Probiotic bacteria impact on greenhouse gas and odor emissions during dairy manure digestion by black soldier fly (Hermetia illucens)(Diptera: Stratiomyidae) larvae

Unprocessed animal manure is a source of environmental pollution including the release of greenhouse gases (GHGs) and malodorous volatile organic compounds (VOCs), which reduce air quality. Hermetia illucens (Diptera: Stratiomyidae), commonly known as the black soldier fly (BSF), has gained attention for the ability of its larvae to reduce these compounds emitted on several types of animal manure. Microbial inoculation of manure can accelerate digestion of these lignocellulose-rich substrates, increasing nutrient availability for BSF larvae. In the present study, we tested dairy manure with three probiotic bacterial treatments, Paenibacillus polymyxa, Rhodococcus rhodochrous 21298, or their combination, on the ability of BSF larvae to reduce emissions of GHGs and malodorous VOCs at an industrial scale. Overall, GHG and odor emissions varied across the time points recorded, with emissions peaking on day 3 and returning to near-baseline levels by day 6 of the trial. The bacterial combination treatment released the highest amount of CO2 on day 3, whereas individual inoculations with P. polymyxa or R. rhodochrous emitted higher amounts of CH4 on day 3 compared to the other treatments. Microbial inoculation did not affect the blend of VOCs emitted. Among the VOCs tentatively identified, several are known to be off-odors emitted during dairy manure digestion. While the VOC blend was similar between treatments and the control, some treatments showed lower VOC emissions compared with the control. Optimizing the combined use of BSF larvae and probiotic bacteria could result in a promising strategy to sustainably manage dairy manure.