Fate of Nitrogen, Phosphate, and Potassium during Hydrothermal Carbonization and the Potential for Nutrient Recovery

Abstract

In this study, the fate of carbon and nutrient elements, nitrogen, phosphorus, and potassium, was investigated during the hydrothermal carbonization (HTC) of three model solutions with different nutrient concentrations to mimic biogas residues from silage and cattle manure. The HTC was conducted at 180 °C, 220 °C, 240 °C, and 260 °C for 3 h reaction time. ICP-OES, GC, IC, and chemical analysis methods were utilized to measure fertilizing elements in HTC products. The distribution of nutrients between HTC product phases was significantly influenced by the compositions of the initial feedstock before HTC. The incorporation of nitrogen to the hydrochar (HC) depends on the nitrogen-containing compounds during HTC; the chemical bonding was the main mechanism for the incorporation of NH4–N into the HC during HTC, the sorption of NH4–N to the HC occurred, however, to a lesser extent (0.8% to 7.4%). Most of the NO3–N stayed in the process water (PW) during HTC (78% to 87%), and the sorption (adsorption/salts precipitation) was confirmed to be the main mechanism for the recovery of NO3–N to the HC during HTC. The uptake of N to the HC is limited and depends on the availability of the carbon network in the HC, the correlation coefficient between HC formation and the recovery of bonded N to the HC showed a high linear regression coefficient R 2 = 0.90–0.91. However, the recovery of N to the HC via sorption showed less correlation to the HC formation during HTC (R 2 = 0.35–0.54). Most of the dissolved K+ (99%) stayed in the PW during HTC. Due to the absence of metal associations in this work, most of the dissolved PO4 3– (99%) stayed in the PW during HTC, which proves that controlling metal cations in the feedstock before HTC has a considerable influence on the distribution of phosphate between the PW and HC.

Speciation of Main Nutrients (N/P/K) in Hydrochars Produced from the Hydrothermal Carbonization of Swine Manure under Different Reaction Temperatures

“…Higher reaction temperatures may decrease N recovery to the hydrochar via enhancing deamination reactions, which cause the transportation of N-compounds to the aqueous product (process water) and promotion of the transportation rate of N to the gaseous phase [ 43 ]. Regarding P recovery, the increase in reaction temperature improved the formation of metal-associated P species (e.g., calcium, aluminum, magnesium, or iron) and insoluble phosphates, as well as potential physical constraints (e.g., embedment of P species into the char structure) [ 44 , 45 ].…”

“…Nitrate N was negatively charged and ammonium N was positively charged. The chemical bonding was the main mechanism for the incorporation of NH 4 -N into the hydrochar during HTC, while the sorption (electrostatic adsorption/salts precipitation) was the main mechanism for the recovery of NO 3 -N to the hydrochar [ 43 ]. This distinct adsorbate nature might be the main cause of the difference between the changes in the situations of NH 4 -N and NO 3 -N contents.…”

“…Especially at higher reaction temperatures (260–280 °C), the content of Alkali-ON in hydrochars reduced by 85.5–90.6%. These results might be due to the following reactions that occurred during the HTC process: (i) the crude proteins in raw SM were hydrolyzed to soluble polypeptides and amino acids, and then the polypeptides and amino acids were converted to organic acids, amines, ammonia and CO 2 through deamination and decarboxylation processes; (ii) the polypeptide/amino acids reacted with the reducing sugar or their derivatives through typical Maillard reactions, forming more stable nitrogenous compounds [ 43 , 57 , 58 ].…”

Continuous synthesis of 5‐hydroxymethylfurfural from biomass in on‐farm biorefinery

“…Typical products of the Maillard reaction (Fan et al, 2018) as a consequence of the presence of small amounts of proteins are not analyzed here. Parallel reactions like the Maillard reaction (Alhnidi et al, 2020) may reduce the yield of HMF.…”

Exploiting the Nutrient Potential of Anaerobically Digested Sewage Sludge: A Review

“…Nitrogen (N), potassium (K), and phosphorus (P) have a key role in biological ecosystems [3][4][5][6][7]. Nitrogen is essential for the biological cycle of plants, being the main element responsible for their growth.…”