Master of Science in Civil Engineering (MSCE)
Civil and Environmental Engineering
Freshwater ornamental fish production is a major component of aquaculture in the southeastern United States. Closed recirculating aquaculture systems (RASs) allow freshwater ornamental fish hatcheries to mimic native water quality conditions for sensitive species. Total ammonia-N (TAN) removal is the major concern for closed RASs. Biological nitrification is the common method to control TAN. However, the nitrification process might be impaired in acidic water condition with pH<7. Another issue of using the nitrification process for TAN removal is that the nitrification is not sufficient to compensate for the amount of ammonia released in larval production systems because of slow growth rate of nitrifying bacteria. To address these issues, this study suggests an aerobic assimilation strategy in which fast growing heterotrophic bacteria directly convert TAN into microbial biomass. The heterotrophic bacteria needs an external carbon source. This study employed polyhydroxybutyrate (PHB) that is a solid insoluble bioplastic, as a carbon source in the aerobic assimilation process to avoid releasing carbon into the system. In order to understand the applicability of an assimilation process instead of nitrification, this study compared the ammonia-N removal rate by aerobic assimilation biofilters operating @ pH 8 and 6.5 in a batch system. The study also quantified the performance of an aerobic assimilation strategy under different continuous nitrogen loading regimes. This investigation can be used to establish the biofilter air pulsing frequency, which is the optimized air pulsing frequency that avoids clogging in the system. The results showed that there was no apparent release of carbon in the water tank. Unlike nitrification, assimilation strategy for TAN removal was not significantly different in two pH of 8 and 6.5 @ 28 ° C. The average consumption rate of the PHB was found as 21.93± 0.43 grams of PHB consumed per gram of TAN. The results from the continuous system, at a continuous feeding rate of 350 mg-N/d, suggested that the optimum air pulsing frequency through the PHB bed for releasing the excess biosolids was about 6-hour. In general, the study found that the aerobic assimilation using polyhydroxybutyrate (PHB) as a carbon source is an applicable method for ammonia-N removal particularly for freshwater ornamental fish production systems. The drawback against this approach is that the PHB beads are expensive. However, our investigations show that the average cost of the PHB beads have been decreased dramatically during the last few years. This might indicate that the assimilation using PHB beads can be a reasonable choice for ammonia-N removal particularly for freshwater ornamental fish production systems.
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Fahandezhsadi, Fatemehsadat, "Assimilation, a Biological Nitrogen Removal Strategy For Freshwater Ornamental Fish Hatcheries" (2014). LSU Master's Theses. 3909.