Aerobic Periodic Feeding

The mechanism of storage imder dynamic conditions is illustrated in Fig 4. Immediately after a substrate pulse, cells previously starved start to synthesise PHA and the oxygen uptake rate (OUR) reaches a maximum 

According to activated sludge are able to accumulate large amounts of PHB when cultivated under alternation of feast and famine of external substrate (acetate). The yield of PHB production by this crdture was up to 50% of its dry weight, which is comparable with the value referred above for the cultures cultivated under microaerophilic-aerobic conditions. The influence of operating conditions, namely frequency of feeding and the ratio between the substrate and initial biomass concentration on PHA production was evaluated. The quality of polymer produced under these conditions was not determined. 

The high PHA storage capacity by activated sludge and the good chain lengths and composition of the polymers produced by these processes deserve further research with the purpose of process optimisation and final application at full scale. 

The authors would like to thank Dr. Valter Tandoi and Dr. Caterina Levantesi from CNR/IRSA, Rome, for the photos presented. Luisa S. Serafim acknowledges FundacSlo para a CiSncia e Tecnologia for grant PRAXIS XXI BD/18287/98 and Paulo C. Lemos acknowledges for grant BD/1217/91-IF. 

Anderson, A. J. and Dawes, E. A., 1990, Occurrence, nnetabolism, metabolic role, and industrial uses of bacterial polyhydroxyalkanoates. Microbiol. Rev., 54 450-472. 

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This work discusses the use of different processes for PHA production by activated sludge enhanced biological phosphorus removal (EBPR), microaerophilic-aerobic process and aerobic periodic feeding (feast/famine conditions). 

The aerobic biofilter used in the study had a capacity of 10 L. The reactor was packed to 60% of the empty bed volume with Cosmo ball media. The biofilter was seeded with active innoculum taken from an active aerated lagoon of a nearby landfill leachate treatment. Fresh raw leachate was used as feed to the reactor at a rate of 5 L/d over 24h. The loading rates applied to the bioreactor were between 1.6 and 22.2 kg COD/m3d. Initial studies were conducted as a batch process lasting for a period of 24 d. Thereafter, the biofilter was fed continuously for a total period of 240 d. 

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