Greenhouse gas emissions from decomposition of biosolids as affected by stabilization method and soil moisture

Computational models are useful to estimate agricultural greenhouse gas emissions at regional scales. However, empirically based parameter values are required for the models to accurately represent carbon (C) and nitrogen (N) mineralization rates of different organic amendments in more and less humid regions or during wet and dry periods of the growing season. A controlled environment study was conducted to assess the rates of C and N mineralization in differently processed sewage sludge (biosolids) in wet and dry soil. Parameter values were estimated for use in modelling the degradation of three types of biosolids. A loam soil with either 49% water-filled pore space (WFPS) or 29% WFPS was amended with mesophilic anaerobically digested (digested), alkaline-stabilized, or composted biosolids. Headspace samples were collected and analysed for carbon dioxide (CO₂) and nitrous oxide (N₂O), and soil samples for nitrate (${\mathrm{NO}}_3^{-}$) and ammonium (${\mathrm{NH}}_4^{+}$). Four different first-order models were fitted to the cumulative CO₂–C and N₂O–N data (R² > 0.98), and soil ${\mathrm{NO}}_3^{-}$ (R² > 0.65) and ${\mathrm{NH}}_4^{+}$ (R² > 0.93) concentrations. CO₂–C data indicated that C mineralization was higher in soil with 49% WFPS than in soils with 29% WFPS. Seventy-nine percent of the C compounds in digested biosolids degraded in soil with 49% WFPS, compared with 52% for alkaline-stabilized biosolids and 8% for composted biosolids. The fitted coefficient values were similar for all of the four first-order models used in this study and provide useful information for parameterizing more sophisticated mechanistic models of the degradation of biosolids in soil.