Combined Acidification and Solar Drying of Pig Slurries for Nutrient Recovery and Controlled Atmospheric Emissions

Francesc X Prenafeta-Boldú,Joan Noguerol,Josep Illa,Belén Fernández,Marc Viñas,Joan Soler

doi:10.3390/agronomy11020222

Francesc X Prenafeta-Boldú, Joan Noguerol + Show 4 more

Open Access

https://doi.org/10.3390/agronomy11020222

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Abstract

The solar drying of pig slurries was tested in a pilot-scale greenhouse (10 m2 footprint), operated with forced ventilation under low and high solar irradiation in Mediterranean conditions. Gaseous emissions were prevented through slurry acidification and by the biofiltration of exhaust gases. Air relative humidity and temperature in and out the greenhouse, as well as the weight of a slurry sample, were monitored online to command the ventilation regime. Daily average drying rate values ranged from 0.3 to 2.8 kg m−2 d−1 and displayed a direct dependency with solar radiation until the pig slurry lost a 60% of its initial weight, with a solar energy efficiency of about 26%. Upon further drying, the water content from pig slurries stabilized at around 10%. Mass balances between the initial slurry and dried product were closed for total solids and organic matter, but the recovery of nutrients ranged from 69% to 81%, apparently because of precipitation and incrustation phenomena. The NPK composition of the final product was 4.3–2.5–3.8 and fulfilled current regulations for solid organic fertilizers. Operational costs of the drying process and fertilizing quality parameters were also discussed.

Highlights

Intensive livestock farming has led to the production of large amounts of manure, which contain more nutrients than what the bystanding crops are able to extract [1]
This manure excess causes significant nitrate and phosphate pollution of water bodies and soils, but it results in harmful atmospheric emissions
The used pig slurries and the obtained dried material were characterized in terms of pH, total and volatile solids (TS/VS), chemical oxygen demand (COD), total nitrogen (Nt), total ammonia nitrogen (TAN), nitrites and nitrates (NO2, NO3 – ), total phosphorus, (Pt), phosphate (PO4 3– ), total potassium (Kt) and sulfate (SO4 2– ), following the Standard

Summary

Introduction

Intensive livestock farming has led to the production of large amounts of manure, which contain more nutrients than what the bystanding crops are able to extract [1]. The key to a sustainable manufacture and export of organic fertilizers from manure is the on-site concentration of nutrients by removing its water, either by physical separation methods [3], chemical precipitation [4], or through thermal or vacuum evaporation [5]. These manure processing technologies require energy, chemical reagents, and costly infrastructure

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