Abstract
Proper disposal and utilization of dead pig carcasses are problems of public concern. The combination of hydrothermal pretreatment (HTP) and anaerobic digestion is a promising method to treat these wastes, provided that digestion inhibition is reduced. For this reason, the aim of this work was to investigate the optimal HTP temperature (140–180°C) for biogas production during anaerobic digestion of dead pigs in batch systems. In addition, the effects of hydrochar addition (6 g/L) on anaerobic digestion of pork products after HTP in continuous stirred tank reactors (CSTR) were determined. According to the results, 90% of lipids and 10% of proteins present in the pork were decomposed by HTP. In addition, the highest chemical oxygen demand (COD) concentration in liquid products (LP) reached 192.6 g/L, and it was obtained after 170°C HTP. The biogas potential from the solid residue (SR) and LP was up to 478 mL/g-VS and 398 mL/g-COD, respectively. A temperature of 170°C was suitable for pork HTP, which promoted the practical biogas yield because of the synergistic effect between proteins and lipids. Ammonia inhibition was reduced by the addition of hydrochar to the CSTR during co-digestion of SR and LP, maximum ammonia concentration tolerated by methanogens increased from 2.68 to 3.38 g/L. This improved total biogas yield and degradation rate of substrates, reaching values of 28.62 and 36.06%, respectively. The acetate content in volatile fatty acids (VFA) may be used as an index that reflects the degree of methanogenesis of the system. The results of the present work may also provide guidance for the digestion of feedstock with high protein and lipid content.
Highlights
China as a country displays an annual production of 451 million swines
The results were consistent with other study that indicated that most lipids were dissolved at 160◦C and the soluble protein content increased as hydrothermal temperature increased (Pavlovicet al., 2013)
volatile fatty acids (VFA) only contributed to 13.2–19.1% of total chemical oxygen demand (COD), because the preliminary decomposition during hydrothermal pretreatment (HTP) resulted in proteins and lipids hydrolization to produce polypeptides and long chain fatty acids (LCFA), respectively
Summary
China as a country displays an annual production of 451 million swines. For this reason, China is the largest pork producer in the world (National Bureau of Statistics of China [NBSC], 2018). As of November 22, 2019, a total of 160 ASF outbreaks had been reported in China, events that caused the culling of 11.93 million hogs (Ding and Wang, 2020). These data emphasizes the importance of timely vaccination, improving the sanitary conditions
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