Anodic biofilm

These products tend to have the highest degree of surfactant action. The cationic nature permits neutralization of the typically anodic biofilm. Cationics should not be used with anionic biocides, such as chlorophenols. Formulations tend to be based on a blend of BCP, quat, or polyquat and silicone defoamer. 

Second, biofllm thickness, structure, composition, and density affect the flux of substrates and products within the biofllm. The latter can result in large overpotentials, which have a negative impact on the performance of the system. In the case of bioanodes, higher power production was observed from thicker anodic biofilms [120]. Strikingly, the reverse effect has been observed in cathodic biofilms [35]. 

Nevin KP, Kim BC, Glaven RH, Johnson JP, Woodard TL, Methe BA, DiDonato RJ, Covalla SF, Franks AE, Liu A, Lovley DR. Anode biofilm transcriptomics reveals outer surface components essential for high density current production in Geobacter sulfurre-ducens fuel cells. PLoS One 2009 4 e5628. 

Franks AE, Nevin KP, Jia HE, IzaUalen M, Woodard TL, Lovley DR. Novel strategy for three-dimensional real-time imaging of microbial fuel cell communities monitoring the inhibitory effects of proton accumulation within the anode biofilm. Energy Environ Sci 2009 2 113-119. 

Figure 2.2 Schematic of a two-chambered MFC or an MEC configuration, both having an anode electrode (AE), where Geobacter biofilms catalyze the oxidation of the electron donor (Djg to Dgjj). A proton-exchange membrane separates the two chambers to allow the diffusion of protons (H" ) from the anode to the cathode chamber. In the MFC, the anode electrode is wired directly to the cathode electrode (CE), and the amount of electrons (e") generated by the anode biofilms is dependent on the reduction potential of the electron acceptor (reaction A to Ajg) used as catholyte. In the MEC, the cathode limitation is bypassed using a potentiostat, which sets a constant potential of the anode electrode versus a reference electrode (RE) and allows the H" " and the e" to combine on the cathode electrode to generate Hj.

Coulombic Efficiency The eleetrical conversion efficiency is an important parameter to assess the performance of the BES, and it also provides valuable insights into the growth and electroactivity of the anode biofilms. The CE allows to estimate how efficiently the electron donor is oxidized to generate current. CE is calculated by dividing the number of electrons recovered as current (/) over time (t) by the number... 

Quantifying Biofilm Parameters As the amount of biofilm biomass is proportional to current production, quantifying biomass is important to assess BES performance. The anode biofilms can be detached from the electrode with a spatula or razor, and the biofilm biomass can be calculated from the total cell protein [21]. Alternatively, the cells can be stained with fluorescence dyes such as the BacLight viability kit (Invitrogen) and examined by Confocal Laser Scanning Microscopy (CLSM). The... 

Larrosa-Guerrero A, Scott K, Katuri KP, Godinez C, Head IM, Curtis T. Open circuit versus closed circuit enrichment of anodic biofilms in MFC effect on performance and anodic communities. Appl Microbiol Biotechnol 2010 87(5) 1699-1713. 

Lee TK, Van Doan T, Yoo K, Choi S, Kim C, Park J. Discovery of commonly existing anode biofilm microbes in two different wastewater treatment MFCs using FLX Titanium pyrosequencing. Applied Microbiology and Biotechnology 2010 87(6) 2335-2343. 

Chung K, Okabe S. Continuous power generation and microbial conununity structure of the anode biofilms in a three-stage microbial fuel eell system. Appl Microbiol Biotechnol 2009 83(5) 965-977. 

Cathodic biofilms are biofilms that accept electrons from an electrode, as opposed to anodic biofilms, such as the G. sulfurreducens biofilms discussed previously, which deliver electrons to an electrode [34]. Cathodic biofilms are less well understood than their anodic counterparts despite being well documented in biocathode studies. Often, a more operational definition is given to cathodic biofilms. For example, biofilms that... 

The process of electron delocalization is previously observed in many natural and synthetic molecules. For example, in benzene, electrons are delocalized over the carbon ring. In synthetic molecular materials such as polyaniline, electrons become delocalized due to pi orbital overlap between phenyl rings [28]. However, it has long been considered, as proteins are electronic insulators, and metallic-like conductivity or electron delocalization is not possible in proteins [27]. In this chapter, we discuss methods and studies that have revealed metallic-like conductivity in anode biofilms of G. sulfurreducens due to proteinaceous pili nanofilaments present in these biofilms (Fig. 7.2). 

The conductivity values of the anode biofilms with the four-probe method were 10-fold higher than those with the two-probe approach (Fig. 7.5d). This is similar... 

Two-Probe AC Impedance Spectroscopy Measurements In principle, the electrochemical processes of redox charge tfansfer and ion diffusion can contribute to the measured DC conductance [20, 31]. Therefore, to better define the intrinsic biofilm conductivity, it was desirable to use AC impedance measurements as an independent probe of conductance between the electrodes [46-48]. This method also serves to separate electronic and ionic conductivity in mixed-conductor system [49]. The applicability of this approach to anode biofilms was verified by evaluating the linearity and stability conditions described in the following section on the details of this experimental procedure. 

It can be seen from the aforementioned equations that faradic processes dominate over low frequencies due to inverse square root dependence. To estimate biofilm conductivity, we were interested in charge transport across the gap rather than charge transfer across the electrodes. (The latter describes a one-step tunneling process [19].) Hence, it was necessary to eliminate faradic reactions involving charge transfer. In the case of anode biofilms, a low-frequency cut-off of 100 mHz was used to eliminate any possible contributions from electrochemical reactions occurring at very low frequency [31, 46, 48]. Electrolytes with different concentrations were tested to verily this frequency range. 

S.2 Current-Producing PilA Mutant Biofilms Biofilms of PilA mutant of DL-1 strain of G. sulfurreducens and PilA mutant strain of Geobacter sirdin Speedy produced 10 times less current and did not bridge the nonconducting gap. This is consistent with previous studies that have demonstrated that because pili are electrically conductive [60], they are required for the development of the thick anode biofilms necessary for high-density current production by G. sulfurreducens [35,61]. 

---