Comparison of pyrochar, hydrochar and lignite as additive in anaerobic digestion and NH4+ adsorbent. (October 2022) - Leithaeuser, Anna
Graphical abstract: Highlights: Addition of 5 g/l is not sufficient to mitigate severe ammonia inhibition. Degradation of hydrochar is the main contributor to increasing methane yield. Ammonium adsorption capacity for pyrochar, hydrochar and lignite vary significantly. Used blank has major impact on evaluation of additives. Abstract: The impact of pyrochar, hydrochar and lignite addition on anaerobic digestion of food waste was investigated with and without ammonia inhibition under batch conditions. Furthermore, ammonium adsorption capacities of the chars were investigated. To determine anaerobic degradation of char, reference samples containing inoculum and char were analyzed, indicating a significant degradation of hydrochar. Depending on the evaluation method, the increase in methane yield due to hydrochar addition varied between no statistically significant difference and +14 %. No significant impact due to the addition of 5 g/l pyrochar and lignite on AD was found. NH4 + adsorption capacities showed a significantly higher net adsorption capacity of lignite (1.58 mgNH4 + /gL ), compared to pyrochar (0.63 mgNH4 + /gPC ). A negative NH4 + adsorption capacity (−0.51 mgNH4 + /gHC ) was found for hydrochar. A high H/C-ratio, O/C-ratio and cation exchange capacity of hydrochar and lignite indicate many functional groups and low chemical stability, enabling an increased interaction between NH4 + and char.