Polyhydroxyalkanoates Production by Activated Sludge

LUlSA S. SERAFIM, PAULO C. LEMOS, JOAO G. CRESPO, ANA M. RAMOS and MARIA A. M. REIS 

Departamento de Quimica - CQFB, Faculdade die Ciencias e Tecnologia, Universidade Nova de Lisboa, 2825-114 Caparica, Portugal 

Abstract Polyhydroxyalkanoates (PHA) are intracellular polymers stored by many bacterial species. Presently PHA arc industrially produced by pure cultures fermentation where high quality substrates are used. Mixed cultures using raw substrates are able to produce PHA when submitted to transient conditions like oscillations on substrate feeding or on oxygen supply. The yield on PHA produced by activated sludge submitted to these dynamic conditions reach values comparable to those obtained by the pure cultures, being the first process less cost intensive than die last one. The chain length of the polymer produced in both processes is similar. 

Polyhydroxyalkanoates (PHA) are polymers synthesised by bacteria as intracellular carbon and energy sources. PHA are industrially produced by pure cultures psing as main substrates glucose and propionic acid. The major expenses in the PHA production are determined by the cost of substrate and extraction of polymer from inside the cells.  

In biological wastewater treatment processes microorganisms are able to store large amounts of polymers, which play an important role in their metabolism. In some processes the amount of PHA accumulated inside the biomass can account for almost 60 % of the dry weight. This yield is lower than the maximum value reported for industrial PHA production by pure cultures (85 % of the cell dry weight). However, PHA production by 

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