Enhancing anaerobic digestion of lignocellulosic biomass by mechanical cotreatment.

BACKGROUND: The aim of this study was to increase the accessibility and accelerate the breakdown of lignocellulosic biomass to methane in an anaerobic fermentation system by mechanical cotreatment: milling during fermentation, as an alternative to conventional pretreatment prior to biological deconstruction. Effluent from a mesophilic anaerobic digester running with unpretreated senescent switchgrass as the predominant carbon source was collected and subjected to ball milling for 0.5, 2, 5 and 10 min. Following this, a batch fermentation test was conducted with this material in triplicate for an additional 18 days with unmilled effluent as the 'status quo' control. RESULTS: The results indicate 0.5 - 10 min of cotreatment increased sugar solubilization by 5- 13% when compared to the unmilled control, with greater solubilization correlated with increased milling duration. Biogas concentrations ranged from 44% to 55.5% methane with the balance carbon dioxide. The total biogas production was statistically higher than the unmilled control for all treatments with 2 or more minutes of milling (α = 0.1). Cotreatment also decreased mean particle size. Energy consumption measurements of a lab-scale mill indicate that longer durations of milling offer diminishing benefits with respect to additional methane production. CONCLUSIONS: Cotreatment in anaerobic digestion systems, as demonstrated in this study, provides an alternative approach to conventional pretreatments to increase biogas production from lignocellulosic grassy material.

Insights into metabolism and sodium chloride adaptability of carbaryl degrading halotolerant Pseudomonas sp. strain C7.

Pseudomonas sp. strain C7 isolated from sediment of Thane creek near Mumbai, India, showed the ability to grow on glucose and carbaryl in the presence of 7.5 and 3.5% of NaCl, respectively. It also showed good growth in the absence of NaCl indicating the strain to be halotolerant. Increasing salt concentration impacted the growth on carbaryl; however, the specific activity of various enzymes involved in the metabolism remained unaffected. Among various enzymes, 1-naphthol 2-hydroxylase was found to be sensitive to chloride as compared to carbaryl hydrolase and gentisate 1,2-dioxygenase. The intracellular concentration of Cl- ions remained constant (6-8 mM) for cells grown on carbaryl either in the presence or absence of NaCl. Thus the ability to adapt to the increasing concentration of NaCl is probably by employing chloride efflux pump and/or increase in the concentration of osmolytes as mechanism for halotolerance. The halotolerant nature of the strain will be beneficial to remediate carbaryl from saline agriculture fields, ecosystems and wastewaters.