Process Optimiza For Polyhydroxyalkanoates Production Using Mixed Bacterial Cultures

Polyhydroxyalkanoates (PHA) are a class of intracellular carbon source and energy storage materials which can be synthesized by many species of microorgani- sms under imbalanced nutrient conditions. PHA have no harm to environment and can be completed biodegraded, therefore having thepotential to be widely applied in the future. The production of PHA from residual sludge is a new way for PHA synthesis. Sequencing batch reator was applied to inoculate the excess sludge from the secondary sedimentation tank of municipal wastewater treatment plant under alternating anaerobic–aerobic conditions with low molecular fatty acid as carbon source. Inherit the results of previous studies, a single low molecule organic acids as substrates was used to study the process optimal conditions for PHA synthesis.At the mean while, Acid waste water, which contains a varied of low molecule organic acids was used for PHA production, studied the impaction on their monomer composition.The influence of different feeding times on the culture's PHA production capacity under the aerobic condition were investigated with acetate as the carbon source. At the same COD to nitrogen ratio (C/N) and COD to phosphorus ratio (C/P), PHA containing almost 3-hydroxybutyrate(3HB, up to 99.4%) was accumulated up to 36.5% and 56.2 of sludge dry weight in one time feeding batch experiments. The synthesis of PHA obtained during the entire cycle is very smooth by repeatedly feedings, the maximum PHA concentration were 32% and 54.4% (w/w %). The corresponding acetate consumption rates were 597.2mg/(L?h), 648.2 mg/(L?h) and PHA synthesis rate were 110 mg/(L?h), 194.2 mg/(L?h). Nitrogen limitation is more effective for PHA synesis. One time feeding batch experiments have a higher synthesis capability than repeatedly feedings (7 times).pH had a significant impact on PHA synthesis. Without control of pH under the weak alkaline condition (pH=7.9-9.3), it had significant PHA accumulation, peak point and consumption. When pH was no nore than 7.0, PHA synthesis decreased, when the pH was less than 6.0, PHA synthesis and consumption almost stopped. Because of the isoelectric point of the mixed bacterial cultures, Low pH (pH = 5.0, 5.0, 6.0) have an influence on the organic substances absorption and utilization for the bacterium. Neutral and alkaline environment is conducive to PHA synthesis.A varied of low molecule organic acids contained in acid waste water was used for PHA synthesis. VFA were good substrates for PHA production. Without adjust pH of acid waste water had some negative impact on the PHA synthesis. When adjusting the proportion of nutrient ratio of fatty acid wastewater to make a condition that carbon is excess to nitrogen or phosphorus, the accumulation of PHA would increase. The PHA component is mainly determined by carbon substrate, acetic acid and butyric acid could generate PHB polymer when activated sludge was acclimated by acetic acid. In the experiment, acetic acid and butyric acid were the main components in the VFA, so the main product was PHB.