Potential Mineralization of Various Organic Pollutants During Composting

The objectives of this work were to determine the potential mineralization of various organic pollutants that are likely found in compostable materials during composting, and to evaluate the participation of the microflora of the thermophilic and maturation composting phases in pollutant mineralization. Four composts were used: a biowaste compost (BioW), a municipal solid waste compost (MSW), a green waste compost (GW) and a co-compost of green waste and sludge (GW+S). In each composting plant, two samples were withdrawn: one in the thermophilic phase (fresh compost) and one in the maturation phase (mature compost) to have the microflora of thermophilic and maturation phases active, respectively. The mineralization of 5 organic pollutants, 3 polycyclic aromatic hydrocarbons (PAHs) (i.e., phenanthrene, fluoranthene and benzo(a)pyrene), 1 herbicide (dicamba) and 1 polychlorinated biphenyl (PCB, congener 52), was measured in a laboratory setting during incubations at 60 C in fresh composts and at 28 C in mature composts. All molecules were ¹⁴C-labeled, which allowed the mineralization of the molecules to be measured by trapping of produced ¹⁴CO₂ in NaOH. Their volatilization was also measured by trapping molecules on glass wool impregnated with paraffin oil. Mineralization of the organic molecules was only observed when the maturation microflora was present in the mature composts or when it was inoculated into the fresh compost. Phenanthrene mineralization of up to 60% in the fresh GW+S compost was the only exception. Mineralization of PAH decreased when the complexity of the PAH molecules increased. Mineralization of phenanthrene and fluoranthene reached 50%–70% in all mature composts. Benzo(a)pyrene was mineralized (30%) only in the MSW mature compost. Dicamba was moderately mineralized (30%–40%). Finally, no PCB mineralization was detected, but 20% of the PCB had volatilized after 12 d at 60 C. No clear difference was observed in the degrading capacity of the different composts, and the major difference was the larger mineralizing capacity of the maturation microflora compared with the thermophilic microflora.