Efficiency of wood-chip-framework soil infiltration system in treating anaerobically digested swine wastewater

A wood-chip-framework soil infiltrator (WFSI) with slow-release of carbon source was constructed and used to treat an anaerobically digested swine wastewater characterized with high NH⁺₄-N and low C/N ratio. Pollutant removal efficiency of the WFSI was investigated under various influent concentration and varying surface hydraulic load (SHL). Under SHL of 0.2 m³·m^-2·d^-1, influent averaged COD and NH⁺₄-N increased from 152 and 175.5 mg·L^-1 to 421 and 788.7 mg·L^-1, respectively. The resultant COD, NH⁺₄-N and TN removal by the system was 52.3% to 61.2%, 84.2% to 61.5% and 28.6% to 33.5%, respectively. Meanwhile, NH⁺₄-N and TN removal loading reached 75.5 and 41.7 g·m^-3·d^-1, respectively. Though SHL was as high as 0.32 m³·m^-2·d^-1, the system still performed but its efficiency was remarkably influenced. When influent COD and NH⁺₄-N was around 265 and 465 mg·L^-1, COD, NH⁺₄-N and TN removal was about 56.5%, 53.3% and 20.9%, respectively. The wood carrier observably worked as a slow-release carbon source, and protected the ammonia oxidizing bacteria from free ammonia toxicity due to the concentration gradient of NH⁺₄-N in the adhesive layers.