Will dissolved hydrogen reveal the instability of the anaerobic digestion process?

Abstract

Dissolved hydrogen is a critical factor in maintaining the delicate balance among microbial species that drive anaerobic digestion. Since previous findings have demonstrated a correlation between dissolved hydrogen concentration and volatile fatty acid (VFA) levels, we propose to evaluate the use of dissolved hydrogen concentration in digestate as an alternative to traditional VFA measurements. The aim is to determine whether dissolved hydrogen could serve as a faster, more accurate, and more efficient indicator of process instability in anaerobic digestion. An integral part of this task also involves addressing the technical challenge of identifying a suitable sensor that meets our requirements. In this study, we evaluated the ratio of dissolved hydrogen concentration to Total Inorganic Carbon as a potential alternative to the traditional stability indicator, Volatile Fatty Acids/Total Inorganic Carbon (VFA/TIC), also referred to as Fl & uuml;chtige Organische S & auml;uren/Totales Anorganisches Carbonat (FOS/TAC). The single-stage anaerobic digestion process was carried out in a Terrafors IS rotary drum bioreactor for 150 days at an average temperature of 40 degrees C and an organic volatile load of 0.092 kg m-3 d-1. Corn silage was dosed on weekdays as the substrate. With a theoretical retention time of 45 days, a biogas production of 0.219 Nm3kgVs-1 with a CH4 content of 31.6% was achieved. The values of the determined VFA/TIC stability indicator ranged from 0.22 to 5.66, with the highest values obtained when the reactor was overloaded. The dissolved hydrogen concentration ranged 0.005-0.196 mg dm-3. The Pearson correlation coefficient was 0.337 and the Spearman correlation coefficient was 0.468. The amperometric microsensor has proven to be unsuitable for field applications due to its lack of sensitivity and short lifetime. The proposed ratio of dissolved hydrogen concentration to TIC did not prove to be significantly more effective than the established VFA/TIC indicator.