Application of Downflow-Upflow Biological Aerated Filter in the Pretreatment of Raw Water Containing High Ammonia Nitrogen

In a subtropical area, a downflow-upflow biological aerated filter (D-UBAF) was used in the pretreatment of raw water containing seasonal high levels of ammonia nitrogen (${\mathrm{NH}}_3\mathrm{\text{-}}\mathrm{N}$) and organic pollutants. Operating parameters for low-flow periods were as follows: filtration rate of $8\mathrm{m}/\mathrm{h}$ and gas-water ratio of $0.5:1.5$. In terms of water quality, the average concentrations of ${\mathrm{NH}}_3\mathrm{\text{-}}\mathrm{N}$ and permanganate index (${\mathrm{COD}}_{\mathrm{Mn}}$) and the turbidity of the raw water were $5.02–9.45\mathrm{mg}/\mathrm{L}$, $5.79–10.1\mathrm{mg}/\mathrm{L}$, and 19.7–63.1 NTU, respectively. The corresponding indexes of the D-UBAF effluent were $0.30–0.96\mathrm{mg}/\mathrm{L}$, $3.24–5.85\mathrm{mg}/\mathrm{L}$, and 3.83–19.9 NTU, respectively. The removal efficiencies were 90.3%, 42.7%, and 66.3%, respectively. Operating parameters for high-flow periods were as follows: filtration rate of $12\mathrm{m}/\mathrm{h}$ and gas-water ratio of $0.3:0.5$. In terms of water quality, the average concentrations of ${\mathrm{NH}}_3\mathrm{\text{-}}\mathrm{N}$ and ${\mathrm{COD}}_{\mathrm{Mn}}$ and the turbidity of the raw water were $2.19–3.41\mathrm{mg}/\mathrm{L}$, $5.30–7.56\mathrm{mg}/\mathrm{L}$, and 27.3–40.1 NTU, respectively. The corresponding indexes of the D-UBAF effluent were $0.18–0.41\mathrm{mg}/\mathrm{L}$, $2.87–4.50\mathrm{mg}/\mathrm{L}$, and 5.43–16.8 NTU, respectively. The removal efficiencies were 89.3%, 40.2%, and 65.0%, respectively. The D-UBAF with one DBAF and two UBAFs constituted a “”-shaped structure. The space among these three components was used as a common tube gallery. The UBAF is the principal component of the biological pretreatment process. The DBAF runs before the UBAF; it can ensure that the head loss in the UBAF does not exceed $0.2\mathrm{m}{\mathrm{H}}_2\mathrm{O}$ after filtration for 24 h. This also satisfies the head loss control requirement for numerous UBAFs, which share a centralized aeration system to achieve uniform aeration.