Mid Sweden University

Mycoremediation, the application of fungi for pollutant degradation, offers a sustainable solutionfor bioremediating contaminated environments. In mixed microbial settings, microbialcompetition can influence the efficiency of fungi by modulating pollutant degradation andnutrient availability. We investigated the bioremediation potential of boreal white-rot fungi(WRF) in fiberbank sediments, targeting organic pollutants such as polycyclic aromatichydrocarbons (PAHs) and potentially toxic elements (PTEs). Previously isolated and identifiedthirteen WRF species were screened in sterilized and unsterilized substrates to evaluate theeffects of microbial interactions on pollutant degradation and metal uptake. Key findingsrevealed that unsterilized fiberbank material supported superior PAH degradation, withTrametes hirsuta achieving up to 94% removal, suggesting synergistic interactions between WRFand native microbial communities. Conversely, sterilized substrates enhanced PTE uptake, withPhlebia tremellosa demonstrating significant accumulation of cadmium, bioconcentration factor(BCF) of 5.56 in sterile conditions and 0.85 in unsterile conditions, and lead, BCF of 1.65 understerile conditions, and 0.38 for unsterile conditions, this enhanced accumulation might be dueto reduced microbial competition. Statistical analyses confirmed significant differences (p <0.001) in pollutant removal and metal uptake between the two substrate conditions. Theseresults underline the importance of tailoring bioremediation strategies to substrate conditions.A dual approach, employing unsterilized substrates for organic pollutant degradation andsterilized substrates for metal accumulation, emerges as a promising framework. Futureapplications could focus on large-scale implementation of these strategies to rehabilitateindustrially contaminated sites like fiberbanks, balancing ecological sustainability withremediation efficacy.

Background

Wastewater discharges from the old pulp and paper industry led to the accumulation of contaminated wood pulping fbers and debris—referred to as fberbanks (FB)—in the Baltic Sea and freshwater bodies across Sweden and other pulp-producing countries. These anthropogenic sediments are polluted with toxic metal(oid)s and persistent organic pollutants, and their decomposition releases greenhouse gases. Phytoremediation ofers a nature-based solution for the ex-situ treatment of these fbrous sediments, but they present unique challenges due to the abundant and unstable organic matter and aged pollution. This study aims to identify potential plant candidates and to address the limitations of fberbanks as a plants growing media for phytoremediation.In a greenhouse experiment, we assessed the performance of fve plant species (Brassica juncea, Brassica napus, Helianthus annuus, Hordeum vulgare, and Poa annua) grown in substrates formulated with fberbank. The evaluation included plant growth parameters, bioconcentration and uptake efciency of metal(oid)s (V, Cr, Co, Ni, Cu, Zn, As, Cd, and Pb), and the degradation of polycyclic and linear hydrocarbons.

Results

Despite initial concerns, fberbanks displayed favorable physical characteristics and a degree of fertility conducive to plant growth. Even though all tested species seeds could cope with fberbanks acute toxicity, H. vulgare and P. annua showed better tolerance to the fberbanks substrates and superior aerial biomass development, which promoted a highest toxic metal(oid)s uptake efciency, regardless of lower bioconcentration factors for most of the target elements. Zn (17.16–23.25 mg/kg of FB), Cu (4.18–6.48 mg/kg of FB) and Cr (1.05–1.36 mg/kg of FB) were most efectively taken up by these plants. The uptake of Co (0.04–0.18 mg/kg of FB) and Ni (0.05–0.17 mg/kg of FB) was lower. As (0.01–0.02 mg/kg of FB), Cd (0.02–0.06 mg/kg of FB), Pb (0.02–0.04 mg/kg of FB) and V (0.02–0.03 mg/kg of FB) phytoextraction was not signifcant. None of the species exhibited a signifcant removal of targeted organic pollutants.

Conclusions

Phytoremediation, either on its own or in combination with other strategies, shows promise for the remediation of fberbanks. However, further research is needed to understand how the organic matrix and long-term underwater aging of fberbanks afect pollutants bioavailability.

Fiberbanks refer to a type of fibrous sediment originated by the forestry and wood pulping industry in Sweden. These anthropogenic sediments are significantly contaminated with potentially toxic elements, and a diverse array of organic pollutants. Additionally, these sediments are of environmental concern due to their potential role in greenhouse gas emissions. Given the environmental risks posed by these sediments, the development of effective remediation strategies is of critical importance. However, no specialized methods have been established yet for the cleanup of this specific type of contaminated sediments. To identify effective fungal species for the mycoremediation of the fiberbank substrate, we performed a detailed screening experiment. In this research, we primarily aimed at assessing both the growth capacity and the proficiency in degrading organic pollutants of 26 native white-rot fungi (WRF) species. These species were sourced from natural forest environments in northern Sweden. The experimental setup involved evaluating the WRF on plates containing fiberbank material with a central Hagem-agar disc to closely monitor the interaction of these species with fiberbank substrates. Among the fungi tested, Laetiporus sulphureus exhibited the highest growth area percentage at 72%, followed by Hymenochaete tabacina at 68% and Diplomitoporus crustulinus at 67%. For the removal of 2–3 ring polycyclic aromatic hydrocarbons (PAHs), Phellinus punctatus led with 68%, with Cystostereum muraii at 57% and Diplomitoporus crustulinus at 49%. Regarding the removal percentage of 4–6 ring PAHs, Diplomitoporus crustulinus showed the highest efficiency at 44%, followed by Phlebia tremellosa at 40% and Phlebiopsis gigantea at 28%. 

Lignocellulose-bearing sediments are legacies of the previously unregulated wastewater discharge from the pulp and paper industry, causing large quantities of toxic organic waste on the Baltic Sea floor and on the bottom of rivers and lakes. Several km2 are covered with deposits of lignocellulosic residues, typically heavily contaminated with complex mixtures of organic and inorganic pollutants, posing a serious threat to human and ecological health. The high toxicity and the large volume of the polluted material are challenges for remediation endeavours. The lignocellulosic material is also a considerable bioresource with a high energy density, and due to its quantity, it could appeal to commercialization as feedstock for various marketable goods. This study sets out to explore the potential of using this polluted material as a resource for industrial production at the same time as it is detoxified. Information about modern production methods for lignocellulosic material that can be adapted to a polluted feedstock is reviewed. Biochemical methods such as composting, anaerobic digestion, as well as, thermochemical methods, for instance, HTC, HTL, pyrolysis, gasification and torrefaction have been assessed. Potential products from lignocellulose-bearing sediment material include biochar, liquid and gaseous biofuels, growing substrate. The use of a contaminated feedstock may make the process more expensive, but the suggested methods should be seen as an alternative to remediation methods that only involve costs. Several experiments were highlighted that support the conception that combined remediation and generation of marketable goods may be an appropriate way to address polluted lignocellulose-bearing sediments. Graphic abstract: [Figure not available: see fulltext.]