Effect of Reactive and Non-Reactive Additive Treatment on the Recovery of Phosphorus from Biogas Digestate

Naga Sai Tejaswi Uppuluri (), Konstantin Dinkler, Xueling Ran, Jianbin Guo, Joachim Müller and Hans Oechsner ()
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Naga Sai Tejaswi Uppuluri: State Institute of Agricultural Engineering and Bioenergy, University of Hohenheim, 70599 Stuttgart, Germany
Konstantin Dinkler: State Institute of Agricultural Engineering and Bioenergy, University of Hohenheim, 70599 Stuttgart, Germany
Xueling Ran: Key Laboratory of Clean Utilization Technology for Renewable Energy, Ministry of Agriculture, Department of Agricultural Engineering, China Agricultural University, Beijing 100083, China
Jianbin Guo: Key Laboratory of Clean Utilization Technology for Renewable Energy, Ministry of Agriculture, Department of Agricultural Engineering, China Agricultural University, Beijing 100083, China
Joachim Müller: Institute of Agricultural Engineering, Tropics and Subtropics Group, University of Hohenheim, 70599 Stuttgart, Germany
Hans Oechsner: State Institute of Agricultural Engineering and Bioenergy, University of Hohenheim, 70599 Stuttgart, Germany

Energies, 2023, vol. 16, issue 14, 1-16

Abstract: The annual phosphate (PO 4 3? ) utilization has increased, leading to a depletion of existing sources of phosphorus (P). To overcome this, digestate as a source to recover P is being investigated. Due to the abundance of nutrients, the digestate from an agricultural biogas plant is used as fertilizer for crops. The separation of solids and liquids from the digestate by a screw press is the simplest form of concentrating, therefore, recovering PO 4 3? . This is the most commonly employed method in existing biogas plants. However, the separation is not very efficient as only 20–30% of P is recovered in the solid phase. The goal of this study is to increase the separation efficiency and recover more P into the solid phase, in order to improve the transportability. For this, separation trials at a laboratory scale were performed for five experimental groups, with biochar and straw flour as non-reactive additives and kieserite as a reactive additive. In addition, untreated digestate was studied as a control. The control and the treatment with biochar and straw flour were carried out at 25 °C, while the treatment with kieserite was performed at 25 °C and 50 °C. The separation trails were performed at treatment times of 0 h, 1 h, 2 h, 8 h, and 20 h. The results showed that the treatment with additives had a beneficial effect on the recovery of P. It was noted that kieserite treatment at 25 °C and 50 °C bound about 61% of the total P present in the digestate to the solid phase. A sequential extraction was performed to study the effect of additives on the recovery of different P species. The results concluded that, compared to biochar and straw flour, kieserite was efficient in recovering the non-labile fractions (NaOH-P and HCl-P) of P, which act as slow-release fertilizers. This study shows that the use of additives, especially kieserite, has a positive influence on recovering P from digestate, and further research to optimize the recovery process would be beneficial.

Keywords: digestate; phosphorus; additives; solid phase; treatment time; temperature (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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