Abstract
This work investigates an innovative process to valorise agricultural digestate by the exploitation of solar energy. Digestate has been located in a lab-scale greenhouse to evaporate the liquid phase. Digestate vapours, rich in ammonia, are sent in a Drechsler trap, filled with 38% w/w sulfuric acid solution, through three solar air fans. A concentration of about 2 M of ammonium sulphate solution was recovered. The remaining dried solid phase, rich in phosphorous compounds, was evaluated as alternative to the commercial fertilizers (46% P2O5) in the growth of maize plants. Equal amount of P was applied to each pot (25 mg/kg soil). The plants were evaluated along the 8 weeks in a greenhouse monitoring the growth parameters and leaf SPAD index, micro-, macronutrients and non-essential heavy metals. The results evidenced that the dried solid phase of digestate can be used as an alternative source of P.Graphic
Highlights
In 2017 the European Union relaunched the efforts to limit to fossil fuels adoption in the economic activities in favor of renewable sources
It was estimated that 395 million tonnes of dry matter (Tdm) of primary agricultural residues are annually produced in the EU countries but just 62 million Tdm are collectable as feedstock for the synthesis of biobased materials, nutrients recovery and bioenergy applications [2]
Considering the shoot fresh weight (FW) and DW, our data are in line with the results reported in previous work where the comparison of the application of solid fraction of digestate and commonly used fertilizers investigated on different plant species [13, 14, 16, 17]
Summary
In 2017 the European Union relaunched the efforts to limit to fossil fuels adoption in the economic activities in favor of renewable sources. It was estimated that 395 million tonnes of dry matter (Tdm) of primary agricultural residues are annually produced in the EU countries but just 62 million Tdm are collectable as feedstock for the synthesis of biobased materials, nutrients recovery and bioenergy applications [2]. Agrifarm residues are essentially adopted for bioenergy scope, in particular for the biogas production by anaerobic digestion (AD). Digestate is the main byproduct from AD, which can be adopted as soil improvers or fertilizer production in a circular economy optic. Digestate supplies stable carbon on fields increasing the carbon sink capability of soils and is rich in nitrogen (N), phosphorus (P), and potassium (K), important macro and micro- nutrients for intensive agriculture [6]. Nitrogen is the most important and commonly lacking nutrient
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