White-rot Fungus
Background
Fungal remediation refers to the use of fungi to remediate organic soil contaminants, primarily hydrocarbons. One group of fungi, Phanerochaete chyrsosporium , or white-rot fungus, produces a family of enzymes called lignin peroxidases, or ligninases, which have extensive biodegrative properties. Remediation of soil using white-rot fungus has been tested in both in situ and reactor-based systems.
Applicability
White-rot fungus is known to degrade polyaromatic hydrocarbons (PAHs), chlorinated aromatic hydrocarbons (CAHs), polycyclic aromatics, polychlorinated biphenyls, polychlorinated dibenzo(p)dioxins, the pesticides DDT and lindane, and some azo dyes [1]. Degradation of PAHs, which include benzo(a)pyrene, pyrene, fluorene, and phenanthrene, is favored at nitrogen-limiting conditions and low pH (about 4.5) [2]. It has been documented that white-rot fungus is able to mineralize tri-, tera-, and pentachlorophenol (PCP), and a group of microbes in soil can completely mineralize PCP [2]. Degradation of cyclodiene insecticides, including chlordane, by white-rot fungus has been demonstrated [2]. White-rot fungus has been observed to degrade TNT in laboratory-scale studies (using pure cultures), however, factors that limit their effectiveness (see below) may retard wide-spread use in the field. Results from bench-scale studies of mixed fungal and bacterial systems indicate that most of the degradation of TNT is attributable to bacteria and that most of the losses of TNT is due to adsorption onto the fungus and soil amendments [3].
Limitations
A major limitation of white-rot fungus is its sensitivity to biological process operations. It has been observed that the fungus does not grow well in suspended cell systems, enzyme induction is negatively affected by mixing action; and the ability of the fungus to effectively attach itself to fixed media is poor [1]. High concentrations of TNT in the contaminated media, toxicity inhibition, chemical sorption, and competition with indigenous microbes also can limit applicability [3]. The transformations by white-rot fungus are known to be slow and the full potential of its catabolic activity has not been reported widely in the field [2].
Performance
White-rot fungus can grow in a wide temperature range. No growth is observed below 50 deg. F and no significant change in growth rate occurs between 86 and 102 deg. F. It has been reported that optimal growth of white-rot fungus occurs at 102 deg. F, pH range of 4.0 to 4.5, and high oxygen content [1]. In addition, lignin degradation using pure oxygen is 2 to 3 times greater that that using air, the growth rate of white-rot fungus increases significantly when water potential increases from 1.5 to 0.03 MPa, and growth in soil increases directly with nitrogen content [1]. Optimal moisture content is 40-45%.A pilot-scale treatability study using white-rot fungus was performed at a former ordnance area of a Naval submarine base (Bangor, Washington). The initial TNT concentration of 1,844 ppm was reduced 41%, however, final concentration was well above the target level of 30 ppm. Concentrations of 1,267 ppm and 1,087 ppm were attained after 30 and 120 days of treatment, respectively.
Data Requirements
Soil moisture, pH, and temperature need to be monitored. In addition, initial and final explosive contaminant levels, soil characteristics, and levels of other contaminants present in the soil must be known and evaluated.
Cost
Estimated cost for remediation of soil using white-rot fungus is $75 per cubic yard of contaminated soil [3].
Status of Technology
Laboratory- and bench-scale research has been performed. Very few, if any, large scale commercial applications have been conducted.
References
1. Cookson, J.T., 1995, Bioremediation Engineering: Design and Application, McGraw Hill, New York, NY.2. Suthersan, S., 1997, Remediation Engineering Design Concepts, CRC Press, Boca Raton, FL.
3. The EPA Office of Research and Development, 1999, Alternative Treatment Technology Information Center (ATTIC) database.