Doctor of Philosophy (PhD)


Civil and Environmental Engineering

Document Type



Increasing demand of aquacultural products is driving the industry toward more intensive culture practices. Aquacultural operations are constrained by limitations on the availability high quality waters and regulatory pressures on the discharges. Recirculating systems can address these issues by reducing the amount of water required in the operation. Closed systems are especially suited where biosecurity is important. In closed systems, nitrate accumulates, limiting the time the water can be reused. In marine inland systems, water reuse reduces the cost of salt for make up water. To increase the water reuse time, some form of nitrate removal process must be incorporated in the system. The most common is bacterial denitrification with addition of a carbon source. Water soluble carbon sources must be carefully dosed, as excesses facilitate the production of toxic sulfides. In this work a solid non-soluble bioplastic (polyhydroxyalkanoate) was used as a carbon source and bacterial support media in a self controlled denitrification process. The average denitrification rates were 2.38±0.51, 2.49±1.09, 3.19±0.79 and 2.94±0.72 Kg NO3-N/m3-0, 5, 15 and 30 ppt salinity respectively. These rates are in the range of those reported in the literature with other materials. The degradation of the bioplastic increased its content of CH3 and CH2 as determined by FTIR. A tendency to increase with the molecular weight of the plastics was observed but the difference was not significant. In the short term no BOD increase was observed in the anoxic systems. After 18 months around 500 mg/l organic carbon was accumulated. Oxygen limits the denitrification xii process, but some denitrification occurred even at high bulk dissolved oxygen (>5.5 mg/l). A five cell model was developed to simulate a denitrification plug flow reactor. The Root mean squared error of the prediction was less than 20%. The model can be used as a management tool in PHA based denitrification in upflow filters for sizing and management of the denitrification unit. The denitrification process using PHA as a carbon source and support media is feasible and as the PHA prices are reduced. PHA is a viable alternative for a solid-non water soluble, self controlled denitrification system.



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Committee Chair

Ronald F. Malone