Existing swine manure co-aerobic/anaerobic plant improvement: preliminary experimental and energetic analysis

Swine breeding represent one of the most zootechnical diffused activity in many Italian regions. In particular the Umbria region, situated in the middle of Italy, has a long tradition in such activity. Unfortunately, high intensity breeding, represent also a serious threat for the environmental impact due to the production of gaseous, liquid and solid, containing high fraction of potentially pollutant agents, that are represent by nitrogen compounds, organic load (BOD), bacteriological load, sulphur compounds and also heavy metals. These substances can seriously affect the soil, the deep as the surface water and also the quality of the air. With the aim of giving a more environmentally sound and technical as economical sustainable answer to manure management, this preliminary study has been performed on an existing pig breeding, situated in the Umbria region, able to houses about 11.000 swine per cycle from 5 to 25 kg, that currently has a combined anaerobic/aerobic biological cotreatment plant, able to manage the swine manure together with other agricultural residuals. The main scope of this plant is to reduce the manure liquid fraction to be disposed by the field irrigation in favour of a solid, aerobic stabilized, one and to produce renewable energy exploiting the biogas arising from the anaerobic process. The aim of this preliminary study is to optimize the current process trying to increase both the quality of the solid aerobic stabilized products, than the amount of energy recoverable from the whole process. This goal is pursued, without increasing the amount of substances currently exploited, by the introduction of a new biological treatment system, able to work in a serial way with the existing one. The evaluation of the benefits arising from the proposed improvement has been performed by the aid of an experimental analysis conducted both in field than in laboratory tests. The field tests concerns mainly the evaluation of the possibility of obtaining an high quality compost whereas the laboratory test concerns mainly the evaluation of the biogas production from the analysed biomass. These preliminary analysis have been conducted starting from a mixture constituted by a defined swine manure and other agricultural residues mass composition. By the proposed improvement of the aerobic process, the field as the laboratory preliminary analysis, shows that it is possible to produce an high quality compost, if some correction are made on the swine diet. Another important aspect related to the aerobic phase improvement is represented by the possibility of reducing significantly the process time, required by the current plant, and also the amount of the residual liquid fraction exploited for field irrigation. From the energetic point of view, the preliminary laboratory anaerobic test conducted on the analysed mixture, shows that biogas production potential is about 35 Nm3 per treated ton, about 2-3 time higher than the one produced exploiting only the manure. The whole biogas production can be considerably increased taking in to account that the one produced by the current anaerobic plant will be not affected by the proposed improvement. Due to the necessity of exploiting other biodegradable, available and low cost substances, the proposed solution seems to be particularly suitable for low-medium scale intensive breeding, with a limited availability of agricultural field for the manure irrigation practise. Furthermore, the increase in renewable energy production and the possibility of producing high quality compost, starting from the manure and the other residuals, can lead also to a reduction of the whole system costs together with an increase in environmental benefits.