Pilot- to field-scale evaluation of a two-stage vertical flow constructed wetland system for piggery wastewater treatment

Abstract Piggery wastewater is a high-strength effluent requiring efficient and sustainable treatment solutions. This study evaluates a two-stage vertical flow constructed wetland (VFCW) system through pilot- to field-scale investigation, with emphasis on hydraulic loading, passive aeration, and techno-economic feasibility. At pilot scale, the system was operated at flow rates of 4–6 L day⁻1. At 4 L day⁻1 (OLR: 653.4 ± 43 g m⁻2 day⁻1), optimal performance was achieved. The control wetland (CW) exhibited removal efficiencies of 88.95 ± 3.12% (COD), 86.32 ± 5.48% (TOC), 87.71 ± 1.12% (phosphate), 73.37 ± 4.95% (TAN), and 51.25 ± 3.46% (TN). In comparison, the passively aerated system (CW-A) showed improved performance, achieving 90.36 ± 2.98% (COD), 89.68 ± 3.87% (TOC), 90.23 ± 0.98% (phosphate), 87.23 ± 4.23% (TAN), and 67.12 ± 4.23% (TN). Passive aeration achieved using perforated pipes inserted within the VFCW, significantly enhanced nitrogen removal, particularly through improved ammonium oxidation and overall nitrogen transformation, while having only marginal effects on organic matter and phosphate removal. Based on pilot-scale results, scale-up was performed by maintaining a comparable organic loading rate, and a field-scale system treating 7200 L day⁻1 (OLR: 604.3 ± 90.6 g m⁻2 day⁻1) was implemented. The system achieved overall removals of 87.85 ± 12.47% (COD), 86.35 ± 12.08% (TOC), 91.08 ± 10.63% (phosphate), 81.02 ± 13.13% (TAN), 60.45 ± 12.74% (nitrate), and 64.86 ± 13.62% (TN). Stable performance was achieved after a 4–5 week stabilization period, with resilience to influent variability. Techno-economic analysis indicated a treatment cost of ₹45.5 ($ 0.48) m⁻3 and low energy consumption (0.16 kWh m⁻3). The results demonstrate that OLR-based scale-up enables reliable field performance, confirming VFCWs as a robust and cost-effective solution for decentralized piggery wastewater treatment. Key points • OLR-based scale-up ensured successful pilot to field translation. • Passive aeration enhanced TAN and TN removal whereas field-scale system achieved > 85% COD and TOC removal in VFCW. • Low-cost (₹45.5/m3) and energy-efficient (0.16 kWh/m3) treatment. Graphical Abstract