title: Towards the development of a sustainable low-cost bio-active amendment for the in situ remediation of urban brownfield top soil contaminated with Lead (Pb) and Polycyclic aromatic hydrocarbons (PAH)
Creators: name: Sepúlveda Olea, Felipe Esteban
Publisher: name: University of Glasgow
Year: 2020
Subjects: subject: Bioremediation, Pb contamination, PAH contamination, brownfield land, mycoremediation, biostimulation, brewery spent grain.

description: Urban soils present distinctive characteristics resulting from high anthropogenic pressure. Contamination levels (e.g. heavy metals and organic compounds) tend to be higher even in the absence of heavy industry, and can pose a hazard to health. Brownfield land has been defined as any land which has been previously developed, which may or may not be contaminated. Sustainable development of brownfield land encompasses sustainable (e.g. nature-based) methods of restoration-rehabilitation. In the historically industrial city of Glasgow, there are significant areas with derelict land. This not only acts as a key detractor for investment but also denies usability for residents, posing a challenge for the city council. An example of this it the Old Glasgow Meat market site, in the east end of Glasgow, which in preliminary site investigations showed issues with lead (Pb) and polycyclic aromatic hydrocarbon (PAH) contamination. The aim of this PhD project is hence to develop a sustainable, bioactive, low-cost amendment that can both immobilize Pb and support biodegradation of PAHs in urban brownfield top soil, particularly applicable for sites with moderate contamination and no immediate development strategy. Different approaches have been studied for the in situ remediation of Pb contaminated soil, but the immobilization of Pb as pyromorphite (Pb5[PO4]3X; X= F, Cl, B or OH) with phosphate amendments has shown the most promise for the reduction of Pb bioavailability. There are limitations to this method in the urban environment, however, as acidic soil pH is required for Pb and P to react forming pyromorphite. Recent studies have shown that the fungus Paecilomyces javanicus, isolated from Pb contaminated soils in Scotland, is able to induce the biomineralization of Pb as pyromorphite in laboratory cultures. Biodegradation is one of the main processes responsible for the reduction of PAH concentrations in soil. For this reason, both bioaugmentation with allochthonous microorganisms and biostimulation of native microorganisms, with the addition of nutrients, have been used for the remediation of PAH contaminated soil. Biodegradation of PAHs has been extensively researched with bacteria. However, fungi have also been proposed as important promoters of PAH biodegradation. Biosorption of PAHs to microbial biomass may also occur in the environment. Brewery spent grain is an important agro-industrial waste in Scotland, and has a high nutrient content. As a lignocellulosic material it also has potential to stimulate PAHs biodegradation through enzymatic co-metabolism. The use of unprocessed brewery spent grain for bioaugmentation strategies in the context of soil remediation, has not been studied before, to the knowledge of the author. For these reasons, brewery spent grain was selected to be tested as a carrier matrix for the cultivation and subsequent inoculation of P.javanicus in soil. The Pb-biomineralizing capability of P.javanicus combined with the use of brewery spent grain as an inoculum carrier and soil amendment, was studied as a bioaugmentation/biostimulation strategy for the co-remediation of Pb and PAHs in soil. Liquid culture experiments were carried out as a first experimental stage. In cultures spiked with Pb and an organic P source, the ability of P.javanicus to biomineralize Pb as pyromorphite was corroborated with x-ray diffraction (XRD) and energy-dispersive X-ray (EDX) spectroscopy. An initial capture of Pb by P.javanicus as Pb-oxalate, during the first 10 days of incubation, was followed by an increase in pH and a transformation in pseudomorphism to pyromorphite. P.javanicus showed tolerance to the presence of both benzo(a)pyrene (B(a)p) and phenanthrene (Phen) in spiked culture media. With high-performance liquid chromatography (HPLC) analysis of culture media, no Phen was detected in solution after 10 days. Gas chromatography–mass spectrometry (GC-MS) analysis of fungal biomass, showed that biosorption was the main process responsible for the removal of Phen from solution. These liquid culture experiments showed that the use of active P.javanicus biomass has potential for the removal (remediation) of Pb and Phen-PAHs in aqueous matrices. Out of eleven samples collected from the Old Glasgow Meat market, for use as a matrix in co-remediation experiments, three had concentrations of Pb above selected reference guideline values, and none had detectable PAH concentrations. For this reason, Meat market samples were used in preliminary qualitative experiments and spiked soils in quantitative microcosm experiments. Sterile spent grain proved to be a suitable matrix for the cultivation of P.javanicus, and the preparation of inoculum carriers. P.javanicus appeared to be successfully introduced in soil in microcosm and pot experiments, with the use of spent grain as an inoculum carrier and soil amendment to encourage fungal colonisation of soil, indicating that the use of spent grain as an inoculum carrier and soil amendment has significant potential as a bioaugmentation strategy for soil remediation. In microcosm experiments, sorption of Pb and other metals to added brewery spent grain occurred. This could have positive effects in reducing environmental mobility of metals. A reduction of the P concentration in spent grain used as a soil amendment indicated that P may have been released from the brewery spent grain into the soil system, providing an additional positive benefit of spent grain amendments as an organic P source in soils. In microcosm experiments with treated Pb-spiked soils, no significant changes in Pb UBM-bioaccessibility or BCR-residual Pb (sequential extraction) were observed, indicating that the limitations of P amendments in soils with neutral to alkaline pH, were not overcome with P.javanicus-bioaugmentation and that the ability of P.javanicus to biomineralize pyromorphite in liquid cultures was not easily transferred to a soil matrix. While the inoculation of P.javanicus in microcosms with Phen and B(a)p spiked soil did not appear to have an effect in their concentration over time, the amendment of spiked soil with sterile or non-sterile spent grain produced a significant decrease in B(a)p concentrations after 150 days of incubation. In pot experiments with poor quality urban soil, the use of brewery spent grain as an amendment, non-sterile and as a P.javanicus inoculum carrier, significantly increased above ground and root biomass of a native grass and wildflower mixture. A combination of the proposed bioaugmentation/biostimulation strategy with the growth of native grass and wildflower species, may help enhance the biodegradation of PAHs and availability of P for the biomineralization of Pb as pyromorphite, and is hence recommended for future studies on the co-remediation of Pb and PAHs in urban brownfield soils. The use of nature based approaches such as the latter, may be acceptable best practice for brownfield land with poor soil quality and discrete, moderate contamination. Although they may not completely resolve all pollution issues, they improve soil health and may have added benefits such as the provision of ecosystem services.