Biodegradation of lignin in a compost environment: a review

Composting is nowadays a general treatment method for municipal solid waste . Compostable household waste contains, together with vegetable material, v arying amounts of papers and boards. In the European Union composting is re garded as one recycling method for packages and this will probably favour c ompostable packages, like papers and boards, in the future. Paper is made u p of lignocellulose and it may contain up to 20% of lignin. Efficient degra dation of papers in composting plants means that biodegradation of lignin i s also needed. However, very little is known about lignin degradation by mi xed microbial compost populations, although lignin degradation by white-rot fungi has been extensively studied in recent years. Organic material is co nverted to carbon dioxide, humus, and heat by compost microorganisms. It is assumed that humus is formed mainly from lignin. Thus, lignin is not total ly mineralized during composting The elevated temperatures found during the thermophilic phase are essential for rapid degradation of lignocellulose. Complex organic compounds like lignin are mainly degraded by thermophilic m icrofungi and actinomycetes. The optimum temperature for thermophilic fungi is 40-50 degrees C which is also the optimum temperature for lignin degrad ation in compost. (C) 1999 Elsevier Science Ltd. All rights reserved.