Anaerobic Biodegradation of Polyhydroxybutyrate in Municipal Sewage Sludge

Anaerobic biodegradation in sewage sludge of polyhydroxybutyrate (PHB) was investigated. Evolved gaseous carbon was measured to assess biodegradability according to ASTM D5210. Mass-loss experiments were performed to determine degradation kinetics. Changes in the polymer properties were investigated. The impact of a natural plasticizer [tributyl citrate (TBC)] on biodegradation was determined. Polylactic acid was also biodegraded for comparison. Melt-pressed plates of PHB (with thicknesses of 0.24, 0.5, 1.2, 3.5, and 5.0 mm) were biodegraded to investigate the relationship between initial mass:initial surface area ratios and decay rates. Scanning electron microscopy micrographs of degraded specimens were recorded for visual illustration of the degradation process. A relationship between initial mass:initial surface area and degradation rates indicates that the thickness and surface area of the material affect its degradation. The degradation rates were impacted by the sewage sludge activity. TBC additive hindered PHB's rate of degradation. Thermal properties, molecular bonding, and molecular weight measured by differential scanning calorimetry, Fourier transform infrared, and size exclusion chromatography, respectively, were only slightly affected by biodegradation, indicating that recycling PHB will not affect its performance.