Effect of Sanitizers, Rumensin, and Temperature on Anaerobic Digester Biomass

Reduced biogas production due to toxicants or temperature change can be catastrophic to anaerobic digester operation. Unfortunately, farm manures and wastewaters can contain toxic sanitizers and feed additives, and undergo biomass temperature changes and long-term storage. To understand these impacts, we used mesophilic and thermophilic biomass anaerobic toxicity assays and methanogen activity assays to determine the inhibitory concentration causing a 50% decrease in methane production rate (i.e., IC50) of a group of commercial products. The products were Rumensin and 11 cleaners/sanitizers and disinfectants (teat dips) from dairy farms (Genron IV, Della Super, Tri Pfan, Zinicin, 1313-SD, Sheen Ezey, Mandate, Masticide, Artec, Della-Soft, and copper sulfate). The effects of thermophilic biomass storage duration (3 to 28 days) and temperature (4°C to 70°C) were also determined. All products were toxic, with IC50 values in the narrow range of 0.1 to 6 v/v %. The quaternary ammonium salt (QUAT)-based sanitizer (Genron IV) and Rumensin were the most toxic, whereas other products were less toxic and had similar toxicity to ammonia. There was no significant difference between mesophilic and thermophilic biomass IC50 values. At storage temperature >20°C, thermophilic digester biomass activity decreased after storage for 3 to 28 days, with approximately 75% activity loss after 28 days. In contrast, less activity loss was observed at lower temperatures (20°C and 4°C). The activity decrease after storage was from 0.9% to 1.6% per °C for the durations and temperatures tested, with greater decreases at longer durations. This information can be used to help determine a course of action to minimize adverse impacts on anaerobic digesters.