Pilot Study on High-Solid Anaerobic Gradient Prefermentation of Wheat Straw
To address the persistent challenges in conventional straw biogas projects—such as the high hydrophobicity of straw feedstock,severe scum formation,operational instability,low biogas yield,and significant carbon loss associated with traditional hydrolysis and acidification techniques-this study explored the application of a high-concentration anaerobic gra-dient reactor.Using dry wheat straw as feedstock,we conducted pilot-scale(112 m3)experiments to assess the impact of short-term anaerobic pre-fermentation on straw soaking efficiency and methane recovery.Our objective was to achieve a breakthrough in straw pretreatment technology.The findings revealed that as the hydraulic retention time(HRT)decreased from 20 days to 5 days,there was a gradual decline in daily gas production and methane concentration,alongside the accu-mulation of organic acids.However,even with a 5 day HRT,the reactor achieved a methane yield of 1.73 m3·m-3d-1 and a methane content of 39.2％,effectively mitigating carbon loss in the feedstock.Notably,the reactor could replicate the soaking effect of 96 hours of static soaking within just 2.5 days,enabling complete straw hydration and settling.With re-duced HRT,the concentration of organic acids in the reactor increased,with butyric acid ranging from 6600 to 1838.1 mg·L-1,acetic acid from 516 to 4002 mg·L-1,and propionic acid from 196 to 1213 mg·L-1,while the pH remained a-bove 7.High-throughput 16S rRNA gene sequencing identified Firmicutes and Bacteroidetes as the dominant hydrolytic bacteria,and Methanosarcina and Methanobacterium as the key methanogenic archaea.As hydrolysis progressed,the rela-tive abundance of Methanosarcina decreased,while Methanobacterium increased,resulting in a slight reduction in total methanogen populations and a corresponding decrease in methane production.Overall,the results demonstrate that the high-solid anaerobic gradient fermentation approach significantly enhances both straw soaking efficiency and methane recov-ery,offering promising potential for improving the performance of straw-based biogas projects.
straw biogasgradient anaerobic digestionstraw soaking and settlingpre-fermentation biogas productionpi-lot-scale study
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