Modeling of an aerobic bioprocess based on gas exchange and dynamics: a novel approach.

Monitoring of the biological degradation of a substrate by microorganisms is a key issue, especially in the soil bioremediation area. Respiration measurement is the easiest way to obtain online information on the biological activity. Nevertheless, it is indirectly related to substrate consumption and microbial growth. To be able to link these phenomena, a robust and descriptive model has been developed. Both biological and gas/liquid transfer dynamics must be taken into account to link the online measurement with the actual biological respiration. For that, experimental evolution of the respiratory ouotient (RQ) during a biodegradation has been compared against general biodegradation knowledge. To obtain a reliable model, practical and structural sensitivity analyses have been conducted. The model can describe the evolution of both online measurable and non-measurable states. It also gives a new definition of the apparent RQ, measured in the gas phase, compared to the actual biological RQ.

Monitoring the impact of hydrocarbon contamination and nutrient addition on microbial density, activity, and diversity in soil.

The development of optimal in situ bioremediation strategies requires a better knowledge of their impact on the soil microbial communities. We have evaluated the impact of hexadecane contamination and different nutrient amendments on soil microbial density and activity. Microbial density was measured via total DNA quantification, and microbial activity via respiration and RNA variation. The RNA/DNA ratio was also determined, as it is a potential indicator of microbial activity. PCR-amplified 16S rRNA genes were cloned and sequenced to analyze the diversity of bacterial communities. Nutrient addition significantly increased respiration and DNA and RNA concentrations in contaminated soil, indicating a limitation of degradation and growth by the availability of nitrogen and phosphorus in unamended microcosms. Hexadecane treatment slightly affected the diversity of the bacterial community, while it was dramatically reduced by nutrient treatments, particularly the addition of nitrogen and phosphorus. Microbial community composition was also altered with the enrichment of populations related to Nocardia in bioremediated soils, while uncultured Proteobacteria were mostly detected in uncontaminated soil.