Abstract
The problem of current agricultural practices is not limited to land management but also to the unsustainable consumption of essential nutrients for plants, such as phosphorus. This article focuses on the valorization of wood ash and anaerobic digestate for the preparation of a slow-release fertilizer. The underlying chemistry of the blend of these two materials is elucidated by analyzing the applications of the mixture. First, the feasibility of employing low doses (≤1 g total solids (TS) ash/g TS digestate) of wood ash is explained as a way to improve the composition of the feedstock of anaerobic digestion and enhance biogas production. Secondly, a detailed description concerning high doses of wood ash and their uses in the downstream processing of the anaerobic digestate to further enhance its stability is offered. Among all the physico-chemical phenomena involved, sorption processes are meticulously depicted, since they are responsible for nutrient recovery, dewatering, and self-hardening in preparing a granular fertilizer. Simple activation procedures (e.g., carbonization, carbonation, calcination, acidification, wash, milling, and sieving) are proposed to promote immobilization of the nutrients. Due to the limited information on the combined processing of wood ash and the anaerobic digestate, transformations of similar residues are additionally considered. Considering all the possible synergies in the anaerobic digestion and the downstream stages, a dose of ash of 5 g TS ash/g TS digestate is proposed for future experiments.
Highlights
IntroductionThe growth of the human population and the change in their diet (e.g., more consumption of animal products) imply devoting more land to food production at an alarming rate [1]
The growth of the human population and the change in their diet imply devoting more land to food production at an alarming rate [1]
Ash-amended digester provided more than twice the biogas production during the 45-day incubation (2345 mL) The pH of the digester sown with wood ash (WA) was 4.40, but the methanogen archaea were able to adapt to the acidic conditions of the digester media
Summary
The growth of the human population and the change in their diet (e.g., more consumption of animal products) imply devoting more land to food production at an alarming rate [1]. The limiting step is hydrolysis, while the methanogenesis is quick, preventing the accumulation of volatile fatty acids (VFA) in the system In this way, the concentration of VFA in the anaerobic digest ester could be used as an indicator of the correct stationary operation of the bioreactor [17]. Ash-amended digester provided more than twice the biogas production during the 45-day incubation (2345 mL) The pH of the digester sown with WA was 4.40, but the methanogen archaea were able to adapt to the acidic conditions of the digester media. Biogas production rate in ash-added digesters was higher than in control experiment (i.e., unamended BMP) but total yield followed the trend: 20 g/L > 0 g/L/ > 10 g/L > 100 g/L [36] Drop in the pH due enhancement of the hydrolytic and acidogenic processes. Granular WA was able to remove NH4+-N fermented WWTP sludge, which is from the liquid phase due to adsorption via equivalent to 0.14 and 3.2 g ash/g TS or 5.72 cation exchange and 133.94 g ash/L, respectively
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