The anaerobic digestion effect on the chemical-physical characteristics, on some indicator microorganism and on ammonia emission from dairy manure, stored at different temperatures

In recent years, climate change and global warming, generated by human activity, are causing concern among public opinion, and are a topic of debate and research. The agro- zootecnical system has a significant contribution in terms of ammonia and pollutants emissions to the environment. The treatment and correct management of livestock waste can reduce greenhouse gas emissions by up to 25%. Therefore, in order to make the sector more sustainable, various technologies have been developed, such as anaerobic digestion, which allows the obtaining of biogas and organic fertilizer from animal waste. Anaerobic digestion, carried out by specific microorganisms, allows the conversion of the carbon contained in the organic substance to methane (50-75%) and carbon dioxide (25-50%). Four stages make up this process, in which the coordinated enzymatic activity of different microorganisms allows the degradation of the macronutrients that make up animal waste into simpler compounds, which will in turn serve as substrates for the survival of other bacteria. The last stage sees the activity of methanogenic microorganisms of the Achaea domain, which, in favorable conditions, allow the production of methane. Adequate chemical-physical parameters, such as temperature, pH and retention time of the organic substance, allow the waste exploitation to be converted into a resource, reducing the biological risk for spreading in the field and thus obtaining a renewable energy source in full compliance with the principle of the circular economy, much pursued nowadays. The aim of this study is to measure the emissions of ammonia (NH3) in relation to the chemical-physical characteristics of fresh and digested manure, and to the level of some indicator microorganism, at different storage temperatures. The emissive capacity of these gases at different storage temperatures after digestion, at 18°C and 30°C, was also investigated, in order to evaluate the effect of high temperatures, now also typical of Northern Italy on the impact generated by bovine sewage. For this purpose, 6 samples of bovine slurry and 6 samples of digestates were collected in three dairy farms located in the Lombardy region, analysed for pathogen indicator microorganism and for their chemical-physical characteristics. Ammonia emission, measured through the static chamber method (Innova 1512 Photoacoustic gas detector, LumaSense Technologies) resulted affected by the treatment, as it was expected, and by the storage temperature, that are crucial factors for the emission potential of animal waste and digestates.