6 x 10⁵ CFU/ml to 4.74 x 10⁶ CFU/ml respectively with time. The population of GFB_RF had the highest growth rate of 0.057 day^-1 while the population of EOB_RF had the lowest growth rate of 0.021 day^-1. In terms of O₂-sensitivity, the population of FAAB_RF had the highest growth rate of 0.051 day^-1 compared to the population of OAB_RF with growth rate of 0.040 day^-1. The population of GFB_RF predominated (26.3%), while the population of AOM_RF were the minority (10.44%). In terms of O₂-sensitivity, the population of FAAB_RF predominated (56.73%) compared to the population of OAB_RF (43.23%). Rumen fluid significantly (p < 0.05) increased the microbial populations inside AD_RF with respect to time. Therefore, rumen fluid could be used to boost the microbial population in anaerobic digesters as this could enhance depolymerisation, obtain higher degradation rates of cellulosic (or lignocellulosic) substrates and thus higher energy (biogas/methane) benefits.

Keywords:
Anaerobic digestion (AD) Guinea grass Rumen fluid microbial population dynamics

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