Ammonia Removal Using Polyhydroxybutyrate-Starch and Polyhydroxybutyrate-Cellulose Blends for Aerobic Applications

Ammonia accumulation during biofilter acclimation in RAS can compromise animal health. However, this effect may be mitigated by incorporating solid-phase carbon substrates during the start-up phase. This study evaluated poly(3-hydroxybutyrate) (PHB) and its blends with starch (PHB:S) and cellulose (PHB:C) as solid-phase carbon substrates for aerobic ammonia removal, with potential application during RAS start-up. PHB was melt-extruded with 0, 20, 30, and 40 wt% starch or cellulose and tested in triplicate using up-flow fixed-bed reactors treating simulated wastewater (~20 mg/L TAN). All substrates supported bacterial growth and TAN removal over 5 days, with negligible nitrate (<0.2 mg/L) and nitrite (<0.06 mg/L) accumulation. PHB:S blends exhibited the highest apparent TAN removal rates (1.5 ± 0.09 kg TAN/m³ day) but released excessive COD (109–301 mg/L). In contrast, PHB:C blends provided controlled carbon release; the 60:40 PHB:C blend achieved effective TAN removal (0.93 ± 0.05 kg TAN/m³ day) with low COD release (56 ± 8.64 mg/L) and reduced material cost by 33.4%. Based on these findings, the PHB:C 60:40 blend offered the best balance of cost, TAN removal, and carbon control, making it a practical choice for RAS start-up applications.