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

•The model developed can be used to determine the size of the PHA denitrification bed.•The model can predict recharge times for denitrification units based on PHA.•The model can be applied to other solid non-water soluble substrates after determining the appropriate degradation constants.•The results show an average ratio of 2.92g PHA consumed to 1g NO3−-N reduced.•Denitrification rates of 2.97kgm−3d−1 were obtained in water 10–50mgNO3−-NL−1, a common range for aquaculture operations. 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 100ppm NO3−-N. In the conditions tested, an average ratio of 2.92g PHA to 1gNO3−-N reduced was found. The model results showed a denitrification rate of 2.97kgm−3d−1 for ranges from 10 to 50mgNO3−-NL−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.