Nitrogen recovery from intensive livestock farms using a simplified ammonia stripping process

Abstract

The ammonia (NH3) stripping process can recover nitrogen (N) from slurry and digestates as a mineral fertilizer, but it is currently expensive and difficult to manage at the farm level. Hence, a simple process is required. This study aimed to test a modular (based on farm N surplus) slow-release NH3 stripping process at a pilot plant scale. NH3 volatilization was promoted in a closed reactor, and then, the NH3 was removed by an air stream through the reactor headspace. The NH3-loaded air was purified in a scrubber, where NH3 reacted with sulfuric acid to form ammonium sulfate (AS). In total, 11 trials were conducted using pig slurry, dairy cattle slurry, and digestates: 7 trials were carried out with the reactors heated to 40°C, 2 trials were carried out at an ambient temperature, and the other 2 trials were carried out with the addition of sodium hydroxide (NaOH). To assess the technical–economic sustainability of the pilot plant, the total ammoniacal nitrogen (TAN) removal rate, electricity consumption, acid requirements, and AS quality and costs were evaluated. The pilot plant yielded TAN recovery amounts of 45% in 2 weeks with the reactors heated to 40°C, 64% in 1 week with NaOH addition, and 25% in 2 weeks at an ambient temperature. The N concentration in the AS solution reached 85.9 g kg−1, with an average value of 35.2 g kg−1. The electricity consumption, acid requirement, and operational costs in an optimized system were approximately 0.52 kWh kgN−1 recovered, 3.5 kg pure acid kgN−1 recovered, and 0.86 € kgN−1 recovered, respectively. Compared to other technologies, the simplified stripping process is slower but with similar removal efficiencies and lower energy consumption. Thus, this finding could be suitable for improving the N use in intensive livestock farms.