Submersible probe type microbial electrochemical sensor for volatile fatty acids monitoring in the anaerobic digestion process

Abstract

Abstract: Microbial electrochemical sensor with a more simplified architecture is required in the anaerobic digestion (AD) process for in situ on-line volatile fatty acids (VFAs) monitoring. In this study, a submersible probe type microbial electrochemical sensor was constructed, and the current signal showed a linear relationship with the VFAs concentration (0–200 mM) at the specific reaction time from 10 to 120 min (R2 > 0.96), with the slope increased from 0.87 × 10−3 to 1.70 × 10−3 mA mM −1. The sensor showed a good selectivity when VFAs were co-existed with 2 g/L of additional organic matters (cellulose, yeast extract, peptone, and potassium oleate), and 0.1% formaldehyde. Particular attention should be paid when additional electroactive matter such as Cu(II) as well as high concentration of TAN (above 200 mg/L) was co-existed with VFAs in the digestate. When amending the artificial AD digestate with extra 50 mM NaCl to increase the ionic strength, the current generation increased from 0.064 ± 0.002 to 0.185 ± 0.001 mA (50 mM VFAs at 60 min). The sensor was successfully applied for actual digestate samples detection and the results did not show significance differences with the total VFAs measured by GC. The submersible probe type sensor depicted a good repeatability during one-month operation. This study provides a direct approach based on microbial electrochemical technology for VFAs monitoring in the AD process.