We are confident that the biofilm will grow on these carriers, because the material is the same as used in the flowchamber where it grew (Verlinkung auf Flowchamber results). Furthermore, the carrier material was recommended by Prof. Lackner and these carriers are a common method in moving bed biofilm reactors^[4]. If the biofilm does not grow, we will try and use a different more porous carrier such as pumice stone or ceramics. Biofilm growth on the carrier is detectable by a mucous layer on the floating body which is visible by eye.
Diclofenac is a hydrophobic molecule which is positively charged at pH 7.4^[5]. The B. subtilis biofilm matrix is negatively charged and hydrophobic as well so diclofenac should be able to be absorbed into the biofilm^[6]. This test will be successful if the HPLC analysis shows a decrease of diclofenac even at low concentrations over time so we can test at real-life concentrations. The paper we based our assay on also tested diclofenac biofilm sorption but could not see a significant decrease of diclofenac in their bioreactor^[1]. As they used activated sludge and not a B. subtilis biofilm, we cannot directly compare results. Other reasons why this assay might not work could be wrong charge of the matrix or the size of the pores in the matrix. If this situation would occur, we could try to change the pH of the solution to consequently change the charge of the molecule of the matrix, e.g. the extracellular polymer poly-γ-glutamate. However, this approach would likely be not applicable in WWTP due to the high volume and later drain into the environment. Rather, we could change the conditions in which the biofilm is formed because that can affect the biofilm matrix and it also could be done in our proposed implementation^[7]. Furthermore, we would search for other solutions to make the biofilm matrix more receptive to diclofenac. That could be tried by overexpressing genes responsible for resorptive extracellular polymer substance synthesis^[6].
Here we exemplary focused on diclofenac, but there are further substances whose uptake into the biofilm we could test since they are relevant for this project (Verlinkung auf EreB).