Study on anaerobic digestion pretreatment coupled with hydrothermal carbonization of grass

doi:10.11949/0438-1157.20211287

Abstract

Abstract:

Anaerobic digestion (AD) coupled with hydrothermal carbonization (HTC) technology has significant advantages and significance for sustainable resource utilization of garden waste. In this work, the grass was pretreated with AD for 7—28 d. The effects of AD coupled with HTC on the characteristics of hydrochar and its pyrolysis and product release properties were investigated deeply. AD pretreatment promoted mainly the decarboxylation reaction in the HTC process. Besides, the functional properties of hydrochar were regulated effectively by changing the lignocellulose composition ratio and biomass structural characteristics. Noticeably, the dense rigid structure inside the biomass was broken by AD pretreatment, which promoted the formation of rich pores and the increase of the specific surface area of the hydrochar. The best performance of hydrochar was achieved at 17.52% biodegradability (AD 7 d), with mass yield, high heating value (HHV), energy yield and energy density reaching 62.75%, 23.81 MJ·kg^-1, 80.31% and 1.28%, respectively. In addition, TG-MS analysis results revealed that AD pretreatment improves the thermal stability of carbon and the generation of energy gas in pyrolysis products, which is helpful for the upgrading and utilization of pyrolysis gas.

Key words: grass, anaerobic digestion, hydrothermal carbonation, structural properties, TG-MS

摘要：

厌氧消化（AD）耦合水热炭化（HTC）技术对园林废弃物的可持续资源化利用具有显著优势和意义。采用草为研究对象，进行了7~28 d的AD预处理，深入探究了AD预处理耦合HTC对水热炭特性及其热解和产物释放特性的影响。其中，AD促进HTC过程主要发生脱羧反应；通过改变木质纤维素构成比例和结构特征有效调控水热炭的功能特性。此外，AD打破了生物质内部致密的刚性结构，促进了水热炭丰富孔隙的形成和比表面积的增加。在生物可降解程度为17.52%（AD 7 d）时，水热炭性能最佳，质量产率、高位热值（HHV）、能量产率和能量密度分别达62.75%、23.81 MJ·kg^-1、80.31%和1.28。此外， TG-MS分析结果揭示了AD预处理提高了炭的热稳定性以及热解产物中能源气体的生成，有助于热解气的提质和利用。

关键词: 草屑, 厌氧消化, 水热炭化, 结构特性, TG-MS

CLC Number:

X 712

Yanshan WANG, Xiaochao ZHU, Yingjin SONG, Yihang LI. Study on anaerobic digestion pretreatment coupled with hydrothermal carbonization of grass[J]. CIESC Journal, 2022, 73(2): 904-913.

王燕杉, 朱小超, 宋英今, 李易航. 草屑厌氧消化预处理耦合水热炭化研究[J]. 化工学报, 2022, 73(2): 904-913.

Figures/Tables 12

Table 1 Properties of the feedstock and inoculum

参数	草	接种污泥
TS/%	97.39 ± 0.50	2.65 ± 0.30
VS/%	85.66 ± 0.40	1.53 ± 0.40
C/%	39.40	23.72
N/%	2.68	3.70
H/%	7.69	5.02
S/%	0.10	0.63

Fig.1 Cumulative biogas(a) and CH4 (b) production from grass

Fig.2 Ultimate and proximate analysis of untreated and AD pretreated grass-derived hydrochar

Fig.3 Van Krevelen diagram of grass-derived hydrochar pretreated and untreated with AD

Fig.4 Changes in lignocellulose of grass-derived hydrochar pretreated and untreated with AD

Fig.5 Mass yields and HHV(a), energy densification and energy yields (b) of hydrochar derived from untreated and pretreated with AD

Fig.6 Morphological characteristics of hydrochar

Table 2 SSA and pore structure parameters of hydrochar pretreated and untreated with AD

样品	比表面积/ (m²·g^-1)	平均孔径/nm	总孔体积/ (cm³·g^-1)
G-230	23.98	6.21	0.037
ADG-7d-230	34.46	7.78	0.067
ADG-14d-230	27.28	11.84	0.076
ADG-21d-230	54.41	20.55	0.280
ADG-28d-230	44.82	21.87	0.25

Fig.7 FTIR spectra of hydrochar derived from pretreated and untreated with AD

Table 3 Inorganic and heavy metal elements of hydrochar derived from pretreated and untreated with AD

参数/(mg·kg^-1)	G-230	ADG-7d-230
无机元素
K	720.67	869.95
Ca	22323.20	25444.37
Na	133.42	240.95
Mg	2586.22	3327.14
P	5350.21	6157.90
Al	1554.11	6758.90
Si	4920.62	4801.05
Cu	90.44	104.36
Zn	326.45	246.50
Fe	3211.70	7804.13
重金属元素
As	0.76	0.21
Hg	0.54	0.62
Pb	9.90	20.05
Cd	0.08	0.11
Cr	19.12	45.23

Fig.8 TG (a) and DTG (b) analysis of pyrolysis characteristics of hydrochar pretreated and untreated with AD

Fig.9 Mass spectra of product release characteristics of hydrochar pretreated and unpretreated with AD

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