Production of biodegradable plastics by anaerobic aerobic activated sludge (phosphate accumulating sludge.

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The following conclusions were obtained from batch experiments in which anaerobic aerobic activated sludges cultivated in a lab scale plant or practical plant sludges were fed with various organic substrates or an industrial wastewater.1. Phosphate accumulating sludges were capable of producing a biodegradable prastic, PHA, from asetate, propionate, pyruvate, malate, succinate and glucose under anaerobic conditions.2. Phosphate accumulating sludges produce more PHA under aerobic conditions than under anaerobic conditions.3. In the aerobic production of PHA, more PHA is produced with more air supply. There is a threshold value of air supply rate, beyond which the PHA production does not increase any more with the increase of air supply. The optimum air supply rate for the one liter reactor used in the present study was 4.5 ml/min.4. By supplying air, the PHA content of the sludge was raised up to 54% based on initial sludge dry weight and 33% based on final sludge dry weight. But more accumulation may be necessary for commercial production of PHA.5. The DO concentration, when the optimum air supply was achieved, was very low and not controlable. Oxidation-reduction potential(ORP)can be an alternative control parameter for the air supply.6. An inhibition of PHA production was observed at high substrate concentrations. An optimum substrate concentration exists.7. The characteristics of practical plant sludges differ very much from each other, resulting in different optimum air supply rates, suitable substrate concentrations and necessary retention times. Actual sludges accumulated less PHA than lab sludge(15% of sludge dry weight).8. Industrial wastewater from a fermentation unit of a medicine producing factory can be used as substrate for PHA production.