The performance of a sulfide oxidase (SO) based biosensor for online monitoring of sulfatereducing
bacteria (SRB) activity was evaluated by correlating the electrochemical response of the
biosensor to the biogenic sulfide concentration from a SRB-reactor. Facultative Actinomycete strain FR-
3 was used to produce the SO enzyme; the enzyme was immobilized on a graphite paste along with a cofactor
7, 7, 8, 8-tetracyanoquinodimethane (TCNQ) or 1, 1’-dimethylferrocene (DMF). The ferrocenebased
biosensor responded linearly to aqueous sulfide concentration up to 180 mg/L [S-2 (mg/L) = 8.3× I
(µA/cm2)]. When TCNQ was used as a co-factor, the biosensor responded linearly up to biogenic sulfide
concentration of 15 mg/L [S-2 (mg/L) = 0.57 × I (µA/cm2)].
In order to determine the relationship between biogenic sulfide production and corrosion rate, a
carbon steel electrode was immersed in the SRB reactor. The corrosion rate was monitored using the
electrochemical polarization resistance technique. The corrosion rate peaked during the exponential
growth phase of the bacteria and declined afterwards, probably due to the formation of a biofilm on the
biosensor and electrode surface as well as an FeS layer on the surface of carbon steel.
Keywords - Biosensor, enzyme electrode, SRB, MIC, electrochemistry, online monitoring