Nitrogen recovery from a pig slurry and a digestate using a simplified stripping technology

Among the treatments to reduce nitrogen (N) surplus from livestock slurry, ammonia (NH3) stripping is an effective technology, but currently expensive and difficult to manage (Laureni, Palatsi, Llovera, Bonmatí, 2013). In this work we evaluated a simplified treatment based on a slow release of NH3. The study investigated the process to remove N from two different slurry typologies: a pig slurry (PS) collected in a fattening pig farm and a digestate (D) obtained by the codigestion of the PS with other biomass. The experiment lasted 12 days and was conducted in triplicate using 50 L reactors kept at 40°C always mixed and with air insufflation. The airflow was set at 20 L/min. In the first two days 1/3 of the airflow was provided from the bottom of the reactor through airstones. Subsequently, the aeration interested only the headspace. pH, redox, O2, and temperature were continuously monitored, while Total Ammoniacal Nitrogen (TAN), Total Nitrogen (TN), Total (TS) and Volatile Solids (VS) and Alkalinity were analyzed every 2-3 days. Blowing air into the slurry bulk allowed to strip CO2 causing an increment of pH (Zarebska, Romero Nieto, Christensen, Fjerbæk Søtoft, Norddahl, 2014); after two days pH reached the values of 8.7 (PS) and 8.9 (D). Table 1 reports the initial and the final chemical characteristics of PS and D. The N removal efficiencies obtained were 56% (PS) and 64% (D). Although further improvements may increase the efficiency of the process, the slow rate air stripping of NH3 has demonstrated to be a promising option for reducing the environmental impact associated with animal manure management. References • Laureni,M., Palatsi, J., Llovera, M., & Bonmatì, A. (2013). Influence of pig slurry characteristics on ammonia stripping efficiencies and quality of the recovered ammonium-sulfate solution. Journal of Chemical Technology and Biotechnology, 88, 1654-1662. • Zarebska, A., Romero Nieto, D., Christensen, K.V., Fjerbæk Søtoft, L., & Norddahl, B., (2014). Ammonium Fertilizers Production from Manure: A Critical Review. Journal of Environmental Science and Technology, 1547-6537.