Monitoring and quantification of bioelectrochemical Kyrpidia spormannii biofilm development in a novel flow cell setup

Abstract

Spatially resolved data for biofilm structure can often not be assessed easily in bioelectrochemical setups due to the orientation and placement of anode and cathode. However, understanding the interplay of biofilm (structure) development and electrochemical parameters is crucial for optimizing bioelectrochemical biofilm systems. For example, to produce value added products. This study thus, presents a versatile flow cell setup allowing for control of hydrodynamic, substrate (liquid and gaseous), and nutritional conditions as well as physical parameters. Here, a versatile lab-scale flow cell system equipped with a cathode and an anode is presented to monitor the growth of Kyrpidia spormannii biofilm. The monitoring was conducted non-invasively by means of optical coherence tomography. 3D OCT data set analysis revealed that the biofilm accumulation rate is influenced by the distance of Kyrpidia spormannii cells from the cathode surface: the overall accumulation rate of the biofilm decreases when the biovolume exceeds 75 µm3 µm−2. Moreover, a correlation between substratum coverage and measured current density was determined. The increase of substratum coverage led to a decrease of abiotic redox processes at the electrode surface and thereby to a decrease of measured current density with an equilibrium of approx. 13 µA cm−2. The results further show that a well characterized cultivation system was developed for the investigation of any kind of bioelectrochemical biofilm systems. Moreover, this midi-fluidic setup enables the quantitative analysis of representative biofilm volume units, which in turn allow for drawing reliable process parameters.