Biodegradation aspects of Polycyclic Aromatic Hydrocarbons (PAHs): A review

Use of spent mushroom compost to bioremediate PAH-contaminated samples.

One stop mycology

Mushroom industries generate a virtually in-exhaustible supply of a co-product called spent mushroom substrate (SMS). This is the unutilised substrate and the mushroom mycelium left after harvesting of mushrooms. As the mushroom industry is steadily growing, the volume of SMS generated annually is increasing. In recent years, the mushroom industry has faced challenges in storing and disposing the SMS. The obvious solution is to explore new applications of SMS. There has been considerable discussion recently about the potentials of using SMS for production of value-added products. One of them is production of lignocellulosic enzymes such as laccase, xylanase, lignin peroxidase, cellulase and hemicellulase. This paper reviews scientific research and practical applications of SMS as a readily available and cheap source of enzymes for bioremediation, animal feed and energy feedstock.

Potential uses of spent mushroom substrate and its associated lignocellulosic enzymes

ion between fibre lignin and laccase in qualitative difference in temporal phases than laccase does alone. Resulting distinguished lignin modifications may have consequences for subsequent fibre behaviour (Barsberg 2002). Lund & Felby (2001) applied a range of mediators in laccase-modification of spruce and pine fibres and found ABTS and PPT (phenothiazine-10-propionic acid) to be effective in enhancing wet tensile strength of paper handsheets made from the pulp. Similar results were obtained with ABTS by Elegir et al. (2005, 2007). Treatment of fibres with laccase and gallic acid were also reported to change wet tensile strength (Chandra et al. 2004b), indicating that laccase-mediator system can influence properties of the fibre surfaces. Various mediators are therefore currently tested in MDF production with laccase in order to achieve higher reactivity between laccase and lignin and better board properties (Müller et al. 2006). The unfortunately limited availability of cheap and non-toxic mediators is of course a restricting factor in such approaches (Rochefort et al. 2004, Morozova et al. 2007). So far, in laccase-mediated bleaching of lignocellulosic fibres 1-hydroxybenzotriazole and the lignin-derived phenols acetosyringone and syringaldehyde acid have been positively tested as mediators whereas negligible effects were seen with p-coumaric acid (Ibarra et al. 2006, Camamero et al. 2007, Gutiérrez et al. 2007). Oppositional ABTS-mediated depolymerisation and polymerisation effects on kraft lignin samples (González Arzola et al. 2006, Hernández Fernaud et al. 2006) imply that the doses and times of mediators and enzymes applied have to be expected to play an important role in activating of fibre material. In line with this, dosages of 4-hydroxybenzoic acid were most influential in laccase-mediated modification of paper pulp (Chandra et al. 2004a). Further to applications of mediators to improve mechanical properties by laccase action, recent studies suggest that a successive xylanase and laccase treatment with or without mediators might also be useful in efficiently modifying fibre surfaces at least in paper production. As the gallic acid mediator treatment, successive xylanase-laccase treatment has been reported to increase the wet tensile strength of paper (Chandra & Raugaskas 2005, Kapoor et al. 2007). 2-component adhesives based on lignin and enzymes In the wood composite industry, addition of lignosulphonates (spent sulphite liquor) or kraft lignins from sulphate pulping, to conventional PF resins is targeted at replacing parts of the phenol component made from petrochemicals (e.g. see Roffael & Rauch 1971, Shen 1974, Nimz 1983, Ayla & Nimz 1984, Danielson & Simonson 1998a,b, Tejado et al. 2007; further reading in Chapter 16 of this book). Formaldehyde from the PF resin may act in such mixtures as a cross-linker between the reactive sites of the technical lignins and the synthetic phenol binder (Kuo et al. 1991, Vázquez et al. 1999, El Mansouri & Salvadó 2006, 2007). As first

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Anita M. Jackson

Papers

The recovery of lignocellulose-degrading enzymes from spent mushroom compost