In this study, freezing–thawing (FT) pretreatment of different freezing time and freezing temperatures was investigated to find the effect on anaerobic digestion (AD) of wheat straw (WS). The freezing temperature gradient is − 10 °C, − 20 °C, − 40 °C and − 80 °C, and the freezing time gradient is 12 h, 24 h, 48 h and 96 h. Total methane production exhibited a mere distance among all samples. Morphology change sculptured by SEM showed this method broke the structure of WS leaving fragments and pores in varying degrees. Three kinetic models were performed on WS to represent the behavior of experimental data. Kinetic model parameters of total methane production and lag phase time showed that logistic function model had the best fit, followed by modified Gompertz model, yet transfer function model lost efficacy in this experiment. Logistic function model was then used to reveal the influence on lag phase caused by freezing time and freezing temperature, and the results implied that FT pretreatment can shorten the lag phase time of AD, providing a 21.39% improvement under the optimal conditions of − 20 °C 96 h. The analysis of response surface regression shows that the freezing temperature has more effect on the lag phase time of anaerobic digestion than freezing time. Warmer freezing temperature of − 20 °C do better than − 80 °C on lag time, which can be achieved in most cold regions, so this treatment can occur naturally in such area without additional energy input.

Graphical abstract

中文翻译：

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冻融预处理对麦秸厌氧消化的影响及其动力学分析

在这项研究中，研究了不同冷冻时间和冷冻温度的冷冻-解冻（FT）预处理，以发现对小麦秸秆（WS）厌氧消化（AD）的影响。冻结温度梯度为− 10°C，− 20°C，− 40°C和− 80°C，冻结时间梯度为12 h，24 h，48 h和96 h。在所有样品中，甲烷的总产量仅显示出一定的距离。扫描电镜（SEM）雕刻的形态变化表明，该方法破坏了WS的结构，并在不同程度上留下碎片和孔。在WS上执行了三个动力学模型来表示实验数据的行为。总甲烷生成量和滞后时间的动力学模型参数表明，逻辑函数模型最适合，其次是修正的Gompertz模型，但传递函数模型在该实验中失去了功效。然后使用Logistic函数模型揭示了冷冻时间和冷冻温度对滞后阶段的影响，结果表明FT预处理可以缩短AD的滞后阶段时间，在− 20°的最佳条件下改善了21.39％。 C 96小时。响应面回归分析表明，冷冻温度对厌氧消化滞后时间的影响大于冷冻时间。− 20°C的较温暖的冷冻温度在滞后时间上优于− 80°C，这可以在大多数寒冷地区实现，因此这种处理可以自然地在这种区域进行，而无需额外的能量输入。在− 20°C 96 h的最佳条件下改善39％。响应面回归分析表明，冷冻温度对厌氧消化滞后时间的影响大于冷冻时间。− 20°C的较温暖的冷冻温度在滞后时间上优于− 80°C，这可以在大多数寒冷地区实现，因此这种处理可以自然地在这种区域进行，而无需额外的能量输入。在− 20°C 96 h的最佳条件下改善39％。响应面回归分析表明，冷冻温度对厌氧消化滞后时间的影响大于冷冻时间。− 20°C的较温暖的冷冻温度在滞后时间上优于− 80°C，这可以在大多数寒冷地区实现，因此这种处理可以自然地在这种区域进行，而无需额外的能量输入。

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