Backwashing conditions of novel bio-amended sands and its enhanced filtration efficiency

Novel amended sands enveloped in bio-film (B-NAS) were employed to treat the ammonium-nitrogen (NH₄ ⁺-N) in raw water. The backwashing conditions, treatment efficiency, and morphological characteristics of the B-NAS were investigated via bio-filtration experiments. The bare quartz sands (BQS) and NAS exhibited biomass levels of 24.32 nmol-P g-sand ^-1 and 83.71 nmol-P g-sand⁻¹, respectively. B-NAS was most effective when air alone (at a strength of q_air,I = 7 L s⁻¹ m⁻² for t_air,I = 6 min), a combination of air–water (at strengths of q_air,II = 7 L s⁻¹ m⁻² and q_water,II = 5 L s⁻¹ m⁻² for t_air-water,II = 6 min), and water alone (at a strength of q_water,III = 7 L s⁻¹ m⁻² for t_water,III = 4 min) were employed alternately for flushing. The proposed B-NAS with nano-pores surface effectively (1) resisted the shock produced by high NH₄ ⁺-N concentrations (4 mg L⁻¹), (2) exhibited removal rate of 96%, and (3) a high capturing capacity indicated by a high head loss (126.5 cm) for 72 hr.