Do Bio-Inoculants Improve Composting Under Field Conditions? Comparative Study of Homemade, Commercial, and Laboratory-Developed Bio-Inoculants

Microbial bio-inoculants have been proposed to enhance composting efficiency; however, relatively few studies have evaluated their effectiveness under real operating conditions. This study evaluated three bio-inoculant application protocols, including an artisanal inoculant, a commercial inoculant, and a laboratory-developed microbial consortium, for the composting of organic solid waste in a decentralized rural treatment plant in Colombia. Temperature evolution, physicochemical changes, and selected microbiological quality indicators were monitored during a 90-day composting process. All treatments exhibited the characteristic mesophilic, thermophilic, and cooling phases, reaching maximum temperatures between 64.6 and 67.7 °C. Although differences were observed among the evaluated application protocols in thermal descriptors and in the magnitude of certain physicochemical changes, the uninoculated control exhibited composting dynamics and final physicochemical characteristics comparable to, and in some cases greater than, those of the inoculated treatments. All treatments complied with the microbiological criteria of the Colombian Technical Standard NTC 5167 evaluated in this study, with final total coliform counts below the regulatory limit and no Salmonella spp. detected. These findings indicate that none of the evaluated bio-inoculant application protocols provided a consistent advantage over the uninoculated control under the evaluated conditions. Consequently, the effectiveness of bio-inoculant application protocols should not be assumed to be effective or generalized across composting systems, but should instead be demonstrated under the specific substrate composition and operational conditions in which they are intended to be applied.