Ammonia recovery from digestate using gas-permeable membranes: a pilot-scale study

Authors: RIANO, BERTA - Instituto Tecnológico Agrario De Castilla Y León (ITACYL); MOLINUEVO-SALCES, BEATRIZ - Instituto Tecnológico Agrario De Castilla Y León (ITACYL); Vanotti, Matias; GARCIA-GONZALEZ, MARIA CRUZ - Instituto Tecnológico Agrario De Castilla Y León (ITACYL)

Submitted to: Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2021
Publication Date: 11/25/2021
Citation: Riano, B., Molinuevo-Salces, B., Hernandez-Gonzalez, D., Vanotti, M.B., Garcia-Gonzalez, M. 2021. Ammonia recovery from digestate using gas-permeable membranes: a pilot-scale study. Environments. 8(12):133. https://doi.org/10.3390/environments8120133.
DOI: https://doi.org/10.3390/environments8120133

Interpretive Summary: Gas-permeable membranes technology presents a high potential for nitrogen (N) recovery from waste waters rich in ammonia (NH3). Previous studies have been carried out at laboratory scale. The goal of this study was to report the results of an on-farm pilot-scale demonstration using gas-permeable membranes that recovered N from digestate in an agricultural anaerobic co-digestion plant. The anaerobic co-digestion plant treated mainly swine manure from a finishing farm located in Salamanca (Spain) together with other co-substrates such as crop and cereal residues and generated approximately 6000 cubic meters of digestate per year. Land application of digestate is a source of significant N-related emissions in Europe. During anaerobic digestion, the organic matter in the waste is transformed into biogas, a renewable energy, and the organic nitrogen content in the waste is transformed into the mineral form NH3 contained in a dark liquid called digestate. The digestate in this work contained a high concentration of total N, about 3,200 milligrams per liter (mg/L), of which 84% was in the mineral NH3 form (2,700 mg/L). The demonstration was part of an EU project Ammonia Trapping to transfer knowledge from the lab-scale level to on-farm pilot-scale level. After set-up optimization of the pilot-scale plant, stable and continuous operation was achieved. Besides its contribution to reduction of NH3 emissions, this technology contributes to the recovery of nutrients in the form of a concentrated stable ammonium (NH4) solution that can be used for fertigation. The NH4 concentration in the product was about 35,000 mg/L, that is 14 times higher than in the digestate. Therefore, the gas-permeable membrane technology has the capacity for concentrating NH3 from manure digestate with diverse benefits for the farmers and society: 1) more control over nutrient application is possible, which avoid risks of N runoff or leaching, 2) exporting the stable N solution off the farm creating an additional income for the farmer, and 3) nutrient recovery would help development of anaerobic digestion to produce renewable energy in rural areas where manure accumulates.

Technical Abstract: The reduction and recovery of nitrogen (N) from anaerobically digested manure (digestate) is desirable to mitigate N-related emissions, mainly ammonia and nitrate, derived from digestate land application in nutrient saturated zones. This work reports the results of a gas-permeable membrane (GPM) pilot-scale plant to recover ammonia from digestate in the framework of the EU project Ammonia Trapping. Total ammonia nitrogen (TAN) concentration in digestate was reduced 34.2 percent (%) on average (range 9.4-57.4%). The recovery of TAN in the trapping solution in the form of an ammonium sulfate (solution averaged 55.3% of the removed TAN), with a TAN recovery rate of 16.2 grams N per square meter of membrane per day (g N m-2 d-1) (range between 14.5 and 21.0 g N m-2 d-1). The TAN concentration in the trapping solution achieved a value up to 35,000 milligram N per liter. The frequent change of the trapping solution has been proved as an efficient strategy to improve the overall performance of the GPM technology.