Exploring the tension between energy consumption, light provision and CO2 mass transfer through varying gas velocity in the airlift bioreactor

Microbial lifelines in bioprocesses: From concept to application

Bioprocesses are scaled up for the production of large product quantities. With larger fermenter volumes, mixing becomes increasingly inefficient and environmental gradients get more prominent than in smaller scales. Environmental gradients have an impact on the microorganism's metabolism, which makes the prediction of large-scale performance difficult and can lead to scale-up failure. A promising approach for improved understanding and estimation of dynamics of microbial populations in large-scale bioprocesses is the analysis of microbial lifelines. The lifeline of a microbe in a bioprocess is the experience of environmental gradients from a cell's perspective, which can be described as a time series of position, environment and intracellular condition. Currently, lifelines are predominantly determined using models with computational fluid dynamics, but new technical developments in flow-following sensor particles and microfluidic single-cell cultivation open the door to a more interdisciplinary concept. We critically review the current concepts and challenges in lifeline determination and application of lifeline analysis, as well as strategies for the integration of these techniques into bioprocess development. Lifelines can contribute to a successful scale-up by guiding scale-down experiments and identifying strain engineering targets or bioreactor optimisations.

Carbon dioxide and methane emission of denitrification bioreactor filling waste sawdust and industrial sludge for treatment of simulated agricultural surface runoff

Carbon dioxide (CO₂) and methane (CH₄) produced by denitrification bioreactors in processing agricultural surface runoff have contributed to increasing proportion of greenhouse gases (GHG) emissions. It is the first time to monitor and quantify the emission flux of CO₂ and CH₄ produced by laboratory-scale denitrification bioreactors which recycled waste Cunninghamia lanceolata sawdust (CLS) and industrial sludge (IS) as fillers to process simulated agricultural surface runoff. Sludge-water ratio, inflow rate and water flow direction are used as experimental factors to study the effect on the emission flux of CO₂ and CH₄. Results show that emission flux of CO₂ from denitrification bioreactors with different sludge-water ratio approached 20 mg m^-2h^-1, simultaneously the average emission flux of CH₄ produced by all bioreactors was 1.785 mg m^-2h^-1. The addition of sludge increased the emission flux of CH₄ and had no significant effect on the emission flux of CO₂. Increasing the inflow rate reduced the CO₂ emission flux from 21.57 to 1.27 mg m^-2h^-1, and at the same time increased the CH₄ emission flux from 0.007 to 9.54 mg m^-2h^-1. The gravity flow of wastewater reduced the emission flux of CO₂ and CH₄. The emissions of CO₂ and CH₄ from folded plate denitrification bioreactor with CLS and industrial sludge with a volume ratio of 1:2 can be reduced by 24.67% and 73.3%, respectively. There was no need to add special gas collection and treatment devices because CO₂ and CH₄ emission fluxes produced by the folded plate denitrification bioreactor and gravity denitrification bioreactor are not enough to increase the greenhouse effect. This study quantified the CO₂ and CH₄ produced by denitrification bioreactors filling CLS and IS, and provided a reference for future research on the gases produced by the denitrification process.