Biofiltration matrix optimization for efficient nitrogen removal from domestic onsite wastewater

Bench-scale columns were packed with marble chip, zeolite and gravel to treat septic tank effluent at elevated hydraulic loadings (0.48–0.64 m³ m⁻² d⁻¹) to challenge their hydraulic performance and ammonium (NH₄⁺-N) removal performance. The results showed that higher NH₄⁺-N removal efficiency was achieved in zeolite (75.8–94.1 %) and marble chip (54.9–83.9 %) columns than in sand (32.9–76.6 %) column without clogging during the experimental period (4 months). Biochar amendment (30 % v/v) resulted in a 23–29 % decrease of effluent NH₄⁺-N in marble chip columns, while no impact was observed in the zeolite columns. Nitrification rather than adsorption contributed to the major NH₄⁺-N removal (82–95 %) in zeolite, biochar amended zeolite and biochar amended marble chip columns. In addition, higher abundance of nitrifying microorganisms observed in the top layer of zeolite column (1.2 × 10⁷ - 3.1 × 10⁷ amoA copies g⁻¹, 3–10 times higher than marble chip) suggested NH₄⁺-N was concentrated on zeolite surface by adsorption which then facilitated nitrification and promoted nitrifying biomass growth. Collectively, this study suggested that zeolite and biochar amended marble chip could serve as the filter materials for efficient NH₄⁺-N removal from onsite wastewater at elevated wastewater loadings without clogging concerns.