First Results of Digestate Spreading Trials in Mediterranean Crops

Biogas production by Anaerobic Digestion (AD) is more and more widespread due on the one hand to the large quantity of biodegradable residues and by-products produced by livestock and agro-industrial activities and on the other to the growing interest in alternative energy sources. The by-product of the AD, the digestate, allows closing the production cycle: in fact, it is a stabilized bio-fertilizer with an amount of nutrients depending on feedstock features, which can be used as an organic soil improver and can contribute to organic soil matter turnover. In this paper the first results of digestate spreading trials are discussed. The digestate came from an anaerobic digestion plant of 600 kW (electric), which processes agri-food industry by-products. The digestate was separated into the two fractions, liquid and solid, by means of a mechanical separator. The solid fraction was spread in a vineyard and a citrus orchard under effective field conditions, using implements provided by a local agricultural subcontractor and with spreader settings and operating parameters usually adopted by him. The liquid fraction was microfiltered at the digestion plant, and the microfiltered fraction, after dilution and a further microfiltration, was spread in three other citrus orchards by means of drip fertigation plants. First results suggest the need to improve the uniformity of application of the solid fraction and to carefully adjust the parameters of the final microfiltration of the microfiltered fraction so to reduce water consumption and the overall economic costs.