MICROBIAL DEGRADATION OF POLYURETHANE

Abstract

Polyurethane is a non-easily degradable synthetic polymer used as packaging material. Its presence and durability in the environment pose global disposal and degradation problem. Polyurethane releases toxic substances with carcinogenic or mutagenic potential during burning in dumpsites. An alternative to burning of waste materials is the use of microorganisms to degrade them. However, little is known about microbial degradation of polyurethane. Therefore, microbial degradation of polyurethane was investigated as an alternative treatment and management method. Polyurethane samples were collected from a dumpsite in the University of Ibadan and rubbish-bins of two fast foods outlets within Ibadan metropolis. The packs were buried at depths ranging from 15-70 cm in the garden soil of Microbiology Department, University of Ibadan. They were exhumed at predetermined intervals between the dry and rainy seasons of June 2010-June 2012 for isolation of microorganisms. The microbial isolates were screened for ability to utilise polyurethane as nitrogen and/or carbon source using mineral salts medium. Selected polyurethane-utilising microorganisms as carbon and nitrogen sources were characterised and identified using standard microbiological procedures and the advanced bacterial identification software database. Biodegradation study was carried out on sterilised soil in the laboratory and garden soil in the field with the best six polyurethane-utilising bacteria. This was done using complete randomised block design with 4x3x2 factorial experiment for isolates combinations (A: Pseudomonas alcaligenes E14+ Providencia pseudomallei D25, B: Enterobacter amnigenus D12+ Vibrio sp. C32, C: Pseudomonas aeruginosa E32 + Providencia pseudomallei D21 and D: Consortium of the six bacteria) and biostimulation treatments (cassava peels, potato peels, no peels) at 1 and 3 month periods. Changes in the functional groups of degraded polyurethane samples were determined using Fourier transform infrared spectroscopy. Weight loss of polyurethane samples was monitored by measurement. Data were analysed using ANOVA at p = 0.05.

Of the 106 bacterial isolates obtained, 94 utilised polyurethane as carbon, nitrogen or both with highest occurrence (26.0 %) at 70 cm depth. Eighty-seven per cent of the isolates were obtained during the rainy season. Fifteen bacteria isolates that utilised polyurethane as carbon and nitrogen sources were: Pseudomonas (4), Corynebacterium (1), Providencia (2), Enterobacter (2), Comamonas (2), Micrococcus (1), Arthrobacter (1), Vibrio (1) and Bacillus (1). Fungi isolates could not utilise polyurethane. Percentage degradation of polyurethane with potato peels, cassava peels and no peels was respectively 91.0, 33.0 and 57.2 % in laboratory and 35.9, 0.0 and 76.3 % in field. Ether peak was removed by B, C and D in the field biostimulated with cassava peels. Carbonyl peak area was reduced by 87.6 % with D biostimulated with potato peels in the laboratory and changes in the functional groups were significant. The highest weight losses were 22.5 and 15.0 % for the field and laboratory studies after one month.

The isolated bacteria degraded the polyurethane by removal of resistant functional groups. Thus they could be used for degradation and management of polyurethane in the Nigeria environment.