Effects of Wood Ash-Based Alkaline Treatment on Nitrogen, Carbon, and Phosphorus Availability in Food Waste and Agro-Industrial Waste Digestates

Abstract

Handling of food waste and agro-industrial waste digestates, and fly and bottom wood ashes represents an economic and environmental problem for society and industries where they are produced due to the requirement of large capacity storage facilities with special conditions. Since both materials contain important nutrients for crops, two different blending combinations were examined as potential slow-release fertilizers to enhance the circular economy. High share of biomass ashes were selected aiming the chemical alkaline stabilization of the digestates. The concentrations of nitrogen, carbon, and phosphorus in the water-soluble extract of the blends, which was obtained by adding ten parts of milli-Q® per each part of sample and subsequent solid-liquid separation, were measured during a 10-h incubation at 22 °C and 100 rpm. The volatilization of ammonia was the main route of losing nitrogen, with the greatest rate of volatilization at the time of blending and approximately 50 mg NH 3-N/kg blend/hour by the end of the incubation. The hydrolysis taking place at alkaline pH was found responsible of the conversion of organic nitrogen to ammoniacal nitrogen and of the increase of the amount of water-soluble carbon, which rose progressively during the incubation. The release of CO 2 was prevented by the high pH (> 10) of the blends. The drop in the concentration of water-soluble orthophosphate at the time of preparing the mixtures Electronic supplementary material The online version of this article (

Circularity of Bioenergy Residues: Acidification of Anaerobic Digestate Prior to Addition of Wood Ash

“…A detailed description of the bioenergy waste streams employed for the present work can be found in the previous investigation of Moure Abelenda et al [55]. The greater mineralization that the FWD underwent during the AD, compared to that of PVWD, was the reason for the greater chemical instability of the FWD (i.e., more susceptible to lose NH 4 + -N and PO 4 3− -P via NH 3 volatilization and leaching, respectively).…”

“…The present study investigates the implications of acid treatment of food waste digestate (FWD) and post-harvest vegetable waste digestate (PVWD). This is the first step in the manufacturing of the newfangled blended fertilizer, since the acidifications of the anaerobic digestates were found to be necessary to achieve the optimum combinations with wood fly ash (WFA) and wood bottom ash (WBA) [54], which are sources of phosphorus [55]. In this way, the blending conditions would be further optimized to achieve the pH of zero point of charge (pH zpc ) of the sorbents [40,56].…”

Impact of sulphuric, hydrochloric, nitric, and lactic acids in the preparation of a blend of agro-industrial digestate and wood ash to produce a novel fertiliser

“…sedimentation), as part of the first manufacturing operation. In our previous study we evaluated the scenario of dispensing with the acid medium [21].…”

“…acidifying agent) that was added to each sample before blending, followed an approximate S:E ratio 1:10 (Table 3). Our previous studies have proven that adding the extractant before the incubation did not significantly affect the composition of 2.5 g blend undergoing incubation at 100 rpm and 20 ºC [21]. The acid solutions prepared with ultrapure milli-Q water and reagent grade (Fig.…”

Alkaline Wood Ash, Turbulence, and Traps with Excess of Sulfuric Acid Do Not Strip Completely the Ammonia off an Agro-waste Digestate

“…Most of the volatilization of NH3 took place immediately after the blending and the absorption in the H2SO4 trap continued progressively during the course of the incubation, due to the mass transfer resistance [16]. Thereby, in processes with short contact time between the gas and the H2SO4 solution, it might be convenient to use bubbling systems to increase surface area between the two phases and thus the rate of transfer of NH3 [19].…”