Biofilm electrode

A biofilm electrode reactor (BER) has been used by researchers at the University of Cincinnati to dechlorinate pentachlorophenol (PCP), a halogenated organic used in wood and leather treatment. This technology is not commercially available. All information is from the developer and has not been independently verified. 

Stand SE and Carlson DA (1984) Rapid BOD measurement for municipal wastewaters samples using a biofilm electrode. Journal of the Water Pollution Control Federation 56 464-467. 

The positions of the biofilm electrode, supporting electrode, and reference electrode (RE) in a BES have direct effects on the measured current and should be accounted for beyond spatial geometric considerations [59, 67, 68]. For example, the simplest system to configure to study electron transfer in EABs may be an MFC (Fig. 1.1a), although it is generally used to quantify power production in... 

Electrode acclimatization refers to the processes in which EABs are allowed time to populate an electrode surface it is often used for multispecies EABs [54,86,88-97]. The purpose of acclimatization is to increase electrode performance by enhancing biofilm attachment and/or to allow the biofilm electrode to reach a steady state OCP prior to use in a BES [98], The method of acclimatization affects the type of EAB grown on the biofilm electrode and can be focused on control of the current or of the biofilm electrode potential. Four acclimatization methods are common in the literature ... 

Closed circuit The biofilm electrode and the supporting electrode are short circuited or connected across a resistor. 

Open circuit The biofilm electrode is left disconnected. 

Controlled electrode potential A constant polarization potential is placed between the biofilm electrode and the RE. 

The majority of this book is dedicated to describing how to study extracellular electron transfer of EABs. Once the correct reactor configuration has been chosen and the EAB has been successfiiUy grown or acclimatized on an electrode, the next step is to study the electron transfer properties of the biofilm electrode using electrochemical techniques. There are many electrochemical techniques available however, we introduce only those frequently used to study electron transfer processes in EAB literature. 

There is an implicit assumption, however, that EABs growing on electrode surfaces can be described as a well-controlled condition in which CV can be applied to study reaction mechanisms as in pure electrochemical systems. Beyond reproducibility of the biofilm electrode surface, simply characterizing biofilm structure itself has historically been difficult [114-116]. Furthermore, the result of biofilm heterogeneity is local variation of not only diffusion coefficients, but also flow velocities [117-120]. The unknown mass transfer conditions suggest that not all cells in the EAB contribute equally to current production. Several chapters in this book are dedicated to the use of CV to characterize electron transfer processes in EABs. 

Therefore, G. sulfurreducens biofilm electron transfer is generally described as complete acetate oxidation to carbon dioxide, protons, and electrons in which electron transfer outside the cells is the rate-limiting step. The mass transfer of protons and carbon dioxide affects pH buffering and has been shown to affect the biofilm. Throughout the rest of this chapter, we consider only electron transfer and pH effects, ignoring changes in metabolic activity of the biofilm. Only the metabolic respiration rate, approximated by the current measured at the biofilm electrode, is considered. This does not mean that changes in metabolic activity are less important. We refer the readers to Chapter 2 for more information on G. sulfurreducens metabolism. 

Mass TVansfer Effect on the Biofilm Electrode Electron Transfer... 

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