Development of a model for PHA-based denitrification in a packed bed reactor

A model of the denitrification on a polyhydroxyalkanoate (PHA) based reactor for recirculating aquaculture was developed. PHA is a family of non-water soluble bioplastics produced by bacteria. The PHA formulation used in this work was polyhydroxybutyrate (PHB). The model considered nitrate concentration, dissolved oxygen, organic carbon and biomass concentration as the most significant variables. The developed model represents adequately the nitrate reduction with the medium used, for nitrate under 100 ppm NO 3 − -N. In the conditions tested, an average ratio of 2.92 g PHA to 1 g NO 3 − -N reduced was found. The model results showed a denitrification rate of 2.97 kg m −3 d −1 for ranges from 10 to 50 mg NO 3 − -N L −1 . Using this model as a management tool, the required size of denitrification units and PHA recharging time can be predicted based on the expected nitrate loading and the time between PHA recharges desired. The unit sizing should be done for the maximum load expected. The slow rate and the energy required for PHA hydrolysis, make it unavailable as electron donor after the nitrate is consumed, so it will not promote the formation of sulfides. The model can be modified for other biodegradable non-water soluble medium by changing the hydrolysis constant, which must be determined experimentally.