Dynamic population changes during a bioaugmented sewage sludge composting process: Improvement of pharmaceutical active compounds degradation and conversion into an organic soil amendment

Bioaugmentation has resulted in an interesting tool to improve composting technologies. However, the structure and dynamic of native populations might be affected, hence, the whole process performance. Here, we aimed to identify and evaluate the fungal and bacterial dynamic changes produced by the bioaugmentation with an exogenous inoculant: Penicillium oxalicum XD 3.1 and an endogenous natural consortia obtained from enrichment: enriched culture during a sewage sludge composting process (applied and designed for the improvement of pharmaceutical active compounds degradation, under real conditions). To do so, microbial structure of the enriched culture was first described and then, the microbial dynamic population into the composite samples were studied. Microbial DNA was obtained from the enriched culture (before and after the enrichment) and from the compost (at key stages of the process: inoculation, thermophilic and maturation). The amplicon sequencing of 16S rRNA genes and internal transcribed spacer (ITS) region for bacteria and fungi was then performed using an Illumina Platform. Results showed that fungal and bacterial α-diversity in bioaugmented piles was significantly changed during inoculation and thermophilic stages. The inoculation and the fluctuation of the physicochemical parameters, altered by the bioaugmentation, explained the microbial diversity changes. Temperature, mineral matter, conductivity, dry matter, and total solids were the significant explanatory variables for diversity, dominance and ASVs counts. Redundancy analyses of β-diversity revealed the asynchronous interaction with all physicochemical parameters that varied according to the composting stage. In general, these outcomes lead to a deeper understanding of the promising combined bioaugmentation-composting mechanism.