Fungal Technologies for the Treatment of Hazardous Waste

R. A. Haimann CH2M HILL, 251 0 Red Hill Avenue, Santa Ana, CA 92705

Fungi have been harnessed and utilized by humans for thousands of years for many diverse applications. In response to demand for innouatiue technologies to treat hazardous wastes and materials, fungi have been used to degrade hazardous organic waste. This paper presents a review of recent literature regarding the use of

fungi for treating hazardous and other wastes.

INTRODUCTION

Many production processes in use today result in the for- mation o f waste materials which havc hazards associated with them [6, 7, 8, 10, 111. The management and treatment of thesc hazardous wastes pose technical challenges for the en- gineering and scientific community. Recent legal require- ments in the United States place responsibility for damages caused by the wastc on the producer of that waste as well as on other parties who take control of the waste after its pro- duction [ 23, 251. These liabilities last for as long as the waste does. Thcrefore, therc is strong incentive to destroy the wastc or to convert it into harmless materials [10].

HAZARDOUS WASTE TREATMENT

Bacterial-based biological processes have been used to de- grade non-hazardous organic wastes such as sewage into the harmless mineral compounds of carbon dioxide and water [ 101. Recently, biological processes have been applied to haz- ardous wastes with the goal of achieving the same objective. Bacterial based processes have shown success with some xcnobiotic compounds [ 91. There are other xenobiotic com- pounds, however, which appear to be recalcitrant to degrada- tion by bacteria [ I , 3, 9, 19, 20, 231. These compounds tend to be complex organic molecules with one or more aromatic rings and/or halogen substitution. These compounds are also found to be persistent in the natural environment [2] .

Work with fungi-based biological processes have shown that certain lignin-degrading fungi are capable of degrading these complex xenobiotic compounds which are recalcitrant to bac- terial degradation [ 1-23]. Work has progressed from re-

search to commercial applications [ 9, 131. Additionally, in the pulp and paper industry, the same fungi have bccn used in wood-pulping and bleaching applications to reduce costs and waste volumes [ 14, 211.

In particular, the white rot fungi have shown great utility for these applications [I-231. White-rot fungi are a class of fungi which include many genera that are capable of degrad- ing lignins and celluloses. Lignins are complex multi-ringed organic chemicals which constitute a portion of vegetative cell walls. Celluloses are polysaccharides which form rigid and recalcitrant structural matrices of vegetative cell walls. White-rot fungi are responsible for wood decay in nature which is the rate limiting step in the global carbon cycle [14, 171.

LIGNIN DEGRADATION

Lignins, as a class of chemicals, are similar in nature to complex xenobiotic chemicals which are recalcitrant to bacte- rial degradation. Therefore, organisms which can degrade lignins may also be able to degrade those complex xenobiotic chemicals. Such has been observed. Bumpus et al. in 1985 reported that the white-rot fungus Phanerochaete chrysospo- riurn successfully mineralized DDT, 3,4,3’,4‘-tetrachlorobi- phenyl, 2,4,5,2’,4‘,5’-hexachlorobiphenyl, 2,3,7,8-tctrachloro- dibenzo-p-dioxin, lindane, and benzo[a]pyrene to carbon dioxide [ 31. Their study also concluded that the metabolism of those compounds was dependent on the lignin-degrading enzyme system of that fungus. Further investigations have shown white-rot fungi to mineralize a host of xenobiotics [ 171. These chemicals include Aroclor 1254, 4-Chloroaniline, 3,4-Dichloroaniline, Pentachlorophenol, Triphenylmethane dyes, 2,4,5-Trichlorophenoxyacetic acid, Phenanthrene, An-

Environmental Progress Wol. 14, No. 3) August, 1995 201

thracene, Fluoranthene, Benzo[b]fluoranthene, Bcnzo[klflu- oranthene, Indeno[ghi]pyrene, Benzopcrylen, Azo and hete- rocyclic dyes, and 2,4,6-Trinitrotoluene.

Investigations have indicated that t o enhance growth o f the lignin-degrading system in white-rot fungi it is necessary to provide a source of carbohydrates for growth, maintain nitro- gcn-limiting conditions and an aerobic environment [Y, 10, 171. Lignin alone is not sufficient for growth of the organ- isms. Therefore another carbohydrate source is necessary. The lignin-degrading system is expressed under nitrogcn- limiting conditions similar to those found in wood tissue.

A water treatment process (MyCOR-Mycelial Color Re- moval) utilizing P. chrysosporium has been investigated as a dccolorization process for Kraft pulp liquor [10]. The patented reactor is a rotating biological contactor (RBC). Studies involving the reactor have shown degradation of pen- tachlorophcnol. 2,4,6-trinitrotoluene, 2,4-dinitrotoluene and decoloration of pink water associated with munitions produc- tion [ 101. Further investigations with white-rot fungi have shown decolorization and organic degradation of Kraft E l pulp mill effluent [22].

PAH DEGRADATION

Field investigations in which creosote and pentachlorophe- no1 contaminated soils were inoculated with white-rot fungi have shown degradation of polycyclic aromatic hydrocarbons (PAHs) and pentachlorophenol in soils [10, 11, 15, 161. White-rot fungi arc not found in soil environments in nature. However thesc studies indicate that white-rot fungi can suc- cessfully degrade complex xenobiotics in soils if the soils are inoculated properly and appropriate conditions are main- tained.

Rcscarch continues, sponsored by the United States Envi- ronmental Protection Agency and others, to answer questions regarding how these organisms work and how engineers and scientists can enhance white-rot fungi’s xenobiotic degrading properties for waste treatment and site restoration [ 101. Commercial ventures have been established to apply this technology [ 9 , 13, 181. Intec One-Eighty Corp. in Logan, Utah is the exclusive licensee of Utah State University to commcrcialize white-rot fungus technology. Mycotech in Butte, Montana was founded in 1982 to develop and produce fungi as biopcsticides as well as for bioremediation. Tien- zymc in State College, Pennsylvania was founded in 1991 to provide whitc-rot fungi enzymes to the rcscarch community. The Lambert Spawn Company of Coatesville, Pennsylvania has produced fungal inoculum for various purposes since 1904 and is now producing white-rot fungus inoculum for environ- mental applications.

OTHER MICROBIAL PROCESSES

Of note are other applications of fungi which relate to environmental quality. Microbial biomass has been shown to selectively and rapidly take up metal ions from solution [4, 121. A fungus, Aspergillus oryzae was reported to take up heavy metal ions in its mycelial mass [12]. I n another study, Cadmium uptake efficiencies of 97% were reported for an isolatcd fungus [ 41.

An air-phase biofilter was cstablishcd with styrene-degrad- ing fungi in a laboratory setting in which degradation of styrene was observed at a rate of 70 g styrcne per m3 filter bed per hour [5].

Several studies have been conducted using white-rot fungi to pulp wood [ 141. Pulping wood is the removal of lignins to producc stronger more resilient fibers. White-hot fungi, un- der certain conditions, do this naturally and can remove a

higher percentage of lignin than standard mechanical and chemical pulping methods 1/41.

Studies have been conducted using white-rot fungi to bleach Kraft paper pulp [ Z I ] . The Kraft process is a chemical method of pulping wood. One disadvantage is that the residual lignin in the final pulp is a dark brown and so must be bleached for many commercial paper products. The bleaching process typ- ically uses chlorine which produces a waste stream which requires special handling and treatment. White-rot fungi have been shown to degrade this dark-brown residual lignin hence reducing or eliminating the chlorine needed in the bleaching process [ 211.

Another noteworthy study is the production of recyclable plastic materials with a lignin component [20]. This study concludes that grafting of lignin with synthetic side chains such as polystyrene will result in a much more biodegradable material than synthesis of a polymer from pure, petroleum- based products.

CONCLUSION

In conclusion, fungal metabolic processes appear to have many applications to treatment of waste products. Research is advancing to understand how to harness these processes for waste treatment. Commercialization has begun for some applications and is likely to continue.

LITERATURE CITED

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24. Resource Conservation and Recovery Act, 42 USC 6901- 6992k.

25. Comprehensive Environment Responsibility Cleanup and Liability Act, 42 USC 9601-9675.

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