Use of an inverse dispersion technique for estimating ammonia emission from surface-applied slurry

Abstract. Ammonia (NH3) emissions from dairy liquid storage systems can be a source of reactive nitrogen (N) released to the environment, with a potential to adversely affect sensitive ecosystems and human health. However, little on-farm research has been conducted to estimate these emissions and determine the factors that may affect these emissions. Six lagoons in south-central Idaho were monitored for one year using open-path Fourier transform spectrometry, with NH3 emissions estimated using inverse dispersion modeling (WindTrax software). Lagoon physicochemical characteristics thought to contribute to NH3 emissions were also monitored over this period. Average total emissions from the lagoons ranged from 12 to 43 kg NH3 ha-1 d-1, or 5.4 to 85 kg NH3 d-1. Emissions from the settling basin on one dairy were 30% of the total emissions from the liquid storage system, indicating that basins are important sources of on-farm NH3 emissions. Emissions generally trended greater during the summer, when temperatures were greater. High wind events and agitation of the lagoons created temporary increases in NH3 emissions irrespective of temperature. Lagoon physicochemical characteristics, such as total Kjeldahl nitrogen (TKN) and total ammoniacal nitrogen (TAN), were highly correlated with emissions (r = 0.52 and 0.55, respectively). Regression models were developed to predict on-farm NH3 emissions and indicated that TKN, TAN, wind speed, air temperature, and pH were the main drivers of these emissions. An on-farm N balance suggested that lagoon NH3-N losses represented 9% of total N lost from the facility, 65% of total lagoon N, and 5% of dairy herd N intake. A process-based model (Integrated Farm System Model) estimated values for N excretion and NH3-N loss from the lagoon within 5% of that measured on-farm. More on-farm research is needed to better refine both process-based models and emission factor estimates to more accurately predict NH3 emissions from lagoons on dairies in the western U.S. Keywords: Ammonia, Emission, Inverse dispersion, Manure.

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Evaluation of ammonia emissions from filtration of digestate used for fertigation

Journal of Agricultural Engineering ◽

10.4081/jae.2021.1187 ◽

2021 ◽

Vol 52 (3) ◽

Author(s):

Celeste Righi Ricco ◽

Alberto Finzi ◽

Viviana Guido ◽

Elisabetta Riva ◽

Omar Ferrari ◽

...

Keyword(s):

Dispersion Model ◽

Farming Systems ◽

Farming System ◽

Passive Samplers ◽

Ammonia Emission ◽

Specific Reference ◽

Ammonia Emissions ◽

Mean Values ◽

Po Valley ◽

Inverse Dispersion

Fertigation can be a suitable technique for utilizing digestate, minimizing nitrogen losses, and contributing to circularity within a farming system. For this purpose, digestate usually is first processed with a screw-press separator. However, further filtration is required to remove particles that could clog the nozzles of drip or sprinkling irrigation systems. Advanced filtration can be obtained using mechanical separation with screens having openings of 100- 300 μm. This operation can be another source of ammonia emission, but this aspect has not been adequately investigated. This study aimed to address this knowledge gap by evaluating the emissions from three different filtration systems for digestate. The study was conducted in three different farms located in Lombardy (Italy) using digestate to fertigate maize by drip irrigation (two farms) and pivot irrigation (one farm). Ammonia emissions were measured with passive samplers and the fluxes were examined using an inverse dispersion model implemented in Windtrax software. The emissions were measured both when the filtration systems were in operation and when they were switched off. Ammonia emissions (mean values between 375 and 876 μg NH3/m2/s) tended to increase during operation of the filtration systems. However, no significant differences were found in the emissions from active and inactive equipment on any of the farms. The emissions from the filtration systems were higher than from a storage tank (22-67 μg NH3/m2/s). However, the mean emissions amounted to only 0.3% of the nitrogen content of the digestate. These emissions can be considered irrelevant in the context of the whole management scheme for digestate. This work provides a first insight on ammonia emissions arising from advanced filtration of digestate, with specific reference to Po Valley farming systems. Further studies are required to improve knowledge about emissions from the entire digestate management process, including the treatments required for specific application techniques.

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