Effect of Biostimulation and Bioaugmentation on Degradation of Polyurethane Buried in Soil

This work investigated biostimulation and bioaugmentation as strategies for removing polyurethane (PU) waste in soil. Soil microcosms were biostimulated with the PU dispersion agent “Impranil” and/or yeast extract or were bioaugmented with PU-degrading fungi, and the degradation of subsequently buried PU was determined. Fungal communities in the soil and colonizing buried PU were enumerated on solid media and were analyzed using denaturing gradient gel electrophoresis (DGGE). Biostimulation with yeast extract alone or in conjunction with Impranil increased PU degradation 62% compared to the degradation in untreated control soil and was associated with a 45% increase in putative PU degraders colonizing PU. Specific fungi were enriched in soil following biostimulation; however, few of these fungi colonized the surface of buried PU. Fungi used for soil bioaugmentation were cultivated on the surface of sterile wheat to form a mycelium-rich inoculum. Wheat, when added alone to soil, increased PU degradation by 28%, suggesting that wheat biomass had a biostimulating effect. Addition of wheat colonized with Nectria haematococca, Penicillium viridicatum, Penicillium ochrochloron, or an unidentified Mucormycotina sp. increased PU degradation a further 30 to 70%, suggesting that biostimulation and bioaugmentation were operating in concert to enhance PU degradation. Interestingly, few of the inoculated fungi could be detected by DGGE in the soil or on the surface of the PU 4 weeks after inoculation. Bioaugmentation did, however, increase the numbers of indigenous PU-degrading fungi and caused an inoculum-dependent change in the composition of the native fungal populations, which may explain the increased degradation observed. These results demonstrate that both biostimulation and bioaugmentation may be viable tools for the remediation of environments contaminated with polyurethane waste.The polyester polyurethanes (PU) are a diverse group of synthetic polymers with many industrial and commercial applications, including insulating and packaging foams, fibers, fabrics, and synthetic leather goods (20). These polymers contain intramolecular bonds analogous to those found in biological macromolecules (such as ester and urethane linkages), making them susceptible to enzymatic degradation and assimilation by environmental microbial communities (17, 42). The susceptibility of plastics to biodegradation is of increasing importance as the generation of plastic waste material continues to increase and plastics now comprise more than 30% of household waste in the United States (32). By exploiting the biodegradability of plastics such as PU, bioremediation by microorganisms in the environment shows great potential for reducing the burden of plastic waste.Although the diversity of natural microbial populations often means that the potential for waste remediation exists at polluted sites, factors such as absence of electron acceptors or donors, low nitrogen or phosphorus availability, or a lack of induction of the metabolic pathways responsible for degradation can inhibit waste remediation. In these cases, addition of exogenous nutrients can enhance the degradation of waste, a process known as biostimulation. Biostimulation of in situ microbial communities has been used to enhance the degradation of crude oil (22, 29), tetrachloroethene (19), diesel fuel (24, 28), and polyaromatic hydrocarbons (41).If communities native to polluted sites lack significant populations of waste degraders, microbes with the desired phenotypes can be added exogenously in a process known as bioaugmentation. This approach has been successfully used to remediate a wide range of waste products, from hydrocarbons (8, 34) to heavy metals (15, 16). Numerous PU-degrading organisms have been isolated from a range of environments (6, 9, 26, 30), and this has provided a large reservoir of organisms for potential bioaugmentation of PU waste.This study was the first study to assess the potential of biostimulation and bioaugmentation as methods for accelerating the degradation of PU waste in the environment. The response of fungal communities in soil microcosms to (i) addition of nutrients or (ii) a large influx of PU-degrading fungi was investigated using culture-based and molecular techniques, and the effect of these treatments on the degradation of PU coupons buried in these microcosms was determined.