Biodegradation of various forms of cellulose and chitin in natural waters with different salinity

Abstract

This study evaluated the ultimate aerobic biodegradability of cellulose and chitin samples in natural water. The as-prepared cellulose powder, microcrystals, and gel, together with the chitin microcrystals, were observed under an electron microscope and characterized using Fourier transform infrared spectroscopy, X-ray diffraction, and nitrogen-adsorption measurement techniques. The samples were then subjected to biochemical oxygen demand testing at 20 °C, in the dark, for 30 d, in fresh water, brackish water, and seawater collected from the Kamogawa River and Osaka Bay, Japan. The biodegradability of the cellulose and chitin samples was greater than that of the poly(ε-caprolactone) film used as a positive control sample and was in the order of chitin microcrystals > cellulose hydrogel ≈ cellulose microcrystals > cellulose powder. These results indicate that the higher the specific surface area, the higher the degree of degradation of the cellulose samples. Chitin microcrystals displayed a higher degree of degradation than cellulose microcrystals although both had near-identical specific surface areas, indicating that chitin is more easily degraded than cellulose in natural waters. The degree of degradation in natural water was in the order of fresh water > brackish water > seawater. This trend implies that the higher the salinity, the more the degradation was suppressed.