Process optimization and mass transfer characteristics of ammonia stripping from piggery liquid digestate using response surface methodology

High ammonia concentrations in piggery liquid digestate pose a major challenge for subsequent treatment and resource recovery. In this study, ammonia stripping of real piggery liquid digestate, whose initial total ammonia nitrogen (TAN) concentrations were 1190-1232 mg·L -1 , was systematically investigated in a packed-column system by integrating Response Surface methodology (RSM) with mass transfer analysis. The interactive effects of pH, temperature and gas-to-liquid ratio (GLR) on TAN removal were quantified, and the overall volumetric mass transfer coefficient ( K ) was determined under optimized conditions. The results showed that pH exerted the dominant effect on TAN removal, followed by temperature and GLR. Under the optimized conditions (pH 10.5, 60 °C and GLR 50:1), an average TAN removal of 92.02% was achieved within 8.5 h, corresponding to an overall volumetric mass transfer coefficient of 0.267 h -1 . Comparative analysis with literature data indicated that the present process achieved competitive ammonia removal efficiency under moderate gas flow conditions, suggesting suitability for scale-up design of packed columns treating digestate and process optimization in high-ammonia livestock wastewater treatment.