Changes of nutrients and potentially toxic elements during hydrothermal carbonization of pig manure

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

“…NH 4 -N and NO 3 -N belong to inorganic nitrogen, which can be quickly absorbed and utilized by plants, commonly seen as a quick-availability nitrogen fertilizer [ 4 ]. As seen in Table 3 , the content of inorganic N in raw SM feedstock was 5.95 mg/g, accounting for 25.1% of the total nitrogen ( Figure 4 ).…”

“…After the HTC treatment, the content of inorganic N in hydrochars decreased significantly by 48.9–74.8% (NH 4 -N) and 23.1–30.6% (NO 3 -N), respectively, compared with those in the raw SM feedstock. This was due to the fact that the inorganic N in the raw SM feedstock was mainly transferred into the aqueous product (process water) during the HTC process in the forms of NH 4 -N and NO 3 -N by hydrolysis [ 4 , 53 ].…”

“…China is the largest pig producer in the world with an average pig rearing amount of 449 million heads per year, accounting for 50% of the total global production [ 3 ]. The annual output of livestock manure in China has reached 3.8 billion tons, of which swine manure (SM) accounts for 38.3% [ 4 ]. At present, researchers have developed a series of technologies for the treatment/disposal of SM (a wet solid waste), mainly including composting [ 5 , 6 ], anaerobic digestion [ 7 , 8 ], hydrothermal carbonization (HTC) [ 9 , 10 , 11 ], pyrolysis [ 12 , 13 ], gasification [ 14 , 15 ], and liquefaction [ 16 , 17 ].…”

“…In other words, no pre-dewatering/drying is needed for the HTC process as required in other thermal treatment processes (e.g., pyrolysis, dry gasification, and combustion), which makes it an economically attractive option for the treatment of SM [ 19 ]. Generally speaking, the research on the HTC of SM has been currently carried out regarding the following aspects: (i) the effects of the main process parameters, including reaction temperature/time, solid-liquid ratio, catalyst and heating mode, on the yield/property of hydrochar [ 21 , 22 , 23 , 24 , 25 ]; (ii) the Co-HTC of SM and lignocellulosic biomass [ 26 , 27 , 28 ]; (iii) the migration and transformation of pollutants (heavy metals and PAHs) existed in raw SM [ 10 , 29 , 30 ]; (iv) inter-comparison of the properties of hydrochar and biochar (pyrolysis) [ 9 , 31 , 32 , 33 ]; and (v) the fate of nutrients contained in raw SM [ 4 , 23 , 34 , 35 ].…”

“…As mentioned above, some studies have been carried out on the fate of nutrients during the HTC of SM, but the focus is primarily on the total content of nutrients retained in hydrochar [ 23 , 27 , 31 , 32 , 33 ]. A few researchers have also paid attention to the contents of nitrate N, ammonium N, available P, and available K in SM-derived hydrochars [ 4 , 21 , 22 ]. In the research by Huang et al [ 34 ], the transformations of P speciation (including five forms) were explored during the HTC of SM.…”