Ammonia emissions from an anaerobic digestion plant estimated using atmospheric measurements and dispersion modelling

Abstract

Anaerobic digestion (AD) is becoming increasingly implemented within organic waste treatment operations. The storage and processing of large volumes of organic wastes through AD has been identified as a significant source of ammonia (NH3) emissions, however the totality of ammonia emissions from an AD plant have not been previously quantified. The emissions from an AD plant processing food waste were estimated through integrating ambient NH3 concentration measurements, atmospheric dispersion modelling, and comparison with published emission factors (EFs). Two dispersion models (ADMS and a backwards Lagrangian stochastic (bLS) model) were applied to calculate emission estimates. The bLS model (WindTrax) was used to back-calculate a total (top-down) emission rate for the AD plant from a point of continuous NH3 measurement downwind from the plant. The back-calculated emission rates were then input to the ADMS forward dispersion model to make predictions of air NH3 concentrations around the site, and evaluated against weekly passive sampler NH3 measurements. As an alternative approach emission rates from individual sources within the plant were initially estimated by applying literature EFs to the available site parameters concerning the chemical composition of waste materials, room air concentrations, ventilation rates, etc. The individual emission rates were input to ADMS and later tuned by fitting the simulated ambient concentrations to the observed (passive sampler) concentration field, which gave an excellent match to measurements after an iterative process. The total emission from the AD plant thus estimated by a bottom-up approach was 16.8±1.8mgs(-1), which was significantly higher than the back-calculated top-down estimate (7.4±0.78mgs(-1)). The bottom-up approach offered a more realistic treatment of the source distribution within the plant area, while the complexity of the site was not ideally suited to the bLS method, thus the bottom-up method is believed to give a better estimate of emissions. The storage of solid digestate and the aerobic treatment of liquid effluents at the site were the greatest sources of NH3 emissions.

Evaluation of ammonia emissions from filtration of digestate used for fertigation

“…The 'low' height corresponded to the height of the advanced filter surface, while the 'high' height was set at 1.5 m above the filter surface. These positions were selected based on previous research that measured NH3 emissions both from storage facilities and fields (Carozzi et al, 2013;Bell et al, 2016;Ferrara et al, 2016).…”

“…Some studies have already assessed the impact of some processes, such as digestate storage or digestate spreading; however, little research has been conducted on the digestate separation process. The advanced filtration step required for fertigation using digestate has not yet been investigated (Wolf et al, 2014;Bell et al, 2016;Riva et al, 2016;Finzi et al, 2019). Since digestate filtration involves digestate movement in semi-open environments, it is important to evaluate potential emissions that may occur.…”

The Criminogenic Nature of Food Production Harm Responses: A Case Study of Anaerobic Digestion Technology Subsidies in Northern Ireland

“…Yet, it has been claimed that anaerobic digesters may exacerbate pollution rather than reduce it (Bell et al 2016; Friends of the Earth 2018c; Source Material 2018). It was calculated that the net additional ammonia emissions from them would be around 696,740 kg (Friends of the Earth 2018b), thus, questioning the effectiveness of AD in reducing animal waste from farming intensification.…”

“…9 To question the potential of AD for mitigating environmental harms in farming even further, the government officials in Northern Ireland suggested that AD 'does not address the fundamental issue of excess nutrients in the manure, as it requires land spreading of the digestate' (DAERA 2014: 19). Therefore, there is a possibility that AD plants, while creating renewable energy, may increase ammonia emissions in Northern Ireland, primarily through the storage of feedstock and digestate, and the land spreading of the latter (Bell et al 2016).…”

Environmental impact analysis of food waste anaerobic digestion and products utilization process

“…The emissions from IC-engine electricity generation process was based on the historic source test results [16], the emissions from micro-turbine generator wass based on [15]. When food waste is exposed to the air, it will produce toxic gases such as NH 3 and H 2 S [17,18]. The data of gas emissions happened in pretreatment and S-L treatment were from the environmental impact announcement of referenced food waste treatment project which was released by Zhejiang Industrial Environmental Design Institute Co. Ltd.…”