Enhanced anaerobic digestion of refinery waste activated sludge based on pretreatment strategy by spend caustic

doi:10.11949/0438-1157.20241297

Abstract

Abstract:

This study comprehensively considered resource natures of refinery waste activated sludge (WAS) and high alkalinity of refinery spent caustic (RSC), proposing RSC pretreatment and combined pretreatment methods utilizing thermal-RSC, electrolysis-RSC, and alkaline fermentation to enhance the methane yield from anaerobic digestion of WAS. The results showed that alkali slag could significantly promote the dissolution of intracellular organic matter, and the SCOD concentration increased from 128 mg·L^-1 to 2932 mg·L^-1. The combined pretreatments of thermal-RSC, electrolysis-RSC, and alkaline fermentation further facilitated the release of proteins, polysaccharides, and volatile fatty acids, improving the biodegradability of soluble organic matters and enhancing the bioconversion efficiency of refractory substances such as tannins, aromatic compounds, and carboxyl-rich alicyclic compounds. Therefore, the methane yields in three combined pretreatment groups increased 62%, 80%, and 97% compared to the single RSC pretreatment group (58.3 ml·g^-1-VS), respectively. Network analysis revealed that Clostridium_sensu_stricto_5, Clostridium_sensu_stricto_1, and Raineyella played crucial roles in the decomposition of carboxylic rich alicyclic molecules. Economic benefit assessment showed that alkaline fermentation pretreatment obtained the highest net profit, and reduced treatment costs by 58.5 CNY·t^-1. Based on these findings, a new strategy for the synergistic treatment of WAS and RSC was proposed.

Key words: refinery waste activated sludge, refinery spent caustic, pretreatment, anaerobic digestion, methane

摘要：

针对炼厂剩余活性污泥（WAS）资源属性，并结合碱渣高碱度特性，提出碱渣预处理及热-碱渣、电解-碱渣和碱性发酵联合预处理策略，旨在提升WAS厌氧消化的甲烷产率。结果表明，碱渣能显著促进胞内有机物溶出，SCOD浓度从128 mg·L^-1增至2932 mg·L^-1。热-碱渣、电解-碱渣和碱性发酵联合预处理可进一步促进蛋白质、多糖和挥发性脂肪酸释放，改善了溶解性有机物可生化性，提升了单宁、芳香类和富含羧基脂环族化合物等难降解物质的生物转化效率，使得甲烷产率较单独碱渣预处理（58.3 ml·g^-1-VS）分别提高了62%、80%和97%。共现网络分析显示，Clostridium_sensu_stricto_5、Clostridium_sensu_stricto_1和Raineyella在分解富含羧基脂环族化合物中起到关键作用。通过经济效益评估，碱性发酵预处理方式净收益最大，可节省处理成本58.5 CNY·t^-1，并基于此方法提出了一条WAS与碱渣协同处理的新策略。

关键词: 炼厂剩余活性污泥, 碱渣, 预处理, 厌氧消化, 甲烷

CLC Number:

X 703.1

Jin LI, Shuiqing HU, Yibin WENG, Juntao JIANG, Qinghong WANG, Chunmao CHEN. Enhanced anaerobic digestion of refinery waste activated sludge based on pretreatment strategy by spend caustic[J]. CIESC Journal, 2025, 76(7): 3446-3458.

李晋, 胡水清, 翁艺斌, 姜峻韬, 王庆宏, 陈春茂. 基于碱渣预处理策略强化炼厂污泥厌氧消化效能[J]. 化工学报, 2025, 76(7): 3446-3458.

Figures/Tables 9

Fig.1 Solubilization efficiency of SCOD, proteins, polysaccharides, VFA by different pretreatment methods

Fig.2 Three-dimensional fluorescence spectra of dissolved organic matters after RSC pretreatments (a), thermal-RSC (b), electrolysis-RSC (c) and alkaline fermentation (d)

Fig.3 Effects of different pretreatment methods on anaerobic digestion of WAS

Fig.4 van Krevelen diagram of the comparing decomposed, resistant, and produced dissolved organic matters during anaerobic digestion

Fig.5 The bacterial (a) and archaea (b) community structure at the genus level in different groups

Fig.6 Network graph displaying the associations between microbial genus and dissolved organic matters

Fig.7 The properties of dissolved organic matters positively correlated with bacteria

Table 1 Economic evaluation of WAS anaerobic digestion by different pretreatment methods

项目	空白组	碱渣组	热-碱渣组	电解-碱渣组	碱性发酵组
进料TS含量/(g·L^-1)	19.24	19.24	19.24	19.24	19.24
预处理费用/(CNY·t^-1)	0	0	59.21	19.67	14.38
中和费用/(CNY·t^-1)	0	5.86	2.43	4.24	2.98
厌氧消化费用/(CNY·t^-1)	14.38	14.38	0	14.38	0
TS去除率/%	13.52	18.75	25.48	26.23	24.78
委外处置费用/(CNY·t^-1)	294.03	276.25	253.37	250.82	255.75
氢气产率/(dm³·t^-1)	48.00	251.32	142.04	407.80	313.32
甲烷产率/(dm³·t^-1)	233.54	719.63	1176.34	1295.15	1423.46
能源收益/ CNY	-1.81	-5.84	-8.85	-10.39	-11.07
碱渣投加量/(L·t^-1)	0	30	10	27.5	20
减少的碱渣处理费用/(CNY·t^-1)	0	-6	-2	-5.5	-4
总处理费用/(CNY·t^-1)	306.60	284.65	304.36	273.22	258.04

Fig.8 The combined treatment processes for WAS and refinery spend caustic

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