MEASUREMENT OF DISSOLVED HYDROGEN IN AN ANAEROBIC-DIGESTION PROCESS BY A MEMBRANE-COVERED ELECTRODE

Dissolved hydrogen in an anaerobic digestion process was continuously measured by a voltammetric membrane electrode which consisted of a Pt-Pt black and Ag-AgCl covered FEP membrane with 0.1 M KCl and 0.1 M HCl. This sensor showed high reliability and sensitivity (i.e., detection limit: 50 nM) in distilled water. The sensor was not affected by several compounds in the anaerobic digestion media (e.g., inorganic salts, acetate, and propionate) except for sulfide. The indication in a sample containing 1.56 mM sulfide corresponded to that of 0.26-mu-M dissolved hydrogen. The sensor was also applied to measure the dissolved hydrogen in a laboratory-scale anaerobic reactor, and the dissolved hydrogen was continuously monitored for 565-h. The sensor was calibrated every 120-h, and the output signal was very stable during this period. The dissolved hydrogen concentration ranged from 0.5 to 3-mu-M, and H-2 partial pressure from 2 to 7 Pa in the gas phase. A good correlation (r = 0.85) between theoretical values calculated with H-2 partial pressure and the output signals was recognized. The actual dissolved hydrogen concentration was about 60-fold higher than the theoretical values calculated with H-2 partial pressure.