In situ COD monitoring with use of a hybrid of constructed wetland-microbial fuel cell

The hybrid system of constructed wetland and microbial fuel cell (CW-MFC) used as a biosensor is becoming a new research focus with the advantage of resisting the shock loading and enriching more electricigens. In this study, a structural parameter S integrating the size, the position and the spacing of the anode and the cathode was proposed. And the electrogenesis and biosensing performances of the vertical flow CW-MFC biosensors were evaluated at different S values. The results showed that all the three biosensors could achieve good monitoring for COD (R2 > 0.97). And the coulombic yield was more suitable for the response signal than output voltage. But different biosensing properties including detection signal, detection range, detection time, correlation fitting degree and sensitivity were also displayed. Further, in order to optimize the biosensing performance, the coulombic yield in stable voltage stage (Qs) was proposed which can shorten the detection time by 70% at most. On the anodes, abundant nitrogen-transforming bacteria (NTB) were enriched as well as electrochemically active bacteria (EAB). The competition of NTB for substrates and electrons with EAB disturbed the output voltage signal but not affect the stability of coulombic yield signal. Moreover, the significant linear correlation between the S values and the ratios of EAB to NTB colonized both on anodes and on cathodes indicated the differences of the electricity generation and biosensing performance at the different structural parameters.