Study of pig manure digestate pre-treatment for subsequent valorisation by struvite

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WASTE AND BIOMASS MANAGEMENT & VALORIZATION

Study of pig manure digestate pre-treatment for subsequent valorisation by struvite Francisco Corona 1,2 & Dolores Hidalgo 1,2 & Jesús María Martín-Marroquín 1,2 & Erik Meers 3 Received: 24 February 2020 / Accepted: 17 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract This work evaluates the release of phosphorus contained in the digestate from the anaerobic digestion of pig manure, through an acidification process. The objective of this acidification is to increase the amount of phosphorus available in the digestate liquid fraction and, subsequently, recover this element by chemical precipitation in the form of struvite or calcium phosphate. Two digestate samples (one fresh and one old) were studied and treated by adding various amounts of sulphuric acid to the different digestate fractions (raw digestate, solid fraction and liquid fraction). For the raw digestate, phosphorus releases higher than 95% were obtained for pH 4.0. In the last part of the experiment, the influence of acid pre-treatment on the reaction yield of phosphorus precipitation, in the form of struvite or calcium phosphate, was determined. Improvements in reaction yield were obtained up to 15% for struvite and 80% for calcium phosphate, increasing also in 7.5 times the amount of phosphorus available in the digestate liquid fraction, for both cases. Keywords Phosphorus . Acidification . Release . Nutrient recovery . Organic waste . Biofertiliser

Introduction In 2050, the world will have to feed about 9 billion people (Manning 2015). By then, agriculture and livestock could account for an estimated one-third of EU emissions, three times what it currently represents. Agriculture is one of the most important economic sectors in Europe. Its production value in 2018 was around €434 billion. The production value of livestock represented almost 40% of total agricultural production (€172 billion), highlighting the socio-economic relevance of the sector (Eurostat 2019). Intensive livestock farming is an important source of greenhouse gas (GHG) emissions: mainly methane (CH4) and

Responsible Editor: Ta Yeong Wu * Dolores Hidalgo [email protected] 1

CARTIF Centro Tecnológico, 47151, Boecillo, Valladolid, Spain

2

ITAP Institute, University of Valladolid, 47010 Valladolid, Spain

3

Department of Applied Analytical and Physical Chemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium

nitrous oxide (N2O), derived from a multitude of microbial reactions. Their relative importance depends on the composition of the manure (organic waste), the time and conditions of storage, the treatments applied and the application to the field and the climatic conditions of each scenario. Therefore, with these perspectives, the growth of the sector will in turn cause an increase in its weight in terms of climate policy, since, if emissions do not evolve in the sector according to the EU objectives, other sectors will have to compensate them even mor