Circular agriculture: from biogas waste new fertilisers and water for irrigation

From biogas production waste, new products for agriculture. These are fertilisers, soil conditioners and 'purified' water for irrigation. The result has been achieved as part of the "Biosos - BIOgas SOStenibile" project coordinated by the University of Camerino and in which Enea researchers are working.

Thanks to an innovative two-stage filtration process, 'it has been possible to extract nutrients (nitrogen, phosphorus, and potassium) and organic substances that can be used as fertilisers and agricultural soil improvers from the liquid fraction of the digestate'. Moreover, according to the ENEA researchers, the system 'would allow the recovery of up to 80% of the water coming out of the digester, which can be reused within the biogasification process, for the dilution of fertilisers or for irrigating fields, a particularly important element considering the increase in drought events attributable to climate change'.

According to Gian Paolo Leone, of the Circular Bioeconomy Laboratory and responsible for ENEA for the contract commissioned by the University of Camerino, "with this innovation we want to contribute to the achievement of European objectives, in particular the Farm to Fork strategy, which envisages a 20% reduction in the use of synthetic fertilisers by 2030".

The experimentation carried out by researchers from the National Agency has as its strong point the use of a "special filtration technology that has been at the centre of the Sustainable Agrifood Systems Division's research activities for years. "It is based on a liquid separation process where the fluid flows parallel to the surface of the membrane, efficiently separating water and salts from concentrated organic substances," explains Daniele Pizzichini, researcher at ENEA's Circular Bioeconomy Laboratory. The same technology is already being used to extract molecules of food, nutraceutical and cosmetic interest, to recover proteins from dairy wastes, such as cheese whey, and antioxidant molecules such as polyphenols and flavonoids from olive oil vegetation waters, as well as to desalinate brackish and sea water for water supply purposes'.

Specifically, the experimentation involved a series of consecutive filtration stages. "In the first stage we retain potentially present bacteria, reduce turbidity related to suspended solids, and thus reduce the pollutant load for the subsequent treatment stages," adds Gian Paolo Leone. In the second stage we obtain by means of nanofiltration or reverse osmosis a purified water to be used for crop irrigation and a concentration of macronutrients, especially ammoniacal nitrogen, with different characteristics depending on the organic waste (cattle manure or rainbow trout carcass) but completely similar to commercial fertilisers'. A process that, as reiterated by the experts, has the advantage of "ensuring an adequate microbiological safety profile of the concentrated fractions with potential agronomic use".