Low-cost lipid-based substrates for solid-phase denitrification: Performance comparison of soy wax, stearic acid, and polyhydroxybutyrate

Authors

• Chinedu James Chiama, Cain Department of Chemical Engineering
• Maria Teresa Gutierrez-Wing, Inc
• Chimezie John Chiama, Cain Department of Chemical Engineering
• Somtochukwu O. Anyaorah, Cain Department of Chemical Engineering
• Emmanuel Chima Eze, Idaho State University
• Mike Benton, Cain Department of Chemical Engineering
• Ronald F. Malone, Aquaculture Systems Technologies

Document Type

Article

Publication Date

6-30-2026

Abstract

The identification of cost-effective solid carbon substrates for solid-phase denitrification (SPD) in recirculating aquaculture systems (RAS) remains a challenge. This study evaluated the denitrification performance of lipid-based substrates, soy wax (SW) and stearic acid (SA), and polyhydroxybutyrate (PHB) under a flow-through configuration. Upflow biofilters were used for PHB, while downflow biofilters were applied for SW and SA to accommodate substrate buoyancy, and all systems were operated at a flux of 1 m³ m⁻² d⁻¹ . During stable operation, SW and SA achieved maximum denitrification rates of 1.13 ± 0.10 and 1.05 ± 0.10 kg N m⁻³ d⁻¹ , respectively. PHB exhibited a denitrification rate of 0.76 ± 0.03 kg N m⁻³ d⁻¹ . Nitrite accumulation was observed in the SW and SA treatments, whereas it was rarely observed in the PHB reactors. Carbon release differed among substrates, with SA exhibiting higher COD release (20.0 ± 0.5 mg L⁻¹) than PHB (19.5 ± 0.6 mg L⁻¹) and SW (14.4 ± 1.4 mg L⁻¹); however, the difference between SA and PHB was small and of limited practical significance. Substrate consumption normalized to total oxidized nitrogen (NOx–N) removal was 3.12 ± 0.30, 2.91 ± 0.60, and 3.85 ± 0.20 kg NOx–N kg⁻¹ for SW, SA, and PHB, respectively. Microbial analysis showed comparable biofilm diversity in PHB and SA, whereas SW exhibited lower overall diversity; Comamonadaceae dominated PHB treatment, while Pseudomonas pseudoalcaligenes predominated in both SW and SA systems. A pilot-scale demonstration conducted in a commercial RAS using SW as the sole carbon source indicated operational feasibility, with negligible nitrite accumulation when operated alongside an aerobic biofilter. Based on U.S. substrate prices and consumption rates, SW and SA were more cost-effective than PHB, highlighting their potential as alternative carbon sources for SPD in RAS applications.

Publication Source (Journal or Book title)

Aquacultural Engineering

Recommended Citation

Chiama, C., Gutierrez-Wing, M., Chiama, C., Anyaorah, S., Eze, E., Benton, M., & Malone, R. (2026). Low-cost lipid-based substrates for solid-phase denitrification: Performance comparison of soy wax, stearic acid, and polyhydroxybutyrate. Aquacultural Engineering, 114 https://doi.org/10.1016/j.aquaeng.2026.102741