Carbon source priority and availability limit bidirectional electron transfer in freshwater mixed culture electrochemically active bacterial biofilms

Bioresources and Bioprocessing

Table 1 An overview of the research methodology

Phase I	CULTIVATION
Carbon source	NaHCO₃ + CH₃COOH
Procedure	CA (0.2 V)
Phase II	HBPR – half-batch polarization reversal phase
Reactor	S1-BES	S2-BES	S3-BES
Carbon source	NaHCO₃	CH₃COOH	NaHCO₃ + CH₃COOH
Procedures	CA (− 0.5 V) → CV (− 0.5 V to + 0.2 V) → CV with OC controls → CA (+ 0.2 V) → CV (+ 0.2 V to -0.5 V) → CV with OC controls
Phase III	PPR – periodic polarization reversal phase
Reactor	S1-BES	S2-BES	S3-BES
Carbon source	NaHCO₃	CH₃COOH	NaHCO₃ + CH₃COOH
Procedures	CA (− 0.5 V) → CA (0.2 V)	CA (0.2 V) → CA (− 0.5 V)	CA (0.2 V) → CA (− 0.5 V)

CA chronoamperometry—application of a constant potential, CV cyclic voltammetry: application of a periodically changing potential. OC open circuit, i.e., electrodes are suspended in media, but not connected to the potentiostat, except for short periods