Synergistic Effect of Chemical and Photo Treatment on the Rate of Biodegradation of High Density Polyethylene by Indigenous Fungal Isolates

摘要

Although the degradation of plastic is achieved by photo-degradation, thermal degradation, and chemical degradation, the time taken for degradation of plastic by the above treatments requires several years and also complete degradation cannot be achieved. Thus this paper deals with synergistic effect of chemical and photo-oxidative treatments on the possibility of accelerating rate of biodegradation of polyethylene..The microorganisms used in this study were isolated from High Density polyethylene (HDPE) film buried in soil for 3 months and were characterized as Aspergillus niger, Aspergillus flavus, Aspergillus oryzae. Polyethylene films were subjected to microbial treatment with as well as without abiotic treatment (prooxidant and U.V irradiationtreatment).The films were exposed to 1% proxidant solution, manganese stearate for 2 days which acts as a UV sensitizer followed by U.V irradiation (312nm) for 50 hrs. These pretreated films were used as sole carbon source in Czapek-Dox medium inoculatedwith fungal strains. The strains grew better in a medium having abiotically treated polyethylene film than in a medium containing untreated polyethylene film. The changes in properties of HDPE films were determined by Tensile strength, percentage of elongation, elongation break and Fourier Transform infrared spectroscopy (FTIR) analysis. Tensile strength, percentage of elongation and elongation break results showed that among abiotically treated and untreated films, abiotically treated films have undergone more degradation after incubation with fungal strains for one month. Among all the fungal strains A.oryzae grew well and showed maximum biodegradation activity. UV sensitizer treatment followedby Ultraviolet irradiation before incubation with A.oryzae increased the biodegradation by 72% (reduction in percentage of elongation) and when compared with the untreated HDPE, 15% increase was found. FTIR results of abiotically treated HDPE film clearly showed generation of carbonyl peak at 1718.32 cm'1 which was not found in untreated film (control). And when these treated films were incubated in medium containing fungal strains there is a reduction in carbonyl peak to 1715.33, 1715.41 and 1716.42 cm~(-1) respectively by A.oryzae, A.niger and A.flavus. This concludes that UV irradiation before incubation caused functional groups to be generated in the polyethylene and this resulted in biodegradation due to consumption of generated carbonyl groups by fungal strains which were evident by reduction in carbonyl peak. Among the treated HDPE films incubated in medium containing fungal strains, HDPE film incubated in Aspergillus oryzae had showed greater reduction in carbonyl group (1715.33 cm~(-1)).