Biogas Production from Co-digestion of Pennisetum Pururem cv. Pakchong 1 Grass and Layer Chicken Manure Using Completely Stirred Tank

AbstractIn this research, the production of biogas from co-digestion of Pennisetum purpureum cv. Pakchong1 grass and layer chicken manure using completely stirred tank was investigated. The experiment was defined to examine effect of the change in carbon to nitrogen (C/N) ratios and the organic loading rates (OLRs) on biogas production and system steady-state performance. Primary analyses suggested that an approximate content of grass and manure was 50: 50% by weight to achieve C/N ratio of 20 and 70: 30% by weight for C/N ratio of 30 respectively. The experimental reactor was set to operate at a fixed total solid content of 4% with two cases of C/N ratio at four different OLRs of 1.1, 1.4, 1.7 and 2.2kg VS/(m3.d). Each condition was operated for 1.5 time of reactor retention time. The result suggested that maximum steady-state methane yield of 0.27 ± 0.01 L CH4/kg VSadded can be achieved at C/N ratio of 20 with OLR of 1.1kg VS/(m3.d). Moreover, the results also suggested that methane yield decreased for an increase in OLR. Nonetheless, the work presented herein can provide an insight information for design and operation optimization according to economical investment analysis

Microbial community assembly, theory and rare functions. Front. Microbiol. 4:68. doi: 10.3389/fmicb.2013.00068

Views of community assembly have traditionally been based on the contrasting perspectives of the deterministic niche paradigm and stochastic neutral models. This study sought to determine if we could use empirical interventions conceived from a niche and neutral perspective to change the diversity and evenness of the microbial community within a reactor treating wastewater and to see if there was any associated change in the removal of endocrine disrupting compounds (EDCs). The systematic removal of EDCs and micropollutants from biological treatment systems is a major challenge for environmental engineers. We manipulated pairs of bioreactors in an experiment in which "niche" (temporal variation in resource concentration and resource complexity) and "neutral" (community size and immigration) attributes were changed and the effect on the detectable diversity and the removal of steroidal estrogens was evaluated. The effects of manipulations on diversity suggested that both niche and neutral processes are important in community assembly. We found that temporal variation in environmental conditions increased diversity but resource complexity did not. Larger communities had greater diversity but attempting to increase immigration by adding soil had the opposite effect. The effects of the manipulations on EDC removal efficiency were complex. Decreases in diversity, which were associated with a decrease in evenness, were associated with an increase in EDC removal. A simple generalized neutral model (calibrated with parameters typical of wastewater treatment plants) showed that decreases in diversity should lead to the increase in abundance of some ostensibly taxa rare. We conclude that neither niche and neutral perspectives nor the effect of diversity on putative rare functions can be properly understood by naïve qualitative observations. Instead, the relative importance of the key microbial mechanisms must be determined and, ideally, expressed mathematically