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Description of the Project

Waste management is a strategic issue for farming activities. It is fundamental, in fact, to develop and implement technologies that allow to limit the environmental impact of farms, in particular for the treatment of manure, without compromising the profit: environment friendly solutions must be also sustainable from an economic prospective.

The anaerobic digestion of manure represents a valid and actual option.

This project aims to evaluate the possibility of implementing this technology in farms, taking into consideration also the effects on the territory of a widespread diffusion of biogas plants, in order to reach an acceptable degree of environmental sustainability of farms.

Starting from a critical analysis of the anaerobic digestion process, considering its technological and functional aspects studied in several years of activity, a new type of process has been developed for the treatment of swine manure.

This particular technology is derived from fixed bed type digester, in particular from hybrid reactors, characterised by an up-flow of manure: in this reactors the upper portion is occupied by the filling material, while the lower part acts like a UASB reactor. Bacteria are both in the suspended and fixed form, but the main degradation of organic matter is operated by suspended bacteria of the lower portion of the reactor.

Several experiences of the past, of the director of the project and of other authors, allowed to underline the advantages offered by this solution:

• lower size: this type of reactors can treat swine manure with a retention time of 10 days (volume equal to 10 times the daily production of manure), in other words, half of the retention time required by conventional digesters;
• limited energy demand for heating the digester, as a consequence of the lower size;
• higher energy efficiency: the specific biogas yield is increased by the higher microbial population.

The developement and implementation of hybrid anaerobic digestion for the treatment of swine liquid manure is supported by the following considerations:

• this technology is particularly indicated for the treatment of feedstocks with low Total Solids content, like swine liquid manure;
• previous experiences on lab scale and pilot scale digesters (mainly with the liquid fraction of bovine manure, from liquid/solid separation) gave promising results.