Biodegradable Plastics

1999 Nippon Shokuhin Kagaku Kogaku kaishi  
Sequencing batch reactor (SBR) systems were used for the development of a system and operating procedures for the high production and internal storage of polyhydroxyalkanoates (PHAs) by wastewater treatment (activated sludge) bacterial cultures. The SBRs were operated with microaerophilic/aerobic (MAA), anaerobic/aerobic (AN/AE), and fully aerobic (AE) conditions. It was found that unbalanced growth conditions stimulated massive PHA production in activated sludge biomass. Operating conditions
more » ... rating conditions had a significant effect on PHA production and the composition of the accumulated copolymer when either laboratory prepared mixtures of organics or a high acetic acid industrial wastewater were used as the organic substrate mixture. Fully AE conditions with nitrogen (N) and phosphorus (P) limitations were the optimum conditions for PHA production when the laboratory prepared mixtures of organics were used as the substrate. However, fully AE conditions with combinations of N, P, and potassium (K) limitations were better for PHA production when a high acetic acid industrial wastewater was the substrate. Limitation or partial limitation of a single nutrient, either N or P, as used for commercial production utilizing pure cultures, did not promote massive PHA production in activated sludge biomass compared to the simultaneous limitation of two or more nutrients. A maximum cellular PHA accumulation of 70%TSS was obtained under fully AE conditions with multiple alternating periods of growth and N&P limitations. Microaerophilic/aerobic or AN/AE cycling promoted less PHA production compared to fully AE conditions. The relative amounts of the PHA copolymers formed, i.e., polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV), were different under different operating conditions, even though the types and amounts of volatile fatty acids (VFAs) in the feed were the same. It was determined that high total phosphorus (TP) content inside the bacterial cells had a significant detrimental impact on PHA production by activated sludge biomass. A two-stage bioprocess was a better approach for obtaining activated sludge PHA accumulation because a growth phase was necessary to grow a bacterial population that contains minimal TP before starting the subsequent PHA accumulation iii phase. Seeding sludge obtained from a conventional fully aerobic wastewater treatment system was more suitable than seed obtained from a biological phosphorus removal (BPR) system because bacterial populations from BPR systems tended to convert organic substrates to intracellular carbohydrate content rather than PHA under nutrient limitation conditions. The molecular weights and melting point temperatures of PHAs produced by the mixed culture of activated sludge biomass were comparable to those obtained from pure cultures and have the potential to be used for commercial applications. The results of this study indicate that activated sludge biomass has considerable potential for PHA production for commercial purposes, and likely could do so utilizing wastewater sources of organics. In particular organic rich, nutrient limited wastewaters have potential for efficient PHA production. iv
doi:10.3136/nskkk.46.763 fatcat:abjljqwoq5bazdr3wjeetn3f7e