Aging Characteristics and Fate Analysis of Liquid Digestate Ammonium Nitrogen Disposal in Farmland Soil

Abstract

Water environment safety is the focus of engineering measures to eliminate liquid digestate in farmland. It is of great significance to study the aging characteristics of soil absorbing and fate of liquid digestate ammonium nitrogen (NH4+-N) to realize safe and efficient disposal. In this paper, simulation experiments of digesting NH4+-N (with application of 0, 120, 180, and 300 kg/hm2) by static soil column are carried out to study disposal efficiency, migration and transformation characteristics, and fate proportion of NH4+-N in saturated water content soil. The result showed that after 3 days of application, the overlying water NH4+-N concentration decreased by 63.5–80.7%, and the reduction rate of total NH4+-N was 65.8–82.3%. After 4 days, the NH4+-N concentration of pore water in the 0–10 cm soil layer reached the peak value. After 7 days, the NH4+-N concentration adsorbed by the 0–10 cm soil layer reached the peak value. After 15 days, the overlying water NH4+-N concentration decreased by 97.0–98.7%, the reduction rate was 97.9–99.2%, and the proportion of NH4+-N absorbed in the 0–10 cm soil layer accounted for 63.5–76.3%. The disposal is mainly based on soil sorption and pore water migration. A duration of 0–3 days is the rapid disposal period, and 15 days is the completion period of safe digestion.