The aim of this project is to prove the concept that microbioreactors with integrated "on-chip" sensing can investigate the process kinetics of microorganisms under a wide array of shear stress and mass transport conditions. This microbioreactor concept will allow the study of low shear stress in combination with fast mass transport, conditions that are not attainable in current larger bench scale reactors.

The target microorganisms investigated in this project are nitrifying bacteria. These bacteria sequentially oxidize ammonia to nitrite and nitrate and thus render it amenable for subsequent reduction to dinitrogen gas. Nitrifying bacteria play an important role in both natural and engineered environments due to their role in the global nitrogen cycle, for instance in relation to waste management.

Microbioreactors have inherent, transformative advantages over currently used benchscale reactors. They feature more homogeneous flow conditions than larger reactors, direct optical access and large surface to volume ratio, for enhanced mass transfer. For instance, permeable membranes are used for gas diffusion, rather than traditional bubbling techniques that come with increases in shear stress. Control and measurement of nitrite concentration and temperature will be implemented using optical and microfabrication techniques.

Broader impact

The PIs will disseminate the results in their graduate course "Microscale Transport Phenomena". Undergraduate and High School students will be involved in this interdisciplinary research, a practice that is customary to the research laboratories of both the PI and co-PI.

This exploratory research will provide a foundation for the submission of a full size proposal to engineer nitrifying bioreactors for wastewater treatment, effectively overcoming currently observed mass-transfer limitations. This research will integrate into synergistic activities of Columbia University with industry (IBM "Smarter Cities") and with the Department of Chemical Engineering to grow this effort into a possible NSF research Center.

Project Report

Bioreactors find ubiquitous application in diverse spheres ranging from water and wastewater treatment, biochemical production of drugs, fuels and pharmaceuticals. Very often these bioreactors are subject to mass transfer limitation, which reduces the true biological activity. The aim of this NSF EAGER project was to develop a proof of concept for 'uncoupling' mass transfer kinetics from true biological kinetics using state-of-the art microbioreactors with integrated "on-chip" sensing. As part of this project, the individual expertise of two groups (Prof. Kartik Chandran, Columbia University and Prof. Daniel Attinger, Iowa State Unviersity) was synergistically applied to design and fabricate micro-scale (50 micro liters) bioreactors for estimating the biological rate of reaction. These micro-scale reactors were applied for estimating the reaction rates of nitrifying bacteria - which have been traditionally used for wastewater treatment and are now finding application even in the production of biofuels. We were successful in estimating the kinetics of nitrification with the device we developed as a result of NSF EAGER research support. Based on these results,it is expected that a broad array of fields, which employ biological catalyst, will benefit from our micro-scale bioreactor approach. Essentially, these reactors when integrated with approporiate microbiological catalysts and parameter estimation techniques can enable the rapid and high-throughput screening of different operating conditions and substrates for optimization of a given biological process.

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Columbia University
New York
United States
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