Abstract
Hydrothermal carbonization (HTC) has been proved to be a promising technology for swine manure (SM) treatment. Currently, there is a lack of systematic understanding of the transformation characteristics of nutrient speciation in the HTC of SM. In this study, the speciation of the main nutrients (N/P/K) in SM-derived hydrochar produced at different reaction temperatures (200–280 °C) was investigated. The recovery of P (61.0–67.1%) in hydrochars was significantly higher than that of N (23.0–39.8%) and K (25.5–30.0%), and the increase in reaction temperature promoted the recovery of P and reduced the recovery of N. After the HTC treatment, the percentage of soluble/available P was reduced from 61.6% in raw SM to 4.0–23.9% in hydrochars, while that of moderately labile/slow-release P was improved from 29.2% in raw SM feedstock to 65.5–82.7%. An obvious reduction was also found in the amounts of available N (from 51.3% in raw SM feedstock to 33.0–40.5% in hydrochars). The percentages of slow-release N and residual N in hydrochars produced at 240 °C reached the maximum and minimum values (46.4% and 18.9%), respectively. A total of 49.5–58.3% of K retained in hydrochars was residual (invalid) potassium. From the perspective of the mobility and availability of N, P and K only, it was suggested that the HTC of SM should be carried out at 220–240 °C. Compared with the original SM, it is safer and more effective to use the SM-derived hydrochar as an organic fertilizer.
Highlights
IntroductionLivestock production usually generates enormous amounts of manure waste, which demand adequate disposal strategies due to their polluting potentials (e.g., eutrophication, pathogens, antibiotics, and heavy metals) [1,2]
The proportions of insoluble phosphates (ISP) in hydrochars were up to 48.5–79.8%, much higher than those in raw swine manure (SM) (19.6%), and increased with increasing reaction temperatures (Figure 3). These results suggest that P was concentrated in the hydrochars (Figure 1), the amount of insoluble P tended to increase remarkably after the Hydrothermal carbonization (HTC) treatment
After HTC treatment, phosphorus was enriched in hydrochars, while the contents of nitrogen and potassium were decreased
Summary
Livestock production usually generates enormous amounts of manure waste, which demand adequate disposal strategies due to their polluting potentials (e.g., eutrophication, pathogens, antibiotics, and heavy metals) [1,2]. China is the largest pig producer in the world with an average pig rearing amount of 449 million heads per year, accounting for. The annual output of livestock manure in China has reached 3.8 billion tons, of which swine manure (SM) accounts for 38.3% [4]. 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]
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