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. 2023 Jun 15:336:117664.
doi: 10.1016/j.jenvman.2023.117664. Epub 2023 Mar 13.

Acidification and solar drying of manure-based digestate to produce improved fertilizing products

L Morey  1 , B Fernández  2 , L Tey  3 , C Biel  3 , A Robles-Aguilar  4 , E Meers  5 , J Soler  6 , R Porta  7 , M Cots  7 , V Riau  3
Affiliations

Acidification and solar drying of manure-based digestate to produce improved fertilizing products

L Morey et al. J Environ Manage. .

Abstract

The increase in energy and fertilizer consumption makes it necessary to develop sustainable alternatives for agriculture. Anaerobic digestion and digestates appeared to be suitable options. However, untreated digestates still have high water content and can increase greenhouse gas emissions during storage and land application. In this study, manure-derived digestate and solid fraction of digestate after separation were treated with a novel solar drying technology to reduce their water content, combined with acidification to reduce the gaseous emissions. The acidified digestate and acidified solid fraction of digestate recovered more nitrogen and ammonia nitrogen than their respective non-acidified products (1.5-1.3 times for TN; 14 times for TAN). Ammonia and methane emissions were reduced up to 94% and 72% respectively, compared to the non-acidified ones, while N2O increased more than 3 times. Dried digestate and dried acidified digestate can be labeled as NPK organic fertilizer regarding the European regulation, and the dried solid fraction and the improved dried acidified solid fraction can be labeled as N or P organic fertilizer. Moreover, plant tests showed that N concentrations in fresh lettuce leaves were within the EU limit with all products in all the cases. However, zinc concentration appeared to be a limitation in some of the products as their concentration exceeded the European legal limits.

Keywords: Ammonia emissions; Digestate acidification; Greenhouse gas emissions; Greenhouse solar drying; Nutrient recovery; Thermal treatment.

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Conflict of interest statement

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
Diagram with all the digestate-derived fertilizers produced. Abbreviations: D, digestate; AD, acidified digestate; C, centrifuge; SF, solid fraction of digestate; LF, liquid fraction of digestate; ASF, acidified solid fraction; SLF, poor-nitrogen stream after LF stripping process; DD, dried digestate; DAD, dried acidified digestate; DSF, dried solid fraction; DASF, dried acidified solid fraction; DM, dried mixture of ASF and SLF.
Fig. 2
Fig. 2
Greenhouse solar dryer and turning machine in the semi-industrial installation.
Fig. 3
Fig. 3
Profile of emission fluxes (mg/m2h), measured during the solar drying of solid fraction (SF) derived products. (a) N–NH3. (b) C– CH4. (c) N–N2O. Symbols: Solid line: first replicate; dashed line: second replicate; square: DSF; diamond: DASF; circle: DASF2; vertical line: 21 days were selected to calculate the total accumulated emissions per product for comparison purposes. Average values and standard deviations are represented in Table S5.
See this image and copyright information in PMC

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