Relationship between Temperature, Ph and Population of Selected Microbial Indicators during Anaerobic Digestion of Guinea Grass ( Panicum Maximum )

Abstract

In this study, the relationship between process temperature, process pH and population of selected microbial indicators during anaerobic digestion of guinea grass (Panicum maximum) at ambient condition was investigated. A one stage batch-type mesophilic anaerobic digestion system was configured using rumen fluid (RF) as inoculums (ADRF) and a low solid loading of approximately 7.0% total solid (TS). Physicochemical parameters such as process temperature (PTMRF), process pHRF and volatile fatty acid (VFARF) were monitored with time. Selected indicator microbial populations were monitored by standard cultural techniques based on metabolic capacity and oxygen sensitivity with respect to time. Result showed that average PTMRF increased from 27.5°C to 35.2°C, average process pHRF ranged from 6.5 to 7.9 and VFARF ranged from 1,080.00 mg/L to 4,800.33 mg/L with time. In terms of metabolic capacity and oxygen sensitivity, the populations of cellulolytic bacteria (CBRF), lactose and glucose fermenting (acidogenic) bacteria (LFBRF and GFBRF), propionate and ethanol oxidizing (acetogenic) bacteria (POBRF and EOBRF), acetate oxidizing methanogens (AOMRF), obligate anaerobic bacteria (OABRF) and total facultative bacteria (FAABRF) increased (about 10-fold) respectively with time. Correlation analysis showed positive relationships between the process temperature (PTMRF) and the population of selected microbial indicators with time. However, there were negative relationships between the process pHRF and the population of selected microbial indicators with time. Furthermore, there were positive relationships between the populations of selected microbial indicators with time. Rumen fluid significantly (P < 0.05) affected the dynamics of the process temperature (PTMRF) and process pHRF inside the ADRF system with time respectively. These kinds of relationships between biotic factors and between biotic and abiotic factors could be used to monitor the state of anaerobic digestion process with respect to time.