Use of compost extract as acclimatization accelerator for methane oxidation biosystems

The acclimatization process of methane oxidation biosystems typically requires several days or even months for the establishment of efficient and stable microbial communities. Here we assessed whether inoculating methane oxidation media with compost extract from pre-acclimatized compost-based materials accelerated acclimatization and increased methane oxidation capacity. Batch assays using biosolids and leaf compost were tested by the addition of compost extract in different dilutions of 100%, 66.6% (33.3% water), and 33.3% (66.6% water) at two initial CH₄ concentrations (10% and 5% v/v). The most promising dilution (33.3%) was then assessed in continuous-flow column experiments with a structured engineered media (biosolids compost-gravel mixture (1:2 v/v). Results from batch assays showed that for the biosolids compost, the addition of compost extract reduced acclimatization time by 54-82% and increased oxidation rates from 16 to 70 µg CH₄·gdw^-1·h^-1. The test with leaf compost showed a slightly smaller gain in acclimatization time (50-66%) and increase in oxidation rates from 11 to 32 µg CH₄·gdw^-1·h^-1. In column tests, inoculation enabled full CH₄ removal within 3 days, whereas in the test without inoculation, the sample was not yet fully acclimatized after 18 days. Microbiological analysis indicated that the compost extract preserved a diverse methanotrophic community. These findings demonstrate that compost extract inoculation is a simple, low-cost, and effective approach to accelerate start-up and enhance early-stage CH₄ removal in methane oxidation biosystems. Implementing this strategy at full scale will likely shorten the stabilization period needed for methane oxidation biosystems to attain their full methane mitigation capacity.