EFFECTS OF SLURRY TREATMENTS ON GASEOUS EMISSIONS FROM STORAGE AND EVALUATION OF MODELS TO PREDICT AMMONIA RELEASE

Liquid manure storage facilities are sources of methane (CH4), nitrous oxide (N2O) and ammonia (NH3) emissions. CH4 and N2O are relevant greenhouse gases in terms of climate change because of their strong absorption of infrared radiation. NH3 causes various environmental problems, such as odour, eutrophication, acidification of soils and atmospheric particulate matter formation. To mitigate the effect of these emissions on the environment, many guidelines and regulations have been established by governments in various countries. Mitigation options during storage have been proposed, but they are not always easy to be implemented and their adoption in some areas, including Italy, is limited. Furthermore, the introduction of new slurry treatment technologies brings new challenges that require a better knowledge of their effect on the emissions during subsequent storage of the treated manure. This is particularly relevant also in the context of emission inventories, which aim to establish the state of implementation of environmental policies. The research carried out aims to improve the knowledge about the effect on emissions of some slurry management techniques. The activities carried out can be divided in two main groups: 1) Experimental activities a) Pilot scale experiments in controlled temperature conditions which aim to study comparatively the emission and the chemical evolution of treated and untreated slurries during one month storage. In particular it was evaluate how mechanical separation and anaerobic digestion affect NH3 and greenhouse gas emissions from the storage. The experimental plan was designed in order to apply mechanical separation on untreated slurries and digestates and to consider different typologies of slurries, whose characteristics can be considered representative of the average for the region considered. b) Pilot scale experiments in field conditions which aim to study the effect on NH3 and greenhouse emissions of the following treatments and mitigation option: b.1) mechanical separation b.2) application of a coat of clay granules on slurry surface b.3) acidification with sulphuric acid Activities a) and b.1) were carried out at the experimental farm of Landriano (Italy) while Experiments b.2) and b.3) took place at Rothamsted Research Center (UK). The methods used for gas measurement in all experimentations are based on dynamic chamber technique, while the effective nutrient losses have been determined by chemical analyses. 2) Modelling activity: the overall objective of this activity was to identify and calibrate some models, pre-existing in literature, to simulate ammonia emission factors from different storage conditions, suitable over a range of slurry chemical and physical properties. Therefore, 13 different models have been evaluated and a calibration procedure was set using the data obtained in the experimental activities in order to find the best prediction models for each storage condition considered. The main results obtained from experimental activities were the following: • Mechanical separation can cause a significant increase (up to 85%) of ammonia e nitrous oxide emission during storage: the first one is related to the presence of the liquid fraction while the second is mainly caused by the solid fraction • Anaerobic digestion can also increment significantly nitrogen losses up to 45 %, but at the same time it represents a treatment that can effectively reduce methane emissions during storage of digestate • Handling operation have to be carefully considered: increments of nitrogen and carbon losses were observed from mixed slurries. Furthermore it was found that when slurries are mixed, the main factors influencing nitrogen emissions are the TAN concentration and the TAN/TKN ratio. After mixing, the unseparated slurries were associated with higher NH3 emission factors • Floating clay granules proved to be a very effective NH3 (mean reduction 72 %) mitigation technique but had no significant effect on CH4 emission from pig slurry • Acidification of cattle slurry proved to be a very effective mitigation technique for both CH4 (mean reduction of 88 %) and NH3 (up to 100% when pH is kept below 5) • The derivation of country-specific emission factors for pig and cattle slurries in a revised inventory approach need to take into account duration and temperature of storage In general, the results obtained from the experimental activity carried out can be used to estimate the variations of the emissions during storage induced by treatments or mitigation techniques. It is thus possible to quantify the reduction of emissions that can be obtained if best practices are applied with reference to the standard techniques. On the other side, the emissions from the standard technique can be based on models in order to consider the manure characteristics and the local conditions, as demonstrated by the results in the assessment of model to estimate ammonia emissions. In particular models have proved to be very helpful instruments to predict ammonia emission factors in different storage conditions. In some cases, they can also evaluate the effect of a treatment when the latter influence the input variables of the model. In conclusion the use and evaluation of models coupled with the study of slurry treatment effects is advisable for an improved inventory approach and to develop operational guidelines for improved manure management practices to reduce environmental impacts. Further research is necessary to improve models and to better understand the effect of some treatments techniques on emissions. Specific experimentations have to be set in order to validate the models and, at the same time, a wider assessment of treatments across different slurry types is advisable to provide robust values of emission factors, which are the base for a “good” model development.