Denitrification performance of polyhydroxybutyrate/cellulose (PHBC) blend with and without a nitrogen-driven degassing column

Abstract

The solid-phase denitrification (SPD) process can be severely inhibited by the presence of dissolved oxygen (DO). Efficient oxygen management, therefore, remains a critical challenge in designing simple and cost-effective SPD biofilters. This study evaluated the impact of DO on the denitrification performance of a polyhydroxybutyrate/cellulose (PHBC60:40) blend in flow-through biofilters. Two up-flow biofilters were designed: Group A, equipped with a nitrogen-driven degasser maintaining influent DO below 0.5 mg L⁻¹, and Group B, operated without a degasser under influent DO levels of 3–6 mg L⁻¹, at a flux of 2.5 m³ m⁻² d⁻¹ (HRT = 28 min). Group A achieved a maximum denitrification rate of 6.1 ± 0.1 kg NO₃⁻-N m^-³ d⁻¹, significantly higher than Group B’s 5.6 ± 0.2 kg NO₃⁻-N m^-³ d⁻¹, approximately a 9 % increase. Once stabilized after day 3, net effluent COD levels were 104 ± 24 mg L⁻¹ for Group A and 86.4 ± 30 mg L⁻¹ for Group B, with no statistically significant difference. Similarly, BOD₅ values were 101 ± 37 mg L⁻¹ and 86 ± 31 mg L⁻¹ for Groups A and B, respectively, with no observable significant difference. PHBC60:40 consumption rates were also comparable: 4.1 ± 0.4 kg PHBC (kg NO₃⁻-N)⁻¹ for Group A and 4.2 ± 0.7 kg PHBC (kg NO₃⁻-N)⁻¹ for Group B. Despite the improved nitrate removal in Group A, all other parameters were comparable between the systems. Moreover, as oxygen depletion in Group B occurred within just 5–10 % of the media bed, the added cost and complexity of a nitrogen-driven degasser are not justified. These findings indicate that the PHBC blend-packed biofilters can perform effectively without oxygen-stripping pretreatment.