Measurement and modelling of ammonia emissions from an anaerobic digestion plant

Bell, Michael. 2014 Measurement and modelling of ammonia emissions from an anaerobic digestion plant. University of Edinburgh, Geosciences, Masters Thesis, 63pp.

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Anaerobic digestion (AD) is becoming increasingly popular for treating organic waste. The methane produced can be burned to generate electricity, and the digestate, which is rich in mineral nitrogen, can be used as a fertiliser. The storage and processing of large volumes of organic wastes through AD has been identified as a significant source of NH3 emissions, however only one study has previously quantified the totality NH3 emissions that arise in situ at an AD plant. In this study the emissions from an AD plant was estimated through the integration of supportive methodologies involving passive and continuous air NH3 sampling, atmospheric dispersion modelling and the application of published emission factors (EFs) and empirical models within the literature. Two dispersion models (ADMS and a Lagrangian stochastic model) were applied to produce robust emission estimates. The Lagrangian stochastic model (Windtrax) was used for inverse dispersion modelling to back-calculate the total emission rate from the point of continuous measurement. Back-calculated emission rates and literature EFs were applied to the ADMS model to make predictions of air NH3 concentrations. Predicted concentrations were verified against weekly passive (CEH ALPHA) NH3 measurements, where measured concentrations were well described by the numerical model framework using the emission rate estimated by inverse dispersion modelling. EFs that were applied from the literature required adjustment to fit the measured concentrations, however after sensible adjustment an excellent match of observed and predicted concentrations was achieved. Total emissions from the AD plant was estimated to be 16.8 μg s-1 ± 1.8 mg s-1. This is significantly higher than the back-calculated estimate (10.3 ± 1.1 mgs-1), due to a more realistic treatment of the source area. The storage of solid digestate and the aerobic treatment of liquid effluents were the most significant sources of NH3. The representativeness of the existing EF estimated for AD plants is evaluated through application to the present case study and comparing with NH3 measurements and estimated emission rates. The existing AD EF considerably overestimated observed concentrations by an average factor of 54. The applicability of calculated EFs to other AD plants is discussed.

Item Type: Publication - Thesis (Masters)
UKCEH and CEH Sections/Science Areas: Dise
NORA Subject Terms: Atmospheric Sciences
Date made live: 31 Jul 2015 11:30 +0 (UTC)

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