Experimental Results and Integrated Modeling of Bacterial Growth on an Insoluble Hydrophobic Substrate (Phenanthrene)

Metabolism of a low-solubility substrate is limited by dissolution and availability and can hardly be determined. We developed a numerical model for simultaneously calculating dissolution kinetics of such substrates and their metabolism and microbial growth (Monod kinetics with decay) and tested it with three aerobic phenanthrene (PHE) degraders: Novosphingobium pentaromativorans US6-1, Sphingomonas sp. EPA505, and Sphingobium yanoikuyae B1. PHE was present as microcrystals, providing non-limiting conditions for growth. Total PHE and protein concentration were tracked over 6-12 days. The model was fitted to the test results for the rates of dissolution, metabolism, and growth. The strains showed similar efficiency, with v(max) values of 12-18 g dw g(-1) d(-1), yields of 0.21 g g(-1), maximum growth rates of 2.5-3.8 d(-1), and decay rates of 0.04-0.05 d(-1). Sensitivity analysis with the model shows that (i) retention in crystals or NAPLs or by sequestration competes with biodegradation, (ii) bacterial growth conditions (dissolution flux and resulting chemical activity of substrate) are more relevant for the final state of the system than the initial biomass, and (iii) the desorption flux regulates the turnover in the presence of solid-state, sequestered (aged), or NAPL substrate sources

Innovative bio-pyrolytic method for efficient biochar production from maize and pigeonpea stalks and their characterization

Agricultural residues in excess to livestock fodder are garnering global attention and stern concerns owing to their accountable share in environmental hazards due to lack of effective disposal mechanisms and indiscriminate burning. Recycling these residues for biochar production using pyrolysis is a cost effective and locally feasible technique which offers a twin-prong solution addressing both climate and soil health issues. This research work compares a portable kiln prototype that is affordable and easy to use with a muffle furnace at three distinct pyrolytic temperatures (400 °C, 500 °C, and 600 °C) to produce biochar from the stalks of maize and pigeonpea. The biochar properties were characterized using Electron Microscopy-Electron Dispersive X-ray (SEM-EDX), X-ray Diffraction (XRD), Fourier Transmission Infrared Spectroscopy (FTIR), and Thermogravimetric Analysis (TGA). The findings indicate significant variations in biochar properties based on raw material source, pyrolytic method, and varied temperatures. Higher pyrolysis temperatures were found to reduce the amorphous organic phase and alter the ultrastructure of biochar, as evidenced by XRD analysis. SEM imaging showed macropores in oval and round shapes with crystalline deposits. The carbon content, as per EDX, decreased with increasing temperature, aligning with changes in functional groups. Edinburgh's stability test revealed that kiln biochar has more stable carbon content compared to biochar from muffle furnace and the stable carbon increased with rise in temperature. A comparative analysis demonstrated that biochar quality at 400–500 °C in a muffle furnace was on par with that produced in the portable kiln at 400 °C. Therefore, considering the kiln's portability, efficiency, cost-effectiveness, and scalability, it is a promising decentralized method for biochar production, offering a cutting-edge solution for agricultural waste management and soil carbon enhancement