Degree

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Document Type

Dissertation

Abstract

Biofilters in RAS rely on nitrification to manage nitrogenous waste; however, during the acclimation phase of biofilters or system recovery, nitrification efficiency is reduced and can lead to accumulation of harmful total ammonia nitrogen (TAN) and nitrite, which can negatively impact the health of cultured species. TAN can be controlled by supplementing solid-phase carbon substrates into the biofiltration reactor, where they serve as start-up media and enhance ammonia removal through heterotrophic assimilation. Poly(3-hydroxybutyrate) (PHB) is a commonly used solid-phase carbon source, but limited by high-costs.  In this study, PHB/starch (PHB:S) and PHB/cellulose (PHB:C) blends were produced and evaluated in an aerobic fixed-film system. Among the blends, PHB:S 60:40 exhibited the highest apparent average volumetric TAN removal rate (VTR) (1.50 ± 0.10 kg TAN m⁻³ media day⁻¹) and reduced estimated material costs by about 36.3% but also released the highest COD (301.0 ± 7.9 mg L⁻¹). In contrast, PHB:C 60:40 achieved a lower apparent average VTR (0.93 ± 0.06 kg TAN m⁻³ media day⁻¹) with a moderate COD (56.0 ± 10.6 mg L⁻¹) while reducing material costs by up to 33.4%, and was identified as the most favorable PHB-based formulation. As an alternative to PHB blends, lipid-based carbon substrates, including soy and coconut wax, were evaluated as lower-cost options. The wax substrates when compared with the PHB blends, demonstrated lower but comparable average VTRs (0.13–0.23 kg TAN m⁻³ day⁻¹, p=0.85). However, among the wax treatments, coconut wax exhibited the highest regression-derived TAN removal rate (2.44 ± 0.13 g TAN m⁻³ day⁻¹), significantly higher than the other treatments (p = 2.24 × 10⁻⁵).  Soy wax treatments released moderate COD (52–57 mg L⁻¹), while coconut accumulated the highest COD ( 93.17 ± 11.03 mg L⁻¹).  Coconut wax achieved lowest cost of nitrogen removal ($34.60 kg⁻¹ TAN removed), compared with $55.58–65.57 kg⁻¹ TAN for soy wax.  Although PHB blends achieved higher apparent VTRs, their cost remains high for adoption. Unless substantial cost reductions (≥90%) are achieved, soy wax substrates offer a potential for more practical options, providing balanced TAN removal, controlled carbon release, and moderate cost for biofilter acclimation in RAS.

Date

7-15-2026

Committee Chair

Benton, Mike

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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